[vsnet-grb-info 17152] GRB 151027B: NOT optical afterglow candidate

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  18501
SUBJECT: GRB 151027B: NOT optical afterglow candidate
DATE:    15/10/28 00:19:30 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani at dark-cosmology.dk>

Daniele Malesani (DARK/NBI), Nial R. Tanvir (Univ. Leicester), Dong Xu 
(NAOC/CAS), Jussi Harmanen (NOT and Univ. Turku), Thomas Reynolds (NOT 
and Turku Univ.), and Pere Blay Serrano (IAC/NOT), report on behalf of a 
larger collaboration:

We observed the field of the #1000 Swift GRB 151027B (Ukwatta et al., 
GCN 18499) with the Nordic Optical Telescope equipped with the StanCam 
imager. Observations started on 2015 Oct 27.988 UT (1.04 hr after the 
GRB trigger), as soon as the field was observable from La Palma.

In our first 5-minute image taken in the R band, we detect a single 
source consistent with the XRT position (Ukwatta et al., GCN 18499), at 
coordinates (J2000):

RA = 05:04:52.69
Dec = -06:27:00.8

with an uncertainty of 0.5".

Calibrating the image against nearby USNO stars, we measure for this 
object R = 18.44 +- 0.05 (Vega). While we have not yet any variability 
information, the positional consistency with the XRT error circle and 
the lack of any object in the DSS at this location suggest that this is 
the optical afterglow of GRB 151027B.