[vsnet-grb-info 1869] GRB 050730, SMARTS optical/IR afterglow observations

[GCN Circulars]

TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3708
SUBJECT: GRB 050730, SMARTS optical/IR afterglow observations
DATE:    05/07/31 01:07:04 GMT
FROM:    Bethany Cobb at Yale U  <cobb at astro.yale.edu>

B. E. Cobb and C. D. Bailyn (Yale), part of the larger SMARTS
consortium, report:

Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained optical/IR imaging of the error region of GRB 050730
(GCN 3704, Holland et al.) with a mid-exposure time of
2005-07-30 23:05 UT, which is ~3.1 hours post-burst.
Total summed exposure times amounted to 15 minutes in I and V and
12 minutes in J and K.

The candidate afterglow (Holland et al, GCN 3704,
Sota et al. GCN 3705, Gomboc et al. GCN 3706) is
well detected in our images.

Assuming the nearby USNO-B1.0 star 0862-0270654
has a magnitude of I = 17.6 (USNO-B1.0 I2 magnitude)
and J = 16.4 (2MASS magnitude), then the magnitude 
of the afterglow candidate is I ~ 17.2 and J ~ 16.3
in the total combine frames.

The afterglow candidate also shows strong evidence of decay
between successive frame.  Preliminary analysis suggests
that the afterglow may have decayed in I by 
~ 0.5 magnitudes between the first and last frame taken
over a 40 minute period.  Given this evidence of decay, 
this source is very likely the optical afterglow
of GRB 050730.