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Bauer F.E.,University of Santiago de Chile | Bauer F.E.,Space Science Institute | Bauer F.E.,Millennium Center for Supernova Science | Zelaya P.,University of Santiago de Chile | And 4 more authors.
Proceedings of the International Astronomical Union | Year: 2011

We report results for two epochs of spectropolarimetry on the luminous type IIn SN2010jl, taken at ≈36 and 85 days post-explosion with VLT FORS2-PMOS. The high signal-to-noise data demonstrate distinct evolution in the continuum and the broad lines point to a complex origin for the various emission components and to a potentially common polarization signal for the type IIn class even over 1-2 orders of magnitude in luminosity output. © 2012 International Astronomical Union. Source

Cano Z.,University of Iceland | Maeda K.,Kyoto University | Maeda K.,University of Tokyo | Schulze S.,University of Santiago de Chile | Schulze S.,Millennium Center for Supernova Science
Monthly Notices of the Royal Astronomical Society | Year: 2014

We present the results of modelling archival observations of Type Ib SN 1999dn. In the spectra, two He . i absorption features are seen: a slower component with larger opacity, and a more rapid He . i component with smaller opacity. Complementary results are obtained from modelling the bolometric light curve of SN 1999dn, where a two-zone model (dense inner region, and less dense outer region) provides a much better fit than a one-zone model. A key result we find is that roughly equal amounts of radioactive material are found in both regions. The two-zone analytical model provides a more realistic representation of the structure of the ejecta, including mixing and asymmetries, which offers a physical explanation for how the radioactive material is propelled to, and mixed within, the outer regions. Our result supports the theoretical expectation that the radioactive content in the outflow of a Type Ib supernova (SN) is thoroughly mixed. We fit our model to six additional SNe Ibc, of which the majority of the SNe Ib are best described by the two-zone model, and the majority of the SNe Ic by the one-zone model. Of the SNe Ic, only SN 2007gr was best fitted by the two-zone model, indicating that the lack of helium spectral features for this event cannot be attributed to poor mixing. © 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society. Source

Levan A.J.,University of Warwick | Tanvir N.R.,University of Leicester | Starling R.L.C.,University of Leicester | Wiersema K.,University of Leicester | And 42 more authors.
Astrophysical Journal | Year: 2014

We present comprehensive multiwavelength observations of three gamma-ray bursts (GRBs) with durations of several thousand seconds. We demonstrate that these events are extragalactic transients; in particular, we resolve the long-standing conundrum of the distance of GRB 101225A (the "Christmas-day burst"), finding it to have a redshift z = 0.847 and showing that two apparently similar events (GRB 111209A and GRB 121027A) lie at z = 0.677 and z = 1.773, respectively. The systems show extremely unusual X-ray and optical light curves, very different from classical GRBs, with long-lasting, highly variable X-ray emission and optical light curves that exhibit little correlation with the behavior seen in the X-ray. Their host galaxies are faint, compact, and highly star-forming dwarf galaxies, typical of "blue compact galaxies." We propose that these bursts are the prototypes of a hitherto largely unrecognized population of ultra-long GRBs, which while observationally difficult to detect may be astrophysically relatively common. The long durations may naturally be explained by the engine-driven explosions of stars of much larger radii than normally considered for GRB progenitors, which are thought to have compact Wolf-Rayet progenitor stars. However, we cannot unambiguously identify supernova signatures within their light curves or spectra. We also consider the alternative possibility that they arise from the tidal disruption of stars by massive black holes and conclude that the associated timescales are only consistent with the disruption of compact stars (e.g., white dwarfs) by black holes of relatively low mass (<105 M). © 2014. The American Astronomical Society. All rights reserved. Source

De Ugarte Postigo A.,Institute Astrofisica Of Andalucia Iaa Csic | De Ugarte Postigo A.,Niels Bohr Institute | Thone C.C.,Institute Astrofisica Of Andalucia Iaa Csic | Rowlinson A.,University of Amsterdam | And 48 more authors.
Astronomy and Astrophysics | Year: 2014

Context. Short duration gamma-ray bursts (SGRBs) are thought to be related to the violent merger of compact objects, such as neutron stars or black holes, which makes them promising sources of gravitational waves. The detection of a "kilonova"-likesignature associated to the Swift-detected GRB 130603B has suggested that this event is the result of a compact object merger. Aims. Our knowledge on SGRB has been, until now, mostly based on the absence of supernova signatures and the analysis of the host galaxies to which they cannot always be securely associated. Further progress has been significantly hampered by the faintness and rapid fading of their optical counterparts (afterglows), which has so far precluded spectroscopy of such events. Afterglow spectroscopy is the key tool to firmly determine the distance at which the burst was produced, crucial to understand its physics, and study its local environment. Methods. Here we present the first spectra of a prototypical SGRB afterglow in which both absorption and emission features are clearly detected. Together with multi-wavelength photometry we study the host and environment of GRB 130603B. Results. From these spectra we determine the redshift of the burst to be z = 0.3565 ± 0.0002, measure rich dynamics both in absorption and emission, and a substantial line of sight extinction of AV = 0.86 ± 0.15 mag. The GRB was located at the edge of a disrupted arm of a moderately star forming galaxy with near-solar metallicity. Unlike for most long GRBs (LGRBs), NHX/AV is consistent with the Galactic ratio, indicating that the explosion site differs from those found in LGRBs. Conclusions. The merger is not associated with the most star-forming region of the galaxy; however, it did occur in a dense region, implying a rapid merger or a low natal kick velocity for the compact object binary. © ESO, 2014. Source

Sparre M.,Copenhagen University | Hartoog O.E.,University of Amsterdam | Kruhler T.,Copenhagen University | Kruhler T.,European Southern Observatory | And 30 more authors.
Astrophysical Journal | Year: 2014

Observations of the afterglows of long gamma-ray bursts (GRBs) allow the study of star-forming galaxies across most of cosmic history. Here we present observations of GRB 111008A, from which we can measure metallicity, chemical abundance patterns, dust-to-metals ratio (DTM), and extinction of the GRB host galaxy at z = 5.0. The host absorption system is a damped Lyα absorber with a very large neutral hydrogen column density of and a metallicity of [S/H] = -1.70 ± 0.10. It is the highest-redshift GRB with such a precise metallicity measurement. The presence of fine-structure lines confirms the z = 5.0 system as the GRB host galaxy and makes this the highest redshift where Fe II fine-structure lines have been detected. The afterglow is mildly reddened with A V = 0.11 ± 0.04 mag, and the host galaxy has a DTM that is consistent with being equal to or lower than typical values in the Local Group. © 2014. The American Astronomical Society. All rights reserved.. Source

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