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  • 101. Aleksic, J.
    et al.
    Alvarez, E. A.
    Antonelli, L. A.
    Antoranz, P.
    Ansoldi, S.
    Asensio, M.
    Backes, M.
    de Almeida, U. Barres
    Barrio, J. A.
    Bastieri, D.
    Becerra Gonzalez, J.
    Bednarek, W.
    Berger, K.
    Bernardini, E.
    Biland, A.
    Blanch, O.
    Bock, R. K.
    Boller, A.
    Bonnoli, G.
    Tridon, D. Borla
    Bretz, T.
    Canellas, A.
    Carmona, E.
    Carosi, A.
    Colin, P.
    Colombo, E.
    Contreras, J. L.
    Cortina, J.
    Cossio, L.
    Covino, S.
    Da Vela, P.
    Dazzi, F.
    De Angelis, A.
    De Caneva, G.
    De Cea del Pozo, E.
    De Lotto, B.
    Delgado Mendez, C.
    Diago Ortega, A.
    Doert, M.
    Dominguez, A.
    Prester, D. Dominis
    Dorner, D.
    Doro, M.
    Eisenacher, D.
    Elsaesser, D.
    Ferenc, D.
    Fonseca, M. V.
    Font, L.
    Fruck, C.
    Garcia Lopez, R. J.
    Garczarczyk, M.
    Garrido Terrats, D.
    Gaug, M.
    Giavitto, G.
    Godinovic, N.
    Gonzalez Munoz, A.
    Gozzini, S. R.
    Hadasch, D.
    Haefner, D.
    Herrero, A.
    Hildebrand, D.
    Hose, J.
    Hrupec, D.
    Huber, B.
    Jankowski, F.
    Jogler, T.
    Kadenius, V.
    Kellermann, H.
    Klepser, S.
    Krahenbuhl, T.
    Krause, J.
    La Barbera, A.
    Lelas, D.
    Leonardo, E.
    Lewandowska, N.
    Lindfors, E.
    Lombardi, S.
    Lopez, M.
    Lopez-Coto, R.
    Lopez-Oramas, A.
    Lorenz, E.
    Makariev, M.
    Maneva, G.
    Mankuzhiyil, N.
    Mannheim, K.
    Maraschi, L.
    Mariotti, M.
    Martinez, M.
    Mazin, D.
    Meucci, M.
    Miranda, J. M.
    Mirzoyan, R.
    Moldon, J.
    Moralejo, A.
    Munar-Adrover, P.
    Niedzwiecki, A.
    Nieto, D.
    Nilsson, K.
    Nowak, N.
    Orito, R.
    Paiano, S.
    Paneque, D.
    Paoletti, R.
    Pardo, S.
    Paredes, J. M.
    Partini, S.
    Perez-Torres, M. A.
    Persic, M.
    Pilia, M.
    Pochon, J.
    Prada, F.
    Moroni, P. G. Prada
    Prandini, E.
    Puerto Gimenez, I.
    Puljak, I.
    Reichardt, I.
    Reinthal, R.
    Rhode, W.
    Ribo, M.
    Rico, J.
    Ruegamer, S.
    Saggion, A.
    Saito, K.
    Saito, T. Y.
    Salvati, M.
    Satalecka, K.
    Scalzotto, V.
    Scapin, V.
    Schultz, C.
    Schweizer, T.
    Shore, S. N.
    Sillanpaa, A.
    Sitarek, J.
    Snidaric, I.
    Sobczynska, D.
    Spanier, F.
    Spiro, S.
    Stamatescu, V.
    Stamerra, A.
    Steinke, B.
    Storz, J.
    Strah, N.
    Sun, S.
    Suric, T.
    Takalo, L.
    Takami, H.
    Tavecchio, F.
    Temnikov, P.
    Terzic, T.
    Tescaro, D.
    Teshima, M.
    Tibolla, O.
    Torres, D. F.
    Treves, A.
    Uellenbeck, M.
    Vogler, P.
    Wagner, R. M.
    Weitzel, Q.
    Zabalza, V.
    Zandanel, F.
    Zanin, R.
    Berdyugin, A.
    Buson, S.
    Jarvela, E.
    Larsson, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC). Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Lahteenmaki, A.
    Tammi, J.
    Discovery of VHE gamma-rays from the blazar 1ES 1215+303 with the MAGIC telescopes and simultaneous multi-wavelength observations2012Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 544, s. A142-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. We present the discovery of very high energy (VHE, E > 100 GeV) gamma-ray emission from the BL Lac object 1ES 1215+303 by the MAGIC telescopes and simultaneous multi-wavelength data in a broad energy range from radio to gamma-rays. Aims. We study the VHE gamma-ray emission from 1ES 1215+303 and its relation to the emissions in other wavelengths. Methods. Triggered by an optical outburst, MAGIC observed the source in 2011 January-February for 20.3 h. The target was monitored in the optical R-band by the KVA telescope that also performed optical polarization measurements. We triggered target of opportunity observations with the Swift satellite and obtained simultaneous and quasi-simultaneous data from the Fermi Large Area Telescope and from the Metsahovi radio telescope. We also present the analysis of older MAGIC data taken in 2010. Results. The MAGIC observations of 1ES 1215+303 carried out in 2011 January-February resulted in the first detection of the source at VHE with a statistical significance of 9.4 sigma. Simultaneously, the source was observed in a high optical and X-ray state. In 2010 the source was observed in a lower state in optical, X-ray, and VHE, while the GeV gamma-ray flux and the radio flux were comparable in 2010 and 2011. The spectral energy distribution obtained with the 2011 data can be modeled with a simple one zone SSC model, but it requires extreme values for the Doppler factor or the electron energy distribution.

  • 102. Aleksic, J.
    et al.
    Alvarez, E. A.
    Antonelli, L. A.
    Antoranz, P.
    Asensio, M.
    Backes, M.
    Barrio, J. A.
    Bastieri, D.
    Becerra Gonzalez, J.
    Bednarek, W.
    Berdyugin, A.
    Berger, K.
    Bernardini, E.
    Biland, A.
    Blanch, O.
    Bock, R. K.
    Boller, A.
    Bonnoli, G.
    Tridon, D. Borla
    Braun, I.
    Bretz, T.
    Canellas, A.
    Carmona, E.
    Carosi, A.
    Colin, P.
    Colombo, E.
    Contreras, J. L.
    Cortina, J.
    Cossio, L.
    Covino, S.
    Dazzi, F.
    De Angelis, A.
    De Caneva, G.
    De Cea del Pozo, E.
    De Lotto, B.
    Delgado Mendez, C.
    Diago Ortega, A.
    Doert, M.
    Dominguez, A.
    Prester, D. Dominis
    Dorner, D.
    Doro, M.
    Elsaesser, D.
    Ferenc, D.
    Fonseca, M. V.
    Font, L.
    Fruck, C.
    Garcia Lopez, R. J.
    Garczarczyk, M.
    Garrido, D.
    Giavitto, G.
    Godinovic, N.
    Hadasch, D.
    Haefner, D.
    Herrero, A.
    Hildebrand, D.
    Ohne-Moench, D. H.
    Hose, J.
    Hrupec, D.
    Huber, B.
    Jogler, T.
    Kellermann, H.
    Klepser, S.
    Kraehenbuehl, T.
    Krause, J.
    La Barbera, A.
    Lelas, D.
    Leonardo, E.
    Lindfors, E.
    Lombardi, S.
    Lopez, M.
    Lopez-Oramas, A.
    Lorenz, E.
    Makariev, M.
    Maneva, G.
    Mankuzhiyil, N.
    Mannheim, K.
    Maraschi, L.
    Mariotti, M.
    Martinez, M.
    Mazin, D.
    Meucci, M.
    Miranda, J. M.
    Mirzoyan, R.
    Miyamoto, H.
    Moldon, J.
    Moralejo, A.
    Munar-Adrover, P.
    Nieto, D.
    Nilsson, K.
    Orito, R.
    Oya, I.
    Paneque, D.
    Paoletti, R.
    Pardo, S.
    Paredes, J. M.
    Partini, S.
    Pasanen, M.
    Pauss, F.
    Perez-Torres, M. A.
    Persic, M.
    Peruzzo, L.
    Pilia, M.
    Pochon, J.
    Prada, F.
    Moroni, P. G. Prada
    Prandini, E.
    Puljak, I.
    Reichardt, I.
    Reinthal, R.
    Rhode, W.
    Ribo, M.
    Rico, J.
    Ruegamer, S.
    Saggion, A.
    Saito, K.
    Saito, T. Y.
    Salvati, M.
    Satalecka, K.
    Scalzotto, V.
    Scapin, V.
    Schultz, C.
    Schweizer, T.
    Shayduk, M.
    Shore, S. N.
    Sillanpaa, A.
    Sitarek, J.
    Sobczynska, D.
    Spanier, F.
    Spiro, S.
    Stamatescu, V.
    Stamerra, A.
    Steinke, B.
    Storz, J.
    Strah, N.
    Suric, T.
    Takalo, L.
    Takami, H.
    Tavecchio, F.
    Temnikov, P.
    Terzic, T.
    Tescaro, D.
    Teshima, M.
    Tibolla, O.
    Torres, D. F.
    Treves, A.
    Uellenbeck, M.
    Vankov, H.
    Vogler, P.
    Wagner, R. M.
    Weitzel, Q.
    Zabalza, V.
    Zandanel, F.
    Zanin, R.
    Buson, S.
    Horan, D.
    Larsson, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    D'Ammando, F.
    PG 1553+113: FIVE YEARS OF OBSERVATIONS WITH MAGIC2012Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 748, nr 1, s. 46-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the results of five years (2005-2009) of MAGIC observations of the BL Lac object PG 1553+113 at very high energies (VHEs; E > 100 GeV). Power-law fits of the individual years are compatible with a steady mean photon index Gamma = 4.27 +/- 0.14. In the last three years of data, the flux level above 150 GeV shows a clear variability (probability of constant flux < 0.001%). The flux variations are modest, lying in the range from 4% to 11% of the Crab Nebula flux. Simultaneous optical data also show only modest variability that seems to be correlated with VHE gamma-ray variability. We also performed a temporal analysis of (all available) simultaneous Fermi/Large Area Telescope data of PG 1553+113 above 1 GeV, which reveals hints of variability in the 2008-2009 sample. Finally, we present a combination of the mean spectrum measured at VHEs with archival data available for other wavelengths. The mean spectral energy distribution can be modeled with a one-zone synchrotron self-Compton model, which gives the main physical parameters governing the VHE emission in the blazar jet.

  • 103. Alexoudi, X.
    et al.
    Mallonn, M.
    von Essen, C.
    Turner, J. D.
    Keles, E.
    Southworth, J.
    Mancini, L.
    Ciceri, Simona
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Granzer, T.
    Denker, C.
    Dineva, E.
    Strassmeier, K. G.
    Deciphering the atmosphere of HAT-P-12b: solving discrepant results2018Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 620, artikel-id A142Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Two independent investigations of the atmosphere of the hot Jupiter HAT-P-12b by two different groups resulted in discrepant solutions. Using broad-band photometry from the ground, one study found a flat and featureless transmission spectrum that was interpreted as gray absorption by dense cloud coverage. The second study made use of Hubble Space Telescope (HST) observations and found Rayleigh scattering at optical wavelengths caused by haze. Aims. The main purpose of this work is to determine the source of this inconsistency and provide feedback to prevent similar discrepancies in future analyses of other exoplanetary atmospheres. Methods. We studied the observed discrepancy via two methods. With further broad-band observations in the optical wavelength regions, we strengthened the previous measurements in precision, and with a homogeneous reanalysis of the published data, we were able to assess the systematic errors and the independent analyses of the two different groups. Results. Repeating the analysis steps of both works, we found that deviating values for the orbital parameters are the reason for the aforementioned discrepancy. Our work showed a degeneracy of the planetary spectral slope with these parameters. In a homogeneous reanalysis of all data, the two literature data sets and the new observations converge to a consistent transmission spectrum, showing a low-amplitude spectral slope and a tentative detection of potassium absorption.

  • 104. Allafort, A.
    et al.
    Baldini, L.
    Ballet, J.
    Barbiellini, G.
    Baring, M. G.
    Bastieri, D.
    Bellazzini, R.
    Bonamente, E.
    Bottacini, E.
    Brandt, T. J.
    Bregeon, J.
    Bruel, P.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Cecchi, C.
    Chaves, R. C. G.
    Chekhtman, A.
    Chiang, J.
    Chiaro, G.
    Ciprini, S.
    Claus, R.
    D'Ammando, F.
    de Palma, F.
    Digel, S. W.
    Di Venere, L.
    Drell, P. S.
    Favuzzi, C.
    Ferrara, E. C.
    Franckowiak, A.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Giglietto, N.
    Giroletti, M.
    Glanzman, T.
    Godfrey, G.
    Grenier, I. A.
    Guiriec, S.
    Hadasch, D.
    Harding, A. K.
    Hayashida, M.
    Hayashi, K.
    Hays, E.
    Hewitt, J.
    Hill, A. B.
    Horan, D.
    Hou, X.
    Jogler, T.
    Johnson, A. S.
    Johnson, T. J.
    Kerr, M.
    Knoedlseder, J.
    Kuss, M.
    Lande, J.
    Larsson, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC). Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Latronico, L.
    Lemoine-Goumard, M.
    Longo, F.
    Loparco, F.
    Lubrano, P.
    Malyshev, D.
    Marelli, M.
    Mayer, M.
    Mazziotta, M. N.
    Mehault, J.
    Mizuno, T.
    Monzani, M. E.
    Morselli, A.
    Murgia, S.
    Nemmen, R.
    Nuss, E.
    Ohsugi, T.
    Omodei, N.
    Orienti, M.
    Orlando, E.
    Paneque, D.
    Pesce-Rollins, M.
    Pierbattista, M.
    Piron, F.
    Pivato, G.
    Porter, T. A.
    Raino, S.
    Rando, R.
    Ray, P. S.
    Razzano, M.
    Reimer, O.
    Reposeur, T.
    Romani, R. W.
    Sartori, A.
    Parkinson, P. M. Saz
    Sgro, C.
    Siskind, E. J.
    Smith, D. A.
    Spinelli, P.
    Strong, A. W.
    Takahashi, H.
    Thayer, J. B.
    Thompson, D. J.
    Tibaldo, L.
    Tinivella, M.
    Torres, D. F.
    Tosti, G.
    Uchiyama, Y.
    Usher, T. L.
    Vandenbroucke, J.
    Vasileiou, V.
    Venter, C.
    Vianello, G.
    Vitale, V.
    Winer, B. L.
    Wood, K. S.
    PSR J2021+4026 IN THE GAMMA CYGNI REGION: THE FIRST VARIABLE gamma-RAY PULSAR SEEN BY THE Fermi LAT2013Ingår i: ASTROPHYS J LETT, ISSN 2041-8205, Vol. 777, nr 1, s. L2-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Long-term monitoring of PSR J2021+4026 in the heart of the Cygnus region with the Fermi Large Area Telescope unveiled a sudden decrease in flux above 100 MeV over a timescale shorter than a week. The jump was near MJD 55850 (2011 October 16), with the flux decreasing from (8.33+/-0.08) x 10(-10) erg cm(-2) s(-1) to (6.86+/-0.13) x 10(-10) erg cm(-2) s(-1). Simultaneously, the frequency spindown rate increased from (7.8 +/- 0.1) x 10(-13) Hz s(-1) to (8.1 +/- 0.1) x 10(-13) Hz s(-1). Significant (>5 sigma) changes in the pulse profile and marginal (<3 sigma) changes in the emission spectrum occurred at the same time. There is also evidence for a small, steady flux increase over the 3 yr preceding MJD 55850. This is the first observation at gamma-ray energies of mode changes and intermittent behavior, observed at radio wavelengths for other pulsars. We argue that the change in pulsed gamma-ray emission is due to a change in emission beaming and we speculate that it is precipitated by a shift in the magnetic field structure, leading to a change of either effective magnetic inclination or effective current.

  • 105. Alp, Dennis
    et al.
    Larsson, Josefin
    Fransson, Claes
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Gabler, Michael
    Wongwathanarat, Annop
    Janka, Hans-Thomas
    X-Ray Absorption in Young Core-collapse Supernova Remnants2018Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 864, nr 2, artikel-id 175Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The material expelled by core-collapse supernova (SN) explosions absorbs X-rays from the central regions. We use SN models based on three-dimensional neutrino-driven explosions to estimate optical depths to the center of the explosion, compare different progenitor models, and investigate the effects of explosion asymmetries. The optical depths below 2 keV for progenitors with a remaining hydrogen envelope are expected to be high during the first century after the explosion due to photoabsorption. A typical optical depth is 100 t(4)(-2 )E(-2), where t(4) is the time since the explosion in units of 10,000 days (similar to 27 years) and E is the energy in units of keV. Compton scattering dominates above 50 keV, but the scattering depth is lower and reaches unity at similar to 1000 days at 1 MeV. The optical depths are approximately an order of magnitude lower for hydrogen-stripped progenitors. The metallicity of the SN ejecta is much higher than that in the interstellar medium, which enhances photoabsorption and makes absorption edges stronger. These results are applicable to young SN remnants in general, but we explore the effects on observations of SN 1987A and the compact object in Cas A in detail. For SN 1987A, the absorption is high and the X-ray upper limits of similar to 100 L-circle dot on a compact object are approximately an order of magnitude less constraining than previous estimates using other absorption models. The details are presented in an accompanying paper. For the central compact object in Cas A, we find no significant effects of our more detailed absorption model on the inferred surface temperature.

  • 106. Alp, Dennis
    et al.
    Larsson, Josefin
    Fransson, Claes
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Indebetouw, Remy
    Jerkstrand, Anders
    Ahola, Antero
    Burrows, David
    Challis, Peter
    Cigan, Phil
    Cikota, Aleksandar
    Kirshner, Robert P.
    van Loon, Jacco Th.
    Mattila, Seppo
    Ng, C. -Y.
    Park, Sangwook
    Spyromilio, Jason
    Woosley, Stan
    Baes, Maarten
    Bouchet, Patrice
    Chevalier, Roger
    Frank, Kari A.
    Gaensler, B. M.
    Gomez, Haley
    Janka, Hans-Thomas
    Leibundgut, Bruno
    Lundqvist, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Marcaide, Jon
    Matsuura, Mikako
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Sonneborn, George
    Staveley-Smith, Lister
    Zanardo, Giovanna
    Gabler, Michael
    Taddia, Francesco
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Wheeler, J. Craig
    The 30 Year Search for the Compact Object in SN 1987A2018Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 864, nr 2, artikel-id 174Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Despite more than 30 years of searching, the compact object in Supernova (SN) 1987A has not yet been detected. We present new limits on the compact object in SN 1987A using millimeter, near-infrared, optical, ultraviolet, and X-ray observations from ALMA, VLT, HST, and Chandra. The limits are approximately 0.1 mJy (0.1 x 10(-26) erg s(-1) cm(-2) Hz(-1)) at 213 GHz, 1 L-circle dot (6 x 10(-29) erg s(-1) cm(-2) Hz(-1)) in the optical if our line of sight is free of ejecta dust, and 10(36) erg s(-1) (2 x 10(-30) erg s(-1) cm(-2) Hz(-1) ) in 2-10 keV X-rays. Our X-ray limits are an order of magnitude less constraining than previous limits because we use a more realistic ejecta absorption model based on three-dimensional neutrino-driven SN explosion models. The allowed bolometric luminosity of the compact object is 22 L-circle dot if our line of sight is free of ejecta dust, or 138L(circle dot) if dust-obscured. Depending on assumptions, these values limit the effective temperature of a neutron star (NS) to <4-8 MK and do not exclude models, which typically are in the range 3-4 MK. For the simplest accretion model, the accretion rate for an efficiency 77 is limited to <10(-11) eta(-1) M-circle dot yr(-1), which excludes most predictions. For pulsar activity modeled by a rotating magnetic dipole in vacuum, the limit on the magnetic field strength (B) for a given spin period (P) is B less than or similar to 10(14) P-2 G s(-2), which firmly excludes pulsars comparable to the Crab. By combining information about radiation reprocessing and geometry, we infer that the compact object is a dust-obscured thermally emitting NS, which may appear as a region of higher-temperature ejecta dust emission.

  • 107. Alp, Dennis
    et al.
    Larsson, Josefin
    Maeda, Keiichi
    Fransson, Claes
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Wongwathanarat, Annop
    Gabler, Michael
    Janka, Hans-Thomas
    Jerkstrand, Anders
    Heger, Alexander
    Menon, Athira
    X-Ray and Gamma-Ray Emission from Core-collapse Supernovae: Comparison of Three-dimensional Neutrino-driven Explosions with SN 1987A2019Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 882, nr 1, artikel-id 22Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    During the first few hundred days after the explosion, core-collapse supernovae (SNe) emit down-scattered X-rays and gamma-rays originating from radioactive line emissions, primarily from the Ni-56 -> Co-56 -> Fe-56 chain. We use supernova (SN) models based on three-dimensional neutrino-driven explosion simulations of single stars and mergers to compute this emission and compare the predictions with observations of SN 1987A. A number of models are clearly excluded, showing that high-energy emission is a powerful way of discriminating between models. The best models are almost consistent with the observations, but differences that cannot be matched by a suitable choice of viewing angle are evident. Therefore, our self-consistent models suggest that neutrino-driven explosions are able to produce, in principle, sufficient mixing, although remaining discrepancies may require small changes to the progenitor structures. The soft X-ray cutoff is primarily determined by the metallicity of the progenitor envelope. The main effect of asymmetries is to vary the flux level by a factor of similar to 3. For the more asymmetric models, the shapes of the light curves also change. In addition to the models of SN 1987A, we investigate two models of SNe II-P and one model of a stripped-envelope SN IIb. The Type II-P models have observables similar to those of the models of SN 1987A, but the stripped-envelope SN model is significantly more luminous and evolves faster. Finally, we make simple predictions for future observations of nearby SNe.

  • 108. Alsubai, Khalid
    et al.
    Mislis, Dimitris
    Tsvetanov, Zlatan I.
    Latham, David W.
    Bieryla, Allyson
    Buchhave, Lars A.
    Esquerdo, Gilbert A.
    Bramich, D. M.
    Pyrzas, Stylianos
    Vilchez, Nicolas P. E.
    Mancini, Luigi
    Southworth, John
    Evans, Daniel F.
    Henning, Thomas
    Ciceri, Simona
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Max Planck Institute for Astronomy, Germany.
    Qatar Exoplanet Survey: Qatar-3b, Qatar-4b, and Qatar-5b2017Ingår i: Astronomical Journal, ISSN 0004-6256, E-ISSN 1538-3881, Vol. 153, nr 4, artikel-id 200Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the discovery of Qatar-3b, Qatar-4b, and Qatar-5b, three new transiting planets identified by the Qatar Exoplanet Survey. The three planets belong to the hot Jupiter family, with orbital periods of P-Q3b = 2.50792 days, P-Q4b = 1.80539 days, and P-Q5b = 2.87923 days. Follow-up spectroscopic observations reveal the masses of the planets to be M-Q3b = 4.31 +/- 0.47 M-J, M-Q4b = 6.10 +/- 0.54 M-J, and M-Q5b = 4.32 +/- 0.18 M-J, while model fits to the transit light curves yield radii of R-Q3b = 1.096 +/- 0.14 RJ, R-Q4b = 1.135 +/- 0.11 R-J, and R-Q5b = 1.107 +/- 0.064 R-J. The host stars are low-mass main sequence stars with masses and radii M-Q3 = 1.145 +/- 0.064 M circle dot, M-Q4 = 0.896 +/- 0.048 M circle dot, M-Q5 = 1.128 +/- 0.056 M circle dot and R-Q3 = 1.272 +/- 0.14 R circle dot, R-Q4 = 0.849 +/- 0.063 R circle dot, and R-Q5 = 1.076 +/- 0.051 R circle dot for Qatar-3, 4, and 5 respectively. The V magnitudes of the three host stars are V-Q3 = 12.88, V-Q4 = 13.60, and V-Q5 = 12.82. All three new planets can be classified as heavy hot Jupiters (M > 4 M-J).

  • 109.
    Amanullah, R.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Goobar, Ariel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Clement, B.
    Cuby, J. -G
    Dahle, H.
    Dahlen, T.
    Hjorth, J.
    Fabbro, S.
    Jönsson, Jakob
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Kneib, J. -P
    Lidman, C.
    Limousin, M.
    Milvang-Jensen, B.
    Mortsell, E.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Nordin, Jakob
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Paech, K.
    Richard, J.
    Riehm, Teresa
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Stanishev, V.
    Watson, D.
    A HIGHLY MAGNIFIED SUPERNOVA AT z=1.703 BEHIND THE MASSIVE GALAXY CLUSTER A16892011Ingår i: ASTROPHYS J LETT, ISSN 2041-8205, Vol. 742, nr 1, s. L7-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Our ability to study the most remote supernova explosions, crucial for the understanding of the evolution of the high-redshift universe and its expansion rate, is limited by the light collection capabilities of telescopes. However, nature offers unique opportunities to look beyond the range within reach of our unaided instruments thanks to the light-focusing power of massive galaxy clusters. Here we report on the discovery of one of the most distant supernovae ever found, at redshift z = 1.703. Due to a lensing magnification factor of 4.3 +/- 0.3, we are able to measure a light curve of the supernova, as well as spectroscopic features of the host galaxy with a precision comparable to what would otherwise only be possible with future generation telescopes.

  • 110.
    Amanullah, Rahman
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Johansson, Joel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Goobar, Ariel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Ferretti, Raphael
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Papadogiannakis, Seméli
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Petrushevska, Tanja
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Brown, P. J.
    Cao, Y.
    Contreras, C.
    Dahle, H.
    Elias-Rosa, N.
    Fynbo, J. P. U.
    Gorosabel, J.
    Guaita, L.
    Hangard, Laura
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Howell, D. A.
    Hsiao, E. Y.
    Kankare, E.
    Kasliwal, M.
    Leloudas, G.
    Lundqvist, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Mattila, S.
    Nugent, P.
    Phillips, M. M.
    Sandberg, Andreas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Stanishev, V.
    Sullivan, M.
    Taddia, Francesco
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Östlin, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Asadi, Saghar
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Herrero-Illana, R.
    Jensen, J. J.
    Karhunen, K.
    Lazarevic, S.
    Varenius, E.
    Santos, P.
    Sridhar, S. Seethapuram
    Wallström, S. H. J.
    Wiegert, J.
    Diversity in extinction laws of Type Ia supernovae measured between 0.2 and 2 mu m2015Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 453, nr 3, s. 3300-3328Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present ultraviolet (UV) observations of six nearby Type Ia supernovae (SNe Ia) obtained with the Hubble Space Telescope, three of which were also observed in the near-IR (NIR) with Wide-Field Camera 3. UV observations with the Swift satellite, as well as ground-based optical and NIR data provide complementary information. The combined data set covers the wavelength range 0.2-2 mu m. By also including archival data of SN 2014J, we analyse a sample spanning observed colour excesses up to E(B - V) = 1.4 mag. We study the wavelength-dependent extinction of each individual SN and find a diversity of reddening laws when characterized by the total-to-selective extinction R-V. In particular, we note that for the two SNe with E(B - V) greater than or similar to 1 mag, for which the colour excess is dominated by dust extinction, we find R-V = 1.4 +/- 0.1 and R-V = 2.8 +/- 0.1. Adding UV photometry reduces the uncertainty of fitted R-V by similar to 50 per cent allowing us to also measure R-V of individual low-extinction objects which point to a similar diversity, currently not accounted for in the analyses when SNe Ia are used for studying the expansion history of the Universe.

  • 111. Amarsi, A. M.
    et al.
    Asplund, M.
    Collet, R.
    Leenaarts, Jorrit
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Non-LTE oxygen line formation in 3D hydrodynamic model stellar atmospheres2016Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 455, nr 4, s. 3735-3751Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The O (Iota) 777 nm lines are among the most commonly used diagnostics for the oxygen abundances in the atmospheres of FGK-type stars. However, they form in conditions that are far from local thermodynamic equilibrium (LTE). We explore the departures from LTE of atomic oxygen, and their impact on O I lines, across the STAGGER-grid of three-dimensional hydrodynamic model atmospheres. For the O (Iota) 777 nm triplet, we find significant departures from LTE. These departures are larger in stars with larger effective temperatures, smaller surface gravities, and larger oxygen abundances. We present grids of predicted 3D non-LTE based equivalent widths for the O (Iota) 616 nm, [O (Iota)] 630 nm, [O (I)] 636 nm, and O (Iota) 777 nm lines, as well as abundance corrections to 1D LTE based results.

  • 112. Amarsi, A. M.
    et al.
    Asplund, M.
    Collet, R.
    Leenaarts, Jorrit
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    The Galactic chemical evolution of oxygen inferred from 3D non-LTE spectral-line-formation calculations2015Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 454, nr 1, s. L11-L15Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We revisit the Galactic chemical evolution of oxygen, addressing the systematic errors inherent in classical determinations of the oxygen abundance that arise from the use of one-dimensional (1D) hydrostatic model atmospheres and from the assumption of local thermodynamic equilibrium (LTE). We perform detailed 3D non-LTE radiative-transfer calculations for atomic oxygen lines across a grid of 3D hydrodynamic STAGGER model atmospheres for dwarfs and subgiants. We apply our grid of predicted line strengths of the [O I] 630 nm and O I 777 nm lines using accurate stellar parameters from the literature. We infer a steep decay in [O/Fe] for [Fe/H] greater than or similar to -1.0, a plateau [O/Fe] approximate to 0.5 down to [Fe/H] approximate to -2.5, and an increasing trend for [Fe/H] less than or similar to -2.5. Our 3D non-LTE calculations yield overall concordant results from the two oxygen abundance diagnostics.

  • 113. Amiaux, J
    et al.
    Andra, 40
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Development approach and first infrared test results of JWST/Mid Infra Red Imager Optical Bench2008Ingår i: Space Telescopes and Instrumentation 2008: Optical, Infrared, and Millimeter, 2008Konferensbidrag (Övrigt vetenskapligt)
  • 114.
    Anderson, Brandon
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Larsson, Stefan
    Li, L.
    Meyer, Manuel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Zimmer, Stephan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Ferretti, Raphael
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Rosswog, Stephan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    SUPPLEMENT: LOCALIZATION AND BROADBAND FOLLOW-UP OF THE GRAVITATIONAL-WAVE TRANSIENT GW150914 (2016, ApJL, 826, L13)2016Ingår i: Astrophysical Journal Supplement Series, ISSN 0067-0049, E-ISSN 1538-4365, Vol. 225, nr 1, artikel-id 8Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands.

  • 115.
    Anderson, Brandon
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Meyer, Manuel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Ferretti, Raphael
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Zimmer, Stephan
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Rosswog, Stephan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    LOCALIZATION AND BROADBAND FOLLOW-UP OF THE GRAVITATIONAL-WAVE TRANSIENT GW 1509142016Ingår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 826, nr 1, artikel-id L13Artikel i tidskrift (Refereegranskat)
    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.

  • 116. Anderson, P.
    et al.
    Dessart, L.
    Gutiérrez, C. P.
    Krühler, T.
    Galbany, L.
    Jerkstrand, A.
    Smartt, S. J.
    Contreras, C.
    Morrell, N.
    Phillips, M. M.
    Stritzinger, M. D.
    Hsiao, E. Y.
    González-Gaitán, S.
    Agliozzo, C.
    Castellón, S.
    Chambers, K. C.
    Chen, T. -W.
    Flewelling, H.
    Gonzalez, C.
    Hosseinzadeh, G.
    Huber, M.
    Fraser, M.
    Inserra, C.
    Kankare, E.
    Mattila, S.
    Magnier, E.
    Maguire, K.
    Lowe, T. B.
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Sullivan, M.
    Young, D. R.
    Valenti, S.
    The lowest-metallicity type II supernova from the highest-mass red supergiant progenitor2018Ingår i: Nature astronomy, ISSN 2397-3366, Vol. 2, nr 7, s. 574-579Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Red supergiants have been confirmed as the progenitor stars of the majority of hydrogen-rich type II supernovae(1). However, while such stars are observed with masses > 25 M-circle dot (ref. (2)), detections of > 18 M-circle dot progenitors remain elusive(1). Red supergiants are also expected to form at all metallicities, but discoveries of explosions from low-metallicity progenitors are scarce. Here, we report observations of the type II supernova, SN 2015bs, for which we infer a progenitor metallicity of <= 0.1 Z(circle dot) from comparison to photospheric-phase spectral models(3), and a zero-age main-sequence mass of 17-25 M-circle dot through comparison to nebular-phase spectral models(4,5). SN 2015bs displays a normal 'plateau' light-curve morphology, and typical spectral properties, implying a red supergiant progenitor. This is the first example of such a high-mass progenitor for a 'normal' type II supernova, suggesting a link between high-mass red supergiant explosions and low-metallicity progenitors.

  • 117.
    Andersson, K.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Peterson, J. R.
    Madejski, G.
    Application of an XMM-Newton epic Monte Carlo technique to analysis and interpretation of data for the abell 1689, RX J0658-55, and centaurus clusters of galaxies2007Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 670, nr 2, s. 1010-1026Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We propose a new Monte Carlo method to study extended X-ray sources with the European Photon Imaging Camera (EPIC) aboard XMM-Newton. The smoothed particle inference (SPI) technique, described in a companion paper, is applied here to the EPIC data for the clusters of galaxies Abell 1689, Centaurus, and RX J0658-55 (the ""bullet cluster""). We aim to show the advantages of this method of simultaneous spectral and spatial modeling over traditional X-ray spectral analysis. In Abell 1689 we confirm our earlier findings about structure in the temperature distribution and produce a high-resolution temperature map. We also find a hint of velocity structure within the gas, consistent with previous findings. In the bullet cluster, RX J0658-55, we produce the highest resolution temperature map ever to be published of this cluster, allowing us to trace what looks like the trail of the motion of the bullet in the cluster. We even detect a south-to-north temperature gradient within the bullet itself. In the Centaurus cluster we detect, by dividing up the luminosity of the cluster in bands of gas temperatures, a striking feature to the northeast of the cluster core. We hypothesize that this feature is caused by a subcluster left over from a substantial merger that slightly displaced the core. We conclude that our method is very powerful in determining the spatial distributions of plasma temperatures and very useful for systematic studies in cluster structure.

  • 118.
    Andersson Lundgren, Andreas
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Molecular gas in the galaxy M83: Its distribution, kinematics, and relation to star formation2004Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The barred spiral galaxy M83 (NGC5236) has been observed in the 12CO J=1–0 and J=2–1 millimetre lines with the Swedish-ESO Submillimetre Telescope (SEST). The sizes of the CO maps are 100×100, and they cover the entire optical disk. The CO emission is strongly peaked toward the nucleus. The molecular spiral arms are clearly resolved and can be traced for about 360º. The total molecular gas mass is comparable to the total Hi mass, but H2 dominates in the optical disk.

    Iso-velocity maps show the signature of an inclined, rotating disk, but also the effects of streaming motions along the spiral arms. The dynamical mass is determined and compared to the gas mass. The pattern speed is determined from the residual velocity pattern, and the locations of various resonances are discussed. The molecular gas velocity dispersion is determined, and a trend of decreasing dispersion with increasing galactocentric radius is found.

    A total gas (H2+Hi+He) mass surface density map is presented, and compared to the critical density for star formation of an isothermal gaseous disk. The star formation rate (SFR) in the disk is estimated using data from various star formation tracers. The different SFR estimates agree well when corrections for extinctions, based on the total gas mass map, are made. The radial SFR distribution shows features that can be associated with kinematic resonances. We also find an increased star formation efficiency in the spiral arms. Different Schmidt laws are fitted to the data. The star formation properties of the nuclear region, based on high angular resolution HST data, are also discussed.

  • 119.
    Andreas, Sandberg
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Östlin, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Melinder, Jens
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Bik, Adrianus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Guaita, L.
    Limits on Lyman Continuum Escape from z = 2.2 Hα-emitting Galaxies2015Ingår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 814, nr 1, artikel-id L10Artikel i tidskrift (Refereegranskat)
    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.

  • 120. Andreoni, I.
    et al.
    Ackley, K.
    Cooke, J.
    Acharyya, A.
    Allison, J. R.
    Anderson, G. E.
    Ashley, M. C. B.
    Baade, D.
    Bailes, M.
    Bannister, K.
    Beardsley, A.
    Bessell, M. S.
    Bian, F.
    Bland, P. A.
    Boer, M.
    Booler, T.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Brown, I. S.
    Buckley, D. A. H.
    Chang, S. -W.
    Coward, D. M.
    Crawford, S.
    Crisp, H.
    Crosse, B.
    Cucchiara, A.
    Cupak, M.
    de Gois, J. S.
    Deller, A.
    Devillepoix, H. A. R.
    Dobie, D.
    Elmer, E.
    Emrich, D.
    Farah, W.
    Farrell, T. J.
    Franzen, T.
    Gaensler, B. M.
    Galloway, D. K.
    Gendre, B.
    Giblin, T.
    Goobar, Ariel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Green, J.
    Hancock, P. J.
    Hartig, B. A. D.
    Howell, E. J.
    Horsley, L.
    Hotan, A.
    Howie, R. M.
    Hu, L.
    Hu, Y.
    James, C. W.
    Johnston, S.
    Johnston-Hollitt, M.
    Kaplan, D. L.
    Kasliwal, M.
    Keane, E. F.
    Kenney, D.
    Klotz, A.
    Lau, R.
    Laugier, R.
    Lenc, E.
    Li, X.
    Liang, E.
    Lidman, C.
    Luvaul, L. C.
    Lynch, C.
    Ma, B.
    Macpherson, D.
    Mao, J.
    McClelland, D. E.
    McCully, C.
    Moller, A.
    Morales, M. F.
    Morris, D.
    Murphy, T.
    Noysena, K.
    Onken, C. A.
    Orange, N. B.
    Oslowski, S.
    Pallot, D.
    Paxman, J.
    Potter, S. B.
    Pritchard, T.
    Raja, W.
    Ridden-Harper, R.
    Romero-Colmenero, E.
    Sadler, E. M.
    Sansom, E. K.
    Scalzo, R. A.
    Schmidt, B. P.
    Scott, S. M.
    Seghouani, N.
    Shang, Z.
    Shannon, R. M.
    Shao, L.
    Shara, M. M.
    Sharp, R.
    Sokolowski, M.
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Staff, J.
    Steele, K.
    Sun, T.
    Suntzeff, N. B.
    Tao, C.
    Tingay, S.
    Towner, M. C.
    Thierry, P.
    Trott, C.
    Tucker, B. E.
    Vaisanen, P.
    Krishnan, V. Venkatraman
    Walker, M.
    Wang, L.
    Wang, X.
    Wayth, R.
    Whiting, M.
    Williams, A.
    Williams, T.
    Wolf, C.
    Wu, C.
    Wu, X.
    Yang, J.
    Yuan, X.
    Zhang, H.
    Zhou, J.
    Zovaro, H.
    Follow Up of GW170817 and Its Electromagnetic Counterpart by Australian-Led Observing Programmes2017Ingår i: Publications Astronomical Society of Australia, ISSN 1323-3580, E-ISSN 1448-6083, Vol. 34, artikel-id e069Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    The discovery of the first electromagnetic counterpart to a gravitational wave signal has generated follow-up observations by over 50 facilities world-wide, ushering in the new era of multi-messenger astronomy. In this paper, we present follow-up observations of the gravitational wave event GW170817 and its electromagnetic counterpart SSS17a/DLT17ck (IAU label AT2017gfo) by 14 Australian telescopes and partner observatories as part of Australian-based and Australian-led research programs. We report early- to late-time multi-wavelength observations, including optical imaging and spectroscopy, mid-infrared imaging, radio imaging, and searches for fast radio bursts. Our optical spectra reveal that the transient source emission cooled from approximately 6 400 K to 2 100 K over a 7-d period and produced no significant optical emission lines. The spectral profiles, cooling rate, and photometric light curves are consistent with the expected outburst and subsequent processes of a binary neutron star merger. Star formation in the host galaxy probably ceased at least a Gyr ago, although there is evidence for a galaxy merger. Binary pulsars with short (100 Myr) decay times are therefore unlikely progenitors, but pulsars like PSR B1534+12 with its 2.7 Gyr coalescence time could produce such a merger. The displacement (similar to 2.2 kpc) of the binary star system from the centre of the main galaxy is not unusual for stars in the host galaxy or stars originating in the merging galaxy, and therefore any constraints on the kick velocity imparted to the progenitor are poor.

  • 121. Andreoni, Igor
    et al.
    Goldstein, Daniel A.
    Anand, Shreya
    Coughlin, Michael W.
    Singer, Leo P.
    Ahumada, Tomás
    Medford, Michael
    Kool, Erik C.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Webb, Sara
    Bulla, Mattia
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (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 Candidate2019Ingår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 881, nr 1, artikel-id L16Artikel i tidskrift (Refereegranskat)
    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.

  • 122. Andrews, Jennifer E.
    et al.
    Sand, D. J.
    Valenti, S.
    Smith, Nathan
    Dastidar, Raya
    Sahu, D. K.
    Misra, Kuntal
    Singh, Avinash
    Hiramatsu, D.
    Brown, P. J.
    Hosseinzadeh, G.
    Wyatt, S.
    Vinko, J.
    Anupama, G. C.
    Arcavi, I.
    Ashall, Chris
    Benetti, S.
    Berton, Marco
    Bostroem, K. A.
    Bulla, Mattia
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Burke, J.
    Chen, S.
    Chomiuk, L.
    Cikota, A.
    Congiu, E.
    Cseh, B.
    Davis, Scott
    Elias-Rosa, N.
    Faran, T.
    Fraser, Morgan
    Galbany, L.
    Gall, C.
    Gal-Yam, A.
    Gangopadhyay, Anjasha
    Gromadzki, M.
    Haislip, J.
    Howell, D. A.
    Hsiao, E. Y.
    Inserra, C.
    Kankare, E.
    Kuncarayakti, H.
    Kouprianov, V.
    Kumar, Brajesh
    Li, Xue
    Lin, Han
    Maguire, K.
    Mazzali, P.
    McCully, C.
    Milne, P.
    Mo, Jun
    Morrell, N.
    Nicholl, M.
    Ochner, P.
    Olivares, F.
    Pastorello, A.
    Patat, F.
    Phillips, M.
    Pignata, G.
    Prentice, S.
    Reguitti, A.
    Reichart, D. E.
    Rodriguez, O.
    Rui, Liming
    Sanwal, Pankaj
    Sarneczky, K.
    Shahbandeh, M.
    Singh, Mridweeka
    Smartt, S.
    Strader, J.
    Stritzinger, M. D.
    Szakats, R.
    Tartaglia, Leonardo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Wang, Huijuan
    Wang, Lingzhi
    Wang, Xiaofeng
    Wheeler, J. C.
    Xiang, Danfeng
    Yaron, O.
    Young, D. R.
    Zhang, Junbo
    SN 2017gmr: An Energetic Type II-P Supernova with Asymmetries2019Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 885, nr 1, artikel-id 43Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present high-cadence UV, optical, and near-infrared data on the luminous Type II-P supernova SN;2017gmr from hours after discovery through the first 180 days. SN;2017gmr does not show signs of narrow, high-ionization emission lines in the early optical spectra, yet the optical light-curve evolution suggests that an extra energy source from circumstellar medium (CSM) interaction must be present for at least 2 days after explosion. Modeling of the early light curve indicates a ?500 R progenitor radius, consistent with a rather compact red supergiant, and late-time luminosities indicate that up to 0.130;;0.026 M of Ni-56 are present, if the light curve is solely powered by radioactive decay, although the Ni-56 mass may be lower if CSM interaction contributes to the post-plateau luminosity. Prominent multipeaked emission lines of H? and [O i] emerge after day 154, as a result of either an asymmetric explosion or asymmetries in the CSM. The lack of narrow lines within the first 2 days of explosion in the likely presence of CSM interaction may be an example of close, dense, asymmetric CSM that is quickly enveloped by the spherical supernova ejecta.

  • 123. Andrievsky, Alexander
    et al.
    Brandenburg, Axel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).
    Noullez, Alain
    Zheligovsky, Vladislav
    NEGATIVE MAGNETIC EDDY DIFFUSIVITIES FROM THE TEST-FIELD METHOD AND MULTISCALE STABILITY THEORY2015Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 811, nr 2, artikel-id 135Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The generation of a large-scale magnetic field in the kinematic regime in the absence of an alpha-effect is investigated by following two different approaches: the test-field method and the multiscale stability theory relying on the homogenization technique. Our computations of the magnetic eddy diffusivity tensor of the parity-invariant flow IV of G. O. Roberts and the modified Taylor-Green flow confirm the findings of previous studies. and also explain some of their apparent contradictions. The two flows have large symmetry groups; this is used to considerably simplify the eddy diffusivity tensor. Finally, a new analytic result is presented: upon expressing the eddy diffusivity tensor in terms of solutions to auxiliary problems for the adjoint operator, we derive relations between the magnetic eddy diffusivity tensors that arise for mutually reverse small-scale flows v(x) and - v(x).

  • 124. Ao, Y.
    et al.
    Matsuda, Y.
    Henkel, C.
    Iono, D.
    Alexander, D. M.
    Chapman, S. C.
    Geach, J.
    Hatsukade, B.
    Hayes, Matthew
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Hine, N. K.
    Kato, Y.
    Kawabe, R.
    Kohno, K.
    Kubo, M.
    Lehnert, M.
    Malkan, M.
    Menten, K. M.
    Nagao, T.
    Norris, R. P.
    Ouchi, M.
    Saito, T.
    Tamura, Y.
    Taniguchi, Y.
    Umehata, H.
    Weiss, A.
    Deep Submillimeter and Radio Observations in the SSA22 Field. I. Powering Sources and the Ly alpha Escape Fraction of Ly alpha Blobs2017Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 850, nr 2, artikel-id 178Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the heating mechanisms and Ly alpha escape fractions of 35 Ly alpha blobs (LABs) at z approximate to 3.1 in the SSA22 field. Dust continuum sources have been identified in 11 of the 35 LABs, all with star formation rates (SFRs) above 100M(circle dot) yr(-1). Likely radio counterparts are detected in 9 out of 29 investigated LABs. The detection of submillimeter dust emission is more linked to the physical size of the Ly alpha emission than to the Ly alpha luminosities of the LABs. A radio excess in the submillimeter/ radio-detected LABs is common, hinting at the presence of active galactic nuclei. Most radio sources without X-ray counterparts are located at the centers of the LABs. However, all X-ray counterparts avoid the central regions. This may be explained by absorption due to exceptionally large column densities along the line-of-sight or by LAB morphologies, which are highly orientation dependent. The median Lya escape fraction is about 3% among the submillimeter-detected LABs, which is lower than a lower limit of 11% for the submillimeter-undetected LABs. We suspect that the large difference is due to the high dust attenuation supported by the large SFRs, the dense large-scale environment as well as large uncertainties in the extinction corrections required to apply when interpreting optical data.

  • 125. Arabaci, M. Özbey
    et al.
    Camero-Arranz, A.
    Zurita, C.
    Gutiérrez-Soto, J.
    Nespoli, E.
    Suso, J.
    Kiaeerad, F.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC). Nordic Optical Telescope, Spain.
    Garcia-Rojas, J.
    Kiziloglu, U.
    Detection of a large Be circumstellar disk during X-ray quiescence of XTE J1946+2742015Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 582, artikel-id A53Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Aims: We present a multiwavelength study of the Be/X-ray binary system XTE J1946+274 with the main goal of better characterizing its behavior during X-ray quiescence. We also aim to shed light on the possible mechanisms which trigger the X-ray activity for this source.

    Methods: XTE J1946+274 was observed by Chandra-ACIS during quiescence in 2013 March 12. In addition, this source has been monitored from the ground-based astronomical observatories of El Teide (Tenerife, Spain), Roque de los Muchachos (La Palma, Spain) and Sierra Nevada (Granada, Spain) since 2011 September, and from the TUBITAK National Observatory (Antalya, Turkey) since 2005 April. We have performed spectral and photometric temporal analyses in order to investigate the quiescent state and transient behavior of this binary system.

    Results: Our optical study revealed that a long mass ejection event from the Be star took place in 2006, lasting for about seven years, and another one is currently ongoing. We also found that a large Be circumstellar disk is present during quiescence, although major X-ray activity is not observed. We made an attempt to explain this by assuming the permanently presence of a tilted (sometimes warped) Be decretion disk. The 0.3-10 keV X-ray spectrum of the neutron star during quiescence was well fitted with either an absorbed black-body or an absorbed power-law models. The main parameters obtained for these models were kT = 1.43 +/- 0.17 and Gamma = 0.9 +/- 0.4 (with N-H similar to 2-7 x 10(22) cm(-2)). The 0.3-10 keV flux of the source was similar to 0.8-1 x 10(-12) erg(-1) cm(-2) s(-1). Pulsations were found with P-pulse = 15.757(1) s (epoch MJD 56 363.115) and an rms pulse fraction of 32.1(3)%. The observed X-ray luminosity during quiescent periods was close to that of expected in supersonic propeller regimen.

  • 126. Arcavi, Iair
    et al.
    Howell, D. Andrew
    Kasen, Daniel
    Bildsten, Lars
    Hosseinzadeh, Griffin
    McCully, Curtis
    Wong, Zheng Chuen
    Katz, Sarah Rebekah
    Gal-Yam, Avishay
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Taddia, Francesco
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Leloudas, Giorgos
    Fremling, Christoffer
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Nugent, Peter E.
    Horesh, Assaf
    Mooley, Kunal
    Rumsey, Clare
    Cenko, S. B. Radley
    Graham, Melissa L.
    Perley, Daniel A.
    Nakar, Ehud
    Shaviv, Nir J.
    Bromberg, Omer
    Shen, Ken J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Ofek, Eran O.
    Cao, Yi
    Wang, Xiaofeng
    Huang, Fang
    Rui, Liming
    Zhang, Tianmeng
    Li, Wenxiong
    Li, Zhitong
    Zhang, Jujia
    Valenti, Stefano
    Guevel, David
    Shappee, Benjamin
    Kochanek, Christopher S.
    Holoien, Thomas W. -S.
    Filippenko, Alexei V.
    Fender, Rob
    Nyholm, Anders
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Yaron, Ofer
    Kasliwal, Mansi M. .
    Sullivan, Mark
    Lagorodnova, Nadja B.
    Walters, Richard S.
    Lunnan, Ragnhild
    Khazov, Danny
    Andreoni, Igor
    Laher, Russ R.
    Konidaris, Nick
    Wozniak, Przemek
    Bue, Brian
    Energetic eruptions leading to a peculiar hydrogen-rich explosion of a massive star2017Ingår i: Nature, ISSN 0028-0836, E-ISSN 1476-4687, Vol. 551, nr 7679, s. 210-213Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Every supernova so far observed has been considered to be the terminal explosion of a star. Moreover, all supernovae with absorption lines in their spectra show those lines decreasing in velocity over time, as the ejecta expand and thin, revealing slower-moving material that was previously hidden. In addition, every supernova that exhibits the absorption lines of hydrogen has one main light-curve peak, or a plateau in luminosity, lasting approximately 100 days before declining(1). Here we report observations of iPTF14hls, an event that has spectra identical to a hydrogen-rich core-collapse supernova, but characteristics that differ extensively from those of known supernovae. The light curve has at least five peaks and remains bright for more than 600 days; the absorption lines show little to no decrease in velocity; and the radius of the line-forming region is more than an order of magnitude bigger than the radius of the photosphere derived from the continuum emission. These characteristics are consistent with a shell of several tens of solar masses ejected by the progenitor star at supernova-level energies a few hundred days before a terminal explosion. Another possible eruption was recorded at the same position in 1954. Multiple energetic pre-supernova eruptions are expected to occur in stars of 95 to 130 solar masses, which experience the pulsational pair instability(2-5). That model, however, does not account for the continued presence of hydrogen, or the energetics observed here. Another mechanism for the violent ejection of mass in massive stars may be required.

  • 127. Archambault, S.
    et al.
    Aune, T.
    Behera, B.
    Beilicke, M.
    Benbow, W.
    Berger, K.
    Bird, R.
    Biteau, J.
    Bugaev, V.
    Byrum, K.
    Cardenzana, J. V.
    Cerruti, M.
    Chen, X.
    Ciupik, L.
    Connolly, M. P.
    Cui, W.
    Dumm, J.
    Errando, M.
    Falcone, A.
    Federici, S.
    Feng, Q.
    Finley, J. P.
    Fleischhack, H.
    Fortson, L.
    Furniss, A.
    Galante, N.
    Gillanders, G. H.
    Griffin, S.
    Griffiths, S. T.
    Grube, J.
    Gyuk, G.
    Hanna, D.
    Holder, J.
    Hughes, G.
    Humensky, T. B.
    Johnson, C. A.
    Kaaret, P.
    Kertzman, M.
    Khassen, Y.
    Kieda, D.
    Krawczynski, H.
    Krennrich, F.
    Kumar, S.
    Lang, M. J.
    Madhavan, A. S.
    Maier, G.
    McCann, A.
    Meagher, K.
    Moriarty, P.
    Mukherjee, R.
    Nieto, D.
    de Bhroithe, A. O'Faolain
    Ong, R. A.
    Otte, A. N.
    Park, N.
    Pohl, M.
    Popkow, A.
    Prokoph, H.
    Quinn, J.
    Ragan, K.
    Rajotte, J.
    Reyes, L. C.
    Reynolds, P. T.
    Richards, G. T.
    Roache, E.
    Sembroski, G. H.
    Shahinyan, K.
    Staszak, D.
    Telezhinsky, I.
    Tucci, J. V.
    Tyler, J.
    Varlotta, A.
    Vassiliev, V. V.
    Vincent, S.
    Wakely, S. P.
    Weinstein, A.
    Welsing, R.
    Wilhelm, A.
    Williams, D. A.
    Ackermann, M.
    Ajello, M.
    Albert, A.
    Baldini, L.
    Bastieri, D.
    Bellazzini, R.
    Bissaldi, E.
    Bregeon, J.
    Buehler, R.
    Buson, S.
    Caliandro, G. A.
    Cameron, R. A.
    Caraveo, P. A.
    Cavazzuti, E.
    Charles, E.
    Chiang, J.
    Ciprini, S.
    Claus, R.
    Cutini, S.
    D'Ammando, F.
    de Angelis, A.
    de Palma, F.
    Dermer, C. D.
    Digel, S. W.
    Di Venere, L.
    Drell, P. S.
    Favuzzi, C.
    Franckowiak, A.
    Fusco, P.
    Gargano, F.
    Gasparrini, D.
    Giglietto, N.
    Giordano, F.
    Giroletti, M.
    Grenier, I. A.
    Guiriec, S.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Jogler, T.
    Kuss, M.
    Larsson, Stefan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Latronico, L.
    Longo, F.
    Loparco, F.
    Lubrano, P.
    Madejski, G. M.
    Mayer, M.
    Mazziotta, M. N.
    Michelson, P. F.
    Mizuno, T.
    Monzani, M. E.
    Morselli, A.
    Murgia, S.
    Nuss, E.
    Ohsugi, T.
    Ormes, J. F.
    Paneque, D.
    Perkins, J. S.
    Piron, F.
    Pivato, G.
    Raino, S.
    Razzano, M.
    Reimer, A.
    Reimer, O.
    Ritz, S.
    Schaal, M.
    Sgro, C.
    Siskind, E. J.
    Spinelli, P.
    Takahashi, H.
    Tibaldo, L.
    Tinivella, M.
    Troja, E.
    Vianello, G.
    Werner, M.
    Wood, M.
    DEEP BROADBAND OBSERVATIONS OF THE DISTANT GAMMA-RAY BLAZAR PKS 1424+2402014Ingår i: The Astrophysical Journal Letters, ISSN 2041-8205, Vol. 785, nr 1, s. L16-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present deep VERITAS observations of the blazar PKS 1424+240, along with contemporaneous Fermi Large Area Telescope, Swift X-ray Telescope, and Swift UV Optical Telescope data between 2009 February 19 and 2013 June 8. This blazar resides at a redshift of z >= 0.6035, displaying a significantly attenuated gamma-ray flux above 100 GeV due to photon absorption via pair-production with the extragalactic background light. We present more than 100 hr of VERITAS observations over three years, a multiwavelength light curve, and the contemporaneous spectral energy distributions. The source shows a higher flux of (2.1 +/- 0.3) x 10(-7) photons m(-2) s(-1) above 120 GeV in 2009 and 2011 as compared to the flux measured in 2013, corresponding to (1.02 +/- 0.08) x 10-7 photons m(-2) s(-1) above 120 GeV. The measured differential very high energy (VHE; E >= 100 GeV) spectral indices are Gamma = 3.8 +/- 0.3, 4.3 +/- 0.6 and 4.5 +/- 0.2 in 2009, 2011, and 2013, respectively. No significant spectral change across the observation epochs is detected. We find no evidence for variability at gamma-ray opacities of greater than tau = 2, where it is postulated that any variability would be small and occur on timescales longer than a year if hadronic cosmic-ray interactions with extragalactic photon fields provide a secondary VHE photon flux. The data cannot rule out such variability due to low statistics.

  • 128. Argyle, J. J.
    et al.
    Méndez-Abreu, J.
    Wild, V.
    Mortlock, Daniel J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Imperial College London, UK.
    Bayesian bulge-disc decomposition of galaxy images2018Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 479, nr 3, s. 3076-3093Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We introduce PHI, a fully Bayesian Markov chain Monte Carlo algorithm designed for the structural decomposition of galaxy images. PHI uses a triple layer approach to effectively and efficiently explore the complex parameter space. Combining this with the use of priors to prevent non-physical models, PHI offers a number of significant advantages for estimating surface brightness profile parameters over traditional optimization algorithms. We apply PHI to a sample of synthetic galaxies with Sloan Digital Sky Survey (SDSS)-like image properties to investigate the effect of galaxy properties on our ability to recover unbiased and well-constrained structural parameters. In two-component bulge+disc galaxies, we find that the bulge structural parameters are recovered less well than those of the disc, particularly when the bulge contributes a lower fraction to the luminosity, or is barely resolved with respect to the pixel scale or point spread function (PSF). There are few systematic biases, apart from for bulge+disc galaxies with large bulge Sersic parameter, n. On application to SDSS images, we find good agreement with other codes, when run on the same images with the same masks, weights, and PSF. Again, we find that bulge parameters are the most difficult to constrain robustly. Finally, we explore the use of a Bayesian information criterion method for deciding whether a galaxy has one or two components.

  • 129. Arthur, S. J.
    et al.
    Henney, W. J.
    Mellema, Garrelt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    De Colle, F.
    Vazquez-Semadeni, E.
    Radiation-magnetohydrodynamic simulations of H II regions and their associated PDRs in turbulent molecular clouds2011Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 414, nr 2, s. 1747-1768Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the results of radiation-magnetohydrodynamic simulations of the formation and expansion of H II regions and their surrounding photodissociation regions (PDRs) in turbulent, magnetized, molecular clouds on scales of up to 4 pc. We include the effects of ionizing and non-ionizing ultraviolet radiation and X-rays from population synthesis models of young star clusters. For all our simulations we find that the H II region expansion reduces the disordered component of the magnetic field, imposing a large-scale order on the field around its border, with the field in the neutral gas tending to lie along the ionization front, while the field in the ionized gas tends to be perpendicular to the front. The highest pressure-compressed neutral and molecular gas is driven towards approximate equipartition between thermal, magnetic and turbulent energy densities, whereas lower pressure neutral/molecular gas bifurcates into, on the one hand, quiescent, magnetically dominated regions and, on the other hand, turbulent, demagnetized regions. The ionized gas shows approximate equipartition between thermal and turbulent energy densities, but with magnetic energy densities that are 1-3 orders of magnitude lower. A high velocity dispersion (similar to 8 km s(-1)) is maintained in the ionized gas throughout our simulations, despite the mean expansion velocity being significantly lower. The magnetic field does not significantly brake the large-scale H II region expansion on the length and time-scales accessible to our simulations, but it does tend to suppress the smallest scale fragmentation and radiation-driven implosion of neutral/molecular gas that forms globules and pillars at the edge of the H II region. However, the relative luminosity of ionizing and non-ionizing radiation has a much larger influence than the presence or absence of the magnetic field. When the star cluster radiation field is relatively soft (as in the case of a lower mass cluster, containing an earliest spectral type of B0.5), then fragmentation is less vigorous and a thick, relatively smooth PDR forms.

  • 130. Artymowicz, Pawel
    et al.
    Peplinski, Adam
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Analytical theory of type III planetary migration2008Ingår i: The Astrophysical JournalArtikel i tidskrift (Refereegranskat)
  • 131. Asad, K. M. B.
    et al.
    Koopmans, L. V. E.
    Jelic, V.
    Pandey, V. N.
    Ghosh, A.
    Abdalla, F. B.
    Bernardi, G.
    Brentjens, M. A.
    de Bruyn, A. G.
    Bus, S.
    Ciardi, B.
    Chapman, E.
    Daiboo, S.
    Fernandez, E. R.
    Harker, G.
    Iliev, I. T.
    Jensen, Hannes
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Martinez-Rubi, O.
    Mellema, Garrelt
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Mevius, M.
    Offringa, A. R.
    Patil, A. H.
    Schaye, J.
    Thomas, R. M.
    van der Tol, S.
    Vedantham, H. K.
    Yatawatta, S.
    Zaroubi, S.
    Polarization leakage in epoch of reionization windows - I. Low Frequency Array observations of the 3C196 field2015Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 451, nr 4, s. 3709-3727Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Detection of the 21-cm signal coming from the epoch of reionization (EoR) is challenging especially because, even after removing the foregrounds, the residual Stokes <italic toggle=yes>I maps contain leakage from polarized emission that can mimic the signal. Here, we discuss the instrumental polarization of Low Frequency Array (LOFAR) and present realistic simulations of the leakages between Stokes parameters. From the LOFAR observations of polarized emission in the 3C196 field, we have quantified the level of polarization leakage caused by the nominal model beam of LOFAR, and compared it with the EoR signal using power spectrum analysis. We found that at 134-166 MHz, within the central 4A degrees of the field the (<italic toggle=yes>Q, <italic toggle=yes>U) -> <italic toggle=yes>I leakage power is lower than the EoR signal at <italic toggle=yes>k < 0.3 Mpc(-1). The leakage was found to be localized around a Faraday depth of 0, and the rms of the leakage as a fraction of the rms of the polarized emission was shown to vary between 0.2 and 0.3 per cent, both of which could be utilized in the removal of leakage. Moreover, we could define an 'EoR window' in terms of the polarization leakage in the cylindrical power spectrum above the point spread function (PSF)-induced wedge and below <italic toggle=yes>k(ayen) similar to 0.5 Mpc(-1), and the window extended up to <italic toggle=yes>k(ayen) similar to 1 Mpc(-1) at all <italic toggle=yes>k(aSyen) when 70 per cent of the leakage had been removed. These LOFAR results show that even a modest polarimetric calibration over a field of view of a parts per thousand(2) 4A degrees in the future arrays like Square Kilometre Array will ensure that the polarization leakage remains well below the expected EoR signal at the scales of 0.02-1 Mpc(-1).

  • 132.
    Asadi, Saghar
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Zackrisson, Erik
    Freeland, Emily
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Probing cold dark matter subhaloes with simulated ALMA observations of macrolensed sub-mm galaxies2017Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 472, nr 1, s. 129-140Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    If the dark matter haloes of galaxies contain large numbers of subhaloes as predicted by the Lambda cold dark matter model, these subhaloes are expected to appear in strong galaxy-galaxy lens systems as small-scale perturbations in individual images. We simulate observations of multiply lensed sub-mm galaxies at z similar to 2 as a probe of the dark matter halo of a lens galaxy at z similar to 0.5. We present detection limits for dark substructures based on a visibility plane analysis of simulated Atacama Large Millimeter/submillimeter Array (ALMA) data in bands 7, 8 and 9. We explore two effects: local surface brightness anomalies on angular scales similar to the Einstein radius and the astrometric shift of macroimages. This improves the sensitivity of our lens modelling to the mass of the lens perturber. We investigate the sensitivity of the detection of low-mass subhaloes to the projected position of the subhalo on the image plane as well as the source structure and inner density profile of the lens. We demonstrate that, using the most extended ALMA configuration, pseudo-Jaffe subhaloes can be detected with 99 per cent confidence down to M = 10(7)M(circle dot) . We show how the detection threshold for the three ALMA bands depends on the projected position of the subhalo with respect to the lensed images and conclude that, despite the highest nominal angular resolution, band 9 provides the poorest sensitivity due to observational noise. All simulations use the ALMA Full ops most extended ALMA configuration setup in CASA.

  • 133.
    Asadi, Saghar
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Zackrisson, Erik
    Varenius, Eskil
    Freeland, Emily
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Conway, John
    Wiik, Kaj
    The case against gravitational millilensing in the multiply-imaged quasar B1152+1992020Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 492, nr 1, s. 742-748Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Previous very long baseline interferometry (VLBI) observations of the quasar B1152+199 at 5 GHz has revealed two images of a strongly lensed jet with seemingly discordant morphologies. Whereas the jet appears straight in one of the images, the other exhibits slight curvature on milliarcsecond scales. This is unexpected from the lensing solution and has been interpreted as possible evidence for secondary, small-scale lensing (millilensing) by a compact object with a mass of 10(5)-10(7) M-circle dot located close to the curved image. The probability for such a superposition is extremely low unless the millilens population has very high surface number density. Here, we revisit the case for millilensing in B1152+199 by combining new global-VLBI data at 8.4 GHz with two data sets from the European VLBI Network (EVN) at 5 GHz (archival), and the previously published 5 GHz Very Long Baseline Array (VLBA) data. We find that the new data with a more circular synthesized beam, exhibits no apparent milliarcsecond-scale curvature in image B. Various observations of the object spanning similar to 15 yr apart enable us to improve the constraints on lens system to the point that the only plausible explanation left for the apparent curvature is the artefact due to the shape of the synthesized beam.

  • 134. Ascenzi, Stefano
    et al.
    Coughlin, Michael W.
    Dietrich, Tim
    Foley, Ryan J.
    Ramirez-Ruiz, Enrico
    Piranomonte, Silvia
    Mockler, Brenna
    Murguia-Berthier, Ariadna
    Fryer, Chris L.
    Lloyd-Ronning, Nicole M.
    Rosswog, Stephan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    A luminosity distribution for kilonovae based on short gamma-ray burst afterglows2019Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 486, nr 1, s. 672-690Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The combined detection of a gravitational-wave signal, kilonova, and short gamma-ray burst (sGRB) from GW170817 marked a scientific breakthrough in the field of multimessenger astronomy. But even before GW170817, there have been a number of sGRBs with possible associated kilonova detections. In this work, we re-examine these ` historical' sGRB afterglows with a combination of state-of-the-art afterglow and kilonova models. This allows us to include optical/near-infrared synchrotron emission produced by the sGRB as well as ultraviolet/optical/near-infrared emission powered by the radioactive decay of r-process elements (i.e. the kilonova). Fitting the light curves, we derive the velocity and the mass distribution as well as the composition of the ejected material. The posteriors on kilonova parameters obtained from the fit were turned into distributions for the peak magnitude of the kilonova emission in different bands and the time at which this peak occurs. From the sGRB with an associated kilonova, we found that the peak magnitude in H bands falls in the range [-16.2, -13.1] (95 per cent of confidence) and occurs within 0.8-3.6 d after the sGRB prompt emission. In g band instead we obtain a peak magnitude in range [-16.8, -12.3] occurring within the first 18 h after the sGRB prompt. From the luminosity distributions of GW170817/AT2017gfo, kilonova candidates GRB130603B, GRB050709, and GRB060614 (with the possible inclusion of GRB150101B, GRB050724A, GRB061201, GRB080905A, GRB150424A, and GRB160821B) and the upper limits from all the other sGRBs not associated with any kilonova detection we obtain for the first time a kilonova luminosity distribution in different bands.

  • 135. Asensio Ramos, A.
    et al.
    de la Cruz Rodriguez, Jaime
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Sparse inversion of Stokes profiles I. Two-dimensional Milne-Eddington inversions2015Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 577, artikel-id A140Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Inversion codes are numerical tools used to infer physical properties from observations. Despite their success, the quality of current spectropolarimetric observations and those expected in the near future presents a challenge to current inversion codes. Aims. The pixel-by-pixel strategy of inverting spectropolarimetric data that we currently use needs to be surpassed and improved. The inverted physical parameters have to take into account the spatial correlation that is present in the data and that contains valuable physical information. Methods. We used the concept of sparsity or compressibility to develop a new generation of inversion codes for the Stokes parameters. The inversion code uses numerical optimization techniques based on the idea of proximal algorithms to impose sparsity. In so doing, we allow for the first time exploiting the spatial correlation on the maps of physical parameters. Sparsity also regularizes the solution by reducing the number of unknowns. Results. We compare the results of the new inversion code with pixel-by-pixel inversions to demonstrate the increased robustness of the solution. We also show how the method can easily compensate for the effect of the telescope point spread function, producing solutions with an enhanced contrast.

  • 136. Asensio Ramos, A.
    et al.
    de la Cruz Rodriguez, Jaime
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Martinez Gonzalez, M. J.
    Pastor Yabar, A.
    Inversion of Stokes profiles with systematic effects2016Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 590, artikel-id A87Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Quantitative thermodynamical, dynamical and magnetic properties of the solar and stellar plasmas are obtained by interpreting their emergent non-polarized and polarized spectrum. This inference requires the selection of a set of spectral lines that are particularly sensitive to the physical conditions in the plasma and a suitable parametric model of the solar/stellar atmosphere. Nonlinear inversion codes are then used to fit the model to the observations. However, the presence of systematic effects, like nearby or blended spectral lines, telluric absorption, or incorrect correction of the continuum, among others, can strongly affect the results. We present an extension to current inversion codes that can deal with these effects in a transparent way. The resulting algorithm is very simple and can be applied to any existing inversion code with the addition of a few lines of code as an extra step in each iteration.

  • 137. Asensio Ramos, A.
    et al.
    de la Cruz Rodríguez, Jaime
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Martínez González, M. J.
    Socas-Navarro, H.
    Inference of the chromospheric magnetic field orientation in the Ca II 8542 angstrom line fibrils2017Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 599, artikel-id A133Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Solar chromospheric fibrils, as observed in the core of strong chromospheric spectral lines, extend from photospheric field concentrations suggesting that they trace magnetic field lines. These images have been historically used as proxies of magnetic fields for many purposes.

    Aims. Use statistical analysis to test whether the association between fibrils and magnetic field lines is justified.

    Methods. We use a Bayesian hierarchical model to analyze several tens of thousands of pixels in spectro- polarimetric chromospheric images of penumbrae and chromospheric fibrils. We compare the alignment between the field azimuth inferred from the linear polarization signals through the transverse Zeeman effect and the direction of the fibrils in the image.

    Results. We conclude that, in the analyzed fields of view, fibrils are often well aligned with the magnetic field azimuth. Despite this alignment, the analysis also shows that there is a non-negligible dispersion. In penumbral filaments, we find a dispersion with a standard deviation of similar to 16 degrees, while this dispersion goes up to similar to 34 degrees in less magnetized regions.

  • 138. Asensio Ramos, A.
    et al.
    de la Cruz Rodríguez, Jaime
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Pastor Yabar, A.
    Real-time, multiframe, blind deconvolution of solar images2018Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 620, artikel-id A73Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The quality of images of the Sun obtained from the ground are severely limited by the perturbing effect of the Earth's turbulent atmosphere. The post-facto correction of the images to compensate for the presence of the atmosphere require the combination of high-order adaptive optics techniques, fast measurements to freeze the turbulent atmosphere, and very time-consuming blind deconvolution algorithms. Under mild seeing conditions, blind deconvolution algorithms can produce images of astonishing quality. They can be very competitive with those obtained from space, with the huge advantage of the flexibility of the instrumentation thanks to the direct access to the telescope. In this contribution we make use of deep learning techniques to significantly accelerate the blind deconvolution process and produce corrected images at a peak rate of similar to 100 images per second. We present two different architectures that produce excellent image corrections with noise suppression while maintaining the photometric properties of the images. As a consequence, polarimetric signals can be obtained with standard polarimetric modulation without any significant artifact. With the expected improvements in computer hardware and algorithms, we anticipate that on-site real-time correction of solar images will be possible in the near future.

  • 139. Asensio Ramos, A.
    et al.
    Díaz Baso, Carlos José
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Stokes inversion based on convolutional neural networks2019Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 626, artikel-id A102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context. Spectropolarimetric inversions are routinely used in the field of solar physics for the extraction of physical information from observations. The application to two-dimensional fields of view often requires the use of supercomputers with parallelized inversion codes. Even in this case, the computing time spent on the process is still very large.

    Aims. Our aim is to develop a new inversion code based on the application of convolutional neural networks that can quickly provide a three-dimensional cube of thermodynamical and magnetic properties from the interpreation of two-dimensional maps of Stokes profiles.

    Methods. We trained two different architectures of fully convolutional neural networks. To this end, we used the synthetic Stokes profiles obtained from two snapshots of three-dimensional magneto-hydrodynamic numerical simulations of different structures of the solar atmosphere.

    Results. We provide an extensive analysis of the new inversion technique, showing that it infers the thermodynamical and magnetic properties with a precision comparable to that of standard inversion techniques. However, it provides several key improvements: our method is around one million times faster, it returns a three-dimensional view of the physical properties of the region of interest in geometrical height, it provides quantities that cannot be obtained otherwise (pressure and Wilson depression) and the inferred properties are decontaminated from the blurring effect of instrumental point spread functions for free. The code, models, and data are all open source and available for free, to allow both evaluation and training.

  • 140.
    Asensio Torres, Ruben
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    High-contrast imaging of faint substellar companions and debris disks2017Licentiatavhandling, monografi (Övrigt vetenskapligt)
    Abstract [en]

    Star formation results in the accumulation of circumstellar material orbiting around their host stars, such as debris disks and planetary-mass objects. A relatively modern technique that has shown to be very valu- able for studying these faint companions is high-contrast imaging, which allows to distinguish the light emitted or scattered off these objects, otherwise hidden behind the brighter stellar halo. In this Licentiate thesis we review the high-contrast imaging technique and its capabilities, giving examples of the latest achievements reached by this method. The star and planet formation scenario within young and gas-rich protoplanetary disks is also briefly discussed. We show that direct imaging observations constrain the protoplanetary disk evolution and the different planet formation processes. We also discuss the debris disk formation scenario and how direct imaging observations can help to understand their morphology and composition. The presence of planetary-mass companions within the disk can be revealed directly via high-contrast imaging or otherwise inferred from their interactions with the debris disk. Finally, we present a recent result on the polarimetry and the flux distribution in the debris disk around the HD 32297 star, which appears to be dominated by micron-sized dust particles and might have indications of a double ring structure (Paper I). 

  • 141.
    Asensio Torres, Ruben
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    High-contrast imaging of low-mass companions and debris disks2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The search for exoplanets, i.e., planets orbiting other stars than the Sun, is a relatively new research field, but has already established itself as one of the most prolific and intriguing areas of astronomy. By now we are in a situation where the focus is not only on finding companions to stars, but also on characterising their atmospheres and physical properties, which overall allows us to put our Solar System into context. In the near future, these efforts could potentially lead to the first confirmation of a life-bearing planet besides the Earth. 

    The great majority of these exoplanet studies have been carried out indirectly, where the presence and characterisation of the companions are inferred solely from the observation of the host star. In the last decade, however, high-contrast direct imaging has been continuously developed to get rid of the starlight and reveal the existence of low-mass companions. Although this technique is currently limited to giant planets orbiting at large separations, it is able to directly detect the light emitted or scattered off the planet’s atmosphere at high signal to noise, which makes it the most promising planet-hunting method to characterise new worlds. Moreover, its capability to image faint objects close to the parent star allows for not only the detection of planetary-mass companions, but also low-mass stars, brown dwarfs, and circumstellar disks where planet formation takes place. This opens up a broad range of science cases where direct observations can be used to understand planet formation, atmospheric physics and stellar evolution.      

    In this PhD thesis I provide an up-to-date introduction to the basis of the direct imaging technique, and explain the star and planet formation mechanisms. Three publications are attached to this introduction, each of them dealing with distinct science cases that can be  assessed with high-contrast observations. In Paper I we resolve and model the aftermath of star formation, the so-called debris disk phase analogue to the asteroid and Kuiper belts in our Solar System, around the HD 32297 star with Subaru/HiCIAO.  We reveal an edge-on disk and find the first indications of a double-ring scenario. We also present the first polarimetric study of this system, constraining the properties of the dust around the star.  In Paper II we focus on the planetary-mass regime, and conduct the first direct imaging survey searching for circumbinary planets orbiting tight binary systems (SPOTS: Search for Planets Orbiting Two Stars). We present the results of the observations of 62 targets with VLT/NaCo and VLT/SPHERE, and perform a statistical analysis on the findings, placing constraints on the population of giant planets and brown dwarfs on wide orbits. Finally, in Paper III we resolve a triple stellar system with the newly-commissioned SCExAO/CHARIS integral field spectrograph. Taking advantage of the coeval nature of the system and the different range of masses involved, we use the data to reaffirm a previously suggested isochronal age discrepancy between the low- and the intermediate-mass population of stars.

  • 142.
    Asensio-Torres, Ruben
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Janson, Markus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Bonavita, M.
    Desidera, S.
    Thalmann, C.
    Kuzuhara, M.
    Henning, Th.
    Marzari, F.
    Meyer, M. R.
    Calissendorff, Per
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Uyama, T.
    SPOTS: The Search for Planets Orbiting Two Stars III. Complete sample and statistical analysis2018Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 619, artikel-id A43Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Binary stars constitute a large percentage of the stellar population, yet relatively little is known about the planetary systems orbiting them. Most constraints on circumbinary planets (CBPs) so far come from transit observations with the Kepler telescope, which is sensitive to close-in exoplanets but does not constrain planets on wider orbits. However, with continuous developments in high-contrast imaging techniques, this population can now be addressed through direct imaging. We present the full survey results of the Search for Planets Orbiting Two Stars (SPOTS) survey, which is the first direct imaging survey targeting CBPs. The SPOTS observational program comprises 62 tight binaries that are young and nearby, and thus suitable for direct imaging studies, with VLT/NaCo and VLT/SPHERE. Results from SPOTS include the resolved circumbinary disk around AK Sco, the discovery of a low-mass stellar companion in a triple packed system, the relative astrometry of up to 9 resolved binaries, and possible indications of non-background planetary-mass candidates around HIP 77911. We did not find any CBP within 300 AU, which implies a frequency upper limit on CBPs (1-15 M-Jup) of 6-10% between 30-300 AU. Coupling these observations with an archival dataset for a total of 163 stellar pairs, we find a best-fit CBP frequency of 1.9% (2-15 M-Jup) between 1 and 300 AU with a 10.5% upper limit at a 95% confidence level. This result is consistent with the distribution of companions around single stars.

  • 143.
    Asensio-Torres, Ruben
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Janson, Markus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Hashimoto, J.
    Thalmann, C.
    Currie, T.
    Buenzli, E.
    Kudo, T.
    Kuzuhara, M.
    Kusakabe, N.
    Abe, L.
    Akiyama, E.
    Brandner, W.
    Brandt, T. D.
    Carson, J.
    Egner, S.
    Feldt, M.
    Goto, M.
    Grady, C.
    Guyon, O.
    Hayano, Y.
    Hayashi, M.
    Hayashi, S.
    Henning, T.
    Hodapp, K.
    Ishii, M.
    Iye, M.
    Kandori, R.
    Knapp, G.
    Kwon, J.
    Matsuo, T.
    McElwain, M.
    Mayama, S.
    Miyama, S.
    Morino, J.
    Moro-Martin, A.
    Nishimura, T.
    Pyo, T.
    Serabyn, E.
    Suenaga, T.
    Suto, H.
    Suzuki, R.
    Takahashi, Y.
    Takami, M.
    Takato, N.
    Terada, H.
    Turner, E.
    Watanabe, M.
    Wisniewski, J.
    Yamada, T.
    Takami, H.
    Usuda, T.
    Tamura, M.
    Polarimetry and flux distribution in the debris disk around HD 322972016Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 593, artikel-id A73Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present high-contrast angular differential imaging (ADI) observations of the debris disk around HD32297 in H-band, as well as the first polarimetric images for this system in polarized differential imaging (PDI) mode with Subaru/HICIAO. In ADI, we detect the nearly edge-on disk at > 5 sigma levels from similar to 0.45 '' to similar to 1.7 '' (50-192AU) from the star and recover the spine deviation from the midplane already found in previous works. We also find for the first time imaging and surface brightness (SB) indications for the presence of a gapped structure on both sides of the disk at distances of similar to 0.75 '' (NE side) and similar to 0.65 '' (SW side). Global forward-modelling work delivers a best-fit model disk and well-fitting parameter intervals that essentially match previous results, with high-forward scattering grains and a ring located at 110AU. However, this single ring model cannot account for the gapped structure seen in our SB profiles. We create simple double ring models and achieve a satisfactory fit with two rings located at 60 and 95AU, respectively, low-forward scattering grains and very sharp inner slopes. In polarized light we retrieve the disk extending from similar to 0.25-1.6 '', although the central region is quite noisy and high S/N are only found in the range similar to 0.75-1.2 ''. The disk is polarized in the azimuthal direction, as expected, and the departure from the midplane is also clearly observed. Evidence for a gapped scenario is not found in the PDI data. We obtain a linear polarization degree of the grains that increases from similar to 10% at 0.55 '' to similar to 25% at 1.6 ''. The maximum is found at scattering angles of similar to 90 degrees, either from the main components of the disk or from dust grains blown out to larger radii.

  • 144.
    Asensio-Torres, Ruben
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Janson, Markus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Tamura, Motohide
    Isochronal age-mass discrepancy of young stars: SCExAO/CHARIS integral field spectroscopy of the HIP 79124 triple system2019Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 622, artikel-id A42Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present SCExAO/CHARIS 1.1--2.4 micron integral field direct spectroscopy of the young HIP 79124 triple system. HIP 79124 is a member of the Scorpius-Centaurus association, consisting of an A0V primary with two low-mass companions at a projected separation of <1 arcsecond. Thanks to the high quality wavefront corrections provided by SCExAO, both companions are decisively detected without the employment of any PSF-subtraction algorithm to eliminate quasi-static noise. The spectrum of the outer C object is very well matched by Upper Scorpius M4 pm 0.5 standard spectra, with a Teff = 2945 pm 100 and a mass of 350 MJup. HIP 79124 B is detected at a separation of only 180 mas in a highly-correlated noise regime, and it falls in the spectral range M6 pm 0.5 with Teff = 2840 pm 190 and 100 MJup. Previous studies of stellar populations in Sco-Cen have highlighted a discrepancy in isochronal ages between the lower-mass and higher-mass populations. This could be explained either by an age spread in the region, or by conventional isochronal models failing to reproduce the evolution of low-mass stars. The HIP 79124 system should be coeval, and therefore it provides an ideal laboratory to test these scenarios. We place the three components in a color-magnitude diagram and find that the models predict a younger age for the two low-mass companions (3 Myr) than for the primary star (6 Myr). These results imply that the omission of magnetic effects in conventional isochronal models inhibit them from reproducing early low-mass stellar evolution, which is further supported by the fact that new models that include such effects provide more consistent ages in the HIP 79124 system.

  • 145. 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
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC). Aarhus University, Denmark.
    Carnegie Supernova Project-II: Using Near-infrared Spectroscopy to Determine the Location of the Outer Ni-56 in Type Ia Supernovae2019Ingår i: Astrophysical Journal Letters, ISSN 2041-8205, E-ISSN 2041-8213, Vol. 875, nr 2, artikel-id L14Artikel i tidskrift (Refereegranskat)
    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.

  • 146. Ashcraft, Teresa A.
    et al.
    Windhorst, Rogier A.
    Jansen, Rolf A.
    Cohen, Seth H.
    Grazian, Andrea
    Paris, Diego
    Fontana, Adriano
    Giallongo, Emanuele
    Speziali, Roberto
    Testa, Vincenzo
    Boutsia, Konstantina
    O'Connell, Robert W.
    Rutkowski, Michael J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Ryan, Russell E.
    Scarlata, Claudia
    Weiner, Benjamin
    Ultra-deep Large Binocular Camera U-band Imaging of the GOODS-North Field: Depth Versus Resolution2018Ingår i: Publications of the Astronomical Society of the Pacific, ISSN 0004-6280, E-ISSN 1538-3873, Vol. 130, nr 988, artikel-id 064102Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a study of the trade-off between depth and resolution using a large number of U-band imaging observations in the GOODS-North field from the Large Binocular Camera (LBC) on the Large Binocular Telescope (LBT). Having acquired over 30 hr of data (315 images with 5-6 minutes exposures), we generated multiple image mosaics, starting with the best atmospheric seeing images (FWHM less than or similar to 0 ''.8), which constitute similar to 10% of the total data set. For subsequent mosaics, we added in data with larger seeing values until the final, deepest mosaic included all images with FWHM less than or similar to 1 ''.8 (similar to 94% of the total data set). From the mosaics, we made object catalogs to compare the optimal-resolution, yet shallower image to the lower-resolution but deeper image. We show that the number counts for both images are similar to 90% complete to U-AB less than or similar to 26 mag. Fainter than U-AB similar to 27 mag, the object counts from the optimal-resolution image start to drop-off dramatically (90% between U-AB = 27 and 28 mag), while the deepest image with better surface-brightness sensitivity (mu(AB)(U) less than or similar to 32 mag arcsec(-2)) show a more gradual drop (10% between U-AB similar or equal to 27 and 28 mag). For the brightest galaxies within the GOODS-N field, structure and clumpy features within the galaxies are more prominent in the optimal-resolution image compared to the deeper mosaics. We conclude that for studies of brighter galaxies and features within them, the optimal-resolution image should be used. However, to fully explore and understand the faintest objects, the deeper imaging with lower resolution are also required. Finally, we find-for 220 brighter galaxies with U-AB less than or similar to 23 mag-only marginal differences in total flux between the optimal-resolution and lower-resolution light-profiles to mu(AB)(U) less than or similar to 32 mag arcsec(-2). In only 10% of the cases are the total-flux differences larger than 0.5 mag. This helps constrain how much flux can be missed from galaxy outskirts, which is important for studies of the Extragalactic Background Light.

  • 147. Ashworth, G.
    et al.
    Fumagalli, M.
    Krumholz, M. R.
    Adamo, Angela
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Calzetti, D.
    Chandar, R.
    Cignoni, M.
    Dale, D.
    Elmegreen, B. G.
    Gallagher, J. S.
    Gouliermis, D. A.
    Grasha, K.
    Grebel, E. K.
    Johnson, K. E.
    Lee, J.
    Tosi, M.
    Wofford, A.
    Exploring the IMF of star clusters: a joint SLUG and LEGUS effort2017Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 469, nr 2, s. 2464-2480Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the implementation of a Bayesian formalism within the Stochastically Lighting Up Galaxies (SLUG) stellar population synthesis code, which is designed to investigate variations in the initial mass function (IMF) of star clusters. By comparing observed cluster photometry to large libraries of clusters simulated with a continuously varying IMF, our formalism yields the posterior probability distribution function (PDF) of the cluster mass, age and extinction, jointly with the parameters describing the IMF. We apply this formalism to a sample of star clusters from the nearby galaxy NGC 628, for which broad-band photometry in five filters is available as part of the Legacy ExtraGalactic UV Survey (LEGUS). After allowing the upper-end slope of the IMF (a3) to vary, we recover PDFs for the mass, age and extinction that are broadly consistent with what is found when assuming an invariant Kroupa IMF. However, the posterior PDF for a3 is very broad due to a strong degeneracy with the cluster mass, and it is found to be sensitive to the choice of priors, particularly on the cluster mass. We find only a modest improvement in the constraining power of a3 when adding Ha photometry from the companion Ha-LEGUS survey. Conversely, Ha photometry significantly improves the age determination, reducing the frequency of multi-modal PDFs. With the aid of mock clusters, we quantify the degeneracy between physical parameters, showing how constraints on the cluster mass that are independent of photometry can be used to pin down the IMF properties of star clusters.

  • 148. Ashworth, G.
    et al.
    Fumagalli, Michele
    Adamo, Angela
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Krumholz, Mark R.
    Theoretical predictions for IMF diagnostics in UV spectroscopy of star clusters2018Ingår i: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 480, nr 3, s. 3091-3104Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We explore the possibility of using UV spectroscopy in combination with broad-band photometry as diagnostic tools for understanding the shape of the initial mass function (IMF) in unresolved stellar populations. Building on our previous work, we extend the Stochastically Lighting Up Galaxies (SLUG) code to include a high-resolution UV spectral synthesizer and equivalent width calculation capabilities. We first gain a qualitative understanding of how UV spectral features behave as the parameters that define a star cluster in SLUG (mass, age, extinction, and IMF slope alpha(3)) are changed. We then exploit Bayesian inference techniques to recover the alpha(3) values for clusters simulated with SLUG, using mock observations of these clusters comprised of broad-band photometry and equivalent width measurements of a selection of UV spectral features. We find some improvement when compared to attempts using broad-band photometry alone (with the interquartile range of the alpha(3) posterior PDF shrinking by similar or equal to 32%), although we still do not yet fully break the known degeneracy between the cluster mass and alpha(3). Finally, we make predictions about how effective real observations will be by quantifying our ability to constrain alpha(3) as a function of limiting equivalent width. We find that observations sensitive to a modest equivalent width of similar or equal to 9 angstrom are sufficient to improve the recovery of the IMF slope parameter by similar or equal to 32% (interquartile range of posterior PDF median residuals), moving to similar or equal to 39% when we include all the significant spectral features in the wavelength range 900 - 3000 angstrom.

  • 149.
    Asplund, Julia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Nordita.
    No sign of a left-handedness in GeV photon arrival directions2019Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    A non-zero helicity of cosmological magnetic fields could, if detected, have important implications for models of the electroweak phase transition in the early Universe. It has been suggested that the helicity of such a field could be related to the handedness of photon arrival directions in the diffuse gamma-ray sky observed by the \emph{Fermi} Large Area Telescope (LAT). \cite{tashiro_search_2014} found a left-handedness when applying this method, implying the existence of an extragalactic magnetic field with negative helicity. In this work the same method is applied, using twice as much data from the LAT due to the longer exposure time, providing higher statistical certainty. Additionally, the potential effects of the non-uniform LAT exposure and contamination of galactic emission are studied using simulated data sets. The results obtained indicate no significant signal, as the simulations suggest that the uncertainty was highly underestimated in \cite{tashiro_search_2014}, and any observed handedness using the updated LAT data is found to be compatible with zero within this new error estimate.

  • 150. Atek, H.
    et al.
    Kunth, D.
    Schaerer, D.
    Hayes, M.
    Deharveng, J. M.
    Östlin, G.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Mas-Hesse, J. M.
    Empirical estimate of Lyα escape fraction in a statistical sample of Lyα emitters2009Ingår i: Astronomy and Astrophysics, ISSN 0004-6361, E-ISSN 1432-0746, Vol. 506, nr 2, s. L1-L4Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Context: The Lyman-alpha (Lyα) recombination line is a fundamental tool for galaxy evolution studies and modern observational cosmology. However, subsequent interpretations are still prone to a number of uncertainties. Besides numerical efforts, empirical data are urgently needed for a better understanding of the Lyα escape process. Aims: We empirically estimate the Lyα escape fraction in a statistically significant sample of galaxies in a redshift range z ~ 0 - 0.3. This estimate will constrain interpretations of current high-redshift Lyα observations. Methods: An optical spectroscopic follow-up of a sub-sample of 24 Lyα emitters detected by GALEX at z ~ 0.2 - 0.3, combined with a UV-optical sample of local starbursts, both with matched apertures, allow us to quantify the dust extinction through Balmer lines, and to estimate the Lyα escape fraction from the Hα flux corrected for extinction in the framework of the recombination theory. Results: The global escape fraction of Lyα radiation spans a wide range of values and fesc(Lyα) clearly decreases with increasing nebular dust extinction E(B-V). Several objects show fesc(Lyα) greater than fesc(continuum), which may be taken as observational evidence for a clumpy ISM geometry or for an aspherical ISM. Selection biases and aperture size effects may still prevail between z ~ 0.2 - 0.3 Lyman-alpha emitters (LAEs) and local starbursts and may explain the difference observed for fesc(Lyα).

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