[vsnet-grb-info 5054] GRB 070810A: ROTSE-III Refined Analysis

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6761
SUBJECT: GRB 070810A: ROTSE-III Refined Analysis
DATE:    07/08/17 00:24:27 GMT
FROM:    Fang Yuan at ROTSE  <yuanfang at 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.