GCN Circular 15971

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

We have searched for optical counterparts of Fermi GBM trigger 416242156
(2014-03-11 14:49:13.10) using the Palomar 48-inch Oschin telescope (P48).
We observed 10 fields, covering 73.0 deg2 and most of the Fermi GBM
1-sigma contour. We estimate a 54% chance that our fields contain the
location of the source. Sifting through candidate variable sources using
image subtraction and standard iPTF vetting procedures including
photometry with the robotic Palomar 60" telescope (P60), we detect the
candidate optical transient iPTF14aak, the coordinates:

  RA(J2000)  =  11h 33m 14.47s (173.310295 deg)
  Dec(J2000) = +62d 05' 10.7"  (+62.086313 deg)

In our P48 image taken dt=0.51 days after the Fermi trigger, we measure
r = 19.7 +/- 0.1 mag. In our P60 image taken dt=0.82 days after the
trigger, we find a limit of r > 20.10 mag.

Given a bright star about 1.3' to the west, it is possible that the P48
detection is a ghost. If not, then the P60 non-detection is evidence of
fading with a power law of at least alpha~0.8.

We have submitted a Swift target of opportunity to search for an X-ray
counterpart of iPTF14aak. Further observations are encouraged to confirm
the nature of the source, and determine if it is associated with the Fermi
trigger.

The diagram http://www.its.caltech.edu/~lsinger/iptf/Fermi416242156.pdf
shows the ten P48 fields and the position of iPTF14aak in relation to the
Fermi GBM 1- and 2-sigma statistical+systematic contours.