TITLE:   GCN CIRCULAR
NUMBER:  12367
SUBJECT: GRB 110918A: Afterglow Confirmation from PTF
DATE:    11/09/20 15:08:34 GMT
FROM:    S. Bradley Cenko at Caltech  <cenko@srl.caltech.edu>

S. B. Cenko (UC Berkeley), N. R. Tanvir (Leicester), E. O. Ofek (Caltech /
Weizmann Institute), K. Wiersema (Leicester), A. J. Levan (Warwick), and
P. E. Nugent (LBNL):

As part of the Palomar Transient Factory (PTF), we have imaged the
location of the afterglow candidate (GCN 12364, GCN 12365) of the IPN GRB
110918A (GCN 12357) with the robotic Palomar 48 inch telescope.  Images
began at 8:49 UT (dt ~ 35.4 hours after the burst trigger time) in the PTF
R-band.

Comparing our images with those obtained by the INT approximately six
hours earlier (GCN 12365), we find the optical candidate has faded by 0.45
+/- 0.13 mag.  The observed variability thus confirms that this object is
the afterglow of GRB 110918A.  Though with large uncertainties, the
inferred power-law decay slope (alpha ~ 2.1) is quite steep for this
period after the trigger.