[vsnet-grb-info 17022] GRB 150911A: WHT optical imaging

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18303
SUBJECT: GRB 150911A: WHT optical imaging
DATE:    15/09/13 20:49:33 GMT
FROM:    Nial Tanvir at U.Leicester  <nrt3 at star.le.ac.uk>

N. R. Tanvir, K. Wiersema (U. Leicester), A. J. Levan (U. Warwick),
F. Riddick (ING), C. Bergfors (UCL) report on behalf of a larger collaboration:

We observed the position of GRB 150911A (Starling et al. GCN 18280), using the ACAM instrument on the 4.2m William Herschel Telescope (La Palma, Spain).  We acquired imaging in Sloan r, i and z bands, with midpoint 03:46 UT on 12 September 2015 (i.e. 8.9 hours after burst). Data consist of 4x300 seconds exposure time in each filter. No sources are detected within the XRT enhanced position error circle (Goad et al. GCN 18283). Just outside the XRT error circle are two faint sources, detected in all filters:

Source 1  at  RA, Dec = 04:29:44.279, +5:44:08.52
Source 2 at   RA, Dec = 04:29:44.120, +5:44:04.34

We note that source 1 is slightly extended and provisional photometric calibration gives magnitude r=24.1.  Source 2 appears point-like with magnitude r=25.2.

A second epoch observation would be required to ascertain which if any of these sources is associated with the GRB.