GCN Circular 6844
Subject
GRB 071003: OA power-law decay indices from KAIT
Date
2007-10-03T23:14:54Z (17 years ago)
From
Weidong Li at UC Berkeley KAIT/LOSS <weidong@astron.berkeley.edu>
W. Li, R. Chornock, A. V. Filippenko, D. A. Perley, J. S. Bloom (University
of California, Berkeley), on behalf of the KAIT GRB team, report:
We have analyzed the KAIT observations of the GRB 071003 optical
afterglow (OA) reported by Li (GCN 6838) and confirmed by Cenko
and Fox (GCN 6839). Our preliminary unfiltered light curve, calibrated
with USNO B1.0, shows two potential breaks for the OA in the first
10 minutes after the burst. We measured a steep power law index of
-1.52 +/- 0.06 between t = 0.7 min and 1.2 min after the burst (from
5 x 5s images), possibly signaling the detection of the optical reverse
shock emission from the GRB. A shallower power law index of -0.89
+/- 0.03 is measured between t = 1.2 min and 4.3 min (from 3 images),
suggesting a break in the light curve between t = 1.2 min to 2.8 min.
The second potential break occurred at about 4 minutes after the burst,
with the power law decay index measured as -1.85 +/- 0.10 from 3 images
observed between t = 4.3 min to 7.4 min. We note this power law decay
index is consistent with the value reported by Swan et al. (GCN 6841)
at later times. Our observations ended at about 27 minutes after the
burst due to physical limits of KAIT. The analysis of all the data is
still ongoing.
The overall behavior of the OA of GRB 071003 OA is similar to that of
GRB 061126 (Perley et al., astro-ph/0703538), but with the breaks
occurring at an earlier stage of the evolution. We expect contamination
from the nearby bright star as discussed by Li (GCN 6838), Cenko and Fox
(GCN 6839), and Misra et al. (GCN 6840) to slightly affect the above
power indices, but not the overall photometric behavior.
Some selected KAIT unfiltered photometry:
t_start(s) Exptime(s) Mag Mag(err)
42 5.000 12.83 0.02
67 5.000 13.56 0.03
249 20.000 14.82 0.03
431 20.000 15.89 0.06
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