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Author(s): C. H. Blake [1]; J. S. Bloom (corresponding author) [1, 2]; D. L. Starr [13]; E. E. Falco [3]; M. Skrutskie [9]; E. E. Fenimore [7]; G. Duchêne [12]; [...]

Gamma-ray bursts (GRBs) are believed to be due to relativistic outflow of particles from a major explosion interacting with material around the explosion site. Gamma-ray, optical, infrared, submillimetre, millimetre and radio observations of the GRB990123 burst and its afterglow suggest that the initial and afterglow emissions are linked to three distinct areas in the fireball. The peak flux of the afterglow was lower in frequency than other bursts, explaining the short-lived radio emission.

The explosion that results in a cosmic?-ray burst (GRB) is thought to produce emission from two physical processes: the central engine gives rise to the high-energy emission of the burst through internal shocking, and the subsequent interaction of the flow with the external environment produces long-wavelength afterglows. Although observations of afterglows continue to refine our understanding of GRB progenitors and relativistic shocks,?-ray observations alone have not yielded a clear picture of the origin of the prompt emission nor details of the central engine. Only one concurrent visible-light transient has been found and it was associated with emission from an external shock. Here we report the discovery of infrared emission contemporaneous with a GRB, beginning 7.2 minutes after the onset of GRB 041219a (ref. 8). We acquired 21 images during the active phase of the burst, yielding early multi-colour observations. Our analysis of the initial infrared pulse suggests an origin consistent with internal shocks. [ABSTRACT FROM AUTHOR]