GRB 081007 and GRB 090424: The Surrounding Medium, Outflows, and Supernovae

Jin, Zhi-Ping; Covino, Stefano; Della Valle, Massimo; Ferrero, P.; Fugazza, Dino; Malesani, Daniele; Melandri, Andrea; Pian, Elena; Salvaterra, Ruben; Bersier, David; Campana, Sergio; Cano, Zach; Castro-Tirado, Alberto J.; D'Avanzo, Paolo; Fynbo, Johan P. U.; Gomboc, Andreja; Gorosabel, Javier; Guidorzi, Cristiano; Haislip, Joshua B.; Hjorth, Jens; Kobayashi, Shiho; LaCluyze, Aaron P.; Marconi, Gianni; Mazzali, Paolo A.; Mundell, Carole G.; Piranomonte, Silvia; Reichart, Daniel E.; Sánchez-Ramírez, Rubén; Smith, Robert J.; Steele, Ian A.; Tagliaferri, Gianpiero; Tanvir, Nial R.; Valenti, Stefano; Vergani, Susanna D.; Vestrand, Thomas; Walker, Emma S.; Woźniak, Przemek
Bibliographical reference

The Astrophysical Journal, Volume 774, Issue 2, article id. 114, 9 pp. (2013).

Advertised on:
9
2013
Number of authors
37
IAC number of authors
1
Citations
51
Refereed citations
46
Description
We 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 GRB 081007, 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 GRB 090424, likely due to 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 GRB 081007 is estimated to be Γ ~ 200, while for GRB 090424 a lower limit of Γ > 170 is derived. We also discuss the prompt emission of GRB 081007, 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.
Related projects
Project Image
Formation and Evolution of Galaxies: Observations in Infrared and other Wavelengths
This IAC research group carries out several extragalactic projects in different spectral ranges, using space as well as ground-based telescopes, to study the cosmological evolution of galaxies and the origin of nuclear activity in active galaxies. The group is a member of the international consortium which built the SPIRE instrument for the
Ismael
Pérez Fournon