GRB 011121: A Collimated Outflow into Wind-blown Surroundings

Greiner, J.; Klose, S.; Salvato, M.; Zeh, A.; Schwarz, R.; Hartmann, D. H.; Masetti, N.; Stecklum, B.; Lamer, G.; Lodieu, N.; Scholz, R. D.; Sterken, C.; Gorosabel, J.; Burud, I.; Rhoads, J.; Mitrofanov, I.; Litvak, M.; Sanin, A.; Grinkov, V.; Andersen, M. I.; Castro Cerón, J. M.; Castro-Tirado, A. J.; Fruchter, A.; Fynbo, J. U.; Hjorth, J.; Kaper, L.; Kouveliotou, C.; Palazzi, E.; Pian, E.; Rol, E.; Tanvir, N. R.; Vreeswijk, P. M.; Wijers, R. A. M. J.; van den Heuvel, E.
Bibliographical reference

The Astrophysical Journal, Volume 599, Issue 2, pp. 1223-1237.

Advertised on:
12
2003
Number of authors
34
IAC number of authors
0
Citations
58
Refereed citations
53
Description
We report optical and near-infrared follow-up observations of GRB 011121 collected predominantly at ESO telescopes in Chile. We discover a break in the afterglow light curve after 1.3 days, which implies an initial jet opening angle of about 9°. The jet origin of this break is supported by the fact that the spectral energy distribution is achromatic during the first 4 days. During later phases, GRB 011121 shows significant excess emission above the flux predicted by a power law, which we interpret as additional light from an underlying supernova. In particular, the spectral energy distribution of the optical transient approximately 2 weeks after the burst is clearly not of power-law type but can be presented by a blackbody with a temperature of ~6000 K. The deduced parameters for the decay slope and the spectral index favor a wind scenario, i.e., an outflow into a circumburst environment shaped by the stellar wind of a massive gamma-ray burst (GRB) progenitor. Because of its low redshift of z=0.36, GRB 011121 has been the best example for the GRB-supernova connection until GRB 030329 and provides compelling evidence for a circumburster wind region expected to exist if the progenitor was a massive star. Based on observations collected at the European Southern Observatory, La Silla and Paranal, Chile (ESO Programme 165.H-0464).