GCN Circular 6303

B. E. Schaefer (Louisiana State), F. Yuan (U Mich), S.A. Yost (U Mich), 
report on behalf of the ROTSE collaboration:

ROTSE-IIIb, located at McDonald Observatory, Texas, responded to GRB
070419A (Swift trigger 276205), producing images beginning 6.3 s after the
GCN notice time. An automated response took the first image at 10:00:47.3
UT, 81.2 s after the burst, under excellent conditions. We took 10 5-sec,
10 20-sec and 20 60-sec eposures, with further exposures still continuing.  
These unfiltered images are calibrated relative to USNO A2.0 (R).

There is a bright star in the BAT error circle, but this is well removed
from the XRT position. Comparison to the DSS (second epoch) reveals no new
sources within the 3-sigma XRT error circle, for both single images and
coadding into sets of 10;  the field is not crowded. Individual images
have limiting magnitudes ranging from 15.2-17.6; we set the following
specific limits.

start UT       end UT      t_exp(s)   mlim   t_start-tGRB(s)  Coadd?
--------------------------------------------------------------------
10:00:47.3   10:00:52.3         5     16.0           81.2       N
10:00:47.3   10:01:54.4        67     17.8           81.2       Y