[vsnet-grb-info 2028] GRB 050824: ROTSE-III Optical Limits

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3867
SUBJECT: GRB 050824: ROTSE-III Optical Limits
DATE:    05/08/25 01:58:31 GMT
FROM:    Brad Schaefer at LSU  <schaefer at grb.phys.lsu.edu>

B. E. Schaefer (Louisiana State), Fang Yuan (U Mich), and K. Alatalo
(Berkeley)  report on behalf of the ROTSE collaboration:

ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia,
responded to GRB 050824 (Swift trigger 151905), producing images beginning
7.1 s after the GCN notice time. An automated response took the first
image at 23:22:02.1 UT, 585.8 s after the burst, under good conditions
although with the gibbous Moon only 25 degrees away. We took 10 5-sec, 10
20-sec and 130 60-sec eposures. These unfiltered images are calibrated
relative to USNO A2.0 (R).

ROTSE-IIId, located at the Turkish National Observatory at Bakirlitepe,
Turkey, also responded, producing images beginning 5.8 s after the GCN
notice time. An automated response took the first image at 23:22:00.8 UT,
584.5 s after the burst, under good conditions (but again, with the
gibbous Moon nearby). We took 10 5-sec, 10 20-sec and 80 60-sec eposures.
These unfiltered images are also calibrated relative to USNO A2.0 (R).

Comparison to the DSS (second epoch) reveals no new sources within the 
3-sigma error circle, for both single images and coadding into sets of 10. 
Individual images have limiting magnitudes ranging from 15.4-17.0; we set 
the following specific limits.

ROTSE  start UT       end UT     t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------------
III-c  23:22:02.1   23:23:27.1       85     17.3          585.8       Y
III-c  23:23:27.7   23:28:21.7      294     18.2          671.4       Y
III-d  23:22:00.8   23:24:20.8      140     17.4          584.5       Y
III-d  23:24:21.5   23:29:20.5      299     17.9          725.2       Y

In particular, we do not see the new source described by Gorosabel et al. 
(GCN 3865), with this source being near or below our detection threshold.