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GCN Circular 1754

Subject
GRB 021211: early break in light curve
Date
2002-12-13T20:34:27Z (21 years ago)
From
Ryan Chornock at UC Berkeley <chornock@astro.berkeley.edu>
R. Chornock, W. Li, A. V. Filippenko, and S. Jha, University of
California, Berkeley report:

We have further analysed the unfiltered KAIT dataset (GCN 1737) for the 
afterglow associated with GRB 021211 (GCN 1731).  The data show a
steeply declining light curve, falling from magnitude 14.8 to mag 19.0
in the first half hour after the burst. It is apparent that the light
curve underwent an early break.  A fit to our first nine data points,
spanning the time interval of 2.2-6.5 minutes after the GRB, shows a
decay with a power-law index of -1.60 +/- 0.02.  The light curve then
shows a break at about 12 minutes after the burst.  A fit to later
data, taken 20 to 150 minutes after the GRB, gives a slope of 
-0.96 +/- 0.04, consistent with the decay seen in concurrent
observations by Price and Fox (GCN 1733).

This break from a steep initial decline to a shallow later decline is 
reminiscent of the early behavior of GRB 990123 (Akerlof et al. 1999, 
Nature, 398, 400).  The early emission in that object is believed to
be due to the reverse shock, while the later emission is ascribed to
the normal forward shock (Sari and Piran 1999, ApJ, 517, L109).  We
hypothesize that our data for GRB 021211 show a similar evolution for
this object, but it is substantially fainter (~5 mags) than 990123 at
similar epochs.

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