[vsnet-grb-info 19293] GRB 170405A: NOT optical observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  20988
SUBJECT: GRB 170405A: NOT optical observations
DATE:    17/04/06 01:22:36 GMT
FROM:    Daniele Malesani at Dark Cosmology Centre, Niels Bohr Inst  <malesani at dark-cosmology.dk>

Daniele Malesani (DARK/NBI), K. E. Heintz (DARK/NBI and Univ. Iceland), 
and Tapio Pursimo (NOT) report on behalf of a larger collaboration:

We observed the optical afterglow of GRB 170405A (Troja et al., GCN 
20984; Hui & Meegan, GCN 20986; Vianello & Kocevski, GCN 20987) with the 
Nordic Optical Telescope (NOT) equipped with the ALFOSC imager. 
Observations were carried out in the SDSS griz filters, with a 
sub-optimal PSF (1.6-2.0").

Inspection of the r-band image (with mean time Apr 6.01 UT, that is 5.47 
hr after the trigger) clearly shows the optical afterglow first 
localized by UVOT (Troja et al., GCN 20984), which has now faded to r = 
21.05 +- 0.08 AB, calibrated against nearby stars from the Pan-STARRS 
catalog. In our images, the afterglow coordinates are perfectly 
consistent with the UVOT values:

RA(J2000) = 14:39:18.72
Dec(J2000) = -25:14:35.3

We also note the presence of a nearby object approximately 2.3" W of the 
afterglow, also visible in the Pan-STARRS archival images (with a 
Pan-STARRS magnitude r = 21.82 +- 0.19 AB). Its relation to the GRB is 
not clear, but its proximity may affect the afterglow photometry.