GCN Circular 13188
Subject
GRB 120327A: SMARTS optical/IR afterglow observations
Date
2012-04-02T04:00:35Z (12 years ago)
From
Bethany Cobb at GWU <bcobb@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).