GCN Circular 14401
Subject
GRB 130418A: SMARTS optical/IR afterglow observations
Event
Date
2013-04-19T22:41:06Z (13 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 130418A (GCN 14377,
De Pasquale et al.) at two epochs (with mid-exposure times of
2013-04-19 00:03 UT & 01:24 UT). 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 130418A (e.g. GCN 14377, De Pasquale
et al.; GCN 14378, Gorosabel et al.; GCN 14379, Quadri et al.)
was detected with the following magnitudes:
mid-exposure
time
(hours) V mag I mag J
mag K mag
5.03944 hours 18.41 +/- 0.03 17.57 +/- 0.03 16.46 +/- 0.10 14.82 +/-
0.10
6.38972 hours 18.59 +/- 0.03 17.69 +/- 0.03 16.70 +/- 0.10 15.05 +/-
0.10
(Optical photometry is calibrated against Landolt standard stars
and IR photometry is calibrated against a 2MASS star in the field.)
Between about 5 hrs and 6.4 hrs post-burst, the GRB afterglow fades with
a decay rate of approximately alpha = 0.6 +/- 0.2 in the optical
(where afterglow flux is proportional to t^-alpha).