2002/11/06 by S. B. Pandey, D. K. Sahu, Pandey, S. B. +22
Engineering · Physics and Astronomy · #Astronomical Observations and Instrumentation #Astrophysics (astro-ph) #FOS: Physical sciences #Gamma-ray bursts and supernovae #SAS software applications and methods #astro-ph
paper · pdf · doi:10.48550/arxiv.astro-ph/0211108
19 pages, 3 figures, BASI, 31, 19
openalex publication_date 2002/11/06 · arxiv created 2003/10/17 · arxiv updated 2009/12/01 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The CCD magnitudes in Johnson B,V and Cousins R and I photometric passbands are determined for the bright long duration GRB 021004 afterglow from 2002 October 4 to 16 starting ∼ 3 hours after the γ-ray burst. Light curves of the afterglow emission in B,V,R and I passbands are obtained by combining these measurements with other published data. The earliest optical emission appears to originate in a revese shock. Flux decay of the afterglow shows a very uncommon variation relative to other well-observed GRBs. Rapid light variations, especially during early times (Δt < 2 days) is superposed on an underlying broken power law decay typical of a jetted afterglow. The flux decay constants at early and late times derived from least square fits to the light curve are 0.99±0.05 and 2.0±0.2 respectively, with a jet break at around 7 day. Comparison with a standard fireball model indicates a total extinction of E(B-V)=0.20 mag in the direction of the burst. Our low-resolution spectra corrected for this extinction provide a spectral slope β= 0.6±0.02. This value and the flux decay constants agree well with the electron energy index p∼ 2.27 used in the model. The derived jet opening angle of about 7∘ implies a total emitted gamma-ray energy Eγ = 3.5×1050 erg at a cosmological distance of about 20 Gpc. Multiwavelength observations indicate association of this GRB with a star forming region, supporting the case for collapsar origin of long duration GRBs.