TITLE:   GCN GRB OBSERVATION REPORT
NUMBER:  3506
SUBJECT: GRB 050525a, SMARTS optical/IR afterglow observations 
DATE:    05/05/31 20:45:24 GMT
FROM:    Bethany Cobb at Yale U  <cobb@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 simultaneous optical/IR imaging of the error region of
GRB 050525a (Band et al. GCN 3466). Several dithered images were obtained
in each filter, with total summed exposure times of 180s in each of BRIYJK 
and 120s in each of H and V.  Imaging was carried out in a symmetrical 
manner so that the mid-exposure time is the same for all final combined 
images, in this case being ~5.2 hours post-burst (2005-05-25 05:13 UT). 
 
The afterglow reported by Rykoff et al. (GCNs 3465, 3468) is detected in 
each summed image, though the source appears only slightly above the 
background.  Preliminary comparison with USNO B1.0 stars in the optical 
and 2MASS stars in the IR yields the following approximate afterglow magnitudes:
 
 filter          AG mag
 ------          ------
 B               18.8+/-0.4
 R               18.1+/-0.3
 I               18.8+/-0.3
 
 J               17.4+/-0.3
 H               16.6+/-0.3
 K               16.15+/-0.35
 
Furthermore, a second epoch of imaging was obtained at a mid-exposure time 
of ~53.4 hours post-burst (2005-05-27 05:27 UT).  Total summed exposure 
times for these images was 36 min in I and 30 min in J.  The afterglow 
experienced significant decay between epochs and is not detectable in the 
second epoch images to a limiting magnitude of I > 21.2+/-0.2 
and J > 18.8+/-0.1.