TITLE: GCN CIRCULAR NUMBER: 16497 SUBJECT: Fermi 425667201: optical counterpart search DATE: 14/06/30 17:45:25 GMT FROM: Leo Singer at CIT/PTF L. P. Singer (Caltech), M. M. Kasliwal (Carnegie Observatories/Princeton), V. B. Bhalerao (IUCAA), S. B. Cenko (NASA/GSFC), Y. Cao (Caltech), G. Duggan (Caltech), D. A. Perley (Caltech), and J. Johansson (Stockholm University) report on behalf of the intermediate Palomar Transient Factory (iPTF) collaboration: Fermi GBM reported trigger 425667201 at 2014-06-28 16:53:18.98 UT. Starting 2014-06-29 09:17:13 UT (JD 2456837.88696, 16.4 hours after the trigger), we began our search for optical counterparts using the Palomar 48-inch Oschin telescope (P48). Based on the final Fermi GBM localization, we selected 10 fields covering an area of 76 deg^2, with a 20% chance of containing the true location of the source. Sifting through candidate transient sources using image subtraction and standard intermediate Palomar Transient Factory vetting procedures, we detected several optical transients, of which we list five below. iPTF14deq, at r = 19.74 +/- 0.05 mag, at the coordinates: RA(J2000) = 23h 49m 29.57s (357.373189 deg) Dec(J2000) = +30d 47' 50.4" (+30.797328 deg) iPTF14det, at r = 17.62 +/- 0.01 mag, at the coordinates: RA(J2000) = 23h 29m 53.05s (352.471034 deg) Dec(J2000) = +29d 12' 12.3" (+29.203413 deg) iPTF14dev, at r = 19.13 +/- 0.03, at the coordinates: RA(J2000) = 23h 44m 29.96s (356.124852 deg) Dec(J2000) = +27d 04' 26.2" (+27.073938 deg) iPTF14dfc, at r = 20.58 +/- 0.09 mag, at the coordinates: RA(J2000) = 23h 39m 53.79s (354.974131 deg) Dec(J2000) = +35d 23' 43.3" (+35.395371 deg) iPTF14dfd, at r = 20.24 +/- 0.07 and rising, at the coordinates: RA(J2000) = 23h 55m 11.06s (358.796090 deg) Dec(J2000) = +27d 05' 21.2" (+27.089213 deg) The first four (iPTF14deq, iPTF14det, iPTF14dev, iPTF14dfc) showed no significant optical evolution over the course of an hour, nonetheless consistent (within the uncertainty in our photometry) with a fading of ~0.08 mag per hour for a typical optical afterglow (assuming a decay index alpha ~ -1). The last, iPTF14dfd, brightened by 0.65 +/- 0.01 mag over the course of half an hour. The first four had plausible nearby host galaxies in SDSS, but none had known redshifts. However, the candidates listed above had host galaxies with photometric redshifts that were compatible with the absolute magnitudes of typical long GRB afterglows, M_B >~ -20 (see Kann et al. 2011, http://dx.doi.org/10.1088/0004-637X/734/2/96). We obtained spectra of these five candidates with the Low Resolution Imaging Spectrometer (LRIS) mounted on the 10-m Keck I telescope. None of the spectra are consistent with an optical afterglow. We interpret iPTF14deq as an SN II at z=0.083 due to a blue continuum and weak Ha emission lines with a low-velocity P-cygni profile. We classify iPTF14det as an SN II-p at z=0.0197 due to broad Ha emission with a pronounced P-cygni profile. iPTF14dev is a type Ia supernova at a redshift of z=0.0655 with a spectrum consistent with a phase of about 6 days before maximum light. iPTF14dfc is a type I (probably, type Ia or Ic) supernova. Based on fitting the SN features with SNID (Stephane & Tonry 2007, http://dx.doi.org/10.1086/520494), we tentatively suggest a redshift of z=0.25. In iPTF14dfd, we find double-peaked Ha emission lines and He II 4686 at a redshift of z=0, superimposed on a blue continuum. Combined with its rapid brightening and lack of an associated galaxy, it is likely a CV outburst. The diagram http://www.its.caltech.edu/~lsinger/iptf/Fermi425667201.pdf shows the locations of the optical transients and the 10 P48 fields in relation to the Fermi GBM 1- and 2-sigma statistical+systematic contours. We thank the Fermi-GBM team for promptly sharing their detailed localizations with us.