[vsnet-grb-info 5756] GRB 080310: ROTSE-III Observations of Optical Counterpart

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7411
SUBJECT: GRB 080310: ROTSE-III Observations of Optical Counterpart 
DATE:    08/03/12 03:32:31 GMT
FROM:    Fang Yuan at ROTSE  <yuanfang at umich.edu>

F. Yuan (U Mich), R. Quimby (Caltech), H. Swan (U Mich), C. Akerlof (U 
Mich), report on behalf of the ROTSE collaboration:

ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB 
080310 (Swift trigger 305288; Cummings et al., GCN 7382) and began 
imaging at UT 08:38:25.7 (5.7 sec after the GCN notice time) under 
cloudy conditions. The first usable image with a detection of the OT 
(Chornock et al. GCN 7381) starts at UT 09:03:03.4. Observations 
continued in fluctuating weather conditions until about 3 hours after 
the trigger.
 
The OT is slightly blended with the two nearby stars in ROTSE images. To 
reduce the contamination, we tried two different methods to obtain the 
OT magnitudes, first by subtracting the scaled PSF of the two nearby 
stars, and, second, by subtracting a reference image constructed from 
images taken on Mar. 11  between UT 05:26:28.5 and 06:00:53.6 (when the 
OT has dropped below our detection threshold). The two methods yield 
similar results. From 0.42 to 1.72 hour after the burst, the OT is 
observed to decay with a power-law index 0.6+/-0.1, consistent with the 
observation by the LBT (Garnavich et al., GCN 7390). The later images 
have degraded seeing and don't constrain the time dependence of the OT 
very well. The magnitudes reported below are unfiltered calibrated to 
SDSS r using standard stars in the pre-burst SDSS observations (Cool et 
al., GCN 7396).

Start_UT     End_UT      mag    magerror    mlim(of image)
---------------------------------------------------------------
09:03:03.4  09:07:31.2   17.2    0.1         18.4
09:56:17.5  10:09:49.8   18.0    0.1         19.4