[vsnet-grb-info 11797] GRB 120327A: SMARTS optical/IR afterglow observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  13188
SUBJECT: GRB 120327A: SMARTS optical/IR afterglow observations
DATE:    12/04/02 04:00:35 GMT
FROM:    Bethany Cobb at GWU  <bcobb at gwu.edu>

B. E. Cobb (GWU), reports:

Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained
optical/IR imaging of the error region of GRB 120327A (GCN 13123,
Sbarufatti et al.) over several epochs, starting ~1.8 hours post-burst.
For each epoch, several dithered images were obtained
with
total summed exposure times of 15 min in V and I and 12 min in J and K.

The fading afterglow of GRB 120327A (e.g. GCN 13123, Sbarufatti et al.; GCN
13124,
Klotz et al.; GCN 13125, Smith et al.) was detected with the following
magnitudes (or
3-sigma limits):

mid-exposure
time              V mag               I mag               J
mag               K mag
 1.8 hrs        18.92+/-0.03     17.73+/-0.04    16.46+/-0.07
14.83+/-0.09
 4.1 hrs        19.97+/-0.03     18.57+/-0.04    17.42+/-0.08
15.73+/-0.09
25.8 hrs       >21.9                >20.9                >19.0
   >17.4

(Optical photometry is calibrated against Landolt standard stars
and IR photometry is calibrated against 2MASS stars in the field.)

Between about 1.8 hrs and 4.1 hrs post-burst, the GRB afterglow fades with
a decay rate of approximately alpha = 1 (where afterglow flux is
proportional to t^-alpha).