[vsnet-grb-info 15495] GRB 140903A: Possible optical variability

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16784
SUBJECT: GRB 140903A: Possible optical variability
DATE:    14/09/05 14:49:26 GMT
FROM:    Andrew Levan at U.of Leicester  <A.J.Levan at warwick.ac.uk>

A.J. Levan (U. Warwick), S.B. Cenko, A. Cucchiara (NASA-GSFC), D.A. Perley (Caltech) report for a larger collaboration: 

"We observed the location of the short GRB 140903A (Cummings et al. GCN 16763, 16765) with Gemini-N beginning at 5 Sep 2014, 05:16 UT. At this epoch we obtained observations in iJ and K utilising GMOS-N and NIRI. The source reported by Capone et al. (GCN 16769) and Cenko et al. (GCN 1677) is well detected in all bands. 

A comparison between these images and the acquisition images taken on 4 Sept 2014 (Cucchiaria et al. GCN 16774) is indicative of a fading by 0.12 +/- 0.04 mag. An image subtraction shows a residual consistent with this fading, although both photometry and image subtraction are complicated by the presence of the nearby bright star.

This decay is very slow in comparison to most GRB afterglows and implies a significant contribution from the underlying host galaxy, consistent with its pre-trigger detection (Fruchter GCN 16776, Xu et al. GCN 16783). We note that the source remains largely point like in our observation, and the centroid of the subtraction residual is offset only ~0.1" from the centre of the combined host+afterglow source."