[vsnet-grb-info 5991] GRB 080420A: ROTSE-III Optical Limits on a possible short burst

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  7633
SUBJECT: GRB 080420A: ROTSE-III Optical Limits on a possible short burst
DATE:    08/04/20 04:50:49 GMT
FROM:    Brad Schaefer at LSU  <schaefer at grb.phys.lsu.edu>

B. E. Schaefer (Louisiana State), F. Yuan (U Mich), W. Rujopakarn 
(Steward), report on behalf of the ROTSE collaboration:

ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB
080420 (Swift trigger 309665; Vetere, L. et al., GCN 7632) a possible
short burst, producing images beginning 8.1 s after the GCN notice time.
An automated response took the first image at 04:13:10.2 UT, 23.0 s after
the burst, under fair conditions.  These observations were affected by the
Full Moon 75 degrees away. We took 10 5-sec, and 60 20-sec exposures.
These unfiltered images are calibrated relative to USNO A2.0 (R). Imaging
is on going.

Comparison to the DSS (second epoch) reveals no new sources within the 
3-sigma Swift/BAT error circle; the field is not crowded. Individual 
images have limiting magnitudes ranging from 16.1-17.1; we set the 
following specific limits.

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
04:13:10.2   04:13:15.2         5     16.1           23.0       N
04:13:10.2   04:14:17.3        67     18.1           23.0       Y
04:24:09.3   04:28:51.6       282     18.5          682.1       Y