GCN Circular 20014

A. de Ugarte Postigo (IAA-CSIC), D. A. Kann (TLS Tautenburg), 
L. Izzo, C. C. Thoene (both IAA-CSIC), N. Castro-Rodriguez, and 
G. Gomez Velarde (GRANTECAN/IAC/Universidad de La Laguna) 
report:

We observed the field of GRB 161007A (Swift 716127, D'Elia et al., 
GCN #20008), with the 10.4m GTC on La Palma, Canary Islands, 
Spain. We obtained four 30 sec images in the Sloan i' band at an 
airmass of 1.8. The midtime of our observations was 0.2228 days 
after the GRB trigger.

At the UVOT-enhanced Swift XRT position (Goad et al., GCN #20013), 
we detect a source at the edge of the error circle, at:

RA (J2000) =     06:53:38.10
Dec. (J2000) = +23:18:24.6

For this source, we measure:

i��� (Vega) = 22.23 +/- 0.15 

The photometric calibration was done by comparing to USNOB-1.0 
stars in the I-band filter, therefore this is only a preliminary value.
 
No statement can be made about fading. We note that the X-ray 
spectrum of this GRB's afterglows shows evidence for excess 
absorption, therefore this may be a dark GRB, with this source being 
its host galaxy. The source looks extended in our image, which has a 
seeing of 1.2".