{
  "bibcode": "2014GCN.16497....1S",
  "body": "L. P. Singer (Caltech), M. M. Kasliwal (Carnegie Observatories/Princeton),\nV. B. Bhalerao (IUCAA), S. B. Cenko (NASA/GSFC), Y. Cao (Caltech),\nG. Duggan (Caltech), D. A. Perley (Caltech), and J. Johansson\n(Stockholm University) report on behalf of the intermediate Palomar\nTransient Factory (iPTF) collaboration:\n\nFermi GBM reported trigger 425667201 at 2014-06-28 16:53:18.98 UT.\nStarting 2014-06-29 09:17:13 UT (JD 2456837.88696, 16.4 hours after\nthe trigger), we began our search for optical counterparts using the\nPalomar 48-inch Oschin telescope (P48). Based on the final Fermi GBM\nlocalization, we selected 10 fields covering an area of 76 deg^2,\nwith a 20% chance of containing the true location of the source.\n\nSifting through candidate transient sources using image subtraction\nand standard intermediate Palomar Transient Factory vetting\nprocedures, we detected several optical transients, of which we list\nfive below.\n\niPTF14deq, at r = 19.74 +/- 0.05 mag, at the coordinates:\n RA(J2000)  =  23h 49m 29.57s (357.373189 deg)\n Dec(J2000) = +30d 47' 50.4\"  (+30.797328 deg)\n\niPTF14det, at r = 17.62 +/- 0.01 mag, at the coordinates:\n RA(J2000)  =  23h 29m 53.05s (352.471034 deg)\n Dec(J2000) = +29d 12' 12.3\"  (+29.203413 deg)\n\niPTF14dev, at r = 19.13 +/- 0.03, at the coordinates:\n RA(J2000)  =  23h 44m 29.96s (356.124852 deg)\n Dec(J2000) = +27d 04' 26.2\"  (+27.073938 deg)\n\niPTF14dfc, at r = 20.58 +/- 0.09 mag, at the coordinates:\n RA(J2000)  =  23h 39m 53.79s (354.974131 deg)\n Dec(J2000) = +35d 23' 43.3\"  (+35.395371 deg)\n\niPTF14dfd, at r = 20.24 +/- 0.07 and rising, at the coordinates:\n RA(J2000)  =  23h 55m 11.06s (358.796090 deg)\n Dec(J2000) = +27d 05' 21.2\"  (+27.089213 deg)\n\nThe first four (iPTF14deq, iPTF14det, iPTF14dev, iPTF14dfc) showed no\nsignificant optical evolution over the course of an hour, nonetheless\nconsistent (within the uncertainty in our photometry) with a fading\nof ~0.08 mag per hour for a typical optical afterglow (assuming a\ndecay index alpha ~ -1). The last, iPTF14dfd, brightened by\n0.65 +/- 0.01 mag over the course of half an hour.\n\nThe first four had plausible nearby host galaxies in SDSS, but none\nhad known redshifts. However, the candidates listed above had host\ngalaxies with photometric redshifts that were compatible with the\nabsolute magnitudes of typical long GRB afterglows, M_B >~ -20 (see\nKann et al. 2011, http://dx.doi.org/10.1088/0004-637X/734/2/96).\n\nWe obtained spectra of these five candidates with the Low Resolution\nImaging Spectrometer (LRIS) mounted on the 10-m Keck I telescope. None\nof the spectra are consistent with an optical afterglow.\n\nWe interpret iPTF14deq as an SN II at z=0.083 due to a blue continuum\nand weak Ha emission lines with a low-velocity P-cygni profile.\n\nWe classify iPTF14det as an SN II-p at z=0.0197 due to broad Ha\nemission with a pronounced P-cygni profile.\n\niPTF14dev is a type Ia supernova at a redshift of z=0.0655 with a\nspectrum consistent with a phase of about 6 days before maximum light.\n\niPTF14dfc is a type I (probably, type Ia or Ic) supernova. Based on fitting the\nSN features with SNID (Stephane & Tonry 2007, http://dx.doi.org/10.1086/520494),\nwe tentatively suggest a redshift of z=0.25.\n\nIn iPTF14dfd, we find double-peaked Ha emission lines and He II 4686 at a\nredshift of z=0, superimposed on a blue continuum. Combined with its rapid\nbrightening and lack of an associated galaxy, it is likely a CV outburst.\n\nThe diagram http://www.its.caltech.edu/~lsinger/iptf/Fermi425667201.pdf\nshows the locations of the optical transients and the 10 P48 fields\nin relation to the Fermi GBM 1- and 2-sigma statistical+systematic\ncontours.\n\nWe thank the Fermi-GBM team for promptly sharing their detailed\nlocalizations with us.",
  "circularId": 16497,
  "createdOn": 1404150325000,
  "email": "lsinger@caltech.edu",
  "subject": "Fermi 425667201: optical counterpart search",
  "submitter": "Leo Singer at CIT/PTF  <lsinger@caltech.edu>"
}