[vsnet-grb-info 19603] GRB 170714A: z-band afterglow candidate for OSIRIS/GTC

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  21346
SUBJECT: GRB 170714A: z-band afterglow candidate for OSIRIS/GTC
DATE:    17/07/15 06:37:17 GMT
FROM:    Antonio de Ugarte Postigo at IAA-CSIC  <deugarte at iaa.es>

A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), D. A. Kann 
L. Izzo, C. C. Thoene (HETH/IAA-CSIC), N. Castro-Rodriguez 
(GTC, IAC, ULL), A. Marante, J. A. Melian (GTC) report:

We observed the field of GRB 170714A (D'Ai et al. GCN 21340), an 
ULGRB or RTDE candidate (Kann et al., GCN 21345) with OSIRIS at 
the 10.4m GTC telescope in La Palma (Spain). Observations consisted 
in several short exposures in i and z filters. The observations were not 
easy, as the field was located 30 deg away from the 68% illuminated 
Moon, implying a very high background.

In the combined z-band frame, with mean epoch at 05:10:24 UT (16.75 hr 
after the burst) we detect a single object within the refined XRT error box 
(Evans et al. GCN 21341) which is not present in PanSTARRS imaging, 
with coordinates (J2000):

R.A.: 02:17:23.99
Dec.: +01:59:29.51

and a magnitude of z(AB)=22.3+/-0.2, which we identify as the possible 
GRB afterglow, although we cannot make any statement about 
variability at this time. In our preliminary analysis we do not detect the 
object in any other band, implying a possible strong reddening.

Further follow up, especially in NIR bands is encouraged.