[vsnet-grb-info 15972] GRB 141230A: iPTF Optical Observations and Candidate Afterglow iPTF14jko

[GCN Circulars]

TITLE:   GCN CIRCULAR
NUMBER:  17254
SUBJECT: GRB 141230A: iPTF Optical Observations and Candidate Afterglow iPTF14jko
DATE:    14/12/30 08:28:03 GMT
FROM:    Leo Singer at CIT/PTF  <lsinger at caltech.edu>

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

Fermi GBM detected GRB 141230A (Fermi trigger 441602665 / bn141230142) at
2014-12-30 03:24:22.64. We searched for optical counterparts using the
Palomar 48-inch Oschin telescope (P48), imaging 20 fields spanning an area
of 147 deg2, covering about half of the 1-sigma statistical+systematic
region of the final Fermi GBM localization and part of the 2-sigma region.
Based on the GBM localization, we estimate a 43% 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 detect the optical transient
iPTF14jko, at the coordinates:
  RA(J2000)  =  4h 08m 41.48s (62.172836 deg)
  Dec(J2000) = -6d 40' 36.0"  (-6.676663 deg)
No source is detectable at this location in SDSS images. The last iPTF
survey visit was on September 16. We report the following P48 photometry:
  -104.7 day:   R > 20.12
  +54.80 min:   R = 19.91 +/- 0.11
  +129.9 min:   R = 19.75 +/- 0.14
The source does not appear to be fading at this time. Times are relative
to the GBM trigger. Magnitudes are in the Mould R filter and in the AB
system, calibrated with respect to point sources in SDSS as described in
Ofek et al. (2012, http://dx.doi.org/10.1086/664065).

We also detect the optical transient iPTF14jkn, at the coordinates:
  RA(J2000)  =  3h 55m 02.59s (58.760779 deg)
  Dec(J2000) = -6d 44' 04.2"  (-6.734503 deg)
We note that this position is near the bright (r = 13.59 mag) star,
SDSS J035501.84-064404.9. We report our P48 photometry:
  -104.7 day:   R > 20.34
  +98.02 min:   R = 19.60 +/- 0.10
Poor seeing conditions may call into question the veracity of this optical
transient and the accuracy of its photometry.

We have submitted a Swift TOO for iPTF14jko. Further observations are
encouraged to determine the nature of the source.

The diagram http://www.its.caltech.edu/~lsinger/iptf/Fermi441602665.pdf
shows our P48 fields and the location of the optical transient candidates
in relation to the Fermi GBM 1- and 2-sigma statistical+systematic
contours.