TITLE:   GCN CIRCULAR
NUMBER:  9481
SUBJECT: GRB 090531b, SMARTS optical/IR observations
DATE:    09/06/02 21:50:32 GMT
FROM:    Bethany Cobb at UC Berkeley  <bcobb@astro.berkeley.edu>

B. E. Cobb (UC Berkeley) reports:

Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained
optical/IR imaging of the error region of GRB 090531b (GCN 9461, Cummings
et al.) over two epochs with mid-exposure times of 2009-06-01 02:56 UT
and 2009-06-02 05:26 UT (8.3 and 34.8 hours post-burst). Total summed 
exposure times for each observation amounted to 36 minutes in R and
30 minutes in J.

While there are a number of sources in and around the position of
the GRB X-ray afterglow (GCN 9463, Sbarufatti et al.; GCN 9480, Rossi
et al.), image differencing of the two epochs using the ISIS image
subtraction program does not reveal any significant variable source.  The
sky limiting magnitude of the images is I>21.1 and J>18.5 (where optical
photometry is calibrated using USNO-B1 stars and IR photometry with 2MASS;
these limits have not been corrected for Galactic reddening).