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GRB 081007 AND GRB 090424: THE SURROUNDING MEDIUM, OUTFLOWS, AND SUPERNOVAE

Jin, Z-P and Covino, S and Della Valle, M and Ferrero, P and Fugazza, D and Malesani, D and Melandri, A and Pian, E and Salvaterra, R and Bersier, D and Campana, S and Cano, Z and Castro-Tirado, AJ and D'Avanzo, P and Fynbo, JPU and Gomboc, A and Gorosabel, J and Guidorzi, C and Haislip, JB and Hjorth, J and Kobayashi, S and LaCluyze, AP and Marconi, G and Mazzali, PA and Mundell, CG and Piranomonte, S and Reichart, DE and Sanchez-Ramirez, R and Smith, RJ and Steele, IA and Tagliaferri, G and Tanvir, NR and Valenti, S and Vergani, SD and Vestrand, T and Walker, ES and Wozniak, P (2013) GRB 081007 AND GRB 090424: THE SURROUNDING MEDIUM, OUTFLOWS, AND SUPERNOVAE. ASTROPHYSICAL JOURNAL, 774 (2). pp. 1-9. ISSN 0004-637X

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Abstract

We discuss the results of the analysis of multi-wavelength data for the afterglows of GRB 081007 and GRB 09042We discuss the results of the analysis of multi-wavelength data for the afterglows of GRB 081007 and GRB 090424, two bursts detected by Swift. One of them, GRB 081007, also shows a spectroscopically confirmed supernova, SN 2008hw, which resembles SN 1998bw in its absorption features, while the maximum magnitude may be fainter, up to 0.7 mag, than observed in SN 1998bw. Bright optical flashes have been detected in both events, which allows us to derive solid constraints on the circumburst-matter density profile. This is particularly interesting in the case of GRB081007, whose afterglow is found to be propagating into a constant-density medium, yielding yet another example of a gamma-ray burst (GRB) clearly associated with a massive star progenitor which did not sculpt the surroundings with its stellar wind. There is no supernova component detected in the afterglow of GRB090424, likely because of the brightness of the host galaxy, comparable to the Milky Way. We show that the afterglow data are consistent with the presence of both forward- and reverse-shock emission powered by relativistic outflows expanding into the interstellar medium. The absence of optical peaks due to the forward shock strongly suggests that the reverse-shock regions should be mildly magnetized. The initial Lorentz factor of outflow of GRB081007 is estimated to be ?? ~ 200, while for GRB090424 a lower limit of ?? > 170 is derived. We also discuss the prompt emission of GRB081007, which consists of just a single pulse. We argue that neither the external forward-shock model nor the shock-breakout model can account for the prompt emission data and suggest that the single-pulse-like prompt emission may be due to magnetic energy dissipation of a Poynting-flux-dominated outflow or to a dissipative photosphere.

Item Type: Article
Uncontrolled Keywords: 0201 Astronomical And Space Sciences, 0305 Organic Chemistry, 0306 Physical Chemistry (Incl. Structural)
Subjects: Q Science > QB Astronomy
Divisions: Astrophysics Research Institute
Publisher: IOP PUBLISHING LTD
Related URLs:
Date Deposited: 08 Feb 2016 11:11
Last Modified: 08 Feb 2016 11:11
DOI or Identification number: 10.1088/0004-637X/774/2/114
URI: http://researchonline.ljmu.ac.uk/id/eprint/2859

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