GCN Circular 12878

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 120119A (GCN 12859
Not found
 
 
,
Beardmore et al.) over several epochs, starting ~0.6 hours post-burst.
For the first epoch, several dithered images were obtained in each filter,
with total summed exposure times of 180s in each of BRIJK and 120s in each
of H and V.  For later epochs, total summed exposure times amounted to 15
minutes in I and V and 12 minutes in J and K.

At a mid-exposure time of 2012-01-19 04:43 UT (0.64 hrs post-burst), the
GRB afterglow (e.g. GCN 12859
Not found
 
 
, Beardmore et al., GCN 12860
Not found
 
 
, Morgan et
al., GCN 12863
Not found
 
 
, Schady et al.) is detected with the following magnitudes:

B = 20.07 +/- 0.06
V = 18.91 +/- 0.05
R = 18.02 +/- 0.03
I = 16.96 +/- 0.03
J = 15.14 +/- 0.05
H = 14.02 +/- 0.06
K = 12.89 +/- 0.10

Between about 0.6 hrs and 3 hrs post-burst, the GRB afterglow fades with a
decay rate of approximately alpha = 1.6 (where afterglow flux is
proportional to t^-alpha).

time
post-burst      I-band magnitude
0.64 hrs        16.96 +/- 0.03
1.71 hrs        18.52 +/- 0.03
2.97 hrs        19.39 +/- 0.05

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