[vsnet-grb-info 21140] GRB 180914B: Optical counterpart observation from OAJ

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  23239
SUBJECT: GRB 180914B: Optical counterpart observation from OAJ
DATE:    18/09/16 08:58:16 GMT
FROM:    Antonio de Ugarte Postigo at IAA-CSIC  <deugarte at iaa.es>

A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), L. Izzo (HETH/IAA-CSIC), 
D.A. Kann (HETH/IAA-CSIC), C.C. Thoene (HETH/IAA-CSIC), H. Vazquez 
Ramio (CEFCA), N. Maicas (CEFCA) and V. Tilve (CEFCA) report:

We have observed the field of GRB 180914B (Ursi et al., GCN 23226; 
Verrecchia et al., GCN 23231; Bissaldi et al. GCN 23232; D’Ai et al., GCN 23236) 
with the 0.8m T80 telescope of the Javalambre Astrophysical Observatory 
(Teruel, Spain). The observation consisted of 12x300s i-band exposures, each 
covering the complete LAT error box. The exposures started at 22:03:46 UT of 
the 15th September, 27.68 hr after the burst. The counterpart identified by Zheng 
& Filippenko (GCN 23237) and Troja et al. (GCN 23238) is well detected in the 
individual images. Photometry of the first epoch, as compared with SDSS 
reference stars yields i(AB)=18.84+/-0.03.

Comparing with the RATIR photometry (roja et al. GCN 23238), our photometry 
implies a decay rate of alpha ~ -1.9 (where F_nu ~ t^alpha), indicating that the 
afterglow has possibly entered a post-jet-break regime evolution.