GCN Circular 10244
Subject
GRB 091127, SMARTS optical/IR afterglow observations
Event
Date
2009-12-03T23:50:51Z (16 years ago)
From
Bethany Cobb at UC Berkeley <bcobb@astro.berkeley.edu>
B. E. Cobb (UC Berkeley) reports:
Using the ANDICAM instrument on the 1.3m telescope at CTIO, we obtained
optical/IR imaging of the error region of GRB 091127 (GCN 10191, Troja
et al.) over seven epochs with mid-exposure times between ~2.2 and 100.8
hours post burst.
The optical afterglow of GRB 091127 (e.g. GCN 10192, Smith et al. & GCN
10193, Immler et al., GCN 10194) is observed in our imaging. In our first
epoch, with a mid-exposure time of ~2.2 hours post-burst, the afterglow
is clearly detected in our imaging with the following magnitudes:
B = 17.21 +/- 0.02 +/- 0.20 (error in zeropoint)
R = 16.70 +/- 0.02 +/- 0.23 (error in zeropoint)
I = 16.61 +/- 0.02 +/- 0.30 (error in zeropoint)
J = 15.56 +/- 0.05
H = 15.40 +/- 0.05
K = 14.77 +/- 0.05
(Optical photometry is calibrated against USNO-B1.0 stars in the field, so
suffers from a large photometric calibration error. IR photometry is
calibrated against 2MASS stars.)
The afterglow remains visible in our optical imaging over all our epochs
of observation. Between 2.2 and 5.4 hours post burst, the afterglow decays
with a power-law of alpha ~ -0.6 (where afterglow flux is proportional
to t^alpha). From 27.8 to 100.8 hours post-burst, the afterglow appears
to have steepened its decay rate to alpha ~ -1.6. This agrees with the
behavior observed by Haislip et. al (GCNs 10219 & 10230).
mid-exposure
time (hours
post-burst) I mag
--------------------------------------------------------
2.2 16.61 +/- 0.02 [+/- 0.30, zp error]
3.8 16.90 +/- 0.02 [+/- 0.30, zp error]
5.4 17.18 +/- 0.03 [+/- 0.30, zp error]
27.8 19.28 +/- 0.03 [+/- 0.30, zp error]
30.6 19.34 +/- 0.03 [+/- 0.30, zp error]
51.7 21.10 +/- 0.12 [+/- 0.30, zp error]
100.8 21.38 +/- 0.07 [+/- 0.30, zp error]