[vsnet-grb-info 15533] GRB 140916B: iPTF Optical Observations

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  16822
SUBJECT: GRB 140916B: iPTF Optical Observations
DATE:    14/09/16 18:28:07 GMT
FROM:    Leo Singer at CIT/PTF  <lsinger at caltech.edu>

L. P. Singer (Caltech), V. Bhalerao (IUCAA), M. M. Kasliwal (Carnegie
Observatories/Princeton), and S. B. Cenko (NASA/GSFC) report on behalf of
the intermediate Palomar Transient Factory (iPTF) collaboration:

Fermi detected GRB 140916B (Fermi trigger 432538612 / bn140916234) at
2014-09-16 05:36:49.80. At 09:28:17, 3.86 hours after the burst, we began
searching for optical counterparts using the Palomar 48-inch Oschin
telescope (P48).

We imaged 20 fields covering an area of 146 deg^2 inside the 1-sigma
statistical+systematic region of the final Fermi GBM localization. We
estimate a 53% prior probability that these fields contain the true
location of the source. Sifting through candidate variable sources using
image subtraction and standard iPTF vetting procedures, we detected the
following optical transient candidates.

iPTF14fok is located near a galaxy with unknown redshift, at the
coordinates:
 RA(J2000)  =  3h 43m 14.11s (55.808775 deg)
 Dec(J2000) = -8d 17' 33.5"  (-8.292649 deg)
At R = 19.57 +/- 0.07 mag, the lightcurve from 4.17 to 5.85 hours after
the burst is consistent with no evolution or with a decline by ~0.1 mag.

iPTF14fow is located near the nuclear region of a galaxy with unknown
redshift, at the coordinates:
 RA(J2000)  =  4h 24m 54.71s (66.227963 deg)
 Dec(J2000) = -6d 47' 09.7"  (-6.786030 deg)
At R = 20.14 +/- 0.14 mag, the source shows no clear photometric evolution.

Further observations are encouraged to determine the nature of these
sources.

The diagram http://www.its.caltech.edu/~lsinger/iptf/Fermi432538612.pdf
shows the locations of our candidates and the P48 fields in relation to
the Fermi GBM 1- and 2-sigma statistical+systematic contours.