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  • 201. Chomiuk, Laura
    et al.
    Soderberg, Alicia M.
    Chevalier, Roger A.
    Bruzewski, Seth
    Foley, Ryan J.
    Parrent, Jerod
    Strader, Jay
    Badenes, Carles
    Fransson, Claes
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Kamble, Atish
    Margutti, Raffaella
    Rupen, Michael P.
    Simon, Joshua D.
    A DEEP SEARCH FOR PROMPT RADIO EMISSION FROM THERMONUCLEAR SUPERNOVAE WITH THE VERY LARGE ARRAY2016Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 821, nr 2, artikel-id 119Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Searches for circumstellar material around Type Ia supernovae (SNe Ia) are some of the most powerful tests of the nature of SN Ia progenitors, and radio observations provide a particularly sensitive probe of this material. Here, we report radio observations for SNe. Ia and their lower-luminosity thermonuclear cousins. We present the largest, most sensitive, and spectroscopically diverse study of prompt (Delta t less than or similar to 1 years) radio observations of 85 thermonuclear SNe, including 25 obtained by our team with the unprecedented depth of the Karl G. Jansky Very Large Array. With these observations, SN 2012cg joins SN 2011fe and SN 2014J as an SN. Ia with remarkably deep radio limits and excellent temporal coverage (six epochs, spanning 5-216 days after explosion, implying <(M)over dot>/v(w) less than or similar to 5 x 10(-9) M-circle dot yr(-1)/100 km s(-1), assuming epsilon(B) = 0.1 and epsilon(e) = 0.1). All observations yield non-detections, placing strong constraints on the presence of circumstellar material. We present analytical models for the temporal and spectral evolution of prompt radio emission from thermonuclear SNe as expected from interaction with either wind-stratified or uniform density media. These models allow us to constrain the progenitor mass loss rates, with limits in the range of <(M)over dot> less than or similar to 10(-9) - 10(-4) M-circle dot yr(-1), assuming a wind velocity of v(w) = 100 km s(-1). We compare our radio constraints with measurements of Galactic symbiotic binaries to conclude that less than or similar to 10% of thermonuclear SNe have red giant companions.

  • 202. Chomiuk, Laura
    et al.
    Söderberg, Alicia M.
    Moe, Maxwell
    Chevalier, Roger A.
    Rupen, Michael P.
    Badenes, Carles
    Margutti, Raffaella
    Fransson, Claes
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Fong, Wen-fai
    Dittmann, Jason A.
    EVLA OBSERVATIONS CONSTRAIN THE ENVIRONMENT AND PROGENITOR SYSTEM OF Type Ia SUPERNOVA 2011fe2012Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 750, nr 2, s. 164-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report unique Expanded Very Large Array observations of SN 2011fe representing the most sensitive radio study of a Type Ia supernova to date. Our data place direct constraints on the density of the surrounding medium at radii similar to 10(15)-10(16) cm, implying an upper limit on the mass loss rate from the progenitor system of (M) over dot less than or similar to 6x10(-10) M-circle dot yr(-1) (assuming a wind speed of 100 km s(-1)) or expansion into a uniform medium with density n(CSM) less than or similar to 6 cm(-3). Drawing from the observed properties of non-conservative mass transfer among accreting white dwarfs, we use these limits on the density of the immediate environs to exclude a phase space of possible progenitor systems for SN 2011fe. We rule out a symbiotic progenitor system and also a system characterized by high accretion rate onto the white dwarf that is expected to give rise to optically thick accretion winds. Assuming that a small fraction, 1%, of the mass accreted is lost from the progenitor system, we also eliminate much of the potential progenitor parameter space for white dwarfs hosting recurrent novae or undergoing stable nuclear burning. Therefore, we rule out much of the parameter space associated with popular single degenerate progenitor models for SN 2011fe, leaving a limited phase space largely inhabited by some double degenerate systems, as well as exotic single degenerates with a sufficient time delay between mass accretion and SN explosion.

  • 203. Cigan, Phil
    et al.
    Matsuura, Mikako
    Gomez, Haley L.
    Indebetouw, Remy
    Abellán, Fran
    Gabler, Michael
    Richards, Anita
    Alp, Dennis
    Davis, Timothy A.
    Janka, Hans-Thomas
    Spyromilio, Jason
    Barlow, M. J.
    Burrows, David
    Dwek, Eli
    Fransson, Claes
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Gaensler, Bryan
    Larsson, Josefin
    Bouchet, P.
    Lundqvist, Peter
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Marcaide, J. M.
    Ng, C. -Y.
    Park, Sangwook
    Roche, Pat
    van Loon, Jacco Th.
    Wheeler, J. C.
    Zanardo, Giovanna
    High Angular Resolution ALMA Images of Dust and Molecules in the SN 1987A Ejecta2019Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 886, nr 1, artikel-id 51Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present high angular resolution (similar to 80 mas) ALMA continuum images of the SN.1987A system, together with CO J = 2 -> 1, J = 6 -> 5, and SiO J = 5 -> 4 to J = 7 -> 6 images, which clearly resolve the ejecta (dust continuum and molecules) and ring (synchrotron continuum) components. Dust in the ejecta is asymmetric and clumpy, and overall the dust fills the spatial void seen in H alpha images, filling that region with material from heavier elements. The dust clumps generally fill the space where CO J = 6 -> 5 is fainter, tentatively indicating that these dust clumps and CO are locationally and chemically linked. In these regions, carbonaceous dust grains might have formed after dissociation of CO. The dust grains would have cooled by radiation, and subsequent collisions of grains with gas would also cool the gas, suppressing the CO J = 6 -> 5 intensity. The data show a dust peak spatially coincident with the molecular hole seen in previous ALMA CO J = 2 -> 1 and SiO J = 5 -> 4 images. That dust peak, combined with CO and SiO line spectra, suggests that the dust and gas could be at higher temperatures than the surrounding material, though higher density cannot be totally excluded. One of the possibilities is that a compact source provides additional heat at that location. Fits to the far-infrared-millimeter spectral energy distribution give ejecta dust temperatures of 18-23 K. We revise the ejecta dust mass to M-dust = 0.2-0.4 M-circle dot for carbon or silicate grains, or a maximum of <0.7 M-circle dot for a mixture of grain species, using the predicted nucleosynthesis yields as an upper limit.

  • 204. Cignoni, M.
    et al.
    Sacchi, E.
    Aloisi, A.
    Tosi, M.
    Calzetti, D.
    Lee, J. C.
    Sabbi, E.
    Adamo, Angela
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Cook, D. O.
    Dale, D. A.
    Elmegreen, B. G.
    Gallagher, J. S.
    Gouliermis, D. A.
    Grasha, K.
    Grebel, E. K.
    Hunter, D. A.
    Johnson, K. E.
    Messa, Matteo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Smith, L. J.
    Thilker, D. A.
    Ubeda, L.
    Whitmore, B. C.
    Star Formation Histories of the LEGUS Dwarf Galaxies. I. Recent History of NGC 1705, NGC 4449, and Holmberg II2018Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 856, nr 1, artikel-id 62Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We use Hubble Space Telescope observations from the Legacy Extragalactic UV Survey to reconstruct the recent star formation histories (SFHs) of three actively star-forming dwarf galaxies, NGC 4449, Holmberg II, and NGC 1705, from their UV color-magnitude diagrams (CMDs). We apply a CMD fitting technique using two independent sets of stellar isochrones, PARSEC-COLIBRI and MIST, to assess the uncertainties related to stellar evolution modeling. Irrespective of the adopted stellar models, all three dwarfs are found to have had almost constant star formation rates (SFRs) in the last 100-200 Myr, with modest enhancements (a factor of similar to 2) above the 100 Myr averaged SFR. Significant differences among the three dwarfs are found in terms of the overall SFR, the timing of the most recent peak, and the SFR/area. The initial mass function of NGC. 1705 and Holmberg II is consistent with a Salpeter slope down to approximate to 5 M-circle dot, whereas it is slightly flatter, s = -2.0, in NGC 4449. The SFHs derived with the two different sets of stellar models are consistent with each other, except for some quantitative details, attributable to their input assumptions. They also share the drawback that all synthetic diagrams predict a clear separation in color between the upper main-sequence and helium-burning stars, which is not apparent in the data. Since neither differential reddening, which is significant in NGC 4449, nor unresolved binaries appear to be sufficient to fill the gap, we suggest this calls for a revision of both sets of stellar evolutionary tracks.

  • 205. Cignoni, M.
    et al.
    Sacchi, E.
    Tosi, M.
    Aloisi, A.
    Cook, D. O.
    Calzetti, D.
    Lee, J. C.
    Sabbi, E.
    Thilker, D. A.
    Adamo, Angela
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Dale, D. A.
    Elmegreen, B. G.
    Gallagher, J. S.
    Grebel, E. K.
    Johnson, K. E.
    Messa, Matteo
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Smith, L. J.
    Ubeda, L.
    Star Formation Histories of the LEGUS Dwarf Galaxies. III. The Nonbursty Nature of 23 Star-forming Dwarf Galaxies2019Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 887, nr 2, artikel-id 112Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We derive the recent star formation histories (SFHs) of 23 active dwarf galaxies using Hubble Space Telescope observations from the Legacy Extragalactic UV Survey. We apply a color-magnitude diagram (CMD) fitting technique using two independent sets of stellar models, PARSEC-COLIBRI and MIST. Despite the nonnegligible recent activity, none of the 23 star-forming dwarfs show enhancements in the last 100 Myr larger than three times the 100 Myr average. The unweighted mean of the individual SFHs in the last 100 Myr is also consistent with a rather constant activity, irrespective of the atomic gas fraction. We confirm previous results that for dwarf galaxies, the CMD-based average star formation rates (SFRs) are generally higher than the FUV-based SFRs. For half of the sample, the 60 Myr average CMD-based SFR is more than two times the FUV SFR. In contrast, we find remarkable agreement between the 10 Myr average CMD-based SFR and the H alpha-based SFR. Finally, using core helium-burning stars of intermediate mass, we study the pattern of star formation spatial progression over the past 60 Myr and speculate on the possible triggers and connections of the star formation activity with the environment in which these galaxies live. Approximately half of our galaxies show spatial progression of star formation in the last 60 Myr and/or very recent diffuse and off-center activity compared to RGB stars.

  • 206. Clayton, Geoffrey C.
    et al.
    Sugerman, Ben E. K.
    Stanford, S. Adam
    Whitney, B. A.
    Honor, J.
    Babler, B.
    Barlow, M. J.
    Gordon, K. D.
    Andrews, J. E.
    Geballe, T. R.
    Bond, Howard E.
    De Marco, O.
    Lawson, W. A.
    Sibthorpe, B.
    Olofsson, Göran
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Polehampton, E.
    Gomez, H. L.
    Matsuura, M.
    Hargrave, P. C.
    Ivison, R. J.
    Wesson, R.
    Leeks, S. J.
    Swinyard, B. M.
    Lim, T. L.
    THE CIRCUMSTELLAR ENVIRONMENT OF R CORONAE BOREALIS: WHITE DWARF MERGER OR FINAL-HELIUM-SHELL FLASH?2011Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 743, nr 1, s. 44-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In 2007, R Coronae Borealis (R CrB) went into a historically deep and long decline. In this state, the dust acts like a natural coronagraph at visible wavelengths, allowing faint nebulosity around the star to be seen. Imaging has been obtained from 0.5 to 500 mu m with Gemini/GMOS, Hubble Space Telescope/WFPC2, Spitzer/MIPS, and Herschel/SPIRE. Several of the structures around R CrB are cometary globules caused by wind from the star streaming past dense blobs. The estimated dust mass of the knots is consistent with their being responsible for the R CrB declines if they form along the line of sight to the star. In addition, there is a large diffuse shell extending up to 4 pc away from the star containing cool 25 K dust that is detected all the way out to 500 mu m. The spectral energy distribution of R CrB can be well fitted by a 150 AU disk surrounded by a very large diffuse envelope which corresponds to the size of the observed nebulosity. The total masses of the disk and envelope are 10(-4) and 2M(circle dot), respectively, assuming a gas-to-dust ratio of 100. The evidence pointing toward a white dwarf merger or a final-helium-shell flash origin for R CrB is contradictory. The shell and the cometary knots are consistent with a fossil planetary nebula. Along with the fact that R CrB shows significant lithium in its atmosphere, this supports the final-helium-shell flash. However, the relatively high inferred mass of R CrB and its high fluorine abundance support a white dwarf merger.

  • 207.
    Conrad, Jan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Dickinson, Hugh J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Farnier, Christian
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    LONG-TERM TeV AND X-RAY OBSERVATIONS OF THE GAMMA- RAY BINARY HESS J0632+0572014Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 780, nr 2, s. 168-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    HESS J0632+057 is the only gamma-ray binary known so far whose position in the sky allows observations with ground-based observatories in both the northern and southern hemispheres. Here we report on long-term observations of HESS J0632+057 conducted with the Very Energetic Radiation Imaging Telescope Array System and High Energy Stereoscopic System Cherenkov telescopes and the X-ray satellite Swift, spanning a time range from 2004 to 2012 and covering most of the system's orbit. The very-high-energy (VHE) emission is found to be variable and is correlated with that at X-ray energies. An orbital period of 315(-4)(+6) days is derived from the X-ray data set, which is compatible with previous results, P = (321 +/- 5) days. The VHE light curve shows a distinct maximum at orbital phases close to 0.3, or about 100 days after periastron passage, which coincides with the periodic enhancement of the X-ray emission. Furthermore, the analysis of the TeV data shows for the first time a statistically significant (> 6.5 sigma) detection at orbital phases 0.6-0.9. The obtained gamma-ray and X-ray light curves and the correlation of the source emission at these two energy bands are discussed in the context of the recent ephemeris obtained for the system. Our results are compared to those reported for other gamma-ray binaries.

  • 208.
    Conrad, Jan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Dickinson, Hugh J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Ripken, Joachim
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    THE 2010 VERY HIGH ENERGY gamma-RAY FLARE AND 10 YEARS OF MULTI-WAVELENGTH OBSERVATIONS OF M 872012Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 746, nr 2, s. 151-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The giant radio galaxy M 87 with its proximity (16 Mpc), famous jet, and very massive black hole ((3-6) x 10(9) M-circle dot) provides a unique opportunity to investigate the origin of very high energy (VHE; E > 100 GeV) gamma-ray emission generated in relativistic outflows and the surroundings of supermassive black holes. M 87 has been established as a VHE gamma-ray emitter since 2006. The VHE gamma-ray emission displays strong variability on timescales as short as a day. In this paper, results from a joint VHE monitoring campaign on M 87 by the MAGIC and VERITAS instruments in 2010 are reported. During the campaign, a flare at VHE was detected triggering further observations at VHE (H.E.S.S.), X-rays (Chandra), and radio (43 GHz Very Long Baseline Array, VLBA). The excellent sampling of the VHE gamma-ray light curve enables one to derive a precise temporal characterization of the flare: the single, isolated flare is well described by a two-sided exponential function with significantly different flux rise and decay times of tau(rise)(d) = (1.69 +/- 0.30) days and tau(decay)(d) = (0.611 +/- 0.080) days, respectively. While the overall variability pattern of the 2010 flare appears somewhat different from that of previous VHE flares in 2005 and 2008, they share very similar timescales (similar to day), peak fluxes (Phi(>0.35 TeV) similar or equal to (1-3) x 10(-11) photons cm(-2) s(-1)), and VHE spectra. VLBA radio observations of 43 GHz of the inner jet regions indicate no enhanced flux in 2010 in contrast to observations in 2008, where an increase of the radio flux of the innermost core regions coincided with a VHE flare. On the other hand, Chandra X-ray observations taken similar to 3 days after the peak of the VHE gamma-ray emission reveal an enhanced flux from the core (flux increased by factor similar to 2; variability timescale <2 days). The long-term (2001-2010) multi-wavelength (MWL) light curve of M 87, spanning from radio to VHE and including data from Hubble Space Telescope, Liverpool Telescope, Very Large Array, and European VLBI Network, is used to further investigate the origin of the VHE gamma-ray emission. No unique, common MWL signature of the three VHE flares has been identified. In the outer kiloparsec jet region, in particular in HST-1, no enhanced MWL activity was detected in 2008 and 2010, disfavoring it as the origin of the VHE flares during these years. Shortly after two of the three flares (2008 and 2010), the X-ray core was observed to be at a higher flux level than its characteristic range (determined from more than 60 monitoring observations: 2002-2009). In 2005, the strong flux dominance of HST-1 could have suppressed the detection of such a feature. Published models for VHE gamma-ray emission from M 87 are reviewed in the light of the new data.

  • 209.
    Conrad, Jan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Ripken, Joachim
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Yang, Zhaoyu
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    INSIGHTS INTO THE HIGH-ENERGY gamma-RAY EMISSION OF MARKARIAN 501 FROM EXTENSIVE MULTIFREQUENCY OBSERVATIONS IN THE FERMI ERA2011Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 727, nr 2, s. 129-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on the gamma-ray activity of the blazar Mrk 501 during the first 480 days of Fermi operation. We find that the average Large Area Telescope (LAT) gamma-ray spectrum of Mrk 501 can be well described by a single power-law function with a photon index of 1.78 +/- 0.03. While we observe relatively mild flux variations with the Fermi-LAT (within less than a factor of two), we detect remarkable spectral variability where the hardest observed spectral index within the LAT energy range is 1.52 +/- 0.14, and the softest one is 2.51 +/- 0.20. These unexpected spectral changes do not correlate with the measured flux variations above 0.3 GeV. In this paper, we also present the first results from the 4.5 month long multifrequency campaign (2009 March 15-August 1) on Mrk 501, which included the Very Long Baseline Array (VLBA), Swift, RXTE, MAGIC, and VERITAS, the F-GAMMA, GASP-WEBT, and other collaborations and instruments which provided excellent temporal and energy coverage of the source throughout the entire campaign. The extensive radio to TeV data set from this campaign provides us with the most detailed spectral energy distribution yet collected for this source during its relatively low activity. The average spectral energy distribution of Mrk 501 is well described by the standard one-zone synchrotron self-Compton (SSC) model. In the framework of this model, we find that the dominant emission region is characterized by a size less than or similar to 0.1 pc (comparable within a factor of few to the size of the partially resolved VLBA core at 15-43 GHz), and that the total jet power (similar or equal to 10(44) erg s(-1)) constitutes only a small fraction (similar to 10(-3)) of the Eddington luminosity. The energy distribution of the freshly accelerated radiating electrons required to fit the time-averaged data has a broken power-law form in the energy range 0.3 GeV-10 TeV, with spectral indices 2.2 and 2.7 below and above the break energy of 20 GeV. We argue that such a form is consistent with a scenario in which the bulk of the energy dissipation within the dominant emission zone of Mrk 501 is due to relativistic, proton-mediated shocks. We find that the ultrarelativistic electrons and mildly relativistic protons within the blazar zone, if comparable in number, are in approximate energy equipartition, with their energy dominating the jet magnetic field energy by about two orders of magnitude.

  • 210.
    Conrad, Jan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Ripken, Joachim
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Yang, Zhaoyu
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    MULTI-WAVELENGTH OBSERVATIONS OF THE FLARING GAMMA-RAY BLAZAR 3C 66A IN 2008 OCTOBER2011Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 726, nr 1, artikel-id 43Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The BL Lacertae object 3C 66A was detected in a flaring state by the Fermi Large Area Telescope (LAT) and VERITAS in 2008 October. In addition to these gamma-ray observations, F-GAMMA, GASP-WEBT, PAIRITEL, MDM, ATOM, Swift, and Chandra provided radio to X-ray coverage. The available light curves show variability and, in particular, correlated flares are observed in the optical and Fermi-LAT gamma-ray band. The resulting spectral energy distribution can be well fitted using standard leptonic models with and without an external radiation field for inverse Compton scattering. It is found, however, that only the model with an external radiation field can accommodate the intra-night variability observed at optical wavelengths.

  • 211.
    Conrad, Jan
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Yang, Zhaoyu
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    FERMI LARGE AREA TELESCOPE OBSERVATIONS OF MARKARIAN 421: THE MISSING PIECE OF ITS SPECTRAL ENERGY DISTRIBUTION2011Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 736, nr 2, s. 131-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report on the gamma-ray activity of the high-synchrotron-peaked BL Lacertae object Markarian 421 (Mrk 421) during the first 1.5 years of Fermi operation, from 2008 August 5 to 2010 March 12. We find that the Large Area Telescope (LAT) gamma-ray spectrum above 0.3 GeV can be well described by a power-law function with photon index Gamma = 1.78 +/- 0.02 and average photon flux F(>0.3 GeV) = (7.23 +/- 0.16) x 10(-8) ph cm(-2) s(-1). Over this time period, the Fermi-LAT spectrum above 0.3 GeV was evaluated on seven-day-long time intervals, showing significant variations in the photon flux (up to a factor similar to 3 from the minimum to the maximum flux) but mild spectral variations. The variability amplitude at X-ray frequencies measured by RXTE/ASM and Swift/BAT is substantially larger than that in gamma-rays measured by Fermi-LAT, and these two energy ranges are not significantly correlated. We also present the first results from the 4.5 month long multifrequency campaign on Mrk 421, which included the VLBA, Swift, RXTE, MAGIC, the F-GAMMA, GASP-WEBT, and other collaborations and instruments that provided excellent temporal and energy coverage of the source throughout the entire campaign (2009 January 19 to 2009 June 1). During this campaign, Mrk 421 showed a low activity at all wavebands. The extensive multi-instrument (radio to TeV) data set provides an unprecedented, complete look at the quiescent spectral energy distribution (SED) for this source. The broadband SED was reproduced with a leptonic (one-zone synchrotron self-Compton) and a hadronic model (synchrotron proton blazar). Both frameworks are able to describe the average SED reasonably well, implying comparable jet powers but very different characteristics for the blazar emission site.

  • 212. Corsi, A.
    et al.
    Gal-Yam, A.
    Kulkarni, S. R.
    Frail, D. A.
    Mazzali, P. A.
    Cenko, S. B.
    Kasliwal, M. M.
    Cao, Y.
    Horesh, A.
    Palliyaguru, N.
    Perley, D. A.
    Laher, R. R.
    Taddia, Francesco
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Leloudas, G.
    Maguire, K.
    Nugent, P. E.
    Sollerman, J.
    Sullivan, M.
    RADIO OBSERVATIONS OF A SAMPLE OF BROAD-LINE TYPE IC SUPERNOVAE DISCOVERED BY PTF/IPTF: A SEARCH FOR RELATIVISTIC EXPLOSIONS2016Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 830, nr 1, artikel-id 42Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Long duration gamma-ray bursts are a rare subclass of stripped-envelope core-collapse supernovae (SNe) that launch collimated relativistic outflows (jets). All gamma-ray-burst-associated SNe are spectroscopically Type Ic, with broadlines, but the fraction of broad-lined SNe Ic harboring low-luminosity gamma-ray bursts remains largely unconstrained. Some SNe should be accompanied by off-axis gamma-ray burst jets that initially remain invisible, but then emerge as strong radio sources (as the jets decelerate). However, this critical prediction of the jet model for gamma-ray bursts has yet to be verified observationally. Here, we present K. G. Jansky Very Large Array observations of 15 broad-lined SNe of Type Ic discovered by the Palomar Transient Factory in an untargeted manner. Most of the SNe in our sample exclude radio emission observationally similar to that of the radio-loud, relativistic SN 1998bw. We constrain the fraction of 1998bw-like broad-lined SNe Ic to be less than or similar to 41% (99.865% confidence). Most of the events in our sample also exclude off-axis jets similar to GRB 031203 and GRB 030329, but we cannot rule out off-axis gamma-ray bursts expanding in a low-density wind environment. Three SNe in our sample are detected in the radio. PTF11qcj and PTF14dby show late-time radio emission with average ejecta speeds of approximate to 0.3-0.4 c, on the dividing line between relativistic and ordinary SNe. The speed of PTF11cmh radio ejecta is poorly constrained. We estimate that less than or similar to 85% (99.865% confidence) of the broad-lined SNe Ic in our sample may harbor off-axis gamma-ray bursts expanding in media with densities in the range probed by this study.

  • 213. Corsi, Alessandra
    et al.
    Cenko, S. B.
    Kasliwal, M. M.
    Quimby, Robert
    Kulkarni, S. R.
    Frail, D. A.
    Goldstein, A. M.
    Blagorodnova, N.
    Connaughton, V.
    Perley, D. A.
    Singer, L. P.
    Copperwheat, C. M.
    Fremling, Christoffer
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Kupfer, T.
    Piascik, A. S.
    Steele, I. A.
    Taddia, Francesco
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Vedantham, H.
    Kutyrev, A.
    Palliyaguru, N. T.
    Roberts, O.
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Troja, E.
    Veilleux, S.
    iPTF17cw: An Engine-driven Supernova Candidate Discovered Independent of a Gamma-Ray Trigger2017Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 847, nr 1, artikel-id 54Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the discovery, classification, and radio-to-X-ray follow-up observations of iPTF17cw, a broad-lined (BL) type Ic supernova (SN) discovered by the intermediate Palomar Transient Factory (iPTF). Although it is unrelated to the gravitational wave trigger, this SN was discovered as a happy by-product of the extensive observational campaign dedicated to the follow-up of Advanced LIGO event GW 170104. The spectroscopic properties and inferred peak bolometric luminosity of iPTF17cw are most similar to the gamma-ray-burst (GRB)associated SN, SN 1998bw, while the shape of the r-band light curve is most similar to that of the relativistic SN, SN 2009bb. Karl G. Jansky Very Large Array (VLA) observations of the iPTF17cw field reveal a radio counterpart approximate to 10 times less luminous than SN 1998bw, and with a peak radio luminosity comparable to that of SN 2006aj/GRB 060218 and SN 2010bh/GRB 100316D. Our radio observations of iPTF17cw imply a relativistically expanding outflow. However, further late-time observations with the VLA in its most extended configuration are needed to confirm fading of the iPTF17cw radio counterpart at all frequencies. X-ray observations carried out with Chandra reveal the presence of an X-ray counterpart with a luminosity similar to that of SN 2010bh/GRB 100316D. Searching the Fermi catalog for possible gamma-rays reveals that GRB 161228B is spatially and temporally compatible with iPTF17cw. The similarity to SN 1998bw and SN 2009bb, the radio and X-ray detections, and the potential association with GRB 161228B all point to iPTF17cw being a new candidate member of the rare sample of optically discovered engine-driven BL-Ic SNe associated with relativistic ejecta.

  • 214. Cowperthwaite, P. S.
    et al.
    Berger, E.
    Rest, A.
    Chornock, R.
    Scolnic, D. M.
    Williams, P. K. G.
    Fong, W.
    Drout, M. R.
    Foley, R. J.
    Margutti, R.
    Lunnan, Ragnhild
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Metzger, B. D.
    Quataert, E.
    An Empirical Study of Contamination in Deep, Rapid, and Wide-field Optical Follow-up of Gravitational Wave Events2018Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 858, nr 1, artikel-id 18Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present an empirical study of contamination in wide-field optical follow-up searches of gravitational wave sources from Advanced LIGO/Virgo using dedicated observations with the Dark Energy Camera. Our search covered similar to 56 deg(2), with two visits per night, in the i and z bands, followed by an additional set of griz images three weeks later to serve as reference images for subtraction. We achieve 5 sigma point-source limiting magnitudes of i approximate to 23.5 and z approximate to 22.4 mag in the coadded single-epoch images. We conduct a search for transient objects that mimic the i - z color behavior of both red (i-z > 0.5 mag) and blue (i-z < 0 mag) kilonova emission, finding 11 and 10 contaminants, respectively. Independent of color, we identify 48 transients of interest. Additionally, we leverage the rapid cadence of our observations to search for sources with characteristic timescales of approximate to 1 day and approximate to 3 hr, finding no potential contaminants. We assess the efficiency of our search with injected point sources, finding that we are 90% (60%) efficient when searching for red (blue) kilonova-like sources to a limiting magnitude of i less than or similar to 22.5 mag. Using our efficiencies, we derive sky rates for kilonova contaminants of R-red approximate to 0.16 deg(-2) and R-blue approximate to 0.80 deg(-2). The total contamination rate is R-all approximate to 1.79 deg(-2). We compare our results to previous optical follow-up efforts and comment on the outlook for gravitational wave follow-up searches as additional detectors (e.g., KAGRA, LIGO India) come online in the next decade.

  • 215. Cristaldi, A.
    et al.
    Guglielmino, S. L.
    Zuccarello, F.
    Romano, P.
    Falco, M.
    van der Voort, L. Rouppe
    Rodriguez, Jaime de la Cruz
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Ermolli, I.
    Criscuoli, S.
    DYNAMIC PROPERTIES ALONG THE NEUTRAL LINE OF A DELTA SPOT INFERRED FROM HIGH-RESOLUTION OBSERVATIONS2014Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 789, nr 2, s. 162-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Delta (delta) spots are complex magnetic configurations of sunspots characterized by umbrae of opposite polarity sharing a common penumbra. In order to investigate the fine structure of the region separating the two magnetic polarities of a delta spot, we studied the morphology, the magnetic configuration, and the velocity field in such a region using observations of active region (AR) NOAA 11267 obtained with the CRisp Imaging SpectroPolarimeter (CRISP) at the Swedish Solar Telescope on 2011 August 6. The analysis of CRISP data shows upflows and downflows of similar to +/- 3 km s(-1) in proximity of the delta spot polarity inversion line (PIL), and horizontal motions along the PIL of the order of similar to 1 km s(-1). The results obtained from the SIR inversion of CRISP data also indicate that the transverse magnetic field in the brighter region separating the two opposite magnetic polarities of the delta spot is tilted about similar to 45 degrees with respect to the PIL. Solar Dynamics Observatory/Helioseismic and Magnetic Imager observations confirm the presence of motions of similar to +/- 3 km s(-1) in proximity of the PIL, which were observed to last 15 hr. From the data analyzed, we conclude that the steady, persistent, and subsonic motions observed along the delta spot PIL can be interpreted as being due to Evershed flows occurring in the penumbral filaments that show a curved, wrapped configuration. The fluting of the penumbral filaments and their bending, continuously increased by the approaching motion of the negative umbra toward the positive one, give rise to the complex line-of-sight velocity maps that we observed.

  • 216. Czekala, Ian
    et al.
    Berger, E.
    Chornock, R.
    Pastorello, A.
    Marion, G. H.
    Margutti, R.
    Botticella, M. T.
    Challis, P.
    Ergon, Mattias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Smartt, S.
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Vinko, J.
    Wheeler, J. C.
    THE UNUSUALLY LUMINOUS EXTRAGALACTIC NOVA SN 2010U2013Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 765, nr 1, s. 57-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present observations of the unusual optical transient SN 2010U, including spectra taken 1.03 days to 15.3 days after maximum light that identify it as a fast and luminous Fe II type nova. Our multi-band light curve traces the fast decline (t(2) = 3.5 +/- 0.3 days) from maximum light (M-V = -10.2 +/- 0.1 mag), placing SN 2010U in the top 0.5% of the most luminous novae ever observed. We find typical ejecta velocities of approximate to 1100 km s(-1) and that SN 2010U shares many spectral and photometric characteristics with two other fast and luminous Fe II type novae, including Nova LMC 1991 and M31N-2007-11d. For the extreme luminosity of this nova, the maximum magnitude versus rate of decline relationship indicates a massive white dwarf (WD) progenitor with a low pre-outburst accretion rate. However, this prediction is in conflict with emerging theories of nova populations, which predict that luminous novae from massive WDs should preferentially exhibit an alternate spectral type (He/N) near maximum light.

  • 217. Daemgen, Sebastian
    et al.
    Bonavita, Mariangela
    Jayawardhana, Ray
    Lafreniere, David
    Janson, Markus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    SUB-STELLAR COMPANIONS AND STELLAR MULTIPLICITY IN THE TAURUS STAR-FORMING REGION2015Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 799, nr 2, artikel-id 155Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present results from a large, high- spatial- resolution near- infrared imaging search for stellar and sub- stellar companions in the Taurus- Auriga star- forming region. The sample covers 64 stars with masses between those of the most massive Taurus members at 3 M-circle dot and low-mass stars at 0.2 M-circle dot. We detected 74 companion candidates, 34 of these reported for the first time. Twenty- five companions are likely physically bound, partly confirmed by follow- up observations. Four candidate companions are likely unrelated field stars. Assuming physical association with their host star, estimated companion masses are as low as 2M(Jup.) The inferred multiplicity frequency within our sensitivity limits between 10-1500 AU is 26.3(-4.9)(+ 6.6)% - 4.9%. Applying a completeness correction, 62% 14% of all Taurus stars between 0.7 and 1.4 M appear to be multiple. Higher order multiples were found in 1.8+ 4.2 - 1.5 % of the cases, in agreement with previous observations of the field. We estimate a sub- stellar companion frequency of 3.5%- 8.8% within our sensitivity limits from the discovery of two likely bound and three other tentative very low- mass companions. This frequency appears to be in agreement with what is expected from the tail of the stellar companion mass ratio distribution, suggesting that stellar and brown dwarf companions share the same dominant formation mechanism. Further, we find evidence for possible evolution of binary parameters between two identified sub- populations in Taurus with ages of 2 Myr and 20 Myr, respectively.

  • 218.
    Dahlen, Tomas
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Mobasher, Bahram
    Dickinson, Mark
    Ferguson, Henry C.
    Giavalisco, Mauro
    Kretchmer, Claudia
    Ravindranath, Swara
    Evolution of the luminosity function, star formation rate, morphology, and size of star-forming galaxies selected at rest-frame 1500 and 2800 angstrom2007Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 654, nr 1, s. 172-185Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Using the multiwavelength photometric and spectroscopic data covering the Chandra Deep Field South obtained within the Great Observatories Origins Deep Survey, we investigate the rest-frame UV properties of galaxies to z similar to 2.2, including the evolution of the luminosity function, the luminosity density, star formation rate (SFR), and galaxy morphology. We find a significant brightening (similar to 1 mag) in the rest-frame 2800 angstrom characteristic magnitude (M*) over the redshift range 0.3 less than or similar to z less than or similar to 1.7 and no evolution at higher redshifts. The rest-frame 2800 angstrom luminosity density shows an increase by a factor of similar to 4 over the redshift range investigated. We estimate the SFR density to z similar to 2.2 from the 1500 and 2800 angstrom luminosities. When no correction for extinction is made, we find that the SFR derived from the 2800 angstrom luminosity density is almost a factor of 2 higher than that derived from the 1500 8 luminosities. Attributing this difference to differential dust extinction, we find that E(B - V) = 0.20 results in the same extinction-corrected SFR from both 1500 and 2800 angstrom luminosities. The extinction-corrected SFR is a factor of similar to 6.5 (similar to 3.7) higher than the uncorrected SFR derived from 1500 8 ( 2800 8) luminosity. We investigate the morphological composition of our sample by fitting Sersic profiles to the HST ACS galaxy images at a fixed rest-frame wavelength of 2800 angstrom at 0.5 less than or similar to z less than or similar to 2.2. We find that the fraction of apparently bulge-dominated galaxies (Sersic index n > 2.5) increases from similar to 10% at z similar to 0.5 to similar to 30% at z similar to 2.2. At the same time, we note that galaxies get bluer at increasing redshift. This suggests a scenario where an increased fraction of the star formation takes place in bulge-dominated systems at high redshift. This could be evidence that the present-day elliptical galaxies are a result of assembly (i.e., mergers) of galaxies at z greater than or similar to 1. Finally, we find that galaxy size for a luminosity-selected sample evolves as r(h) proportional to (1+z)(-1.1) between redshifts z = 2.2 and 1.1. This is consistent with previous measurements and suggests a similar evolution over the redshift range 0 less than or similar to z less than or similar to 6.

  • 219. Dall'Ora, M.
    et al.
    Botticella, M. T.
    Pumo, M. L.
    Zampieri, L.
    Tomasella, L.
    Pignata, G.
    Bayless, A. J.
    Pritchard, T. A.
    Taubenberger, S.
    Kotak, R.
    Inserra, A.
    Della Valle, M.
    Cappellaro, E.
    Benetti, S.
    Benitez, S.
    Bufano, F.
    Elias-Rosa, N.
    Fraser, M.
    Haislip, J. B.
    Harutyunyan, A.
    Howell, D. A.
    Hsiao, E. Y.
    Iijima, T.
    Kankare, E.
    Kuin, P.
    Maund, J. R.
    Morales-Garoffolo, A.
    Morrell, N.
    Munari, U.
    Ochner, P.
    Pastorello, A.
    Patat, F.
    Phillips, M. M.
    Reichart, D.
    Roming, P. W. A.
    Siviero,
    Smartt, S. J.
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC). Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Taddia, Francesco
    Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC). Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Valenti, S.
    Wright, D.
    THE TYPE IIP SUPERNOVA 2012aw IN M95: HYDRODYNAMICAL MODELING OF THE PHOTOSPHERIC PHASE FROM ACCURATE SPECTROPHOTOMETRIC MONITORING2014Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 787, nr 2, s. 139-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present an extensive optical and near-infrared photometric and spectroscopic campaign of the Type IIP supernova SN 2012aw. The data set densely covers the evolution of SN 2012aw shortly after the explosion through the end of the photospheric phase, with two additional photometric observations collected during the nebular phase, to fit the radioactive tail and estimate the Ni-56 mass. Also included in our analysis is the previously published Swift UV data, therefore providing a complete view of the ultraviolet-optical-infrared evolution of the photospheric phase. On the basis of our data set, we estimate all the relevant physical parameters of SN 2012aw with our radiation-hydrodynamics code: envelope mass M-env similar to 20 M-circle dot, progenitor radius R similar to 3 x 10(13) cm (similar to 430 R-circle dot), explosion energy E similar to 1.5 foe, and initial Ni-56 mass similar to 0.06 M-circle dot. These mass and radius values are reasonably well supported by independent evolutionary models of the progenitor, and may suggest a progenitor mass higher than the observational limit of 16.5 +/- 1.5 M-circle dot of the Type IIP events.

  • 220. Damjanov, Ivana
    et al.
    Jayawardhana, Ray
    Scholz, Alexander
    Ahmic, Mirza
    Nguyen, Duy C.
    Brandeker, Alexis
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    van Kerkwijk, Marten H.
    A Comprehensive View of Circumstellar Disks in Chamaeleon I: Infrared Excess, Accretion Signatures, and Binarity2007Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 670, nr 2, s. 1337-1346Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a comprehensive study of disks around 81 young, low‐mass stars and brown dwarfs in the nearby 2 Myr old Chamaeleon I star‐forming region. We use mid‐infrared photometry from the Spitzer Space Telescope, supplemented by findings from ground‐based high‐resolution optical spectroscopy and adaptive optics imaging. We derive disk fractions of 52%±6% and 58-7+6% based on 8 and 24 μm color excesses, respectively, consistent with those reported for other clusters of similar age. Within the uncertainties, the disk frequency in our sample of K3–M8 objects in Cha I does not depend on stellar mass. Diskless and disk‐bearing objects have similar spatial distributions. There are no obvious transition disks in our sample, implying a rapid timescale for the inner disk clearing process; however, we find two objects with weak excess at 3–8 μm and substantial excess at 24 μm, which may indicate grain growth and dust settling in the inner disk. For a subsample of 35 objects with high‐resolution spectra, we investigate the connection between accretion signatures and dusty disks: in the vast majority of cases (29/35) the two are well correlated, suggesting that, on average, the timescale for gas dissipation is similar to that for clearing the inner dust disk. The exceptions are six objects for which dust disks appear to persist even though accretion has ceased or dropped below measurable levels. Adaptive optics images of 65 of our targets reveal that 17 have companions at (projected) separations of 10–80 AU. Of the five <20 AU binaries, four lack infrared excess, possibly indicating that a close companion leads to faster disk dispersal. The closest binary with excess is separated by ~20 AU, which sets an upper limit of ~8 AU for the outer disk radius. The overall disk frequency among stars with companions (35-13+15%) is lower than (but still statistically consistent with) the value for the total sample.

  • 221. D'Andrea, Chris B.
    et al.
    Sako, Masao
    Dilday, Benjamin
    Frieman, Joshua A.
    Holtzman, Jon
    Kessler, Richard
    Konishi, Kohki
    Schneider, D. P.
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Wheeler, J. Craig
    Yasuda, Naoki
    Cinabro, David
    Jha, Saurabh
    Nichol, Robert C.
    Lampeitl, Hubert
    Smith, Mathew
    Atlee, David W.
    Bassett, Bruce
    Castander, Francisco J.
    Goobar, Ariel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Miquel, Ramon
    Nordin, Jakob
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Östman, Linda
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Prieto, José L.
    Quimby, Robert
    Riess, Adam G.
    Stritzinger, Maximilian
    Type II-P Supernovae from the SDSS-II Supernova Survey and the Standardized Candle Method2010Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 708, nr 1, s. 661-674Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We apply the Standardized Candle Method (SCM) for Type II Plateau supernovae (SNe II-P), which relates the velocity of the ejecta of a SN to its luminosity during the plateau, to 15 SNe II-P discovered over the three season run of the Sloan Digital Sky Survey-II Supernova Survey. The redshifts of these SNe—0.027 < z < 0.144—cover a range hitherto sparsely sampled in the literature; in particular, our SNe II-P sample contains nearly as many SNe in the Hubble flow (z > 0.01) as all of the current literature on the SCM combined. We find that the SDSS SNe have a very small intrinsic I-band dispersion (0.22 mag), which can be attributed to selection effects. When the SCM is applied to the combined SDSS-plus-literature set of SNe II-P, the dispersion increases to 0.29 mag, larger than the scatter for either set of SNe separately. We show that the standardization cannot be further improved by eliminating SNe with positive plateau decline rates, as proposed in Poznanski et al. We thoroughly examine all potential systematic effects and conclude that for the SCM to be useful for cosmology, the methods currently used to determine the Fe II velocity at day 50 must be improved, and spectral templates able to encompass the intrinsic variations of Type II-P SNe will be needed. Based in part on data collected at Subaru Telescope, which is operated by the National Astronomical Observatory of Japan.

  • 222. Davis, Tamara M.
    et al.
    Hui, Lam
    Frieman, Joshua A.
    Haugbølle, Troels
    Kessler, Richard
    Sinclair, Benjamin
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Bassett, Bruce
    Marriner, John
    Mörtsell, Edvard
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Nichol, Robert C.
    Richmond, Michael W.
    Sako, Masao
    Schneider, Donald P.
    Smith, Mathew
    The Effect of Peculiar Velocities on Supernova Cosmology2011Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 741, s. 67-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We analyze the effect that peculiar velocities have on the cosmological inferences we make using luminosity distance indicators, such as Type Ia supernovae. In particular we study the corrections required to account for (1) our own motion, (2) correlations in galaxy motions, and (3) a possible local under- or overdensity. For all of these effects we present a case study showing the impact on the cosmology derived by the Sloan Digital Sky Survey-II Supernova Survey (SDSS-II SN Survey). Correcting supernova (SN) redshifts for the cosmic microwave background (CMB) dipole slightly overcorrects nearby SNe that share some of our local motion. We show that while neglecting the CMB dipole would cause a shift in the derived equation of state of Δw ~ 0.04 (at fixed Ω m ), the additional local-motion correction is currently negligible (Δw <~ 0.01). We then demonstrate a covariance-matrix approach to statistically account for correlated peculiar velocities. This down-weights nearby SNe and effectively acts as a graduated version of the usual sharp low-redshift cut. Neglecting coherent velocities in the current sample causes a systematic shift of Δw ~ 0.02. This will therefore have to be considered carefully when future surveys aim for percent-level accuracy and we recommend our statistical approach to down-weighting peculiar velocities as a more robust option than a sharp low-redshift cut.

  • 223. De Cia, Annalisa
    et al.
    Gal-Yam, A.
    Rubin, A.
    Leloudas, G.
    Vreeswijk, P.
    Perley, D. A.
    Quimby, R.
    Yan, Lin
    Sullivan, M.
    Flörs, A.
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Bersier, D.
    Cenko, S. B.
    Gal-Yam, M.
    Maguire, K.
    Ofek, E. O.
    Prentice, S.
    Schulze, S.
    Spyromilio, J.
    Valenti, S.
    Arcavi, I.
    Corsi, A.
    Howell, D. A.
    Mazzali, P.
    Kasliwal, M. M.
    Taddia, Francesco
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Yaron, O.
    Light Curves of Hydrogen-poor Superluminous Supernovae from the Palomar Transient Factory2018Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 860, nr 2, artikel-id 100Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We investigate the light-curve properties of a sample of 26 spectroscopically confirmed hydrogen- poor superluminous supernovae (SLSNe-I) in the Palomar Transient Factory survey. These events are brighter than SNe Ib/c and SNe Ic-BL, on average, by about 4 and 2. mag, respectively. The peak absolute magnitudes of SLSNe-I in rest-frame g band span -22 less than or similar to M-g less than or similar to -20 mag, and these peaks are not powered by radioactive Ni-56, unless strong asymmetries are at play. The rise timescales are longer for SLSNe than for normal SNe Ib/c, by roughly 10 days, for events with similar decay times. Thus, SLSNe-I can be considered as a separate population based on photometric properties. After peak, SLSNe-I decay with a wide range of slopes, with no obvious gap between rapidly declining and slowly declining events. The latter events show more irregularities (bumps) in the light curves at all times. At late times, the SLSN-I light curves slow down and cluster around the 56Co radioactive decay rate. Powering the late-time light curves with radioactive decay would require between 1 and 10M(circle dot) of Ni masses. Alternatively, a simple magnetar model can reasonably fit the majority of SLSNe-I light curves, with four exceptions, and can mimic the radioactive decay of 56Co, up to similar to 400 days from explosion. The resulting spin values do not correlate with the host-galaxy metallicities. Finally, the analysis of our sample cannot strengthen the case for using SLSNe-I for cosmology.

  • 224. de Jaeger, T.
    et al.
    Anderson, J. P.
    Pignata, G.
    Hamuy, M.
    Kankare, E.
    Stritzinger, M. D.
    Benetti, S.
    Bufano, F.
    Elias-Rosa, N.
    Folatelli, G.
    Foerster, F.
    Gonzaez-Gaitan, S.
    Gutierrez, C. P.
    Inserra, C.
    Kotak, R.
    Lira, P.
    Morrell, N.
    Taddia, Francesco
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Tomasella, L.
    SN 2011A: A LOW-LUMINOSITY INTERACTING TRANSIENT WITH A DOUBLE PLATEAU AND STRONG SODIUM ABSORPTION2015Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 807, nr 1, artikel-id 63Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present optical photometry and spectroscopy of the optical transient SN 2011A. Our data span 140 days after discovery including BVRI u'g'r'i'z' photometry and 11 epochs of optical spectroscopy. Originally classified as a type IIn supernova (SN IIn) due to the presence of narrow Ha emission, this object shows exceptional characteristics. First, the light curve shows a double plateau, a property only observed before in the impostor SN 1997bs. Second, SN 2011A has a very low luminosity (M-V = -15.72), placing it between normal luminous SNe IIn and SN impostors. Third, SN 2011A shows low velocity and high equivalent width absorption close to the sodium doublet, which increases with time and is most likely of circumstellar origin. This evolution is also accompanied by a change in line profile; when the absorption becomes stronger, a P Cygni profile appears. We discuss SN 2011A in the context of interacting SNe IIn and SN impostors, which appears to confirm the uniqueness of this transient. While we favor an impostor origin for SN 2011A, we highlight the difficulty in differentiating between terminal and non-terminal interacting transients.

  • 225. De, Kishalay
    et al.
    Kasliwal, Mansi M.
    Cantwell, Therese
    Cao, Yi
    Cenko, S. Bradley
    Gal-Yam, Avishay
    Johansson, Joel
    Kong, Albert
    Kulkarni, Shrinivas R.
    Lunnan, Ragnhild
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Masci, Frank
    Matuszewski, Matt
    Mooley, Kunal P.
    Neill, James D.
    Nugent, Peter E.
    Ofek, Eran O.
    Perrott, Yvette
    Rebbapragada, Umaa D.
    Rubin, Adam
    O' Sullivan, Donal
    Yaron, Ofer
    iPTF 16hgs: A Double-peaked Ca-rich Gap Transient in a Metal-poor, Star-forming Dwarf Galaxy2018Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 866, nr 1, artikel-id 72Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Calcium-rich gap transients represent an intriguing new class of faint and fast-evolving supernovae that exhibit strong [Ca II] emission in their nebular phase spectra. In this paper, we present the discovery and follow-up observations of a faint and fast-evolving transient, iPTF 16hgs, that exhibited a double-peaked light curve. Exhibiting a Type Ib spectrum in the photospheric phase and an early transition to a [Ca II] dominated nebular phase, iPTF 16hgs shows properties consistent with the class of Ca-rich gap transients, with two important exceptions. First, while the second peak of the light curve is similar to other Ca-rich gap transients, the first blue and fast-fading peak (declining over approximate to 2 days) is unique to this source. Second, we find that iPTF 16hgs occurred in the outskirts (projected offset of approximate to 6 kpc approximate to 1.9 R-eff) of a low-metallicity (approximate to 0.4 Z(circle dot)), star-forming, dwarf spiral galaxy. Deep limits from late-time radio observations suggest a low-density environment for the source. If iPTF 16hgs shares explosion physics with the class of Ca-rich gap transients, the first peak can be explained by the presence of 0.01 M-circle dot of Ni-56 in the outer layers the ejecta, reminiscent of some models of He-shell detonations on WDs. However, if iPTF 16hgs is physically unrelated to the class, the first peak is consistent with shock cooling emission (of an envelope with a mass of approximate to 0.08 M-circle dot and radius of approximate to 13 R-circle dot) in a core-collapse explosion of a highly stripped massive star in a close binary system.

  • 226.
    de la Cruz Rodriguez, Jaime
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Hansteen, Viggo
    Bellot-Rubio, Luis
    Ortiz, Ada
    EMERGENCE OF GRANULAR-SIZED MAGNETIC BUBBLES THROUGH THE SOLAR ATMOSPHERE. II. NON-LTE CHROMOSPHERIC DIAGNOSTICS AND INVERSIONS2015Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 810, nr 2, artikel-id 145Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Magnetic flux emergence into the outer layers of the Sun is a fundamental mechanism for releasing energy into the chromosphere and the corona. In this paper, we study the emergence of granular-sized flux concentrations and the structuring of the corresponding physical parameters and atmospheric diagnostics in the upper photosphere and in the chromosphere. We make use of a realistic 3D MHD simulation of the outer layers of the Sun to study the formation of the Ca II 8542 line. We also derive semi-empirical 3D models from non-LTE inversions of our observations. These models contain information on the line-of-sight stratifications of temperature, velocity, and the magnetic field. Our analysis explains the peculiar Ca II 8542 angstrom profiles observed in the flux emerging region. Additionally, we derive detailed temperature and velocity maps describing the ascent of a magnetic bubble from the photosphere to the chromosphere. The inversions suggest that, in active regions, granular-sized bubbles emerge up to the lower chromosphere where the existing large-scale field hinders their ascent. We report hints of heating when the field reaches the chromosphere.

  • 227. De Rosa, G.
    et al.
    Fausnaugh, M. M.
    Grier, C. J.
    Peterson, B. M.
    Denney, K. D.
    Horne, Keith
    Bentz, M. C.
    Ciroi, S.
    Dalla Bonta, E.
    Joner, M. D.
    Kaspi, S.
    Kochanek, C. S.
    Pogge, R. W.
    Sergeev, S. G.
    Vestergaard, M.
    Adams, S. M.
    Antognini, J.
    Salvo, C. Araya
    Armstrong, E.
    Bae, J.
    Barth, A. J.
    Beatty, T. G.
    Bhattacharjee, A.
    Borman, G. A.
    Boroson, T. A.
    Bottorff, M. C.
    Brown, J. E.
    Brown, J. S.
    Brotherton, M. S.
    Coker, C. T.
    Clanton, C.
    Cracco, V.
    Crawford, S. M.
    Croxall, K. V.
    Eftekharzadeh, S.
    Eracleous, M.
    Fiorenza, S. L.
    Frassati, A.
    Hawkins, K.
    Henderson, C. B.
    Holoien, T. W. -S.
    Hutchison, T.
    Kellar, J.
    Kilerci-Eser, E.
    Kim, S.
    King, A. L.
    La Mura, G.
    Laney, C. D.
    Li, M.
    Lochhaas, C.
    Ma, Z.
    MacInnis, F.
    Manne-Nicholas, E. R.
    Mason, M.
    McGraw, S. M.
    Mogren, K.
    Montouri, C.
    Moody, J. W.
    Mosquera, A. M.
    Mudd, D.
    Musso, R.
    Nazarov, S. V.
    Nguyen, M. L.
    Ochner, P.
    Okhmat, D. N.
    Onken, C. A.
    Ou-Yang, B.
    Pancoast, A.
    Pei, L.
    Penny, M.
    Poleski, R.
    Portaluri, E.
    Prieto, J. -L.
    Price-Whelan, A. M.
    Pulatova, N. G.
    Rafter, S.
    Roettenbacher, Rachael M.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. University of Michigan, USA.
    Romero-Colmenero, E.
    Runnoe, J.
    Schimoia, J. S.
    Shappee, B. J.
    Sherf, N.
    Simonian, G. V.
    Siviero, A.
    Skowron, D. M.
    Skowron, J.
    Somers, G.
    Spencer, M.
    Starkey, D. A.
    Stevens, D. J.
    Stoll, R.
    Tamajo, E.
    Tayar, J.
    van Saders, J. L.
    Valenti, S.
    Villanueva, S.
    Villforth, C.
    Weiss, Y.
    Winkler, H.
    Zastrow, J.
    Zhu, W.
    Zu, Y.
    Velocity-resolved Reverberation Mapping of Five Bright Seyfert 1 Galaxies2018Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 866, nr 2, artikel-id 133Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the first results from a reverberation-mapping campaign undertaken during the first half of 2012, with additional data on one active galactic nucleus (AGN) (NGC 3227) from a 2014 campaign. Our main goals are (1) to determine the black hole masses from continuum-H beta reverberation signatures, and (2) to look for velocity-dependent time delays that might be indicators of the gross kinematics of the broad-line region. We successfully measure H beta time delays and black hole masses for five AGNs, four of which have previous reverberation mass measurements. The values measured here are in agreement with earlier estimates, though there is some intrinsic scatter beyond the formal measurement errors. We observe velocity-dependent H beta lags in each case, and find that the patterns have changed in the intervening five years for three AGNs that were also observed in 2007.

  • 228.
    de Val-Borro, Miguel
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Harvard University, USA.
    Karovska, M.
    Sasselov, D.
    Numerical simulations of wind accretion in symbiotic binaries2009Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 700, nr 2, s. 1148-1160Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    About half of the binary systems are close enough to each other for mass to be exchanged between them at some point in their evolution, yet the accretion mechanism in wind accreting binaries is not well understood. We study the dynamical effects of gravitational focusing by a binary companion on winds from late-type stars. In particular, we investigate the mass transfer and formation of accretion disks around the secondary in detached systems consisting of an asymptotic giant branch (AGB) mass-losing star and an accreting companion. The presence of mass outflows is studied as a function of mass-loss rate, wind temperature, and binary orbital parameters. A two-dimensional hydrodynamical model is used to study the stability of mass transfer in wind accreting symbiotic binary systems. In our simulations we use an adiabatic equation of state and a modified version of the isothermal approximation, where the temperature depends on the distance from the mass losing star and its companion. The code uses a block-structured adaptive mesh refinement method that allows us to have high resolution at the position of the secondary and resolve the formation of bow shocks and accretion disks. We explore the accretion flow between the components and formation of accretion disks for a range of orbital separations and wind parameters. Our results show the formation of stream flow between the stars and accretion disks of various sizes for certain orbital configurations. For a typical slow and massive wind from an AGB star the flow pattern is similar to a Roche lobe overflow with accretion rates of 10% of the mass loss from the primary. Stable disks with exponentially decreasing density profiles and masses of the order 10(-4) solar masses are formed when wind acceleration occurs at several stellar radii. The disks are geometrically thin with eccentric streamlines and close to Keplerian velocity profiles. The formation of tidal streams and accretion disks is found to be weakly dependent on the mass loss from the AGB star. Our simulations of gravitationally focused wind accretion in symbiotic binaries show the formation of stream flows and enhanced accretion rates onto the compact component. We conclude that mass transfer through a focused wind is an important mechanism in wind accreting interacting binaries and can have a significant impact on the evolution of the binary itself and the individual components.

  • 229.
    Delahaye, Timur
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC). Université Pierre and Marie Curie, France; Université de Savoie, France.
    Kotera, Kumiko
    Silk, Joseph
    WHAT COULD WE LEARN FROM A SHARPLY FALLING POSITRON FRACTION?2014Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 794, nr 2, s. 168-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recent results from the AMS-02 data have confirmed that the cosmic-ray positron fraction increases with energy between 10 and 200 GeV. This quantity should not exceed 50%, and it is hence expected that it will either converge toward 50% or fall. We study the possibility that future data may show the positron fraction dropping down abruptly to the level expected with only secondary production, and forecast the implications of such a feature in term of possible injection mechanisms that include both dark matter and pulsars. Were a sharp steepening to be found, rather surprisingly, we conclude that pulsar models would do at least as well as dark matter scenarios in terms of accounting for any spectral cut-off.

  • 230. Desai, A.
    et al.
    Ajello, M.
    Omodei, N.
    Hartmann, D. H.
    Dominguez, A.
    Paliya, V. S.
    Helgason, K.
    Finke, J.
    Meyer, Manuel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Probing the EBL Evolution at High Redshift Using GRBs Detected with the Fermi-LAT2017Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 850, nr 1, artikel-id 73Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The extragalactic background light (EBL), from ultraviolet to infrared wavelengths, is predominantly due to emission from stars, accreting black holes and reprocessed light due to Galactic dust. The EBL can be studied through the imprint it leaves, via gamma-gamma absorption of high-energy photons, in the spectra of distant.-ray sources. The EBL has been probed through the search for the attenuation it produces in the spectra of BL Lacertae (BL Lac) objects and individual.-ray bursts (GRBs). GRBs have significant advantages over blazars for the study of the EBL especially at high redshifts. Here we analyze a combined sample of 22 GRBs, detected by the Fermi Large Area Telescope between 65 MeV and 500 GeV. We report a marginal detection (at the similar to 2.8 sigma level) of the EBL attenuation in the stacked spectra of the source sample. This measurement represents a first constraint of the EBL at an effective redshift of similar to 1.8. We combine our results with prior EBL constraints and conclude that Fermi-LAT is instrumental to constrain the UV component of the EBL. We discuss the implications on existing empirical models of EBL evolution.

  • 231. Dey, Lankeswar
    et al.
    Valtonen, M. J.
    Gopakumar, A.
    Zola, S.
    Hudec, R.
    Pihajoki, P.
    Ciprini, S.
    Matsumoto, K.
    Sadakane, K.
    Kidger, M.
    Nilsson, K.
    Mikkola, S.
    Sillanpaa, A.
    Takalo, L. O.
    Lehto, H. J.
    Berdyugin, A.
    Piirola, V.
    Jermak, H.
    Baliyan, K. S.
    Pursimo, T.
    Caton, D. B.
    Alicavus, F.
    Baransky, A.
    Blay, P.
    Boumis, P.
    Boyd, D.
    Campas Torrent, M.
    Campos, F.
    Carrillo Gomez, J.
    Chandra, S.
    Chavushyan, V.
    Dalessio, J.
    Debski, B.
    Drozdz, M.
    Er, H.
    Erdem, A.
    Escartin Perez, A.
    Ramazani, V. Fallah
    Filippenko, A. V.
    Gafton, Emanuel
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Ganesh, S.
    Garcia, F.
    Gazeas, K.
    Godunova, V.
    Gomez Pinilla, F.
    Gopinathan, M.
    Haislip, J. B.
    Harmanen, J.
    Hurst, G.
    Janik, J.
    Jelinek, M.
    Joshi, A.
    Kagitani, M.
    Karjalainen, R.
    Kaur, N.
    Keel, W. C.
    Kouprianov, V. V.
    Kundera, T.
    Kurowski, S.
    Kvammen, A.
    LaCluyze, A. P.
    Lee, B. C.
    Liakos, A.
    Lindfors, E.
    Lozano de Haro, J.
    Mugrauer, M.
    Naves Nogues, R.
    Neely, A. W.
    Nelson, R. H.
    Ogloza, W.
    Okano, S.
    Pajdosz-Smierciak, U.
    Pandey, J. C.
    Perri, M.
    Poyner, G.
    Provencal, J.
    Raj, A.
    Reichart, D. E.
    Reinthal, R.
    Reynolds, T.
    Saario, J.
    Sadegi, S.
    Sakanoi, T.
    Salto Gonzalez, J. -L.
    Sameer,
    Schweyer, T.
    Simon, A.
    Siwak, M.
    Soldan Alfaro, F. C.
    Sonbas, E.
    Steele, I.
    Stocke, J. T.
    Strobl, J.
    Tomov, T.
    Tremosa Espasa, L.
    Valdes, J. R.
    Valero Perez, J.
    Verrecchia, F.
    Vasylenko, V.
    Webb, J. R.
    Yoneda, M.
    Zejmo, M.
    Zheng, W.
    Zielinski, P.
    Authenticating the Presence of a Relativistic Massive Black Hole Binary in OJ 287 Using Its General Relativity Centenary Flare: Improved Orbital Parameters2018Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 866, nr 1, artikel-id 11Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Results from regular monitoring of relativistic compact binaries like PSR 1913+16 are consistent with the dominant (quadrupole) order emission of gravitational waves (GWs). We show that observations associated with the binary black hole (BBH) central engine of blazar OJ 287 demand the inclusion of gravitational radiation reaction effects beyond the quadrupolar order. It turns out that even the effects of certain hereditary contributions to GW emission are required to predict impact flare timings of OJ 287. We develop an approach that incorporates this effect into the BBH model for OJ 287. This allows us to demonstrate an excellent agreement between the observed impact flare timings and those predicted from ten orbital cycles of the BBH central engine model. The deduced rate of orbital period decay is nine orders of magnitude higher than the observed rate in PSR 1913+16, demonstrating again the relativistic nature of OJ 287's central engine. Finally, we argue that precise timing of the predicted 2019 impact flare should allow a test of the celebrated black hole no-hair theorem at the 10% level.

  • 232. Dikpati, Mausumi
    et al.
    Anderson, Jeffrey L.
    Mitra, Dhrubaditya
    Stockholms universitet, Nordiska institutet för teoretisk fysik (Nordita).
    DATA ASSIMILATION IN A SOLAR DYNAMO MODEL USING ENSEMBLE KALMAN FILTERS: SENSITIVITY AND ROBUSTNESS IN RECONSTRUCTION OF MERIDIONAL FLOW SPEED2016Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 828, nr 2, artikel-id 91Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We implement an Ensemble Kalman Filter procedure using the. Data Assimilation Research Testbed for assimilating synthetic meridional flow-speed data in a Babcock-Leighton-type flux-transport solar dynamo model. By performing several observing system simulation experiments, we reconstruct time. variation in meridional flow. speed and analyze sensitivity and robustness of reconstruction. Using 192 ensemble members including 10 observations, each with 4% error, we find that flow. speed is reconstructed best if observations of near-surface poloidal fields from low. latitudes and tachocline toroidal fields from midlatitudes are assimilated. If observations include a mixture of poloidal and toroidal fields from different latitude locations, reconstruction is reasonably good for. <= 40% error in low-latitude data, even if observational error in polar region data becomes 200%, but deteriorates when observational error increases in low- and midlatitude data. Solar polar region observations are known to contain larger errors than those in low latitudes; our forward operator (a flux-transport dynamo model here) can sustain larger errors in polar region data, but is more sensitive to errors in low- latitude data. An optimal reconstruction is obtained if an assimilation interval of 15 days is used; 10- and 20-day assimilation intervals also give reasonably good results. Assimilation intervals <5 days do not produce faithful reconstructions of flow. speed, because the system requires a minimum time to develop dynamics to respond to flow. variations. Reconstruction also deteriorates if an assimilation interval >45 days is used, because the system's inherent memory interferes with its short-term dynamics during a substantially long run without updating.

  • 233. Dilday, Benjamin
    et al.
    Bassett, Bruce
    Becker, Andrew
    Bender, Ralf
    Castander, Francisco
    Cinabro, David
    Frieman, Joshua A.
    Galbany, Lluís
    Garnavich, Peter
    Goobar, Ariel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Hopp, Ulrich
    Ihara, Yutaka
    Jha, Saurabh W.
    Kessler, Richard
    Lampeitl, Hubert
    Marriner, John
    Miquel, Ramon
    Mollá, Mercedes
    Nichol, Robert C.
    Nordin, Jakob
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Riess, Adam G.
    Sako, Masao
    Schneider, Donald P.
    Smith, Mathew
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Wheeler, J. Craig
    Östman, Linda
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Bizyaev, Dmitry
    Brewington, Howard
    Malanushenko, Elena
    Malanushenko, Viktor
    Oravetz, Dan
    Pan, Kaike
    Simmons, Audrey
    Snedden, Stephanie
    A Measurement of the Rate of Type Ia Supernovae in Galaxy Clusters from the SDSS-II Supernova Survey2010Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 715, s. 1021-1035Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present measurements of the Type Ia supernova (SN) rate in galaxy clusters based on data from the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. The cluster SN Ia rate is determined from 9 SN events in a set of 71 C4 clusters at z <= 0.17 and 27 SN events in 492 maxBCG clusters at 0.1 <= z <= 0.3. We find values for the cluster SN Ia rate of (0.37+0.17+0.01 -0.12-0.01) SNur h 2 and (0.55+0.13+0.02 -0.11-0.01) SNur h 2 (SNux = 10-12 L -1 xsun yr-1) in C4 and maxBCG clusters, respectively, where the quoted errors are statistical and systematic, respectively. The SN rate for early-type galaxies is found to be (0.31+0.18+0.01 -0.12-0.01) SNur h 2 and (0.49+0.15+0.02 -0.11-0.01) SNur h 2 in C4 and maxBCG clusters, respectively. The SN rate for the brightest cluster galaxies (BCG) is found to be (2.04+1.99+0.07 -1.11-0.04) SNur h 2 and (0.36+0.84+0.01 -0.30-0.01) SNur h 2 in C4 and maxBCG clusters, respectively. The ratio of the SN Ia rate in cluster early-type galaxies to that of the SN Ia rate in field early-type galaxies is 1.94+1.31+0.043 -0.91-0.015 and 3.02+1.31+0.062 -1.03-0.048, for C4 and maxBCG clusters, respectively. The SN rate in galaxy clusters as a function of redshift, which probes the late time SN Ia delay distribution, shows only weak dependence on redshift. Combining our current measurements with previous measurements, we fit the cluster SN Ia rate data to a linear function of redshift, and find rL = [(0.49+0.15 -0.14)+(0.91+0.85 -0.81) × z] SNuB h 2. A comparison of the radial distribution of SNe in cluster to field early-type galaxies shows possible evidence for an enhancement of the SN rate in the cores of cluster early-type galaxies. With an observation of at most three hostless, intra-cluster SNe Ia, we estimate the fraction of cluster SNe that are hostless to be (9.4+8.3 -5.1)%.

  • 234. Dilday, Benjamin
    et al.
    Smith, Mathew
    Bassett, Bruce
    Becker, Andrew
    Bender, Ralf
    Castander, Francisco
    Cinabro, David
    Filippenko, Alexei V.
    Frieman, Joshua A.
    Galbany, Lluís
    Garnavich, Peter M.
    Goobar, Ariel
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Hopp, Ulrich
    Ihara, Yutaka
    Jha, Saurabh W.
    Kessler, Richard
    Lampeitl, Hubert
    Marriner, John
    Miquel, Ramon
    Mollá, Mercedes
    Nichol, Robert C.
    Nordin, Jakob
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Riess, Adam G.
    Sako, Masao
    Schneider, Donald P.
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Wheeler, J. Craig
    Östman, Linda
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum.
    Bizyaev, Dmitry
    Brewington, Howard
    Malanushenko, Elena
    Malanushenko, Viktor
    Oravetz, Dan
    Pan, Kaike
    Simmons, Audrey
    Snedden, Stephanie
    Measurements of the Rate of Type Ia Supernovae at Redshift lsim0.3 from the Sloan Digital Sky Survey II Supernova Survey2010Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 713, s. 1026-1036Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present a measurement of the volumetric Type Ia supernova (SN Ia) rate based on data from the Sloan Digital Sky Survey II (SDSS-II) Supernova Survey. The adopted sample of supernovae (SNe) includes 516 SNe Ia at redshift z <~ 0.3, of which 270(52%) are spectroscopically identified as SNe Ia. The remaining 246 SNe Ia were identified through their light curves; 113 of these objects have spectroscopic redshifts from spectra of their host galaxy, and 133 have photometric redshifts estimated from the SN light curves. Based on consideration of 87 spectroscopically confirmed non-Ia SNe discovered by the SDSS-II SN Survey, we estimate that 2.04+1.61 -0.95% of the photometric SNe Ia may be misidentified. The sample of SNe Ia used in this measurement represents an order of magnitude increase in the statistics for SN Ia rate measurements in the redshift range covered by the SDSS-II Supernova Survey. If we assume an SN Ia rate that is constant at low redshift (z < 0.15), then the SN observations can be used to infer a value of the SN rate of rV = (2.69+0.34+0.21 -0.30-0.01)×10-5 SNe yr-1 Mpc-3 (H 0/(70 km s-1 Mpc-1))3 at a mean redshift of ~0.12, based on 79 SNe Ia of which 72 are spectroscopically confirmed. However, the large sample of SNe Ia included in this study allows us to place constraints on the redshift dependence of the SN Ia rate based on the SDSS-II Supernova Survey data alone. Fitting a power-law model of the SN rate evolution, rV (z) = Ap × ((1 + z)/(1 + z 0))ν, over the redshift range 0.0 < z < 0.3 with z 0 = 0.21, results in Ap = (3.43+0.15 -0.15) × 10-5 SNe yr-1 Mpc-3 (H 0/(70 km s-1 Mpc-1))3 and ν = 2.04+0.90 -0.89.

  • 235. Durkan, Stephen
    et al.
    Janson, Markus
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Carson, Joseph C.
    HIGH CONTRAST IMAGING WITH SPITZER: CONSTRAINING THE FREQUENCY OF GIANT PLANETS OUT TO 1000 au SEPARATIONS2016Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 824, nr 1, artikel-id 58Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report results of a re-analysis of archival Spitzer IRAC direct imaging surveys encompassing a variety of nearby stars. Our sample is generated from the combined observations of 73 young stars (median age, distance, spectral type = 85 Myr, 23.3 pc, G5) and 48 known exoplanet host stars with unconstrained ages (median distance, spectral type = 22.6 pc, G5). While the small size of Spitzer provides a lower resolution than 8 m class AO-assisted ground-based telescopes, which have been used for constraining the frequency of 0.5-13 M-J planets at separations of 10-10(2) au, its exquisite infrared sensitivity provides the ability to place unmatched constraints on the planetary populations at wider separations. Here we apply sophisticated high-contrast techniques to our sample in order to remove the stellar point-spread function and to open up sensitivity to planetary mass companions down to 5. separations. This enables sensitivity to 0.5-13 M-J planets at physical separations on the order of 10(2)-10(3) au, allowing us to probe a parameter space that has not previously been systematically explored to any similar degree of sensitivity. Based on a color and proper motion analysis, we do not record any planetary detections. Exploiting this enhanced survey sensitivity, employing Monte Carlo simulations with a Bayesian approach, and assuming a mass distribution of dn/dm alpha m(-1.31), we constrain (at 95% confidence) a population of 0.5-13 M-J planets at separations of 100-1000 au with an upper frequency limit of 9%.

  • 236. Eichler, M.
    et al.
    Arcones, A.
    Kelic, A.
    Korobkin, Oleg
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Langanke, K.
    Marketin, T.
    Martinez-Pinedo, G.
    Panov, I.
    Rauscher, T.
    Rosswog, Stephan
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Winteler, C.
    Zinner, N. T.
    Thielemann, F. -K.
    THE ROLE OF FISSION IN NEUTRON STAR MERGERS AND ITS IMPACT ON THE r-PROCESS PEAKS2015Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 808, nr 1, artikel-id 30Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Comparing observational abundance features with nucleosynthesis predictions of stellar evolution or explosion simulations, we can scrutinize two aspects: (a) the conditions in the astrophysical production site and (b) the quality of the nuclear physics input utilized. We test the abundance features of r-process nucleosynthesis calculations for the dynamical ejecta of neutron star merger simulations based on three different nuclear mass models: The Finite Range Droplet Model, the (quenched version of the) Extended Thomas Fermi Model with Strutinsky Integral, and the Hartree-Fock-Bogoliubov mass model. We make use of corresponding fission barrier heights and compare the impact of four different fission fragment distribution models on the final r-process abundance distribution. In particular, we explore the abundance distribution in the second r-process peak and the rare-earth sub-peak as a function of mass models and fission fragment distributions, as well as the origin of a shift in the third r-process peak position. The latter has been noticed in a number of merger nucleosynthesis predictions. We show that the shift occurs during the r-process freeze-out when neutron captures and beta-decays compete and an (n,gamma)-(gamma,n) equilibrium is no longer maintained. During this phase neutrons originate mainly from fission of material above A = 240. We also investigate the role of beta-decay half-lives from recent theoretical advances, which lead either to a smaller amount of fissioning nuclei during freeze-out or a faster (and thus earlier) release of fission neutrons, which can (partially) prevent this shift and has an impact on the second and rare-earth peak as well.

  • 237. Eide, Marius B.
    et al.
    Gronke, Max
    Dijkstra, Mark
    Hayes, Matthew
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Unlocking the Full Potential of Extragalactic Ly alpha through Its Polarization Properties2018Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 856, nr 2, artikel-id 156Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Ly alpha is a powerful astrophysical probe. Not only is it ubiquitous at high redshifts, it is also a resonant line, making Ly alpha photons scatter. This scattering process depends on the physical conditions of the gas through which Ly alpha propagates, and these conditions are imprinted on observables such as the Ly alpha spectrum and its surface brightness profile. In this work, we focus on a less-used observable capable of probing any scattering process: polarization. We implement the density matrix formalism of polarization into the Monte Carlo radiative transfer code tlac. This allows us to treat it as a quantum mechanical process where single photons develop and lose polarization from scatterings in arbitrary gas geometries. We explore static and expanding ellipsoids, biconical outflows, and clumpy multiphase media. We find that photons become increasingly polarized as they scatter and diffuse into the wings of the line profiles, making scattered Ly alpha polarized in general. The degree and orientation of Ly alpha polarization depends on the kinematics and distribution of the scattering H I gas. We find that it generally probes spatial or velocity space asymmetries and aligns itself tangentially to the emission source. We show that the mentioned observables, when studied separately, can leave similar signatures for different source models. We conclude by revealing how a joint analysis of the Ly alpha spectra, surface brightness profiles, and polarization can break these degeneracies and help us extract unique physical information on galaxies and their environments from their strongest, most prominent emission line.

  • 238. Elias-Rosa, Nancy
    et al.
    Van Dyk, Schuyler D.
    Benetti, Stefano
    Cappellaro, Enrico
    Smith, Nathan
    Kotak, Rubina
    Turatto, Massimo
    Filippenko, Alexei V.
    Pignata, Giuliano
    Fox, Ori D.
    Galbany, Lluis
    González-Gaitán, Santiago
    Miluzio, Matteo
    Monard, L. A. G.
    Ergon, Mattias
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    The Type IIn Supernova SN 2010bt: The Explosion of a Star in Outburst2018Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 860, nr 1, artikel-id 68Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    It is well known that massive stars (M > 8M(circle dot)) evolve up to the collapse of the stellar core, resulting in most cases in a supernova (SN) explosion. Their heterogeneity is related mainly to different configurations of the progenitor star at the moment of the explosion and to their immediate environments. We present photometry and spectroscopy of SN. 2010bt, which was classified as a Type. IIn. SN from a spectrum obtained soon after discovery and was observed extensively for about 2 months. After the seasonal interruption owing to its proximity to the Sun, the SN was below the detection threshold, indicative of a rapid luminosity decline. We can identify the likely progenitor with a very luminous star (log L/L-circle dot approximate to 7) through comparison of Hubble Space Telescope images of the host galaxy prior to explosion with those of the SN obtained after maximum light. Such a luminosity is not expected for a quiescent star, but rather for a massive star in an active phase. This progenitor candidate was later confirmed via images taken in 2015 (similar to 5 yr post-discovery), in which no bright point source was detected at the SN position. Given these results and the SN behavior, we conclude that SN. 2010bt was likely a Type IIn SN and that its progenitor was a massive star that experienced an outburst shortly before the final explosion, leading to a dense H-rich circumstellar environment around the SN progenitor.

  • 239. Elíasdóttir, Á.
    et al.
    Fynbo, J. P. U.
    Hjorth, J.
    Ledoux, C.
    Watson, D. J.
    Andersen, A. C.
    Malesani, D.
    Vreeswijk, P. M.
    Prochaska, J. X.
    Sollerman, Jesper
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Jaunsen, A. O.
    Dust Extinction in High-z Galaxies with Gamma-Ray Burst Afterglow Spectroscopy: The 2175 Å Feature at z = 2.452009Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 697, s. 1725-1740Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the clear detection of the 2175 Å dust absorption feature in the optical afterglow spectrum of the gamma-ray burst (GRB) GRB 070802 at a redshift of z = 2.45. This is the highest redshift for a detected 2175 Å dust bump to date, and it is the first clear detection of the 2175 Å bump in a GRB host galaxy, while several tens of optical afterglow spectra without the bump have been recorded in the past decade. The derived extinction curve gives AV = 0.8-1.5 depending on the assumed intrinsic slope. Of the three local extinction laws, a Large Magellanic Cloud (LMC) type extinction gives the best fit to the extinction curve of the host of GRB 070802. Besides the 2175 Å bump we find that the spectrum of GRB 070802 is characterized by unusually strong low-ionization metal lines and possibly a high metallicity for a GRB sightline ([Si/H] = -0.46 ± 0.38, [Zn/H] = -0.50 ± 0.68). In particular, the spectrum of GRB 070802 is unique for a GRB spectrum in that it shows clear C I absorption features, leading us to propose a correlation between the presence of the bump and C I. The gas-to-dust ratio for the host galaxy is found to be significantly lower than that of other GRB hosts with N(H I)/AV = (2.4 ± 1.0) × 1021 cm-2 mag-1, which lies between typical Milky Way and LMC values. Our results are in agreement with the tentative conclusion reached by Gordon et al. that the shape of the extinction curve, in particular the presence of the bump, is affected by the UV flux density in the environment of the dust. Based on observations collected under progs. ID 079.D-0429(B) and 177.D-0591(P,Q), using the FORS2 instrument installed at the Cassegrain focus of the Very Large Telescope (VLT), Unit 1 - Antu, operated by the European Southern Observatory (ESO) on Cerro Paranal, Chile.

  • 240.
    Erb, Dawn K.
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC). University of Wisconsin-Milwaukee, USA.
    Berg, Danielle A.
    Auger, Matthew W.
    Kaplan, David L.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC). University of Wisconsin-Milwaukee, USA.
    Brammer, Gabriel
    Pettini, Max
    Subkiloparsec Imaging of Lyα Emission in a Low-mass, Highly Ionized, Gravitationally Lensed Galaxy at z=1.842019Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 884, nr 1, artikel-id 7Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Low-mass, low-metallicity galaxies at low to moderate (z less than or similar to 3) redshifts offer the best opportunity for detailed examination of the interplay between massive stars, ionizing radiation and gas in sources similar to those that likely reionized the universe. We present new narrowband Hubble Space Telescope observations of Ly alpha emission and the adjacent ultraviolet (UV) continuum in the low-mass (M-star = 2 x 10(8) M-circle dot), low-metallicity (Z similar to 1/20 Z(circle dot)), and highly ionized gravitationally lensed galaxy SL2S J02176-0513 at z.=.1.844. The galaxy has strong Lya emission with photometric equivalent width W-Ly alpha(phot)= 218 +/- 12 angstrom , at odds with the Lya escape fraction of 10%. However, the spectroscopic Ly alpha profile suggests the presence of broad absorption underlying the emission, and the total equivalent width is consistent with the escape fraction once this underlying absorption is included. The Lya emission is more spatially extended than the UV continuum, and the 0 14 spatial resolution of HST coupled with the magnification of gravitational lensing enables us to examine the distribution of Ly alpha and the UV continuum on subkiloparsec scales. We find that the peaks of the Ly alpha emission and the UV continuum are offset by 650 pc, and there is no Ly alpha emission arising from the region with the strongest UV light. Our combined spectroscopic and imaging data imply a significant range in neutral hydrogen column density across the object. These observations offer indirect support for a model in which ionizing radiation escapes from galaxies through channels with low column density of neutral gas.

  • 241. Esteban Pozuelo, S.
    et al.
    Bellot Rubio, L. R.
    de la Cruz Rodriguez, Jaime
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    LATERAL DOWNFLOWS IN SUNSPOT PENUMBRAL FILAMENTS AND THEIR TEMPORAL EVOLUTION2015Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 803, nr 2, artikel-id 93Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the temporal evolution of downflows observed at the lateral edges of penumbral filaments in a sunspot located very close to the disk center. Our analysis is based on a sequence of nearly diffraction-limited scans of the Fe I 617.3 nm line taken with the CRisp Imaging Spectro-Polarimeter instrument at the Swedish 1 m Solar Telescope. We compute Dopplergrams from the observed intensity profiles using line bisectors and filter the resulting velocity maps for subsonic oscillations. Lateral downflows appear everywhere in the center-side penumbra as small, weak patches of redshifts next to or along the edges of blueshifted flow channels. These patches have an intermittent life and undergo mergings and fragmentations quite frequently. The lateral downflows move together with the hosting filaments and react to their shape variations, very much resembling the evolution of granular convection in the quiet Sun. There is a good relation between brightness and velocity in the center-side penumbra, with downflows being darker than upflows on average, which is again reminiscent of quiet Sun convection. These results point to the existence of overturning convection in sunspot penumbrae, with elongated cells forming filaments where the flow is upward but very inclined, and weak lateral downward flows. In general, the circular polarization profiles emerging from the lateral downflows do not show sign reversals, although sometimes we detect three-lobed profiles that are suggestive of opposite magnetic polarities in the pixel.

  • 242.
    Esteban Pozuelo, Sara
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. CSIC, Spain.
    Bellot Rubio, L. R.
    de la Cruz Rodríguez, Jaime
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    PROPERTIES OF SUPERSONIC EVERSHED DOWNFLOWS2016Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 832, nr 2, artikel-id 170Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study supersonic Evershed downflows in a sunspot penumbra by means of high spatial resolution spectropolarimetric data acquired in the Fe I. 617.3 nm line with the CRISP instrument at the Swedish 1 m Solar Telescope. Physical observables, such as Dopplergrams calculated from line bisectors and Stokes. V zero-crossing wavelengths, and Stokes. V maps in the far red-wing, are used to find regions where supersonic Evershed downflows may exist. We retrieve the line-of-sight velocity and the magnetic field vector in these regions using two-component inversions of the observed Stokes profiles with the help of the SIR code. We follow these regions during their lifetime to study their temporal behavior. Finally, we carry out a statistical analysis of the detected supersonic downflows to characterize their physical properties. Supersonic downflows are contained in compact patches moving outward, which are located in the mid-and outer penumbra. They are observed as bright, roundish structures at the outer end of penumbral filaments that resemble penumbral grains. The patches may undergo fragmentations and mergings during their lifetime; some of them are recurrent. Supersonic downflows are associated with strong and rather vertical magnetic fields with a reversed polarity compared to that of the sunspot. Our results suggest that downflows returning back to the solar surface with supersonic velocities are abruptly stopped in dense deep layers and produce a shock. Consequently, this shock enhances the temperature and is detected as a bright grain in the continuum filtergrams, which could explain the existence of outward-moving grains in the mid-and outer penumbra.

  • 243.
    Esteban Pozuelo, Sara
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    de la Cruz Rodríguez, Jaime
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Drews, A.
    van der Voort, L. Rouppe
    Scharmer, Göran B.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Carlsson, M.
    Observationally Based Models of Penumbral Microjets2019Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 870, nr 2, artikel-id 88Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We study the polarization signals and physical parameters of penumbral microjets (PMJs) by using high spatial resolution data taken in the Fe I 630 nm pair, Ca II 854.2 nm, and Ca II K lines with the CRISP and CHROMIS instruments at the Swedish 1 m Solar Telescope. We infer their physical parameters, such as physical observables in the photosphere and chromospheric velocity diagnostics, by different methods, including inversions of the observed Stokes profiles with the STiC code. PMJs harbor overall brighter Ca II K line profiles and conspicuous polarization signals in Ca II 854.2 nm, specifically in circular polarization that often shows multiple lobes mainly due to the shape of Stokes I They usually overlap photospheric regions with a sheared magnetic field configuration, suggesting that magnetic reconnections could play an important role in the origin of PMJs. The discrepancy between their low LOS velocities and the high apparent speeds reported on earlier, as well as the existence of different vertical velocity gradients in the chromosphere, indicate that PMJs might not be entirely related to mass motions. Instead, PMJs could be due to perturbation fronts induced by magnetic reconnections occurring in the deep photosphere that propagate through the chromosphere. This reconnection may be associated with current heating that produces temperature enhancements from the temperature minimum region. Furthermore, enhanced collisions with electrons could also increase the coupling to the local conditions at higher layers during the PMJ phase, giving a possible explanation for the enhanced emission in the overall Ca II K profiles emerging from these transients.

  • 244. Fantin, Nicholas J.
    et al.
    Côté, Patrick
    McConnachie, Alan W.
    Bergeron, Pierre
    Cuillandre, Jean-Charles
    Gwyn, Stephen D. J.
    Ibata, Rodrigo A.
    Thomas, Guillaume F.
    Carlberg, Raymond G.
    Fabbro, Sébastien
    Haywood, Misha
    Lançon, Ariane
    Lewis, Geraint F.
    Malhan, Khyati
    Stockholms universitet, Naturvetenskapliga fakulteten, Fysikum. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Martin, Nicolas F.
    Navarro, Julio F.
    Scott, Douglas
    Starkenburg, Else
    The Canada-France Imaging Survey: Reconstructing the Milky Way Star Formation History from Its White Dwarf Population2019Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 887, nr 2, artikel-id 148Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    As the remnants of stars with initial masses less than or similar to 8M(circle dot), white dwarfs contain valuable information on the formation histories of stellar populations. In this paper, we use deep, high-quality, u-band photometry from the Canada-France Imaging Survey, griz photometry from Pan-STARRS1, as well as proper motions from Gaia DR2, to select 25,156 white dwarf candidates over similar to 4500 deg(2) using a reduced proper motion diagram. We develop a new white dwarf population synthesis code that returns mock observations of the Galactic field white dwarf population for a given star formation history, while simultaneously taking into account the geometry of the Milky Way (MW), survey parameters, and selection effects. We use this model to derive the star formation histories of the thin disk, thick disk, and stellar halo. Our results show that the MW disk began forming stars (11.3 +/- 0.5) Gyr ago, with a peak rate of (8.8 +/- 1.4) M-circle dot yr(-1) at (9.8 +/- 0.4) Gyr, before a slow decline to a constant rate until the present day-consistent with recent results suggesting a merging event with a satellite galaxy. Studying the residuals between the data and best-fit model shows evidence for a slight increase in star formation over the past 3 Gyr. We fit the local fraction of helium-atmosphere white dwarfs to be (21 +/- 3)%. Incorporating this methodology with data from future wide-field surveys such as the Large Synoptic Survey Telescope, Euclid, The Cosmological Advanced Survey Telescope for Optical and ultraviolet Research, and the Wide Field Infrared Survey Telescope should provide an unprecedented view into the formation of the MW at its earliest epoch through its white dwarfs.

  • 245.
    Fathi, Kambiz
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Axon, David J.
    Storchi-Bergmann, Thaisa
    Kharb, Preeti
    Robinson, Andrew
    Marconi, Alessandro
    Maciejewski, Witold
    Capetti, Alessandro
    AN H alpha NUCLEAR SPIRAL STRUCTURE IN THE E0 ACTIVE GALAXY Arp 102B2011Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 736, nr 2, s. 77-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We report the discovery of a two-armed mini-spiral structure within the inner kiloparsec of the E0 LINER/Seyfert 1 galaxy Arp 102B. The arms are observed in H alpha emission and located east and west of the nucleus, extending up to approximate to 1 kpc from it. We use narrow-band imaging from the Hubble Space Telescope Advanced Camera for Surveys, in combination with archival Very Large Array radio images at 3.6 and 6 cm to investigate the origin of the nuclear spiral. From the H alpha luminosity of the spiral, we obtain an ionized gas mass of the order of 10(6) solar masses. One possibility is that the nuclear spiral represents a gas inflow triggered by a recent accretion event which has replenished the accretion disk, giving rise to the double-peaked emission-line profiles characteristic of Arp 102B. However, the radio images show a one-sided curved jet which correlates with the eastern spiral arm observed in the H alpha image. A published milliarcsecond radio image also shows a one-sided structure at position angle approximate to 40 degrees, approximately aligned with the inner part of the eastern spiral arm. The absence of a radio counterpart to the western spiral arm is tentatively interpreted as indicating that the jet is relativistic, with an estimated speed of 0.45c. Estimates of the jet kinetic energy and the ionizing luminosity of the active nucleus indicate that both are capable of ionizing the gas along the spiral arms. We conclude that, although the gas in the nuclear region may have originated in an accretion event, the mini spiral is most likely the result of a jet-cloud interaction rather than an inflowing stream.

  • 246.
    Fathi, Kambiz
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Beckman, J. E.
    Piñol-Ferrer, Nuria
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Hernandez, O.
    Martínez-Valpuesta, I.
    Carignan, C.
    Pattern Speeds of Bars and Spiral Arms from Hα Velocity Fields2009Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 704, s. 1657-1675Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We have applied the Tremaine-Weinberg method to 10 late-type barred spiral galaxies using data cubes, in Hα emission, from the FaNTOmM and GHAFAS Fabry-Perot spectrometers. We have combined the derived bar (and/or spiral) pattern speeds with angular frequency plots to measure the corotation radii for the bars in these galaxies. We base our results on a combination of this method with a morphological analysis designed to estimate the corotation radius to bar-length ratio using two independent techniques on archival near-infrared images, and although we are aware of the limitation of the application of the Tremaine-Weinberg method using Hα observations, we find consistently excellent agreement between bar and spiral arm parameters derived using different methods. In general, the corotation radius, measured using the Tremaine-Weinberg method, is closely related to the bar length, measured independently from photometry and consistent with previous studies. Our corotation/bar-length ratios and pattern speed values are in good agreement with general results from numerical simulations of bars. In systems with identified secondary bars, we measure higher Hα velocity dispersion in the circumnuclear regions, whereas in all the other galaxies, we detect flat velocity dispersion profiles. In the galaxies where the bar is almost purely stellar, Hα measurements are missing, and the Tremaine-Weinberg method yields the pattern speeds of the spiral arms. The excellent agreement between the Tremaine-Weinberg method results and the morphological analysis and bar parameters in numerical simulations suggests that although the Hα emitting gas does not obey the continuity equation, it can be used to derive the bar pattern speed. In addition, we have analyzed the Hα velocity dispersion maps to investigate signatures of secular evolution of the bars in these galaxies. The increased central velocity dispersion in the galaxies with secondary bars suggests that the formation of inner bars or disks may be a necessary step in the formation of bulges in late-type spiral galaxies.

  • 247.
    Fathi, Kambiz
    et al.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Beckman, John
    Lundgren, Andreas
    Carignan, Claude
    Hernandez, Olivier
    Amram, Philippe
    Balard, Philippe
    Gach, Jean-Luc
    Boulesteix, Jacques
    Knapen, Johan
    Spiral Inflow Feeding the Nuclear Starburst in M83: Observed in Hα Emission with the GHαFaS Fabry-Perot Interferometer2008Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 675, nr 1, s. L17-L20Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present observations of the nearby barred starburst galaxy M83 (NGC 5236), with the new Fabry-Perot interferometer GHαFaS mounted on the 4.2 m William Herschel Telescope on La Palma. The unprecedented high-resolution observations, of 16 pc FWHM-1, of the Hα-emitting gas cover the central 2 kpc of the galaxy. The velocity field displays the dominant disk rotation with signatures of gas inflow from kpc scales down to the nuclear regions. At the inner inner Lindblad resonance radius of the main bar and centered at the dynamical center of the main galaxy disk, a nuclear (5.5 +/- 0.9) × 108 Msolar rapidly rotating disk with scale length of 60+/-20 pc has formed. The nuclear starburst is found in the vicinity as well as inside this nuclear disk, and our observations confirm that gas spirals in from the outer parts to feed the nuclear starburst, giving rise to several star formation events at different epochs, within the central 100 pc radius of M83.

  • 248. Feldmeier, John J.
    et al.
    Hagen, Alex
    Ciardullo, Robin
    Gronwall, Caryl
    Gawiser, Eric
    Guaita, Lucia
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Hagen, Lea M. Z.
    Bond, Nicholas A.
    Acquaviva, Viviana
    Blanc, Guillermo A.
    Orsi, Alvaro
    Kurczynski, Peter
    SEARCHING FOR NEUTRAL HYDROGEN HALOS AROUND z similar to 2.1 AND z similar to 3.1 Ly alpha EMITTING GALAXIES2013Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 776, nr 2, s. 75-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We search for evidence of diffuse Ly alpha emission from extended neutral hydrogen surrounding Ly alpha emitting galaxies (LAEs) using deep narrow-band images of the Extended Chandra Deep Field South. By stacking the profiles of 187 LAEs at z = 2.06, 241 LAEs at z = 3.10, and 179 LAEs at z = 3.12, and carefully performing low-surface brightness photometry, we obtain mean surface brightness maps that reach 9.9, 8.7, and 6.2 x 10(-19) erg cm(-2) s(-1) arcsec(-2) in the emission line. We undertake a thorough investigation of systematic uncertainties in our surface brightness measurements and find that our limits are 5-10 times larger than would be expected from Poisson background fluctuations; these uncertainties are often underestimated in the literature. At z similar to 3.1, we find evidence for extended halos with small-scale lengths of 5-8 kpc in some but not all of our sub-samples. We demonstrate that sub-samples of LAEs with low equivalent widths and brighter continuum magnitudes are more likely to possess such halos. At z similar to 2.1, we find no evidence of extended Ly alpha emission down to our detection limits. Through Monte-Carlo simulations, we also show that we would have detected large diffuse LAE halos if they were present in our data sets. We compare these findings to other measurements in the literature and discuss possible instrumental and astrophysical reasons for the discrepancies.

  • 249. Folatelli, Gaston
    et al.
    Phillips, M. M.
    Morrell, Nidia
    Tanaka, Masaomi
    Maeda, Keiichi
    Nomoto, Ken'ichi
    Stritzinger, Maximilian
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi. Stockholms universitet, Naturvetenskapliga fakulteten, Oskar Klein-centrum för kosmopartikelfysik (OKC).
    Burns, Christopher R.
    Hamuy, Mario
    Mazzali, Paolo
    Boldt, Luis
    Campillay, Abdo
    Contreras, Carlos
    Gonzalez, Sergio
    Roth, Miguel
    Salgado, Francisco
    Freedman, W. L.
    Madore, Barry F.
    Persson, S. E.
    Suntzeff, Nicholas B.
    UNBURNED MATERIAL IN THE EJECTA OF TYPE Ia SUPERNOVAE2012Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 745, nr 1, s. 74-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The presence of unburned material in the ejecta of normal Type Ia supernovae (SNe Ia) is investigated using early-time spectroscopy obtained by the Carnegie Supernova Project. The tell-tale signature of pristine material from a C+O white dwarf progenitor star is the presence of carbon, as oxygen is also a product of carbon burning. The most prominent carbon lines in optical spectra of SNe Ia are expected to arise from C II. We find that at least 30% of the objects in the sample show an absorption at approximate to 6300 angstrom which is attributed to C II lambda 6580. An alternative identification of this absorption as Ha is considered to be unlikely. These findings imply a larger incidence of carbon in SNe Ia ejecta than previously noted. We show how observational biases and physical conditions may hide the presence of weak C II lines, and account for the scarcity of previous carbon detections in the literature. This relatively large frequency of carbon detections has crucial implications on our understanding of the explosive process. Furthermore, the identification of the 6300 angstrom absorptions as carbon would imply that unburned material is present at very low expansion velocities, merely approximate to 1000 km s(-1) above the bulk of Si II. Based on spectral modeling, it is found that the detections are consistent with a mass of carbon of 10(-3) to 10(-2) M-circle dot. The presence of this material so deep in the ejecta would imply substantial mixing, which may be related to asymmetries of the flame propagation. Another possible explanation for the carbon absorptions may be the existence of clumps of unburned material along the line of sight. However, the uniformity of the relation between C II and Si II velocities is not consistent with such small-scale asymmetries. The spectroscopic and photometric properties of SNe Ia with and without carbon signatures are compared. A trend toward bluer color and lower luminosity at maximum light is found for objects which show carbon.

  • 250. Foley, R. J.
    et al.
    Matheson, T.
    Blondin, S.
    Chornock, R.
    Silverman, J. M.
    Challis, P.
    Clocchiatti, A.
    Filippenko, A. V.
    Kirshner, R. P.
    Leibundgut, B.
    Sollerman, J.
    Stockholms universitet, Naturvetenskapliga fakulteten, Institutionen för astronomi.
    Spyromilio, J.
    Tonry, J. L.
    Davis, T. M.
    Garnavich, P. M.
    Jha, S. W.
    Krisciunas, K.
    Li, W.
    Pignata, G.
    Rest, A.
    Riess, A. G.
    Schmidt, B. P.
    Smith, R. C.
    Stubbs, C. W.
    Tucker, B. E.
    Wood-Vasey, W. M.
    Spectroscopy of High-Redshift Supernovae from the Essence Project: The First Four Years2009Ingår i: Astrophysical Journal, ISSN 0004-637X, E-ISSN 1538-4357, Vol. 137, s. 3731-3742Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We present the results of spectroscopic observations from the ESSENCE high-redshift supernova (SN) survey during its first four years of operation. This sample includes spectra of all SNe Ia whose light curves were presented by Miknaitis et al. and used in the cosmological analyses of Davis et al. and Wood-Vasey et al. The sample represents 273 hr of spectroscopic observations with 6.5-10 m class telescopes of objects detected and selected for spectroscopy by the ESSENCE team. We present 184 spectra of 156 objects. Combining this sample with that of Matheson et al., we have a total sample of 329 spectra of 274 objects. From this, we are able to spectroscopically classify 118 Type Ia SNe. As the survey has matured, the efficiency of classifying SNe Ia has remained constant while we have observed both higher-redshift SNe Ia and SNe Ia farther from maximum brightness. Examining the subsample of SNe Ia with host-galaxy redshifts shows that redshifts derived from only the SN Ia spectra are consistent with redshifts found from host-galaxy spectra. Moreover, the phases derived from only the SN Ia spectra are consistent with those derived from light-curve fits. By comparing our spectra to local templates, we find that the rate of objects similar to the overluminous SN 1991T and the underluminous SN 1991bg in our sample are consistent with that of the local sample. We do note, however, that we detect no object spectroscopically or photometrically similar to SN 1991bg. Although systematic effects could reduce the high-redshift rate we expect based on the low-redshift surveys, it is possible that SN 1991bg-like SNe Ia are less prevalent at high redshift.

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