[vsnet-grb-info 19901] GRB 171010A: optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21988
SUBJECT: GRB 171010A: optical observations
DATE:    17/10/11 13:45:16 GMT
FROM:    Luca Izzo at IAA-CSIC  <Luca.Izzo at ICRA.it>

L. Izzo (IAA-CSIC) and D. Malesani (DARK/NBI) report:

We observed the field of the Fermi LAT GRB 171010A (Omodei et al., GCN 21985) with the T24 (Plane Wave CDK 0.61m) of the iTelescope.Net <http://itelescope.net/> (http://www.itelescope.net <http://www.itelescope.net/>) located at Auberry (CA, USA).

A set of three images of 300 s each was taken in the I filter, starting on October 11th at 09:55:32 UT, ~14.9 hr after the LAT GRB trigger. In particular, we inspected the position of the X-ray candidate found by XRT (Evans, GCN 21986), reported at http://www.swift.ac.uk/ToO_GRBs/00020778 <http://www.swift.ac.uk/ToO_GRBs/00020778> . Inside the UVOT-enhanced XRT position, we detect a source at coordinates (J2000):

RA = 04:26:19.46
DEC = -10:27:45.9

This position is 1.3" W of an object with i = 20.31 +- 0.05 (AB) visible in the Pan-STARRS archival images. We measure for the source I = 17.85 +- 0.20 mag (AB)

The difference in brightness with respect to the archival Pan-STARRS source, as well as the association with the XRT counterpart, suggests the presence of an additional source which we believe to be due to the GRB afterglow. The Pan-STARRS object could be the host galaxy of the GRB, as also suggested in Thorstensen et al. (GCN 21987), or an unrelated source.

Additional observations are very welcome.