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An infrared flash contemporaneous with the γ-rays of GRB 041219a


The explosion that results in a cosmic γ-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 shocking1, and the subsequent interaction of the flow with the external environment produces long-wavelength afterglows2,3,4. Although observations of afterglows5 continue to refine our understanding of GRB progenitors and relativistic shocks, γ-ray observations alone have not yielded a clear picture of the origin of the prompt emission6 nor details of the central engine. Only one concurrent visible-light transient has been found7 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.

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Figure 1: Images of the IR flash associated with GRB 041219a.
Figure 2: Evolution of the IR flash associated with GRB 041219a.
Figure 3: Long-timescale variability of the IR transient associated with GRB 041219a.
Figure 4: Colour evolution of the afterglow of GRB 041219a, corrected for extinction due to interstellar dust.


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J.S.B. was supported by a Junior Fellowship from the Harvard Society of Fellows. PAIRITEL was made possible by a grant from the Harvard Milton Fund. Additional funding from the Smithsonian Institution for the PAIRITEL project is acknowledged. We thank the entire Mt Hopkins Ridge staff for support of PAIRITEL, especially W. Peters, R. Hutchins and T. Groner. J. Huchra is thanked for stewardship of the telescope under adverse conditions in the week leading up to GRB 041219a. This publication makes use of data products from the Two Micron All Sky Survey (2MASS), which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

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Correspondence to J. S. Bloom.

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Supplementary Table S1

The Peters Automated Infrared Imaging Telescope (PAIRITEL) observations of GRB041219a. (PDF 65 kb)

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Blake, C., Bloom, J., Starr, D. et al. An infrared flash contemporaneous with the γ-rays of GRB 041219a. Nature 435, 181–184 (2005).

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