TITLE:   GCN CIRCULAR
NUMBER:  7553
SUBJECT: GRB 080330, SMARTS optical/IR afterglow observations
DATE:    08/03/31 01:58:36 GMT
FROM:    Bethany Cobb at Yale U  <cobb@astro.yale.edu>

B. E. Cobb (Yale), part of the larger SMARTS consortium, reports:

Using the ANDICAM instrument on the 1.3m telescope at CTIO, we
obtained optical/IR imaging of the error region of GRB 080330
(GCN 7537, Mao et al.), with a mid-exposure time of
2008-03-30 04:17:29 UT, which is ~36 minutes post-burst.
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.

The GRB afterglow (GCN 7537, Mao et al.) is detected in all our images
with the following magnitudes (which have not been corrected
for Galactic reddening):

B= 18.27 +/- 0.04
V= 17.90 +/- 0.04
R= 17.59 +/- 0.03
I= 17.09 +/- 0.03
J= 16.36 +/- 0.07
H= 15.76 +/- 0.07
K= 15.14 +/- 0.06

Optical photometry is calibrated against Landolt standard stars
and IR photometry is calibrated against the 2MASS star at
coordinates RA/DEC=11:17:03.34 +30:38:31.1.

The afterglow clearly decays between individual images.
In R-band images taken between 20 and 52 minutes post-burst,
the afterglow decays by 0.7 magnitudes, indicating
an approximate decay rate of alpha = -0.7 (where afterglow flux
is proportional to t^alpha).