TITLE:   GCN CIRCULAR
NUMBER:  15305
SUBJECT: GRB 131004A: TNG optical afterglow confirmation
DATE:    13/10/04 23:38:34 GMT
FROM:    Paolo D'Avanzo at INAF-OAB  <paolo.davanzo@brera.inaf.it>

D. Malesani (DARK/NBI), P. D'Avanzo (INAF-OAB), L. di Fabrizio, G.
Tessicini (INAF-TNG) report on behalf of the CIBO collaboration:

We observed the field of the possible short GRB 131004A (Hagen et al. GCN
15303) with the Italian 3.6m TNG telescope located in Canary Islands,
equipped with the DOLoRes imager.

The optical candidate reported by Xu et al (GCN 15304) is clearly seen in
a 60 s R-band image taken at a mid t-t0=1.1 hours. From a preliminary
photometry we estimate for this source a magnitude of
R = 20.8 +/- 0.1 (calibrated against the USNOB1 catalogue).

Given the evidence of fading with respect to the report of Xu et al. (GCN
15304) we confirm this source as the optical afterglow of GRB 131004A. The
inferred power-law decay index is
alpha=0.59 +/- 0.15.


We acknowledge the TNG visitor astronomer X. Dumesque for support.