GCN Circular 6761
Subject
GRB 070810A: ROTSE-III Refined Analysis
Event
Date
2007-08-17T00:24:27Z (19 years ago)
From
Fang Yuan at ROTSE <yuanfang@umich.edu>
F. Yuan, E.S. Rykoff (U Mich), report on behalf of the ROTSE collaboration:
ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB
070810A (Swift trigger 287364; Cummings, et al., GCN 6733), and
detected the optical counterpart (Swan, et al., GCN 6734).
The initial aperture photometry reported in GCN 6734 was biased due to
contamination from the nearby star.
With a reference image taken 6 days after the burst, we were able to
subtract the nearby star and obtain better estimate of the OT
brightness with PSF fitting. Our refined analysis shows the OT at 18.0
� 0.2 mag (unfiltered images, calibrated relative to USNO-B1.0 R)
between 1607s and 2290s after the burst.
start UT end UT mag
-------------------------------------
02:38:39.5 02:50:02.3 18.0+/-0.2
03:13:15.7 03:24:39.0 18.5+/-0.2
The OT faded with a decay index 0.7 �0.2 in the next 40 minutes before
dropping below our detection threshold. This decay index is
significantly shallower than seen at later time in Keck photometry
(Perley, et al., GCN 6757), implying a light curve break between 1.2 hr
and 4 hr after the burst.