[vsnet-grb-info 4827] GRB 070621: ROTSE-III Prompt Optical Limits

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  6561
SUBJECT: GRB 070621: ROTSE-III Prompt Optical Limits
DATE:    07/06/21 23:46:58 GMT
FROM:    Eli Rykoff at U of Michigan/ROTSE  <erykoff at umich.edu>

E.S. Rykoff (U Mich), W. Rujopakarn (Steward), B. E. Schaefer (Louisiana 
State), H. Swan (U Mich), J. Aretakis (U Mich), R. Quimby (U Texas), 
report on behalf of the ROTSE collaboration:

ROTSE-IIIc, located at the H.E.S.S. site at Mt. Gamsberg, Namibia, 
responded to GRB 070621 (Swift trigger 282808, Sbarufatti, et al., GCN 
6560), producing images beginning 6.1 s after the GCN notice time. An 
automated response took the first image at 23:18:03.1 UT, 23.3 s after 
the burst, and during gamma-ray emission. We took 10 5-sec, 10 20-sec 
and 10 60-sec exposures. These unfiltered images are calibrated relative 
to USNO A2.0 (R). Imaging is ongoing.

Comparison to the DSS (second epoch) reveals no new sources within the 
3-sigma Swift/BAT error circle or the XRT error circle, for both single 
images and coadding into sets of 10. Individual images have limiting 
magnitudes ranging from 16.4-17.8; we set the following specific limits.

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
23:18:03.1   23:18:08.1         5     16.6           23.3       N
23:18:03.1   23:19:20.7        77     17.5           23.3       Y
23:19:28.5   23:24:16.3       287     18.5          108.7       Y
23:24:25.7   23:35:51.6       685     18.8          405.9       Y