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  • 1. Abellán, F. J.
    et al.
    Indebetouw, R.
    Marcaide, J. M.
    Gabler, M.
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Spyromilio, J.
    Burrows, D. N.
    Chevalier, R.
    Cigan, P.
    Gaensler, B. M.
    Gomez, H. L.
    Janka, H. -Th.
    Kirshner, R.
    Larsson, J.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Matsuura, M.
    McCray, R.
    Ng, C. -Y.
    Park, S.
    Roche, P.
    Staveley-Smith, L.
    van Loon, J. Th.
    Wheeler, J. C.
    Woosley, S. E.
    Very Deep inside the SN 1987A Core Ejecta: Molecular Structures Seen in 3D2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 842, no 2, article id L24Article in journal (Refereed)
    Abstract [en]

    Most massive stars end their lives in core-collapse supernova explosions and enrich the interstellar medium with explosively nucleosynthesized elements. Following core collapse, the explosion is subject to instabilities as the shock propagates outward through the progenitor star. Observations of the composition and structure of the innermost regions of a core-collapse supernova provide a direct probe of the instabilities and nucleosynthetic products. SN 1987A in the Large Magellanic Cloud is one of very few supernovae for which the inner ejecta can be spatially resolved but are not yet strongly affected by interaction with the surroundings. Our observations of SN 1987A with the Atacama Large Millimeter/submillimeter Array are of the highest resolution to date and reveal the detailed morphology of cold molecular gas in the innermost regions of the remnant. The 3D distributions of carbon and silicon monoxide (CO and SiO) emission differ, but both have a central deficit, or torus-like distribution, possibly a result of radioactive heating during the first weeks (nickel heating). The size scales of the clumpy distribution are compared quantitatively to models, demonstrating how progenitor and explosion physics can be constrained.

  • 2. Abramowski, A.
    et al.
    Aharonian, F.
    Benkhali, F. Ait
    Akhperjanian, A. G.
    Uner, E. O. Ang
    Backes, M.
    Balenderan, S.
    Balzer, A.
    Barnacka, A.
    Becherini, Y.
    Tjus, J. Becker
    Berge, D.
    Bernhard, S.
    Bernloehr, K.
    Birsin, E.
    Biteau, J.
    Boettcher, M.
    Boisson, C.
    Bolmont, J.
    Bordas, P.
    Bregeon, J.
    Brun, F.
    Brun, P.
    Bryan, M.
    Bulik, T.
    Carrigan, S.
    Casanova, S.
    Chadwick, P. M.
    Chakraborty, N.
    Chalme-Calvet, R.
    Chaves, R. C. G.
    Chretien, M.
    Colafrancesco, S.
    Cologna, G.
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Couturier, C.
    Cui, Y.
    Dalton, M.
    Davids, I. D.
    Degrange, B.
    Deil, C.
    deWilt, P.
    Djannati-Atai, A.
    Domainko, W.
    Donath, A.
    Drury, L. O 'C.
    Dubus, G.
    Dutson, K.
    Dyks, J.
    Dyrda, M.
    Edwards, T.
    Egberts, K.
    Eger, P.
    Espigat, P.
    Farnier, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Fegan, S.
    Feinstein, F.
    Fernandes, M. V.
    Fernandez, D.
    Fiasson, A.
    Fontaine, G.
    Foerster, A.
    Fuessling, M.
    Gabici, S.
    Gajdus, M.
    Gallant, Y. A.
    Garrigoux, T.
    Giavitto, G.
    Giebels, B.
    Glicenstein, J. F.
    Gottschall, D.
    Grondin, M. -H
    Grudzinska, M.
    Hadasch, D.
    Haeffner, S.
    Hahn, J.
    Harris, J.
    Heinzelmann, G.
    Henri, G.
    Hermann, G.
    Hervet, O.
    Hillert, A.
    Hinton, J. A.
    Hofmann, W.
    Hofverberg, P.
    Holler, M.
    Horns, D.
    Ivascenko, A.
    Jacholkowska, A.
    Jahn, C.
    Jamrozy, M.
    Janiak, M.
    Jankowsky, F.
    Jung-Richardt, I.
    Kastendieck, M. A.
    Katarzynski, K.
    Katz, U.
    Kaufmann, S.
    Khelifi, B.
    Kieffer, M.
    Klepser, S.
    Klochkov, D.
    Kluzniak, W.
    Kolitzus, D.
    Komin, Nu.
    Kosack, K.
    Krakau, S.
    Krayzel, F.
    Krueger, P. P.
    Laffon, H.
    Lamanna, G.
    Lau, J.
    Lefaucheur, J.
    Lefranc, V.
    Lemiere, A.
    Lemoine-Goumard, M.
    Lenain, J. -P
    Lohse, T.
    Lopatin, A.
    Lu, C. -C
    Marandon, V.
    Marcowith, A.
    Marx, R.
    Maurin, G.
    Maxted, N.
    Mayer, M.
    McComb, T. J. L.
    Mehault, J.
    Meintjes, P. J.
    Menzler, U.
    Meyer, Manuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Mitchell, A. M. W.
    Moderski, R.
    Mohamed, M.
    Morå, Knut
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Moulin, E.
    Murach, T.
    de Naurois, M.
    Niemiec, J.
    Nolan, S. J.
    Oakes, L.
    Odaka, H.
    Ohm, S.
    Opitz, B.
    Ostrowski, M.
    Oya, I.
    Panter, M.
    Parsons, R. D.
    Arribas, M. Paz
    Pekeur, N. W.
    Pelletier, G.
    Petrucci, P. -O
    Peyaud, B.
    Pita, S.
    Poon, H.
    Puehlhofer, G.
    Punch, M.
    Quirrenbach, A.
    Raab, S.
    Reichardt, I.
    Reimer, A.
    Reimer, O.
    Renaud, M.
    Reyes, R. de Los
    Rieger, F.
    Romoli, C.
    Rosier-Lees, S.
    Rowell, G.
    Rudak, B.
    Rulten, C. B.
    Sahakian, V.
    Salek, D.
    Sanchez, D. A.
    Santangelo, A.
    Schlickeiser, R.
    Schuessler, F.
    Schulz, A.
    Schwanke, U.
    Schwarzburg, S.
    Schwemmer, S.
    Sol, H.
    Spanier, F.
    Spengler, Gerrit
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Spies, F.
    Stawarz, L.
    Steenkamp, R.
    Stegmann, C.
    Stinzing, F.
    Stycz, K.
    Sushch, I.
    Tavernet, J. -P
    Tavernier, T.
    Taylor, A. M.
    Terrier, R.
    Tluczykont, M.
    Trichard, C.
    Valerius, K.
    Van Eldik, C.
    van Soelen, B.
    Vasileiadis, G.
    Veh, J.
    Venter, C.
    Viana, A.
    Vincent, P.
    Vink, J.
    Voelk, H. J.
    Volpe, F.
    Vorster, M.
    Vuillaume, T.
    Wagner, S. J.
    Wagner, P.
    Wagner, Robert M.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ward, M.
    Weidinger, M.
    Weitzel, Q.
    White, R.
    Wierzcholska, A.
    Willmann, P.
    Woernlein, A.
    Wouters, D.
    Yang, R.
    Zabalza, V.
    Zaborov, D.
    Zacharias, M.
    Zdziarski, A. A.
    Zech, A.
    Zechlin, H. -S
    Fukui, Y.
    Sano, H.
    Fukuda, T.
    Yoshiike, S.
    DISCOVERY OF THE HARD SPECTRUM VHE gamma-RAY SOURCE HESS J1641-4632014In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 794, no 1, p. L1-Article in journal (Refereed)
    Abstract [en]

    This Letter reports the discovery of a remarkably hard spectrum source, HESS J1641-463, by the High Energy Stereoscopic System (H.E.S.S.) in the very high energy (VHE) domain. HESS J1641-463 remained unnoticed by the usual analysis techniques due to confusion with the bright nearby source HESS J1640-465. It emerged at a significance level of 8.5 standard deviations after restricting the analysis to events with energies above 4 TeV. It shows a moderate flux level of phi(E > 1TeV) = (3.64 +/- 0.44(stat)+/- 0.73(sys)) x 10(-13) cm(-2) s(-1), corresponding to 1.8% of the Crab Nebula flux above the same energy, and a hard spectrum with a photon index of Gamma = 2.07 +/- 0.11(stat)+/- 0.20(sys). It is a point-like source, although an extension up to a Gaussian width of sigma = 3 arcmin cannot be discounted due to uncertainties in the H.E.S.S. point-spread function. The VHE gamma-ray flux of HESS J1641-463 is found to be constant over the observed period when checking time binnings from the year-by-year to the 28 minute exposure timescales. HESS J1641-463 is positionally coincident with the radio supernova remnant SNR G338.5+0.1. No X-ray candidate stands out as a clear association; however, Chandra and XMM-Newton data reveal some potential weak counterparts. Various VHE gamma-ray production scenarios are discussed. If the emission from HESS J1641-463 is produced by cosmic ray protons colliding with the ambient gas, then their spectrum must extend close to 1 PeV. This object may represent a source population contributing significantly to the galactic cosmic ray flux around the knee.

  • 3. Ackermann, M.
    et al.
    Ajello, M.
    Albert, A.
    Anderson, Brandon
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Arimoto, M.
    Atwood, W. B.
    Axelsson, M.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Baring, M. G.
    Bastieri, D.
    Gonzalez, J. Becerra
    Bellazzini, R.
    Bissaldi, E.
    Blandford, R. D.
    Bloom, E. D.
    Bonino, R.
    Bottacini, E.
    Brandt, T. J.
    Bregeon, J.
    Britto, R. J.
    Bruel, P.
    Buehler, R.
    Burnett, T. H.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caputo, R.
    Caragiulo, M.
    Caraveo, P. A.
    Casandjian, J. M.
    Cavazzuti, E.
    Charles, E.
    Chekhtman, A.
    Chiang, J.
    Chiaro, G.
    Ciprini, S.
    Cohen-Tanugi, J.
    Cominsky, L. R.
    Condon, B.
    Costanza, F.
    Cuoco, A.
    Cutini, S.
    D'Ammando, F.
    de Palma, F.
    Desiante, R.
    Digel, S. W.
    Di Lalla, N.
    Di Mauro, M.
    Di Venere, L.
    Dominguez, A.
    Drell, P. S.
    Dubois, R.
    Dumora, D.
    Favuzzi, C.
    Fegan, S. J.
    Ferrara, E. C.
    Franckowiak, A.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Gehrels, N.
    Giglietto, N.
    Giomi, M.
    Giommi, P.
    Giordano, F.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Gomez-Vargas, G. A.
    Granot, J.
    Green, D.
    Grenier, I. A.
    Grondin, M. -H.
    Grove, J. E.
    Guillemot, L.
    Guiriec, S.
    Hadasch, D.
    Harding, A. K.
    Hays, E.
    Hewitt, J. W.
    Hill, A. B.
    Horan, D.
    Jogler, T.
    Johannesson, G.
    Kamae, T.
    Kensei, S.
    Kocevski, D.
    Kuss, M.
    La Mura, G.
    Larsson, S.
    Latronico, L.
    Lemoine-Goumard, M.
    Li, J.
    Li, L.
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Madejski, G. M.
    Magill, J.
    Maldera, S.
    Manfreda, A.
    Marelli, M.
    Mayer, M.
    Mazziotta, M. N.
    McEnery, J. E.
    Meyer, Manuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Michelson, P. F.
    Mirabal, N.
    Mizuno, T.
    Moiseev, A. A.
    Monzani, M. E.
    Moretti, E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Negro, M.
    Nuss, E.
    Ohsugi, T.
    Omodei, N.
    Orienti, M.
    Orlando, E.
    Ormes, J. F.
    Paneque, D.
    Perkins, J. S.
    Pesce-Rollins, M.
    Piron, F.
    Pivato, G.
    Porter, T. A.
    Racusin, J. L.
    Raino, S.
    Rando, R.
    Razzaque, S.
    Reimer, A.
    Reimer, O.
    Reposeur, T.
    Ritz, S.
    Rochester, L. S.
    Romani, R. W.
    Parkinson, P. M. Saz
    Sgro, C.
    Simone, D.
    Siskind, E. J.
    Smith, D. A.
    Spada, F.
    Spandre, G.
    Spinelli, P.
    Suson, D. J.
    Tajima, H.
    Thayer, J. G.
    Thayer, J. B.
    Thompson, D. J.
    Tibaldo, L.
    Torres, D. F.
    Troja, E.
    Uchiyama, Y.
    Venters, T. M.
    Vianello, G.
    Wood, K. S.
    Wood, M.
    Zaharijas, G.
    Zhu, S.
    Zimmer, Stephan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    FERMI-LAT OBSERVATIONS OF THE LIGO EVENT GW1509142016In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 823, no 1, article id L2Article in journal (Refereed)
    Abstract [en]

    The Fermi Large Area Telescope (LAT) has an instantaneous field of view (FoV) covering similar to 1/5 of the sky and it completes a survey of the entire sky in high-energy gamma-rays every 3 hr. It enables searches for transient phenomena over timescales from milliseconds to years. Among these phenomena could be electromagnetic counterparts to gravitational wave (GW) sources. In this paper, we present a detailed study of the LAT observations relevant to Laser Interferometer Gravitational-wave Observatory (LIGO) event GW150914, which is the first direct detection of gravitational waves and has been interpreted as being due to the coalescence of two stellar-mass black holes. The localization region for GW150914 was outside the LAT FoV at the time of the GW signal. However, as part of routine survey observations, the LAT observed the entire LIGO localization region within similar to 70 minutes of the trigger and thus enabled a comprehensive search for a.-ray counterpart to GW150914. The study of the LAT data presented here did not find any potential counterparts to GW150914, but it did provide limits on the presence of a transient counterpart above 100 MeV on timescales of hours to days over the entire GW150914 localization region.

  • 4. Ackermann, M.
    et al.
    Ajello, M.
    Albert, A.
    Atwood, W. B.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Becerra Gonzalez, J.
    Bellazzini, R.
    Bissaldi, E.
    Blandford, R. D.
    Bloom, E. D.
    Bonino, R.
    Bottacini, E.
    Bregeon, J.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caputo, R.
    Caragiulo, M.
    Caraveo, P. A.
    Cavazzuti, E.
    Cecchi, C.
    Chekhtman, A.
    Chiang, J.
    Chiaro, G.
    Ciprini, S.
    Cohen-Tanugi, J.
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). The Royal Swedish Academy of Sciences, Sweden.
    Cutini, S.
    D'Ammando, F.
    de Angelis, A.
    de Palma, F.
    Desiante, R.
    Di Venere, L.
    Dominguez, A.
    Drell, P. S.
    Favuzzi, C.
    Fegan, S. J.
    Ferrara, E. C.
    Focke, W. B.
    Fuhrmann, L.
    Fukazawa, Y.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Giglietto, N.
    Giommi, P.
    Giordano, F.
    Giroletti, M.
    Godfrey, G.
    Green, D.
    Grenier, I. A.
    Grove, J. E.
    Guiriec, S.
    Harding, A. K.
    Hays, E.
    Hewitt, J. W.
    Hill, A. B.
    Horan, D.
    Jogler, T.
    Johannesson, G.
    Johnson, A. S.
    Kamae, T.
    Kuss, M.
    Larsson, S.
    Latronico, L.
    Li, J.
    Li, L.
    Longo, F.
    Loparco, F.
    Lott, B.
    Lovellette, M. N.
    Lubrano, P.
    Magill, J.
    Maldera, S.
    Manfreda, A.
    Max-Moerbeck, W.
    Mayer, M.
    Mazziotta, M. N.
    McEnery, J. E.
    Michelson, P. F.
    Mizuno, T.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Murgia, S.
    Nuss, E.
    Ohno, M.
    Ohsugi, T.
    Ojha, R.
    Omodei, N.
    Orlando, E.
    Ormes, J. F.
    Paneque, D.
    Pearson, T. J.
    Perkins, J. S.
    Perri, M.
    Pesce-Rollins, M.
    Petrosian, V.
    Piron, F.
    Pivato, G.
    Porter, T. A.
    Raino, S.
    Rando, R.
    Razzano, M.
    Readhead, A.
    Reimer, A.
    Reimer, O.
    Schulz, A.
    Sgro, C.
    Siskind, E. J.
    Spada, F.
    Spandre, G.
    Spinelli, P.
    Suson, D. J.
    Takahashi, H.
    Thayer, J. B.
    Thompson, D. J.
    Tibaldo, L.
    Torres, D. F.
    Tosti, G.
    Troja, E.
    Uchiyama, Y.
    Vianello, G.
    Wood, K. S.
    Wood, M.
    Zimmer, Stephan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Berdyugin, A.
    Corbet, R. H. D.
    Hovatta, T.
    Lindfors, E.
    Nilsson, K.
    Reinthal, R.
    Sillanpaa, A.
    Stamerra, A.
    Takalo, L. O.
    Valtonen, M. J.
    MULTIWAVELENGTH EVIDENCE FOR QUASI-PERIODIC MODULATION IN THE GAMMA-RAY BLAZAR PG 1553+1132015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 813, no 2, article id L41Article in journal (Refereed)
    Abstract [en]

    We report for the first time a gamma-ray and multiwavelength nearly periodic oscillation in an active galactic nucleus. Using the Fermi Large Area Telescope we have discovered an apparent quasi-periodicity in the gamma-ray flux (E > 100 MeV) from the GeV/TeV BL Lac object PG 1553+113. The marginal significance of the 2.18 +/- 0.08 year period gamma-ray cycle is strengthened by correlated oscillations observed in radio and optical fluxes, through data collected in the Owens Valley Radio Observatory, Tuorla, Katzman Automatic Imaging Telescope, and Catalina Sky Survey monitoring programs and Swift-UVOT. The optical cycle appearing in similar to 10 years of data has a similar period, while the 15 GHz oscillation is less regular than seen in the other bands. Further long-term multiwavelength monitoring of this blazar may discriminate among the possible explanations for this quasi-periodicity.

  • 5. Ackermann, M.
    et al.
    Ajello, M.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Bastieri, D.
    Gonzalez, J. Becerra
    Bellazzini, R.
    Bissaldi, E.
    Blandford, R. D.
    Bloom, E. D.
    Bonino, R.
    Bottacini, E.
    Bregeon, J.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Cameron, R. A.
    Caragiulo, M.
    Caraveo, P. A.
    Cavazzuti, E.
    Cecchi, C.
    Cheung, C. C.
    Chiang, J.
    Chiaro, G.
    Ciprini, S.
    Conrad, Jan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Costantin, D.
    Costanza, F.
    Cutini, S.
    D'Ammando, F.
    de Palma, F.
    Desiante, R.
    Digel, S. W.
    Di Lalla, N.
    Di Mauro, M.
    Di Venere, L.
    Dominguez, A.
    Drell, P. S.
    Favuzzi, C.
    Fegan, S. J.
    Ferrara, E. C.
    Finke, J.
    Focke, W. B.
    Fukazawa, Y.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Giglietto, N.
    Giordano, F.
    Giroletti, M.
    Green, D.
    Grenier, I. A.
    Guillemot, L.
    Guiriec, S.
    Hartmann, D. H.
    Hays, E.
    Horan, D.
    Jogler, T.
    Johannesson, G.
    Johnson, A. S.
    Kuss, M.
    La Mura, G.
    Larsson, Stefan
    Latronico, L.
    Li, J.
    Longo, F.
    Loparco, F.
    Lovellette, M. N.
    Lubrano, P.
    Magill, J. D.
    Maldera, S.
    Manfreda, A.
    Marcotulli, L.
    Mazziotta, M. N.
    Michelson, P. F.
    Mirabal, N.
    Mitthumsiri, W.
    Mizuno, T.
    Monzani, M. E.
    Morselli, A.
    Moskalenko, I. V.
    Negro, M.
    Nuss, E.
    Ohsugi, T.
    Ojha, R.
    Omodei, N.
    Orienti, M.
    Orlando, E.
    Ormes, J. F.
    Paliya, V. S.
    Paneque, D.
    Perkins, J. S.
    Persic, M.
    Pesce-Rollins, M.
    Piron, F.
    Porter, T. A.
    Principe, G.
    Raino, S.
    Rando, R.
    Rani, B.
    Razzano, M.
    Razzaque, S.
    Reimer, A.
    Reimer, O.
    Romani, R. W.
    Sgro, C.
    Simone, D.
    Siskind, E. J.
    Spada, F.
    Spandre, G.
    Spinelli, P.
    Stalin, C. S.
    Stawarz, L.
    Suson, D. J.
    Takahashi, M.
    Tanaka, K.
    Thayer, J. B.
    Thompson, D. J.
    Torres, D. F.
    Torresi, E.
    Tosti, G.
    Troja, E.
    Vianello, G.
    Wood, K. S.
    Gamma-Ray Blazars within the First 2 Billion Years2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 837, no 1, article id L5Article in journal (Refereed)
    Abstract [en]

    The detection of high-redshift (z > 3) blazars enables the study of the evolution of the most luminous relativistic jets over cosmic time. More importantly, high-redshift blazars tend to host massive black holes and can be used to constrain the space density of heavy black holes in the early universe. Here, we report the first detection with the Fermi-Large Area Telescope of five gamma-ray-emitting blazars beyond z. =. 3.1, more distant than any blazars previously detected in.-rays gamma Among these five objects, NVSS J151002+570243 is now the most distant known gamma-ray-emitting blazar at z =. 4.31. These objects have steeply falling gamma-ray spectral energy distributions (SEDs), and. those that have been observed in X-rays have a very hard X-ray spectrum, both typical of powerful blazars. Their Compton dominance ( ratio of the inverse Compton to synchrotron peak luminosities) is also very large (>20). All of these properties place these objects among the most extreme members of the blazar population. Their optical spectra and the modeling of their optical-UV SEDs confirm that these objects harbor massive black holes (MBH similar to 10(8-10) M circle dot 8 10). We find that, at z approximate to 4, the space density of >10(9)M circle dot black holes hosted in radio-loud and radio-quiet active galactic nuclei are similar, implying that radio-loudness may play a key role in rapid black hole growth in the early universe.

  • 6. Acquaviva, Viviana
    et al.
    Vargas, Carlos
    Gawiser, Eric
    Guaita, Lucia
    Stockholm University, Faculty of Science, Department of Astronomy.
    THE CURIOUS CASE OF Ly alpha EMITTERS: GROWING YOUNGER FROM z similar to 3 to z similar to 2?2012In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 751, no 2, article id L26Article in journal (Refereed)
    Abstract [en]

    Ly alpha emitting (LAE) galaxies are thought to be progenitors of present-day L* galaxies. Clustering analyses have suggested that LAEs at z similar to 3 might evolve into LAEs at z similar to 2, but it is unclear whether the physical nature of these galaxies is compatible with this hypothesis. Several groups have investigated the properties of LAEs using spectral energy distribution (SED) fitting, but direct comparison of their results is complicated by inconsistencies in the treatment of the data and in the assumptions made in modeling the stellar populations, which are degenerate with the effects of galaxy evolution. By using the same data analysis pipeline and SED fitting software on two stacked samples of LAEs at z = 3.1 and z = 2.1, and by eliminating several systematic uncertainties that might cause a discrepancy, we determine that the physical properties of these two samples of galaxies are dramatically different. LAEs at z = 3.1 are found to be old (age similar to 1 Gyr) and metal-poor (Z < 0.2 Z(circle dot)), while LAEs at z = 2.1 appear to be young (age similar to 50 Myr) and metal-rich (Z > Z(circle dot)). The difference in the observed stellar ages makes it very unlikely that z = 3.1 LAEs evolve directly into z = 2.1 LAEs. Larger samples of galaxies, studies of individual objects, and spectroscopic measurements of metallicity at these redshifts are needed to confirm this picture, which is difficult to reconcile with the effects of 1 Gyr of cosmological evolution.

  • 7.
    Ahrens, Maryon
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Conrad, Jan M.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dumm, Jonathan P.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Flis, Samuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zoll, Marcel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Meyer, Manuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stanford University, USA.
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Feindt, Ulrich
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Barbarino, Cristina
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Roy, Rupak
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Farnier, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Linnaeus University, Sweden.
    Morå, Knut
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wagner, Robert M.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Multi-messenger Observations of a Binary Neutron Star Merger2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 848, no 2, article id L12Article in journal (Refereed)
    Abstract [en]

    On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of similar to 1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg(2) at a luminosity distance of 40(-8)(+8) Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 M-circle dot. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at similar to 40 Mpc) less than 11 hours after the merger by the One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over similar to 10 days. Following early non-detections, X-ray and radio emission were discovered at the transient's position similar to 9 and similar to 16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta.

  • 8.
    Ahrens, Maryon
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Deoskar, Kunal
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Dumm, Jonathan P.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    O'Sullivan, Erin
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Joint Constraints on Galactic Diffuse Neutrino Emission from the ANTARES and IceCube Neutrino Telescopes2018In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 868, no 2, article id L20Article in journal (Refereed)
    Abstract [en]

    The existence of diffuse Galactic neutrino production is expected from cosmic-ray interactions with Galactic gas and radiation fields. Thus, neutrinos are a unique messenger offering the opportunity to test the products of Galactic cosmic-ray interactions up to energies of hundreds of TeV. Here we present a search for this production using ten years of Astronomy with a Neutrino Telescope and Abyss environmental RESearch (ANTARES) track and shower data, as well as seven years of IceCube track data. The data are combined into a joint likelihood test for neutrino emission according to the KRA(gamma) model assuming a 5 PeV per nucleon Galactic cosmic-ray cutoff. No significant excess is found. As a consequence, the limits presented in this Letter start constraining the model parameter space for Galactic cosmic-ray production and transport.

  • 9.
    Ahrens, Maryon
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Dumm, Jonathan P.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Flis, Samuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wolf, Martin
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zoll, Marcel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    LOWERING ICECUBE'S ENERGY THRESHOLD FOR POINT SOURCE SEARCHES IN THE SOUTHERN SKY2016In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 824, no 2, article id L28Article in journal (Refereed)
    Abstract [en]

    Observation of a point source of astrophysical neutrinos would be a smoking gun signature of a cosmic-ray accelerator. While IceCube has recently discovered a diffuse flux of astrophysical neutrinos, no localized point source has been observed. Previous IceCube searches for point sources in the southern sky were restricted by either an energy threshold above a few hundred TeV or poor neutrino angular resolution. Here we present a search for southern sky point sources with greatly improved sensitivities to neutrinos with energies below 100 TeV. By selecting charged-current nu(mu) interacting inside the detector, we reduce the atmospheric background while retaining efficiency for astrophysical neutrino-induced events reconstructed with sub-degree angular resolution. The new event sample covers three years of detector data and leads to a factor of 10 improvement in sensitivity to point sources emitting below 100 TeV in the southern sky. No statistically significant evidence of point sources was found, and upper limits are set on neutrino emission from individual sources. A posteriori analysis of the highest-energy (similar to 100 TeV) starting event in the sample found that this event alone represents a 2.8 sigma deviation from the hypothesis that the data consists only of atmospheric background.

  • 10.
    Ahrens, Maryon
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Dumm, Jonathan P.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Flis, Samuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zoll, Marcel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Search for High-energy Neutrinos from Binary Neutron Star Merger GW170817 with ANTARES, IceCube, and the Pierre Auger Observatory2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 850, no 2, article id L35Article in journal (Refereed)
    Abstract [en]

    The Advanced LIGO and Advanced Virgo observatories recently discovered gravitational waves from a binary neutron star inspiral. A short gamma-ray burst (GRB) that followed the merger of this binary was also recorded by the Fermi Gamma-ray Burst Monitor (Fermi-GBM), and the Anti-Coincidence Shield for the Spectrometer for the International Gamma-Ray Astrophysics Laboratory (INTEGRAL), indicating particle acceleration by the source. The precise location of the event was determined by optical detections of emission following the merger. We searched for high-energy neutrinos from the merger in the GeV-EeV energy range using the ANTARES, IceCube, and Pierre Auger Observatories. No neutrinos directionally coincident with the source were detected within +/- 500 s around the merger time. Additionally, no MeV neutrino burst signal was detected coincident with the merger. We further carried out an extended search in the direction of the source for high-energy neutrinos within the 14 day period following the merger, but found no evidence of emission. We used these results to probe dissipation mechanisms in relativistic outflows driven by the binary neutron star merger. The non-detection is consistent with model predictions of short GRBs observed at a large off-axis angle.

  • 11.
    Ahrens, Maryon
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bohm, Christian
    Stockholm University, Faculty of Science, Department of Physics.
    Finley, Chad
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Flis, Samuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hulth, Per Olof
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Hultqvist, Klas
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Walck, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wolf, Martin
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zoll, Marcel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    SEARCH FOR PROMPT NEUTRINO EMISSION FROM GAMMA-RAY BURSTS WITH ICECUBE2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 805, no 1Article in journal (Refereed)
    Abstract [en]

    We present constraints derived from a search of four years of IceCube data for a prompt neutrino flux from gammaray bursts (GRBs). A single low-significance neutrino, compatible with the atmospheric neutrino background, was found in coincidence with one of the 506 observed bursts. Although GRBs have been proposed as candidate sources for ultra-high-energy cosmic rays, our limits on the neutrino flux disfavor much of the parameter space for the latest models. We also find that no more than similar to 1% of the recently observed astrophysical neutrino flux consists of prompt emission from GRBs that are potentially observable by existing satellites.

  • 12. Ajello, M.
    et al.
    Gasparrini, D.
    Sánchez-Conde, Miguel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Stanford University, USA.
    Zaharijas, G.
    Gustafsson, M.
    Cohen-Tanugi, J.
    Dermer, C. D.
    Inoue, Y.
    Hartmann, D.
    Ackermann, M.
    Bechtol, K.
    Franckowiak, A.
    Reimer, A.
    Romani, R. W.
    Strong, A. W.
    THE ORIGIN OF THE EXTRAGALACTIC GAMMA-RAY BACKGROUND AND IMPLICATIONS FOR DARK MATTER ANNIHILATION2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 800, no 2, article id L27Article in journal (Refereed)
    Abstract [en]

    The origin of the extragalactic.-ray background (EGB) has been debated for some time. The EGB comprises the.-ray emission from resolved and unresolved extragalactic sources, such as blazars, star-forming galaxies, and radio galaxies, as well as radiation from truly diffuse processes. This Letter focuses on the blazar source class, the most numerous detected population, and presents an updated luminosity function and spectral energy distribution model consistent with the blazar observations performed by the Fermi-Large Area Telescope (LAT). We show that blazars account for 50(-11)(+12)% of the EGB photons (>0.1 GeV), and that Fermi-LAT has already resolved similar to 70% of this contribution. Blazars, and in particular hard-spectrum sources such as BL Lacs, are responsible for most of the EGB emission above 100 GeV. We find that the extragalactic background light, which attenuates blazars' high-energy emission, is responsible for the high-energy cutoff observed in the EGB spectrum. Finally, we show that blazars, star-forming galaxies, and radio galaxies can naturally account for the amplitude and spectral shape of the background in the 0.1-820 GeV range, leaving only modest room for other contributions. This allows us to set competitive constraints on the dark matter annihilation cross section.

  • 13. Akiyama, E.
    et al.
    Muto, T.
    Kusakabe, N.
    Kataoka, A.
    Hashimoto, J.
    Tsukagoshi, T.
    Kwon, J.
    Kudo, T.
    Kandori, R.
    Grady, C. A.
    Takami, M.
    Janson, Markus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Kuzuhara, M.
    Henning, T.
    Sitko, M. L.
    Carson, J. C.
    Mayama, S.
    Currie, T.
    Thalmann, C.
    Wisniewski, J.
    Momose, M.
    Ohashi, N.
    Abe, L.
    Brandner, W.
    Brandt, T. D.
    Egner, S.
    Feldt, M.
    Goto, M.
    Guyon, O.
    Hayano, Y.
    Hayashi, M.
    Hayashi, S.
    Hodapp, K. W.
    Ishi, M.
    Iye, M.
    Knapp, G. R.
    Matsuo, T.
    Mcelwain, M. W.
    Miyama, S.
    Morino, J. -I.
    Moro-Martin, A.
    Nishimura, T.
    Pyo, T. -S.
    Serabyn, G.
    Suenaga, T.
    Suto, H.
    Suzuki, R.
    Takahashi, Y. H.
    Takato, N.
    Terada, H.
    Tomono, D.
    Turner, E. L.
    Watanabe, M.
    Yamada, T.
    Takami, H.
    Usuda, T.
    Tamura, M.
    DISCOVERY OF A DISK GAP CANDIDATE AT 20 AU IN TW HYDRAE2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 802, no 2, article id L17Article in journal (Refereed)
    Abstract [en]

    We present a new Subaru/HiCIAO high-contrast H-band polarized intensity (PI) image of a nearby transitional disk associated with TW Hydrae. The scattered light from the disk was detected from 0 ''.2 to 1 ''.5 (11-81 AU) and the PI image shows a clear axisymmetric depression in PI at similar to 0 ''.4 (similar to 20 AU) from the central star, similar to the similar to 80 AU gap previously reported from Hubble Space Telescope images. The azimuthal PI profile also shows that the disk beyond 0 ''.2 is almost axisymmetric. We discuss two possible scenarios explaining the origin of the PI depression: (1) a gap structure may exist at similar to 20 AU from the central star because of a shallow slope seen in the PI profile, and (2) grain growth may be occurring in the inner region of the disk. Multi-band observations at near-infrared and millimeter/submillimeter wavelengths play a complementary role in investigating dust opacity and may help reveal the origin of the gap more precisely.

  • 14.
    Amanullah, Rahman
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Johansson, Joel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Banerjee, D. P. K.
    Venkataraman, V.
    Joshi, V.
    Ashok, N. M.
    Cao, Y.
    Kasliwal, M. M.
    Kulkarni, S. R.
    Nugent, P. E.
    Petrushevska, Tanja
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Stanishev, V.
    THE PECULIAR EXTINCTION LAW OF SN 2014J MEASURED WITH THE HUBBLE SPACE TELESCOPE2014In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 788, no 2, p. L21-Article in journal (Refereed)
    Abstract [en]

    The wavelength dependence of the extinction of Type Ia SN 2014J in the nearby galaxy M82 has been measured using UV to near-IR photometry obtained with the Hubble Space Telescope, the Nordic Optical Telescope, and the Mount Abu Infrared Telescope. This is the first time that the reddening of an SN Ia is characterized over the full wavelength range of 0.2-2 mu m. A total-to-selective extinction, R-V >= 3.1, is ruled out with high significance. The best fit at maximum using a Galactic type extinction law yields R-V = 1.4 +/- 0.1. The observed reddening of SN 2014J is also compatible with a power-law extinction, A(lambda)/A(V) = (lambda/lambda(V))(p) as expected from multiple scattering of light, with p = -2.1 +/- 0.1. After correcting for differences in reddening, SN 2014J appears to be very similar to SN 2011 fe over the 14 broadband filter light curves used in our study.

  • 15.
    Anderson, Brandon
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Meyer, Manuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Ferretti, Raphael
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Zimmer, Stephan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    LOCALIZATION AND BROADBAND FOLLOW-UP OF THE GRAVITATIONAL-WAVE TRANSIENT GW 1509142016In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 826, no 1, article id L13Article in journal (Refereed)
    Abstract [en]

    A gravitational-wave (GW) transient was identified in data recorded by the Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) detectors on 2015 September 14. The event, initially designated G184098 and later given the name GW150914, is described in detail elsewhere. By prior arrangement, preliminary estimates of the time, significance, and sky location of the event were shared with 63 teams of observers covering radio, optical, near-infrared, X-ray, and gamma-ray wavelengths with ground- and space-based facilities. In this Letter we describe the low-latency analysis of the GW data and present the sky localization of the first observed compact binary merger. We summarize the follow-up observations reported by 25 teams via private Gamma-ray Coordinates Network circulars, giving an overview of the participating facilities, the GW sky localization coverage, the timeline, and depth of the observations. As this event turned out to be a binary black hole merger, there is little expectation of a detectable electromagnetic (EM) signature. Nevertheless, this first broadband campaign to search for a counterpart of an Advanced LIGO source represents a milestone and highlights the broad capabilities of the transient astronomy community and the observing strategies that have been developed to pursue neutron star binary merger events. Detailed investigations of the EM data and results of the EM follow-up campaign are being disseminated in papers by the individual teams.

  • 16.
    Andreas, Sandberg
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Melinder, Jens
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bik, Adrianus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Guaita, L.
    Limits on Lyman Continuum Escape from z = 2.2 Hα-emitting Galaxies2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 814, no 1, article id L10Article in journal (Refereed)
    Abstract [en]

    The leakage of Lyman continuum (LyC) photons from star-forming galaxies is an elusive parameter. When observed, it provides a wealth of information on star formation in galaxies and on the geometry of the interstellar medium, and puts constraints on the role of star-forming galaxies in the reionization of the universe. Hα-selected galaxies at  trace the highest star formation population at the peak of cosmic star formation history, providing a base for directly measuring LyC escape. Here we present this method and highlight its benefits as well as caveats. We also use the method on 10 Hα emitters in the Chandra Deep Field South at  also imaged with the Hubble Space Telescope in the ultraviolet. We find no individual LyC detections, and our stack puts a 5σ upper limit on the average absolute escape fraction of <24%, consistent with similar studies. With future planned observations, the sample sizes should rapidly increase and the method presented here should provide very robust constraints on the escape fraction.

  • 17. Andreoni, Igor
    et al.
    Goldstein, Daniel A.
    Anand, Shreya
    Coughlin, Michael W.
    Singer, Leo P.
    Ahumada, Tomás
    Medford, Michael
    Kool, Erik C.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Webb, Sara
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bloom, Joshua S.
    Kasliwal, Mansi M.
    Nugent, Peter E.
    Bagdasaryan, Ashot
    Barnes, Jennifer
    Cook, David O.
    Cooke, Jeff
    Duev, Dmitry A.
    Fremling, U. Christoffer
    Gatkine, Pradip
    Golkhou, V. Zach
    Kong, Albert K. H.
    Mahabal, Ashish
    Martínez-Palomera, Jorge
    Tao, Duo
    Zhang, Keming
    GROWTH on S190510g: DECam Observation Planning and Follow-up of a Distant Binary Neutron Star Merger Candidate2019In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 881, no 1, article id L16Article in journal (Refereed)
    Abstract [en]

    The first two months of the third Advanced LIGO and Virgo observing run (2019 April-May) showed that distant gravitational-wave (GW) events can now be readily detected. Three candidate mergers containing neutron stars (NS) were reported in a span of 15 days, all likely located more than 100 Mpc away. However, distant events such as the three new NS mergers are likely to be coarsely localized, which highlights the importance of facilities and scheduling systems that enable deep observations over hundreds to thousands of square degrees to detect the electromagnetic counterparts. On 2019 May 10 02: 59:39.292 UT the GW candidate S190510g was discovered and initially classified as a binary neutron star (BNS) merger with 98% probability. The GW event was localized within an area of 3462 deg(2), later refined to 1166 deg(2) (90%) at a distance of 227 +/- 92 Mpc. We triggered Target-of-Opportunity observations with the Dark Energy Camera (DECam), a wide-field optical imager mounted at the prime focus of the 4 m Blanco Telescope at Cerro Tololo Inter-American Observatory in Chile. This Letter describes our DECam observations and our real-time analysis results, focusing in particular on the design and implementation of the observing strategy. Within 24 hr of the merger time, we observed 65% of the total enclosed probability of the final skymap with an observing efficiency of 94%. We identified and publicly announced 13 candidate counterparts. S190510g was reclassified 1.7 days after the merger, after our observations were completed, with a BNS merger probability reduced from 98% to 42% in favor of a terrestrial classification.

  • 18. Ashall, C.
    et al.
    Hsiao, E. Y.
    Hoeflich, P.
    Stritzinger, M.
    Phillips, M. M.
    Morrell, N.
    Davis, S.
    Baron, E.
    Piro, A. L.
    Burns, C.
    Contreras, C.
    Galbany, L.
    Holmbo, S.
    Kirshner, R. P.
    Krisciunas, K.
    Marion, G. H.
    Sand, D. J.
    Shahbandeh, M.
    Suntzeff, N. B.
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Aarhus University, Denmark.
    Carnegie Supernova Project-II: Using Near-infrared Spectroscopy to Determine the Location of the Outer Ni-56 in Type Ia Supernovae2019In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 875, no 2, article id L14Article in journal (Refereed)
    Abstract [en]

    We present the H-band wavelength region of 37 postmaximum light near-infrared spectra of three normal, nine transitional, and four subluminous type. Ia supernovae (SNe Ia), extending from +5. days to +20. days relative to the epoch of B-band maximum. We introduce a new observable, the blue-edge velocity, v(edge), of the prominent Fe/Co/Ni-peak H-band emission feature, which is quantitatively measured. The v(edge) parameter is found to decrease over subtype ranging from around -14,000 km s(-1) for normal SNe Ia, to -10,000 km s(-1) for transitional SNe. Ia, down to -5000 km s(-1) for the subluminous SNe. Ia. Furthermore, inspection of the +10 +/- 3 days spectra indicates that v(edge) is correlated with the color-stretch parameter, s(BV), and hence with peak luminosity. These results follow the previous findings that brighter SNe. Ia tend to have Ni-56 located at higher velocities as compared to subluminous objects. As v(edge) is a model-independent parameter, we propose it can be used in combination with traditional observational diagnostics to provide a new avenue to robustly distinguish between leading SNe. Ia explosion models.

  • 19. Bastian, T. S.
    et al.
    Chintzoglou, G.
    De Pontieu, B.
    Shimojo, M.
    Schmit, D.
    Leenaarts, Jorrit
    Stockholm University, Faculty of Science, Department of Astronomy.
    Loukitcheva, M.
    A First Comparison of Millimeter Continuum and MgII Ultraviolet Line Emission from the Solar Chromosphere2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 845, no 2, article id L19Article in journal (Refereed)
    Abstract [en]

    We present joint observations of the Sun by the Atacama Large Millimeter/submillimeter Array (ALMA) and the Interface Region Imaging Spectrograph (IRIS). Both millimeter/submillimeter-lambda continuum emission and ultraviolet (UV) line emission originate from the solar chromosphere and both have the potential to serve as powerful and complementary diagnostics of physical conditions in this enigmatic region of the solar atmosphere. The observations were made of a solar active region on 2015 December 18 as part of the ALMA science verification effort. A map of the Sun's continuum emission was obtained by ALMA at a wavelength of 1.25 mm (239 GHz). A contemporaneous map was obtained by IRIS in the Mg II h doublet line at 2803.5 angstrom. While a clear correlation between the 1.25 mm brightness temperature T-B and the Mg II h line radiation temperature T-rad is observed, the slope is <1, perhaps as a result of the fact that these diagnostics are sensitive to different parts of the chromosphere and that the Mg II h line source function includes a scattering component. There is a significant difference (35%) between the mean TB (1.25 mm) and mean T-rad (Mg II). Partitioning the maps into sunspot, quiet areas, and plage regions we find the relation between the IRIS Mg II h line Trad and the ALMA TB region-dependent. We suggest this may be the result of regional dependences of the formation heights of the IRIS and ALMA diagnostics and/or the increased degree of coupling between the UV source function and the local gas temperature in the hotter, denser gas in plage regions.

  • 20.
    Beresnyak, Andrey
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Los Alamos National Laboratory, USA.
    ON THE PARALLEL SPECTRUM IN MAGNETOHYDRODYNAMIC TURBULENCE2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 801, no 1, article id L9Article in journal (Refereed)
    Abstract [en]

    Anisotropy of MHD turbulence has been studied extensively for many years, most prominently by measurements in the solar wind and high-resolution simulations. The spectrum parallel to the local magnetic field was observed to be steeper than the perpendicular spectrum, typically k(-2), consistent with the widely accepted Goldreich & Sridhar model. In this Letter, I looked deeper into the nature of the relation between parallel and perpendicular spectra and argue that this k(-2) scaling has the same origin as the omega(-2) scaling of the Lagrangian frequency spectrum in strong hydrodynamic turbulence. This follows from the fact that Alfven waves propagate along magnetic field lines. It has now became clear that the observed anisotropy can be argued without invocation of the critical balance argument and is more robust that was previously thought. The relation between parallel (Lagrangian) and perpendicular (Eulerian) spectra is an inevitable consequence of strong turbulence of Alfven waves, rather than a conjecture based on the uncertainty relation. I tested this using high-resolution simulations of MHD turbulence, in particular, I verified that the cutoff of the parallel spectrum scales as a Kolmogorov timescale, not lengthscale.

  • 21. Bradac, Marusa
    et al.
    Garcia-Appadoo, Diego
    Huang, Kuang-Han
    Vallini, Livia
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Dipartimento di Fisica e Astronomia, Bologna, Italy; INAF, Osservatorio Astronomico di Bologna, Italy.
    Finney, Emily Quinn
    Hoag, Austin
    Lemaux, Brian C.
    Schmidt, Kasper Borello
    Treu, Tommaso
    Carilli, Chris
    Dijkstra, Mark
    Ferrara, Andrea
    Fontana, Adriano
    Jones, Tucker
    Ryan, Russell
    Wagg, Jeff
    Gonzalez, Anthony H.
    ALMA [C II] 158 mu m Detection of a Redshift 7 Lensed Galaxy behind RXJ1347.1-11452017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 836, no 1, article id L2Article in journal (Refereed)
    Abstract [en]

    We present the results of ALMA spectroscopic follow-up of a z = 6.766 Ly alpha emitting galaxy behind the cluster RX J1347.1-1145. We report the detection of [C II] 158 mu m line fully consistent with the Ly alpha redshift and with the peak of the optical emission. Given the magnification of mu = 5.0 +/- 0.3, the intrinsic (corrected for lensing) luminosity of the [C II] line is L[C II]= 1.4(-0.3)(+0.3) x 10(7) L-circle dot, roughly similar to 5 times fainter than other detections of z similar to 7 galaxies. The result indicates that low L[C II] in z similar to 7 galaxies compared to the local counterparts might be caused by their low metallicities and/or feedback. The small velocity offset (Delta v = 20(-40)(+40) km s(-1)) between the Ly alpha and [C II] line is unusual, and may be indicative of ionizing photons escaping.

  • 22.
    Brandenburg, Axel
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Nordic Institute for Theoretical Physics (Nordita). University of Colorado, USA.
    Ashurova, Mohira B.
    Jabbari, Sarah
    Compensating Faraday Depolarization by Magnetic Helicity in the Solar Corona2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 845, no 2, article id L15Article in journal (Refereed)
    Abstract [en]

    A turbulent dynamo in spherical geometry with an outer corona is simulated to study the sign of magnetic helicity in the outer parts. In agreement with earlier studies, the sign in the outer corona is found to be opposite to that inside the dynamo. Line-of-sight observations of polarized emission are synthesized to explore the feasibility of using the local reduction of Faraday depolarization to infer the sign of helicity of magnetic fields in the solar corona. This approach was previously identified as an observational diagnostic in the context of galactic magnetic fields. Based on our simulations, we show that this method can be successful in the solar context if sufficient statistics are gathered by using averages over ring segments in the corona separately for the regions north and south of the solar equator.

  • 23.
    Brandenburg, Axel
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Nordic Institute for Theoretical Physics (Nordita). University of Colorado, USA.
    Giampapa, Mark S.
    Enhanced Stellar Activity for Slow Antisolar Differential Rotation2018In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 855, no 2, article id L22Article in journal (Refereed)
    Abstract [en]

    High-precision photometry of solar-like members of the open cluster M67 with Kepler/K2 data has recently revealed enhanced activity for stars with a large Rossby number, which is the ratio of rotation period to the convective turnover time. Contrary to the well established behavior for shorter rotation periods and smaller Rossby numbers, the chromospheric activity of the more slowly rotating stars of M67 was found to increase with increasing Rossby number. Such behavior has never been reported before, although it was theoretically predicted to emerge as a consequence of antisolar differential rotation (DR) for stars with Rossby numbers larger than that of the Sun, because in those models the absolute value of the DR was found to exceed that for solar-like DR. Using gyrochronological relations and an approximate age of 4 Gyr for the members of M67, we compare with computed rotation rates using just the B - V color. The resulting rotation-activity relation is found to be compatible with that obtained by employing the measured rotation rate. This provides additional support for the unconventional enhancement of activity at comparatively low rotation rates and the possible presence of antisolar differential rotation.

  • 24.
    Brandenburg, Axel
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Kleeorin, Nathan
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Ben-Gurion University of the Negev, Israel; N. I. Lobachevsky State University of Nizhny Novgorod, Russia.
    Rogachevskii, Igor
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Ben-Gurion University of the Negev, Israel; N. I. Lobachevsky State University of Nizhny Novgorod, Russia.
    SELF-ASSEMBLY OF SHALLOW MAGNETIC SPOTS THROUGH STRONGLY STRATIFIED TURBULENCE2013In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 776, no 2, article id L23Article in journal (Refereed)
    Abstract [en]

    Recent studies have demonstrated that in fully developed turbulence, the effective magnetic pressure of a large-scale field (non-turbulent plus turbulent contributions) can become negative. In the presence of strongly stratified turbulence, this was shown to lead to a large-scale instability that produces spontaneous magnetic flux concentrations. Furthermore, using a horizontal magnetic field, elongated flux concentrations with a strength of a few percent of the equipartition value were found. Here we show that a uniform vertical magnetic field leads to circular magnetic spots of equipartition field strengths. This could represent a minimalistic model of sunspot formation and highlights the importance of two critical ingredients: turbulence and strong stratification. Radiation, ionization, and supergranulation may be important for realistic simulations, but are not critical at the level of a minimalistic model of magnetic spot formation.

  • 25.
    Brandenburg, Axel
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Nordic Institute for Theoretical Physics (Nordita). University of Colorado, USA.
    Schober, Jennifer
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    Rogachevskii, Igor
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). University of Colorado, USA; Ben-Gurion University of the Negev, Israel.
    Kahniashvili, Tina
    Boyarsky, Alexey
    Fröhlich, Jürg
    Ruchayskiy, Oleg
    Kleeorin, Nathan
    Stockholm University, Nordic Institute for Theoretical Physics (Nordita). Ben-Gurion University of the Negev, Israel.
    The Turbulent Chiral Magnetic Cascade in the Early Universe2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 845, no 2, article id L21Article in journal (Refereed)
    Abstract [en]

    The presence of asymmetry between fermions of opposite handedness in plasmas of relativistic particles can lead to exponential growth of a helical magnetic field via a small-scale chiral dynamo instability known as the chiral magnetic effect. Here, we show, using dimensional arguments and numerical simulations, that this process produces through the Lorentz force chiral magnetically driven turbulence. A k(-2) magnetic energy spectrum emerges via inverse transfer over a certain range of wavenumbers k. The total chirality (magnetic helicity plus normalized chiral chemical potential) is conserved in this system. Therefore, as the helical magnetic field grows, most of the total chirality gets transferred into magnetic helicity until the chiral magnetic effect terminates. Quantitative results for height, slope, and extent of the spectrum are obtained. Consequences of this effect for cosmic magnetic fields are discussed.

  • 26. Burgess, J. Michael
    et al.
    Preece, Robert D.
    Ryde, Felix
    Veres, Peter
    Meszaros, Peter
    Connaughton, Valerie
    Briggs, Michael
    Pe'er, Asaf
    Iyyani, Shabnam
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Royal Institute of Technology, Sweden.
    Goldstein, Adam
    Axelsson, Magnus
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Royal Institute of Technology, Sweden.
    Baring, Matthew G.
    Bhat, P. N.
    Byrne, David
    Fitzpatrick, Gerard
    Foley, Suzanne
    Kocevski, Daniel
    Omodei, Nicola
    Paciesas, William S.
    Pelassa, Veronique
    Kouveliotou, Chryssa
    Stockholm University, Faculty of Science, Department of Physics.
    Xiong, Shaolin
    Yu, Hoi-Fung
    Zhang, Binbin
    Zhu, Sylvia
    AN OBSERVED CORRELATION BETWEEN THERMAL AND NON-THERMAL EMISSION IN GAMMA-RAY BURSTS2014In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 784, no 2, article id L43Article in journal (Refereed)
    Abstract [en]

    Recent observations by the Fermi Gamma-ray Space Telescope have confirmed the existence of thermal and non-thermal components in the prompt photon spectra of some gamma-ray bursts (GRBs). Through an analysis of six bright Fermi GRBs, we have discovered a correlation between the observed photospheric and non-thermal gamma-ray emission components of several GRBs using a physical model that has previously been shown to be a good fit to the Fermi data. From the spectral parameters of these fits we find that the characteristic energies, E-p and kT, of these two components are correlated via the relation E-p proportional to T-alpha which varies from GRB to GRB. We present an interpretation in which the value of the index alpha indicates whether the jet is dominated by kinetic or magnetic energy. To date, this jet composition parameter has been assumed in the modeling of GRB outflows rather than derived from the data.

  • 27. Carlsson, Mats
    et al.
    Leenaarts, Jorrit
    Stockholm University, Faculty of Science, Department of Astronomy.
    De Pontieu, Bart
    WHAT DO IRIS OBSERVATIONS OF Mg II k TELL US ABOUT THE SOLAR PLAGE CHROMOSPHERE?2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 809, no 2, article id L30Article in journal (Refereed)
    Abstract [en]

    We analyze observations from the Interface Region Imaging Spectrograph of the Mg II k line, the Mg II UV subordinate lines, and the O I 135.6 nm line to better understand the solar plage chromosphere. We also make comparisons with observations from the Swedish 1-m Solar Telescope of the H alpha line, the Ca II 8542 line, and Solar Dynamics Observatory/Atmospheric Imaging Assembly observations of the coronal 19.3 nm line. To understand the observed Mg II profiles, we compare these observations to the results of numerical experiments. The single-peaked or flat-topped Mg II k profiles found in plage imply a transition region at a high column mass and a hot and dense chromosphere of about 6500 K. This scenario is supported by the observed large-scale correlation between moss brightness and filled-in profiles with very little or absent self-reversal. The large wing width found in plage also implies a hot and dense chromosphere with a steep chromospheric temperature rise. The absence of emission in the Mg II subordinate lines constrain the chromospheric temperature and the height of the temperature rise while the width of the O I 135.6 nm line sets a limit to the non-thermal velocities to around 7 km s(-1).

  • 28. Chen, T.-W.
    et al.
    Inserra, C.
    Fraser, M.
    Moriya, T. J.
    Schady, P.
    Schweyer, T.
    Filippenko, A.
    Perley, D. A.
    Ruiter, A. J.
    Seitenzahl, I.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Anderson, J. P.
    Foley, R. J.
    Jerkstrand, A.
    Ngeow, C.-C.
    Pan, Y.-C.
    Pastorello, A.
    Points, S.
    Smartt, S. J.
    Smith, K. W.
    Taubenberger, S.
    Wienlan, P.
    Young, D. R.
    Benetti, S.
    Berton, M.
    Bufano, F.
    Clark, P.
    Della Valle, M.
    Galbany, L.
    Gal-Yam, A.
    Gromadzki, M.
    Gutierrez, C. P.
    Heinze, A.
    Kankare, E.
    Kilpatrick, C. D.
    Kuncarayakti, H.
    Leloudas, G.
    Lin, Z.-Y.
    Maguire, K.
    Mazzali, P.
    McBrien, O.
    Prentice, S. J.
    Rau, A.
    Rest, A.
    Siebert, M. R.
    Stalder, B.
    Tonry, J. L.
    Yu, P.-C.
    SN 2017ens: The Metamorphosis of a Luminous Broadlined Type Ic Supernova into an SN IIn2018In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 867, no 2, article id L31Article in journal (Refereed)
    Abstract [en]

    We present observations of supernova (SN) 2017ens, discovered by the ATLAS survey and identified as a hot blue object through the GREAT program. The redshift z = 0.1086 implies a peak brightness of M-g = -21.1 mag, placing the object within the regime of superluminous supernovae. We observe a dramatic spectral evolution, from initially being blue and featureless, to later developing features similar to those of the broadlined Type Ic SN 1998bw, and finally showing 2000 km s(-1) wide H alpha and H beta emission. Relatively narrow Balmer emission (reminiscent of a SN IIn) is present at all times. We also detect coronal lines, indicative of a dense circumstellar medium. We constrain the progenitor wind velocity to similar to 50-60 km s(-1) based on P-Cygni profiles, which is far slower than those present in Wolf-Rayet stars. This may suggest that the progenitor passed through a luminous blue variable phase, or that the wind is instead from a binary companion red supergiant star. At late times we see the similar to 2000 km s(-1) wide H alpha emission persisting at high luminosity (similar to 3 x 10(40) erg s(-1)) for at least 100 day, perhaps indicative of additional mass loss at high velocities that could have been ejected by a pulsational pair instability.

  • 29. Cole, Elizabeth
    et al.
    Käpylä, Petri J.
    Mantere, Maarit J.
    Brandenburg, Axel
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Nordic Institute for Theoretical Physics (Nordita).
    AN AZIMUTHAL DYNAMO WAVE IN SPHERICAL SHELL CONVECTION2014In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 780, no 2, article id L22Article in journal (Refereed)
    Abstract [en]

    We report the discovery of an azimuthal dynamo wave of a low-order (m = 1) mode in direct numerical simulations (DNS) of turbulent convection in spherical shells. Such waves are predicted by mean-field dynamo theory and have been obtained previously in mean-field models. An azimuthal dynamo wave has been proposed as a possible explanation for the persistent drifts of spots observed on several rapidly rotating stars, as revealed through photometry and Doppler imaging. However, this has been judged unlikely because evidence for such waves from DNS has been lacking. Here we present DNS of large-scale magnetic fields showing a retrograde m = 1 mode. Its pattern speed is nearly independent of latitude and does not reflect the speed of the differential rotation at any depth. The extrema of magnetic m = 1 structures coincide reasonably well with the maxima of m = 2 structures of the temperature. These results provide direct support for the observed drifts being due to an azimuthal dynamo wave.

  • 30.
    Conrad, Jan
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Farnier, Christian
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC). Linnaeus University, Sweden.
    Meyer, Manuel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Morå, Knut
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wagner, Robert M.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    TeV Gamma-Ray Observations of the Binary Neutron Star Merger GW170817 with HESS2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 850, no 2, article id L22Article in journal (Refereed)
    Abstract [en]

    We search for high-energy gamma-ray emission from the binary neutron star merger GW170817 with the H.E.S.S. Imaging Air Cherenkov Telescopes. The observations presented here have been obtained starting only 5.3 hr after GW170817. The H.E.S.S. target selection identified regions of high probability to find a counterpart of the gravitational-wave event. The first of these regions contained the counterpart SSS17a that has been identified in the optical range several hours after our observations. We can therefore present the first data obtained by a ground-based pointing instrument on this object. A subsequent monitoring campaign with the H.E.S.S. telescopes extended over several days, covering timescales from 0.22 to 5.2 days and energy ranges between 270 GeV to 8.55 TeV. No significant gamma-ray emission has been found. The derived upper limits on the very-high-energy gamma-ray flux for the first time constrain non-thermal, high-energy emission following the merger of a confirmed binary neutron star system.

  • 31. Crepp, Justin R.
    et al.
    Rice, Emily L.
    Veicht, Aaron
    Aguilar, Jonathan
    Pueyo, Laurent
    Giorla, Paige
    Nilsson, Ricky
    Stockholm University, Faculty of Science, Department of Astronomy.
    Luszcz-Cook, Statia H.
    Oppenheimer, Rebecca
    Hinkley, Sasha
    Brenner, Douglas
    Vasisht, Gautam
    Cady, Eric
    Beichman, Charles A.
    Hillenbrand, Lynne A.
    Lockhart, Thomas
    Matthews, Christopher T.
    Roberts, Lewis C., Jr.
    Sivaramakrishnan, Anand
    Soummer, Remi
    Zhai, Chengxing
    DIRECT SPECTRUM OF THE BENCHMARK T DWARF HD 19467 B2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 798, no 2, article id L43Article in journal (Refereed)
    Abstract [en]

    HD 19467 B is presently the only directly imaged T dwarf companion known to induce a measurable Doppler acceleration around a solar-type star. We present spectroscopy measurements of this important benchmark object taken with the Project 1640 integral field unit at Palomar Observatory. Our high-contrast R approximate to 30 observations obtained simultaneously across the JH bands confirm the cold nature of the companion as reported from the discovery article and determine its spectral type for the first time. Fitting the measured spectral energy distribution to SpeX/IRTF T dwarf standards and synthetic spectra from BT-Settl atmospheric models, we find that HD 19467 B is a T5.5 +/- 1 dwarf with effective temperature T-eff = 978(-43)(+20) K. Our observations reveal significant methane absorption affirming its substellar nature. HD 19467 B shows promise to become the first T dwarf that simultaneously reveals its mass, age, and metallicity independent from the spectrum of light that it emits.

  • 32. Currie, Thayne
    et al.
    Guyon, Olivier
    Tamura, Motohide
    Kudo, Tomoyuki
    Jovanovic, Nemanja
    Lozi, Julien
    Schlieder, Joshua E.
    Brandt, Timothy D.
    Kuhn, Jonas
    Serabyn, Eugene
    Janson, Markus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Carson, Joseph
    Groff, Tyler
    Kasdin, N. Jeremy
    McElwain, Michael W.
    Singh, Garima
    Uyama, Taichi
    Kuzuhara, Masayuki
    Akiyama, Eiji
    Grady, Carol
    Hayashi, Saeko
    Knapp, Gillian
    Kwon, Jung-mi
    Oh, Daehyeon
    Wisniewski, John
    Sitko, Michael
    Yang, Yi
    Subaru/SCExAO First-light Direct Imaging of a Young Debris Disk around HD 365462017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 836, no 1, article id L15Article in journal (Refereed)
    Abstract [en]

    We present H-band scattered light imaging of a bright debris disk around the A0 star HD 36546 obtained from the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system with data recorded by the HiCIAO camera using the vector vortex coronagraph. SCExAO traces the disk from r similar to 0.3 to r similar to 1 (34-114 au). The disk is oriented in a near east-west direction (PA similar to 75 degrees), is inclined by i similar to 70 degrees-75 degrees, and is strongly forward-scattering (g > 0.5). It is an extended disk rather than a sharp ring; a second, diffuse dust population extends from the disk's eastern side. While HD 36546 intrinsic properties are consistent with a wide age range (t similar to 1-250 Myr), its kinematics and analysis of coeval stars suggest a young age (3-10 Myr) and a possible connection to Taurus-Auriga's star formation history. SCExAO's planet-to-star contrast ratios are comparable to the first-light Gemini Planet Imager contrasts; for an age of 10 Myr, we rule out planets with masses comparable to HR 8799 b beyond a projected separation of 23 au. A massive icy planetesimal disk or an unseen super-Jovian planet at r > 20 au may explain the disk's visibility. The HD 36546 debris disk may be the youngest debris disk yet imaged, is the first newly identified object from the now-operational SCExAO extreme AO system, is ideally suited for spectroscopic follow-up with SCExAO/CHARIS in 2017, and may be a key probe of icy planet formation and planet-disk interactions.

  • 33. Currie, Thayne
    et al.
    Marois, Christian
    Cieza, Lucas
    Mulders, Gijs D.
    Lawson, Kellen
    Caceres, Claudio
    Rodriguez-Ruiz, Dary
    Wisniewski, John
    Guyon, Olivier
    Brandt, Timothy D.
    Kasdin, N. Jeremy
    Groff, Tyler D.
    Lozi, Julien
    Chilcote, Jeffrey
    Hodapp, Klaus
    Jovanovic, Nemanja
    Martinache, Frantz
    Skaf, Nour
    Lyra, Wladimir
    Tamura, Motohide
    Asensio-Torres, Ruben
    Stockholm University, Faculty of Science, Department of Astronomy.
    Dong, Ruobing
    Grady, Carol
    Gerard, Benjamin
    Fukagawa, Misato
    Hand, Derek
    Hayashi, Masahiko
    Henning, Thomas
    Kudo, Tomoyuki
    Kuzuhara, Masayuki
    Kwon, Jungmi
    McElwain, Michael W.
    Uyama, Taichi
    No Clear, Direct Evidence for Multiple Protoplanets Orbiting LkCa 15: LkCa 15 bcd are Likely Inner Disk Signals2019In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 877, no 1, article id L3Article in journal (Refereed)
    Abstract [en]

    Two studies utilizing sparse aperture-masking (SAM) interferometry and H-alpha differential imaging have reported multiple Jovian companions around the young solar-mass star, LkCa 15 (LkCa 15 bcd): the first claimed direct detection of infant, newly formed planets (protoplanets). We present new near-infrared direct imaging/spectroscopy from the Subaru Coronagraphic Extreme Adaptive Optics (SCExAO) system coupled with Coronagraphic High Angular Resolution Imaging Spectrograph (CHARIS) integral field spectrograph and multi-epoch thermal infrared imaging from Keck/NIRC2 of LkCa 15 at high Strehl ratios. These data provide the first direct imaging look at the same wavelengths and in the same locations where previous studies identified the LkCa 15 protoplanets, and thus offer the first decisive test of their existence. The data do not reveal these planets. Instead, we resolve extended emission tracing a dust disk with a brightness and location comparable to that claimed for LkCa 15 bcd. Forward-models attributing this signal to orbiting planets are inconsistent with the combined SCExAO/CHARIS and Keck/NIRC2 data. An inner disk provides a more compelling explanation for the SAM detections and perhaps also the claimed H-alpha detection of LkCa 15 b. We conclude that there is currently no clear, direct evidence for multiple protoplanets orbiting LkCa 15, although the system likely contains at least one unseen Jovian companion. To identify Jovian companions around LkCa 15 from future observations, the inner disk should be detected and its effect modeled, removed, and shown to be distinguishable from planets. Protoplanet candidates identified from similar systems should likewise be clearly distinguished from disk emission through modeling.

  • 34. Currie, Thayne
    et al.
    Muto, Takayuki
    Kudo, Tomoyuki
    Honda, Mitsuhiko
    Brandt, Timothy D.
    Grady, Carol
    Fukagawa, Misato
    Burrows, Adam
    Janson, Markus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Kuzuhara, Masayuki
    McElwain, Michael W.
    Follette, Katherine
    Hashimoto, Jun
    Henning, Thomas
    Kandori, Ryo
    Kusakabe, Nobuhiko
    Kwon, Jungmi
    Mede, Kyle
    Morino, Jun-ichi
    Nishikawa, Jun
    Pyo, Tae-Soo
    Serabyn, Gene
    Suenaga, Takuya
    Takahashi, Yasuhiro
    Wisniewski, John
    Tamura, Motohide
    RECOVERY OF THE CANDIDATE PROTOPLANET HD 100546 b WITH GEMINI/NICI AND DETECTION OF ADDITIONAL (PLANET-INDUCED ?) DISK STRUCTURE AT SMALL SEPARATIONS2014In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 796, no 2, p. L30-Article in journal (Refereed)
    Abstract [en]

    We report the first independent, second epoch (re-) detection of a directly imaged protoplanet candidate. Using L' high-contrast imaging of HD 100546 taken with the Near-Infrared Coronagraph and Imager on Gemini South, we recover HD 100546 b with a position and brightness consistent with the original Very Large Telescope/NAos-COnica detection from Quanz et al., although data obtained after 2013 will be required to decisively demonstrate common proper motion. HD 100546 b may be spatially resolved, up to approximate to 12-13 AU in diameter, and is embedded in a finger of thermal IR-bright, polarized emission extending inward to at least 0 ''.3. Standard hot-start models imply a mass of approximate to 15 M-J. However, if HD 100546 b is newly formed or made visible by a circumplanetary disk, both of which are plausible, its mass is significantly lower (e.g., 1-7 M-J). Additionally, we discover a thermal IR-bright disk feature, possibly a spiral density wave, at roughly the same angular separation as HD 100546 b but 90 degrees. away. Our interpretation of this feature as a spiral arm is not decisive, but modeling analyses using spiral density wave theory implies a wave launching point exterior to approximate to 0 ''.45 embedded within the visible disk structure: plausibly evidence for a second, hitherto unseen, wide-separation planet. With one confirmed protoplanet candidate and evidence for one to two others, HD 100546 is an important evolutionary precursor to intermediate-mass stars with multiple super-Jovian planets at moderate/wide separations like HR 8799.

  • 35. Dalda, Alberto Sainz
    et al.
    de la Cruz Rodríguez, Jaime
    Stockholm University, Faculty of Science, Department of Astronomy.
    De Pontieu, Bart
    Gošić, Milan
    Recovering Thermodynamics from Spectral Profiles observed by IRIS: A Machine and Deep Learning Approach2019In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 875, no 2, article id L18Article in journal (Refereed)
    Abstract [en]

    Inversion codes allow the reconstruction of a model atmosphere from observations. With the inclusion of optically thick lines that form in the solar chromosphere, such modeling is computationally very expensive because a non-LTE evaluation of the radiation field is required. In this study, we combine the results provided by these traditional methods with machine and deep learning techniques to obtain similar-quality results in an easy-to-use, much faster way. We have applied these new methods to Mg II h and k lines observed by the Interface Region Imaging Spectrograph (IRIS). As a result, we are able to reconstruct the thermodynamic state (temperature, line-of-sight velocity, nonthermal velocities, electron density, etc.) in the chromosphere and upper photosphere of an area equivalent to an active region in a few CPU minutes, speeding up the process by a factor of 10(5) - 10(6). The opensource code accompanying this Letter will allow the community to use IRIS observations to open a new window to a host of solar phenomena.

  • 36.
    de la Cruz Rodriguez, Jaime
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Leenaarts, Jorrit
    Stockholm University, Faculty of Science, Department of Astronomy.
    Asensio Ramos, Andrés
    NON-LTE INVERSIONS OF THE Mg II h & k AND UV TRIPLET LINES2016In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 830, no 2, article id L30Article in journal (Refereed)
    Abstract [en]

    The Mg II h & k lines are powerful diagnostics for studying the solar chromosphere. They have become particularly popular with the launch of the Interface Region Imaging Spectrograph (IRIS) satellite, and a number of studies that include these lines have lead to great progress in understanding chromospheric heating, in many cases thanks to the support from 3D MHD simulations. In this study, we utilize another approach to analyze observations: non-LTE inversions of the Mg II h & k and UV triplet lines including the effects of partial redistribution. Our inversion code attempts to construct a model atmosphere that is compatible with the observed spectra. We have assessed the capabilities and limitations of the inversions using the FALC atmosphere and a snapshot from a 3D radiation-MHD simulation. We find that Mg II h & k allow reconstructing a model atmosphere from the middle photosphere to the transition region. We have also explored the capabilities of a multi-line/multi-atom setup, including the Mg IIh & k, the Ca II 854.2. nm, and the Fe I. 630.25 lines to recover the full stratification of physical parameters, including the magnetic field vector, from the photosphere to the chromosphere. Finally, we present the first inversions of observed IRIS spectra from quiet-Sun, plage, and sunspot, with very promising results.

  • 37. de Leon, Jerome
    et al.
    Takami, Michihiro
    Karr, Jennifer L.
    Hashimoto, Jun
    Kudo, Tomoyuki
    Sitko, Michael
    Mayama, Satoshi
    Kusakabe, Nobuyuki
    Akiyama, Eiji
    Liu, Hauyu Baobab
    Usuda, Tomonori
    Abe, Lyu
    Brandner, Wolfgang
    Brandt, Timothy D.
    Carson, Joseph
    Currie, Thayne
    Egner, Sebastian E.
    Feldt, Markus
    Follette, Katherine
    Grady, Carol A.
    Goto, Miwa
    Guyon, Olivier
    Hayano, Yutaka
    Hayashi, Masahiko
    Hayashi, Saeko
    Henning, Thomas
    Hodapp, Klaus W.
    Ishii, Miki
    Iye, Masanori
    Janson, Markus
    Stockholm University, Faculty of Science, Department of Astronomy.
    Kandori, Ryo
    Knapp, Gillian R.
    Kuzuhara, Masayuki
    Kwon, Jungmi
    Matsuo, Taro
    McElwain, Michael W.
    Miyama, Shoken
    Morino, Jun-Ichi
    Moro-Martin, Amaya
    Nishimura, Tetsuo
    Pyo, Tae-Soo
    Serabyn, Eugene
    Suenaga, Takuya
    Suto, Hiroshi
    Suzuki, Ryuji
    Takahashi, Yasuhiro
    Takato, Naruhisa
    Terada, Hiroshi
    Thalmann, Christian
    Tomono, Daigo
    Turner, Edwin L.
    Watanabe, Makoto
    Wisniewski, John P.
    Yamada, Toru
    Takami, Hideki
    Tamura, Motohide
    NEAR-IR HIGH-RESOLUTION IMAGING POLARIMETRY OF THE SU Aur DISK: CLUES FOR TIDAL TAILS?2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 806, no 1, article id L10Article in journal (Refereed)
    Abstract [en]

    We present new high-resolution (similar to 0.09) H-band imaging observations of the circumstellar disk around the T Tauri star SU Aur. Our observations with Subaru-HiCIAO have revealed the presence of scattered light as close as 0.15 (similar to 20 AU) to the star. Within our image, we identify bright emission associated with a disk with a minimum radius of similar to 90 AU, an inclination of similar to 35 degrees from the plane of the sky, and an approximate PA of 15 degrees for the major axis. We find a brightness asymmetry between the northern and southern sides of the disk due to a non-axisymmetric disk structure. We also identify a pair of asymmetric tail structures extending east and west from the disk. The western tail extends at least 2.5 (350 AU) from the star, and is probably associated with a reflection nebula previously observed at optical and near-IR wavelengths. The eastern tail extends at least 1. (140 AU) at the present signal-to-noise. These tails are likely due to an encounter with an unseen brown dwarf, but our results do not exclude the explanation that these tails are outflow cavities or jets.

  • 38. Drlica-Wagner, A.
    et al.
    Albert, A.
    Bechtol, K.
    Wood, M.
    Strigari, L.
    Sanchez-Conde, Miguel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Baldini, L.
    Essig, R.
    Cohen-Tanugi, J.
    Anderson, B.
    Bellazzini, R.
    Bloom, E. D.
    Caputo, R.
    Cecchi, C.
    Charles, E.
    Chiang, J.
    de Angelis, A.
    Funk, S.
    Fusco, P.
    Gargano, F.
    Giglietto, N.
    Giordano, F.
    Guiriec, S.
    Gustafsson, M.
    Kuss, M.
    Loparco, F.
    Lubrano, P.
    Mirabal, N.
    Mizuno, T.
    Morselli, A.
    Ohsugi, T.
    Orlando, E.
    Persic, M.
    Raino, S.
    Sehgal, N.
    Spada, F.
    Suson, D. J.
    Zaharijas, G.
    Zimmer, Stephan
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Abbott, T.
    Allam, S.
    Balbinot, E.
    Bauer, A. H.
    Benoit-Levy, A.
    Bernstein, R. A.
    Bernstein, G. M.
    Bertin, E.
    Brooks, D.
    Buckley-Geer, E.
    Burke, D. L.
    Carnero Rosell, A.
    Castander, F. J.
    Covarrubias, R.
    D'Andrea, C. B.
    da Costa, L. N.
    DePoy, D. L.
    Desai, S.
    Diehl, H. T.
    Cunha, C. E.
    Eifler, T. F.
    Estrada, J.
    Evrard, A. E.
    Fausti Neto, A.
    Fernandez, E.
    Finley, D. A.
    Flaugher, B.
    Frieman, J.
    Gaztanaga, E.
    Gerdes, D.
    Gruen, D.
    Gruendl, R. A.
    Gutierrez, G.
    Honscheid, K.
    Jain, B.
    James, D.
    Jeltema, T.
    Kent, S.
    Kron, R.
    Kuehn, K.
    Kuropatkin, N.
    Lahav, O.
    Li, T. S.
    Luque, E.
    Maia, M. A. G.
    Makler, M.
    March, M.
    Marshall, J.
    Martini, P.
    Merritt, K. W.
    Miller, C.
    Miquel, R.
    Mohr, J.
    Neilsen, E.
    Nord, B.
    Ogando, R.
    Peoples, J.
    Petravick, D.
    Pieres, A.
    Plazas, A. A.
    Queiroz, A.
    Romer, A. K.
    Roodman, A.
    Rykoff, E. S.
    Sako, M.
    Sanchez, E.
    Santiago, B.
    Scarpine, V.
    Schubnell, M.
    Sevilla, I.
    Smith, R. C.
    Soares-Santos, M.
    Sobreira, F.
    Suchyta, E.
    Swanson, M. E. C.
    Tarle, G.
    Thaler, J.
    Thomas, D.
    Tucker, D.
    Walker, A. R.
    Wechsler, R. H.
    Wester, W.
    Williams, P.
    Yanny, B.
    Zuntz, J.
    SEARCH FOR GAMMA-RAY EMISSION FROM DES DWARF SPHEROIDAL GALAXY CANDIDATES WITH FERMI-LAT DATA2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 809, no 1, article id L4Article in journal (Refereed)
    Abstract [en]

    Due to their proximity, high dark-matter (DM) content, and apparent absence of non-thermal processes, Milky Way dwarf spheroidal satellite galaxies (dSphs) are excellent targets for the indirect detection of DM. Recently, eight new dSph candidates were discovered using the first year of data from the Dark Energy Survey (DES). We searched for gamma-ray emission coincident with the positions of these new objects in six years of Fermi Large Area Telescope data. We found no significant excesses of gamma-ray emission. Under the assumption that the DES candidates are dSphs with DM halo properties similar to the known dSphs, we computed individual and combined limits on the velocity-averaged DM annihilation cross section for these new targets. If the estimated DM content of these dSph candidates is confirmed, they will constrain the annihilation cross section to lie below the thermal relic cross section for DM particles with masses less than or similar to 20 GeV annihilating via the b (b) over bar or pi(+)pi(-) channels.

  • 39. Eftekhari, T.
    et al.
    Berger, E.
    Margalit, B.
    Blanchard, P. K.
    Patton, L.
    Demorest, P.
    Williams, P. K. G.
    Chatterjee, S.
    Cordes, J. M.
    Lunnan, Ragnhild
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Metzger, B. D.
    Nicholl, M.
    A Radio Source Coincident with the Superluminous Supernova PTF10hgi: Evidence for a Central Engine and an Analog of the Repeating FRB 121102?2019In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 876, no 1, article id L10Article in journal (Refereed)
    Abstract [en]

    We present the detection of an unresolved radio source coincident with the position of the Type I superluminous supernova (SLSN) PTF10hgi (z = 0.098) about 7.5 yr post-explosion, with a flux density of F-nu(6 GHz) approximate to 47.3 mu Jy and a luminosity of L-nu(6 GHz) approximate to 1.1 x 10(28) erg s(-1) Hz(-1). This represents the first detection of radio emission coincident with an SLSN on any timescale. We investigate various scenarios for the origin of the radio emission: star formation activity, an active galactic nucleus, and a non-relativistic supernova blastwave. While any of these would be quite novel if confirmed, none appear likely when considered within the context of the other properties of the host galaxy, previous radio observations of SLSNe, and the general population of hydrogen-poor supernovae (SNe). Instead, the radio emission is reminiscent of the quiescent radio source associated with the repeating FRB 121102, which has been argued to be powered by a magnetar born in a SLSN or long gamma-ray burst explosion several decades ago. We show that the properties of the radio source are consistent with a magnetar wind nebula or an off-axis jet, indicating the presence of a central engine. Our directed search for fast radio bursts from the location of PTF10hgi using 40 minutes of Very Large Array phased-array data reveals no detections to a limit of 22 mJy (10 sigma; 10 ms duration). We outline several follow-up observations that can conclusively establish the origin of the radio emission.

  • 40.
    Fathi, Kambiz
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Izumi, Takuma
    Romeo, Alessandro B.
    Martin, Sergio
    Imanishi, Masatoshi
    Hatziminaoglou, Evanthia
    Aalto, Susanne
    Espada, Daniel
    Kohno, Kotaro
    Krips, Melanie
    Matsushita, Satoki
    Meier, David S.
    Nakai, Naomasa
    Terashima, Yuichi
    LOCAL INSTABILITY SIGNATURES IN ALMA OBSERVATIONS OF DENSE GAS IN NGC 74692015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 806, no 2, article id L34Article in journal (Refereed)
    Abstract [en]

    We present an unprecedented measurement of the disk stability and local instability scales in the luminous infrared Seyfert 1 host, NGC 7469, based on ALMA observations of dense gas tracers and with a synthesized beam of 165 x 132 pc. While we confirm that non-circular motions are not significant in redistributing the dense interstellar gas in this galaxy, we find compelling evidence that the dense gas is a suitable tracer for studying the origin of its intensely high-mass star-forming ringlike structure. Our derived disk stability parameter Q accounts for a thick disk structure, and its value falls below unity at the radii in which intense star formation is found. Furthermore, we derive the characteristic instability scale lambda(c) and find a striking agreement between our measured scale of similar to 180 pc and the typical sizes of individual complexes of young and massive star clusters seen in high-resolution images.

  • 41.
    Ferretti, Raphael
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Amanullah, Rahman
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bulla, Mattia
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Goobar, Ariel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Johansson, Joel
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    No Evidence of Circumstellar Gas Surrounding Type Ia Supernova SN 2017cbv2017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 851, no 2, article id L43Article in journal (Refereed)
    Abstract [en]

    Nearby type Ia supernovae (SNe Ia), such as SN 2017cbv, are useful events to address the question of what the elusive progenitor systems of the explosions are. Hosseinzadeh et al. suggested that the early blue excess of the light curve of SN 2017cbv could be due to the supernova ejecta interacting with a non-degenerate companion star. Some SN Ia progenitor models suggest the existence of circumstellar (CS) environments in which strong outflows create low-density cavities of different radii. Matter deposited at the edges of the cavities should be at distances at which photoionization due to early ultraviolet (UV) radiation of SNe. Ia causes detectable changes to the observable Na I D and Ca II H&K absorption lines. To study possible narrow absorption lines from such material, we obtained a time series of high-resolution spectra of SN 2017cbv at phases between -14.8 and +83 days with respect to B-band maximum, covering the time at which photoionization is predicted to occur. Both narrow Na I D and Ca II H&K are detected in all spectra, with no measurable changes between the epochs. We use photoionization models to rule out the presence of Na I and Ca II gas clouds along the line of sight of SN 2017cbv between similar to 8 x 10(16)-2 x 10(19) cm and similar to 10(15)-10(17) cm, respectively. Assuming typical abundances, the mass of a homogeneous spherical CS gas shell with radius R must be limited to M-HI(CSM) < 3 x 10(-4) x (R/10(17)[cm(2)]) M-circle dot. The bounds point to progenitor models that deposit little gas in their CS environment.

  • 42. France, Kevin
    et al.
    McCray, Richard
    Fransson, Claes
    Stockholm University, Faculty of Science, Department of Astronomy.
    Larsson, Josefin
    Frank, Kari A.
    Burrows, David N.
    Challis, Peter
    Kirshner, Robert P.
    Chevalier, Roger A.
    Garnavich, Peter
    Heng, Kevin
    Lawrence, Stephen S.
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy.
    Smith, Nathan
    Sonneborn, George
    MAPPING HIGH-VELOCITY H alpha AND Ly alpha EMISSION FROM SUPERNOVA 1987A2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 801, no 1, article id L16Article in journal (Refereed)
    Abstract [en]

    We present new Hubble Space Telescope images of high-velocity H alpha and Ly alpha emission in the outer debris of SN 1987 A. The Ha images are dominated by emission from hydrogen atoms crossing the reverse shock (RS). For the first time we observe emission from the RS surface well above and below the equatorial. ring (ER), suggesting a bipolar or conical structure perpendicular to the ring plane. Using the H alpha imaging, we measure the mass flux of hydrogen atoms crossing the RS front, in the velocity intervals (-7500 < V-obs < -2800 km s(-1)) and (1000 < V-obs < 7500 km s(-1)), (M)(H) over dot = 1.2 x 10(-3) M-circle dot yr(-1). We also present the first Ly alpha imaging of the whole remnant and new Chandra X-ray observations. Comparing the spatial distribution of the Ly alpha and X-ray emission, we observe that the majority of the high-velocity Ly alpha emission originates interior to the ER. The observed Ly alpha/H alpha photon ratio, < R(L alpha/H alpha)> approximate to 17, is significantly higher than the theoretically predicted ratio of approximate to 5 for neutral atoms crossing the RS front. We attribute this excess to Ly alpha emission produced by X-ray heating of the outer debris. The spatial orientation of the Ly alpha and X-ray emission suggests that X-ray heating of the outer debris is the dominant Ly alpha production mechanism in SN 1987 A at this phase in its evolution.

  • 43.
    Fransson, Claes
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Jerkstrand, Anders
    RECONCILING THE INFRARED CATASTROPHE AND OBSERVATIONS OF SN 2011fe2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 814, no 1, article id L2Article in journal (Refereed)
    Abstract [en]

    The observational effects of the Infrared Catastrophe are discussed in view of the very late observations of the Type Ia SN 2011fe. Our model spectra at 1000 days take non-local radiative transfer into account and find that this has a crucial impact on the spectral formation. Although rapid cooling of the ejecta to a few 100 K occurs also in these models, the late-time optical/NIR flux is brighter by 1-2 mag due to redistribution of UV emissivity, resulting from non-thermal excitation and ionization. This effect brings models into better agreement with late-time observations of SN 2011fe, and other SNe Ia, and offers a solution to the long-standing discrepancy between models and observations. The models show that spectral formation shifts from Fe II and Fe III at 300 days to Fe I at 1000 days, which explains the apparent wavelength shifts seen in SN 2011fe. We discuss the effects of time dependence and energy input from Co-57, finding both to be important at 1000 days.

  • 44.
    Fransson, Claes
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Larsson, Josefin
    Migotto, Katia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Pesce, Dominic
    Challis, Peter
    Chevalier, Roger A.
    France, Kevin
    Kirshner, Robert P.
    Leibundgut, Bruno
    Lundqvist, Peter
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    McCray, Richard
    Spyromilio, Jason
    Taddia, Francesco
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Jerkstrand, Anders
    Mattila, Seppo
    Smith, Nathan
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Wheeler, J. Craig
    Crotts, Arlin
    Garnavich, Peter
    Heng, Kevin
    Lawrence, Stephen S.
    Panagia, Nino
    Pun, Chun S. J.
    Sonneborn, George
    Sugerman, Ben
    THE DESTRUCTION OF THE CIRCUMSTELLAR RING OF SN 1987A2015In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 806, no 1, article id L19Article in journal (Refereed)
    Abstract [en]

    We present imaging and spectroscopic observations with Hubble Space Telescope and Very Large Telescope of the ring of SN 1987A from 1994 to 2014. After an almost exponential increase of the shocked emission from the hotspots up to day similar to 8000 (similar to 2009), both this and the unshocked emission are now fading. From the radial positions of the hotspots we see an acceleration of these up to 500-1000 km s(-1), consistent with the highest spectroscopic shock velocities from the radiative shocks. In the most recent observations (2013 and 2014), we find several new hotspots outside the inner ring, excited by either X-rays from the shocks or by direct shock interaction. All of these observations indicate that the interaction with the supernova ejecta is now gradually dissolving the hotspots. We predict, based on the observed decay, that the inner ring will be destroyed by similar to 2025.

  • 45.
    Fransson, Claes
    et al.
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Larsson, Josefin
    Spyromilio, Jason
    Leibundgut, Bruno
    McCray, Richard
    Jerkstrand, Anders
    DISCOVERY OF MOLECULAR HYDROGEN IN SN 1987A2016In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 821, no 1, article id L5Article in journal (Refereed)
    Abstract [en]

    Both CO and SiO have been observed at early and late phases in SN 1987A. H-2 was predicted to form at roughly the same time as these molecules, but was not detected at early epochs. Here, we report the detection of NIR lines from H-2 at 2.12 and 2.40 mu m in VLT/SINFONI spectra obtained between days 6489 and 10,120. The emission is concentrated to the core of the SN in contrast to Ha and approximately coincides with the [Si I]/[Fe II] emission detected previously in the ejecta. Different excitation mechanisms and power sources of the emission are discussed. From the nearly constant H-2 luminosities, we favor excitation resulting from the Ti-44 decay.

  • 46. Fremling, C.
    et al.
    Ko, H.
    Dugas, A.
    Ergon, Mattias
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Bagdasaryan, A.
    Barbarino, Cristina
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Belicki, J.
    Bellm, E.
    Blagorodnova, N.
    De, K.
    Dekany, R.
    Frederick, S.
    Gal-Yam, A.
    Goldstein, D. A.
    Golkhou, V. Z.
    Graham, M.
    Kasliwal, M.
    Kowalski, M.
    Kulkarni, S. R.
    Kupfer, T.
    Laher, R. R.
    Masci, F. J.
    Miller, A. A.
    Neill, J. D.
    Perley, D. A.
    Rebbapragada, U. D.
    Riddle, R.
    Rusholme, B.
    Schulze, S.
    Smith, R. M.
    Tartaglia, Leonardo
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Yan, Lin
    Yao, Y.
    ZTF18aalrxas: A Type IIb Supernova from a Very Extended Low-mass Progenitor2019In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 878, no 1, article id L5Article in journal (Refereed)
    Abstract [en]

    We investigate ZTF18aalrxas, a double-peaked Type IIb core-collapse supernova (SN) discovered during science validation of the Zwicky Transient Facility. ZTF18aalrxas was discovered while the optical emission was still rising toward the initial cooling peak (0.7 mag over 2 days). Our observations consist of multi-band (ultraviolet and optical) light curves (LCs), and optical spectra spanning from approximate to 0.7 to approximate to 480 days past the explosion. We use a Monte-Carlo based non-local thermodynamic equilibrium model that simultaneously reproduces both the Ni-56-powered bolometric LC and our nebular spectrum. This model is used to constrain the synthesized radioactive nickel mass (0.17 M-circle dot) and the total ejecta mass (1.7 M-circle dot) of the SN. The cooling emission is modeled using semi-analytical extended envelope models to constrain the progenitor radius (790-1050 R-circle dot) at the time of explosion. Our nebular spectrum shows signs of interaction with a dense circumstellar medium (CSM), and this spectrum is modeled and analyzed to constrain the amount of ejected oxygen (0.3-0.5 M-circle dot) and the total hydrogen mass (approximate to 0.15 M-circle dot) in the envelope of the progenitor. The oxygen mass of ZTF18aalrxas is consistent with a low (12-13 M-circle dot) zero-age main-sequence mass progenitor. The LCs and spectra of ZTF18aalrxas are not consistent with massive single-star SN Type IIb progenitor models. The presence of an extended hydrogen envelope of low mass, the presence of a dense CSM, the derived ejecta mass, and the late-time oxygen emission can all be explained in a binary model scenario.

  • 47. Gall, Christa
    et al.
    Hjorth, Jens
    Rosswog, Stephan
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Tanvir, Nial R.
    Levan, Andrew J.
    Lanthanides or Dust in Kilonovae: Lessons Learned from GW1708172017In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 849, no 2, article id L19Article in journal (Refereed)
    Abstract [en]

    The unprecedented optical and near-infrared lightcurves of the first electromagnetic counterpart to a gravitationalwave source, GW170817, a binary neutron star merger, exhibited a strong evolution from blue to near-infrared (a so-called kilonova or macronova). The emerging near-infrared component is widely attributed to the formation of r-process elements that provide the opacity to shift the blue light into the near-infrared. An alternative scenario is that the light from the blue component gets extinguished by dust formed by the kilonova and subsequently is reemitted at near-infrared wavelengths. We test here this hypothesis using the lightcurves of AT 2017gfo, the kilonova accompanying GW170817. We find that of the order of 10(-5) M-circle dot. of carbon is required to reproduce the optical/near-infrared lightcurves as the kilonova fades. This putative dust cools from similar to 2000. K at similar to 4 days after the event to similar to 1500 K over the course of the following week, thus requiring dust with a high condensation temperature, such as carbon. We contrast this with the nucleosynthetic yields predicted by a range of kilonova wind models. These suggest that at most 10(-9) M-circle dot of carbon is formed. Moreover, the decay in the inferred dust temperature is slower than that expected in kilonova models. We therefore conclude that in current models of the blue component of the kilonova, the near-infrared component in the kilonova accompanying GW170817 is unlikely to be due to dust.

  • 48.
    Goobar, Ariel
    et al.
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Johansson, Joel
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Amanullah, Rahman
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Cao, Y.
    Perley, D. A.
    Kasliwal, M. M.
    Ferretti, Raphael
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Nugent, P. E.
    Harris, C.
    Gal-Yam, A.
    Ofek, E. O.
    Tendulkar, S. P.
    Dennefeld, M.
    Valenti, S.
    Arcavi, I.
    Banerjee, D. P. K.
    Venkataraman, V.
    Joshi, V.
    Ashok, N. M.
    Cenko, S. B.
    Diaz, R. F.
    Fremling, Christoffer
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Horesh, A.
    Howell, D. A.
    Kulkarni, S. R.
    Papadogiannakis, Seméli
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Petrushevska, Tanja
    Stockholm University, Faculty of Science, Department of Physics. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Sand, D.
    Sollerman, Jesper
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Stanishev, V.
    Bloom, J. S.
    Surace, J.
    Dupuy, T. J.
    Liu, M. C.
    THE RISE OF SN 2014J IN THE NEARBY GALAXY M822014In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 784, no 1, article id L12Article in journal (Refereed)
    Abstract [en]

    We report on the discovery of SN 2014J in the nearby galaxy M82. Given its proximity, it offers the best opportunity to date to study a thermonuclear supernova (SN) over a wide range of the electromagnetic spectrum. Optical, near-IR, and mid-IR observations on the rising light curve, orchestrated by the intermediate Palomar Transient Factory, show that SN 2014J is a spectroscopically normal Type Ia supernova (SN Ia), albeit exhibiting high-velocity features in its spectrum and heavily reddened by dust in the host galaxy. Our earliest detections start just hours after the fitted time of explosion. We use high-resolution optical spectroscopy to analyze the dense intervening material and do not detect any evolution in the resolved absorption features during the light curve rise. Similar to other highly reddened SNe Ia, a low value of total-to-selective extinction, R-V less than or similar to 2, provides the best match to our observations. We also study pre-explosion optical and near-IR images from Hubble Space Telescope with special emphasis on the sources nearest to the SN location.

  • 49. Greaves, J. S.
    et al.
    Sibthorpe, B.
    Acke, B.
    Pantin, E. E.
    Vandenbussche, B.
    Olofsson, Göran
    Stockholm University, Faculty of Science, Department of Astronomy.
    Dominik, C.
    Barlow, M. J.
    Bendo, G. J.
    Blommaert, J. A. D. L.
    Brandeker, Alexis
    Stockholm University, Faculty of Science, Department of Astronomy.
    de Vries, Bernard L.
    Stockholm University, Faculty of Science, Department of Astronomy.
    Dent, W. R. F.
    Di Francesco, J.
    Fridlund, M.
    Gear, W. K.
    Harvey, P. M.
    Hogerheijde, M. R.
    Holland, W. S.
    Ivison, R. J.
    Liseau, R.
    Matthews, B. C.
    Pilbratt, G. L.
    Walker, H. J.
    Waelkens, C.
    EXTREME CONDITIONS IN A CLOSE ANALOG TO THE YOUNG SOLAR SYSTEM: HERSCHEL OBSERVATIONS OF is an element of ERIDANI2014In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 791, no 1, p. L11-Article in journal (Refereed)
    Abstract [en]

    Far-infrared Herschel images of the is an element of Eridani system, seen at a fifth of the Sun's present age, resolve two belts of debris emission. Fits to the 160 mu m PACS image yield radial spans for these belts of 12-16 and 54-68 AU. The south end of the outer belt is approximate to 10% brighter than the north end in the PACS+SPIRE images at 160, 250, and 350 mu m, indicating a pericenter glow attributable to a planet c From this asymmetry and an upper bound on the offset of the belt center, this second planet should be mildly eccentric (e(c) approximate to 0.03-0.3). Compared to the asteroid and Kuiper Belts of the young Sun, the is an element of Eri belts are intermediate in brightness and more similar to each other, with up to 20 km sized collisional fragments in the inner belt totaling approximate to 5% of an Earth mass. This reservoir may feed the hot dust close to the star and could send many impactors through the Habitable Zone, especially if it is being perturbed by the suspected planet is an element of Eri b, at semi-major axis approximate to 3 AU.

  • 50. Hayes, Matthew
    et al.
    Östlin, Göran
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Schaerer, Daniel
    Verhamme, Anne
    Mas-Hesse, J. Miguel
    Adamo, Angela
    Atek, Hakim
    Cannon, John M.
    Duval, Florent
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Guaita, Lucia
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Herenz, E. Christian
    Kunth, Daniel
    Laursen, Peter
    Melinder, Jens
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    Orlitova, Ivana
    Oti-Floranes, Hector
    Sandberg, Andreas
    Stockholm University, Faculty of Science, Department of Astronomy. Stockholm University, Faculty of Science, The Oskar Klein Centre for Cosmo Particle Physics (OKC).
    THE LYMAN ALPHA REFERENCE SAMPLE: EXTENDED LYMAN ALPHA HALOS PRODUCED AT LOW DUST CONTENT2013In: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 765, no 2, p. L27-Article in journal (Refereed)
    Abstract [en]

    We report on new imaging observations of the Lyman alpha emission line (Ly alpha), performed with the Hubble Space Telescope, that comprise the backbone of the Lyman alpha Reference Sample. We present images of 14 starburst galaxies at redshifts 0.028 < z < 0.18 in continuum-subtracted Ly alpha, H alpha, and the far ultraviolet continuum. We show that Ly alpha is emitted on scales that systematically exceed those of the massive stellar population and recombination nebulae: as measured by the Petrosian 20% radius, RP20, Ly alpha radii are larger than those of H alpha by factors ranging from 1 to 3.6, with an average of 2.4. The average ratio of Ly alpha-to-FUV radii is 2.9. This suggests that much of the Ly alpha light is pushed to large radii by resonance scattering. Defining the Relative Petrosian Extension of Ly alpha compared to H alpha, xi(Ly alpha) = R-P20(Ly alpha)/R-P20(H alpha), we find xi(Ly alpha) to be uncorrelated with total Ly alpha luminosity. However, xi(Ly alpha) is strongly correlated with quantities that scale with dust content, in the sense that a low dust abundance is a necessary requirement (although not the only one) in order to spread Ly alpha photons throughout the interstellar medium and drive a large extended Ly alpha halo.

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