Please use this identifier to cite or link to this item: http://hdl.handle.net/2289/1351

 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, PadmakarCastro-Tirado, A.J. Keywords: PhotometrySpectroscopyGRB AfterglowFlux DecaySpectral 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. URI: http://hdl.handle.net/2289/1351 ISSN: 0304-9523 Alternative Location: http://adsabs.harvard.edu/cgi-bin/bib_query?2003BASI...31...19P 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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