TITLE:   GCN CIRCULAR
NUMBER:  17700
SUBJECT: GRB150413A, optical observations                                                
DATE:    15/04/14 13:57:16 GMT
FROM:    Kosmas Gazeas at U of Athens  <kgaze@phys.uoa.gr>

Kosmas Gazeas and Konstantinos Sapountzis (National Univ. of Athens) report:

On 13 April 2015, we observed the GRB candidate optical counterpart
GRB150413A, as reported by Markwardt et al., GCN 17688 and Serino et al., GCN
17691. The observations have been obtained with the 0.40 m f/8 robotic
telescope at the University of Athens in R-band (Bessell specifications). Data
collection has started on Apr., 13 (UT) 17:38:58 and finishing on Apr. 13 (UT)
18:08:08 (mid-exposure time). A sum of 15 exposures of 120 sec each was
collected and all data were combined into a single image, although the optical
afterglow was barley seen in each individual exposure. Photometry with a 3
pixel (approximately 4 arcsec) radius aperture yields an R magnitude
estimation of R = 17.9 +- 0.3 mag for GRB150413A, as compared with respect to
the nearby USNO-B1.0 stars, which lie within a radius of 3-4 arcminutes around
the source. No absolute photometric calibration has been applied on these data.

This message is quotable in publications.