TITLE: GCN CIRCULAR NUMBER: 15524 SUBJECT: Fermi407254341: iPTF optical afterglow candidates DATE: 13/11/28 07:49:40 GMT FROM: Leo Singer at CIT/PTF L. P. Singer (Caltech) and M. M. Kasliwal (Carnegie Observatories/Princeton) report on behalf of the intermediate Palomar Transient Factory (iPTF) collaboration: We imaged about 60 deg^2 in the vicinity of the localization of the Fermi-GBM trigger Fermi407254341 with the Palomar 48-inch Oschin telescope (P48), starting at 2013-11-28 03:40 UT (13.5 hours after the Fermi trigger). Sifting through 17,353 candidate variable sources in the GBM error circle using standard iPTF vetting procedures, we find the following optical afterglow candidates: iPTF13ecv, possibly fading, at R=18.6mag and with no coincident source visible in SDSS or in our reference images, at the coordinates: RA(J2000) = 20h 31m 47.76s Dec(J2000) = +00d 59' 23.4" iPTF13ect, at R=17.9 and near the core of a z=0.025 galaxy, at the coordinates: RA(J2000) = 20h 46m 44.63s Dec(J2000) = -01d 22' 07.8" iPTF13ecu, at R=19.1 and near the core of a z=0.030 galaxy, at the coordinates: RA(J2000) = 20h 40m 11.04s Dec(J2000) = -01d 37' 09.2" A diagram of the locations of these candidates and the nine P48 fields that we imaged in relation to the Fermi-GBM statistical+systematic error contours can be found at . We have submitted a Swift ToO request to follow up iPTF13ecv. We caution that many transient or variable sources are found in any such wide-area targeted search, and that at this burst's galactic latitude of -20 deg many foreground sources are likely. Further observations are encouraged to determine the nature of these sources, and whether one of them is related to the Fermi trigger.