[vsnet-grb-info 6435] GRB 080727B: IR photometry

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  8049
SUBJECT: GRB 080727B: IR photometry
DATE:    08/07/29 15:15:00 GMT
FROM:    Andrew Levan at U.of Leicester  <anl at star.le.ac.uk>

A.J. Levan (U. Warwick) and K. Wiersema (U. Leicester) report for
a larger collaboration:

We observed the location of GRB 080727B (Immler et al. GCN 8022)
using UKIRT. The automatic observations begin at 08:27:13 UT, roughly
800 seconds after the burst. An initial set of K-band observations
were acquired, followed by a shallower JHK sequence. At the location
of the X-ray (Goad et al. GCN 8026) and optical/IR afterglows
(D'Avanzo et al. GCN 8023; Li et al. GCN 8024) we clearly identify
the fading afterglow of GRB080727B in all filters. The photometry,
calibrated against several 2MASS stars within the field of view is
shown below:

===========================================
T_s T_s-T_b     Band    Mag     err
===========================================
08:27:13 0.00959        K       13.952 0.03
08:31:38 0.01266        K       14.243 0.03
08:36:03 0.01573        K       14.392 0.03
08:50:08 0.02551        K       14.952 0.05
09:00:10 0.03248        K       15.276 0.05
09:10:09 0.03940        K       15.549 0.05
===========================================
08:47:04 0.023389       H       16.144 0.06
08:58:06 0.031042       H       16.560 0.06
09:07:05 0.037280       H       16.775 0.08
==========================================
08:43:13 0.02071        J       17.855 0.10
08:53:15 0.02767        J       18.300 0.10
09:03:16 0.03463        J       18.626 0.11
===========================================
*Data have not been corrected for the significant foreground
extinciton

The K-band is suggestive of a break occurring at t_b ~ 1600s, with
pre- and post-break slopes of alpha_1 =0.84 and alpha_2 =1.26. The
initial slope is significantly shallower than that suggested by the
KAIT observations (Li et al GCN 8046), and implies either that the
afterglow decay flatenned after those observations, or that the
optical and IR were not tracking eachother in this case.

We thank the staff of UKIRT for their rapid response to these alerts.