Detection of a Supernova Signature Associated with GRB 011121
Piro, L.; Axelrod, T. S.; Frontera, F.; Price, P. A.; Harrison, F. A.; Galama, T. J.; Berger, E.; Bloom, J. S.; Djorgovski, S. G.; Frail, D. A.; Hurley, K.; Kulkarni, S. R.; Sari, R.; Schmidt, B. P.; Costa, E.; Chevalier, R. A.; Wheeler, J. C.; Halpern, J. P.; McCarthy, P. J.; Kimble, R. A.; Reichart, D.; Fox, D. W.; Holtzman, J.
United States, Australia, Italy
Abstract
Using observations from an extensive monitoring campaign with the Hubble Space Telescope, we present the detection of an intermediate-time flux excess that is redder in color relative to the afterglow of GRB 011121, currently distinguished as the gamma-ray burst with the lowest known redshift. The red ``bump,'' which exhibits a spectral rollover at ~7200 Å, is well described by a redshifted Type Ic supernova that occurred approximately at the same time as the gamma-ray burst event. The inferred luminosity is about half that of the bright supernova SN 1998bw. These results serve as compelling evidence for a massive star origin of long-duration gamma-ray bursts. Models that posit a supernova explosion weeks to months preceding the gamma-ray burst event are excluded by these observations. Finally, we discuss the relationship between spherical core-collapse supernovae and gamma-ray bursts. Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555.