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Title: Optical observations of the bright long duration peculiar GRB 021004 afterglow
Authors: Pandey, S.B.
Sahu, D.K.
Resmi, L.
Sagar, R.
Anupama, G.C.
Bhattacharya, D.
Mohan, V.
Prabhu, T.P.
Bhatt, B.C.
Pandey, J.C.
Parihar, Padmakar
Castro-Tirado, A.J.
Keywords: Photometry
GRB Afterglow
Flux Decay
Spectral Index
Issue Date: 2003
Publisher: The Astronomical Society of India
Citation: Bulletin of the Astronomical Society of India, 2003, Vol.31, p19-36
Abstract: 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 $\sim$ 3 hours after the $\gamma-$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 ($\Delta t < 2$ 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 $0.99\pm0.05$ and $2.0\pm0.2$ 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 $\beta = 0.6\pm0.02$. This value and the flux decay constants agree well with the electron energy index $p\sim 2.27$ used in the model. The derived jet opening angle of about $7^{\circ}$ implies a total emitted gamma-ray energy $E_{\gamma} = 3.5\times10^{50}$ 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.
ISSN: 0304-9523
Alternative Location:
Copyright: (2003) by the Astronomical Society of India. Scanned images provided by the NASA ADS Data System.
Appears in Collections:Research Papers (A&A)

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