TITLE: GCN CIRCULAR NUMBER: 16092 SUBJECT: Fermi418277210: iPTF optical observations DATE: 14/04/10 02:32:55 GMT FROM: Leo Singer at CIT/PTF L. P. Singer (Caltech), S. B. Cenko (NASA/GSFC), M. M. Kasliwal (Carnegie Observatories/Princeton), Adam Waszczak (Caltech), Sagi Ben-Ami (Weizmann), Joel Johansson (Stockholm University), and Avishay Gal-Yam (Weizmann) report on behalf of the intermediate Palomar Transient Factory (iPTF) collaboration: We have searched for optical counterparts of Fermi GBM trigger Fermi418277210 (2014-04-04 04:06:47.51) using the Palomar 48-inch Oschin telescope (P48). Based on the last automated Fermi ground software localization sent at 04:07:29, we began observing 10 fields covering 73 deg2, 12 minutes after the trigger. Since the final Fermi localization sent at 05:16:07 differed by 3 deg (well within the 1-sigma statistical-only uncertainty), we observed five more fields for a total area of 109 deg2. We estimate a 68% chance that one of these 15 fields contains 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 detected several optical transients, none of which showed evidence of significant fading. For the following sources, we obtained spectra with the Double Spectrograph (DBSP) on the Palomar 200" Hale telescope (P200): 14ain, detected at r = 18.67 +/- 0.03 mag and possibly rising, coincident with galaxy SDSS J111725.00+293457.4, identified as SN Ia, at z = 0.08, also reported by MASTER (Rufanov et al. 2014, ATel 6055), at the coordinates: RA(J2000) = 11h 17m 25.04s (169.354352 deg) Dec(J2000) = +29d 34' 58.3" (+29.582861 deg) 14ait, detected at r = 20.5 +/- 0.1 mag, on the outskirts of the galaxy SDSS J113303.95+330719.3, with the nebular spectrum of an old SN Ib/c at z = 0.039, at the coordinates: RA(J2000) = 11h 33m 04.04s (173.266841 deg) Dec(J2000) = +33d 07' 23.9" (+33.123292 deg) 14aiz, detected at r = 19.28 +/- 0.04 mag, coincident with the z=0.09701 galaxy SDSS J111407.50+390243.0, with an inconclusive spectrum showing only host light, at the coordinates: RA(J2000) = 11h 14m 07.28s (168.530319 deg) Dec(J2000) = +39d 02' 43.2" (+39.045337 deg) The following transient candidates were placed on the P200 queue, but not observed due to other higher-priority targets: 14aim, detected at r = 19.68 +/- 0.06 mag and coincident with the galaxy SDSS J114155.45+351813.9, at the coordinates: RA(J2000) = 11h 41m 55.57s (175.481562 deg) Dec(J2000) = +35d 18' 14.9" (+35.304133 deg) 14aip, detected at r = 19.40 +/- 0.05 mag and rising, clearly offset from the galaxy SDSS J111215.58+313056.2, at the coordinates: RA(J2000) = 11h 12m 16.02s (168.066732 deg) Dec(J2000) = +31d 30' 57.9" (+31.516089 deg) 14aiq, detected at r = 20.62 +/- 0.17 mag, coincident at the galaxy SDSS J111506.79+292025.1, at the coordinates: RA(J2000) = 11h 15m 06.89s (168.778719 deg) Dec(J2000) = +29d 20' 24.0" (+29.340007 deg) 14ais, detected at r = 20.33 +/- 0.08 mag, with no clearly associated host in SDSS, at the coordinates: RA(J2000) = 11h 51m 08.46s (177.785253 deg) Dec(J2000) = +31d 17' 03.2" (+31.284218 deg) 14aiu, detected at r = 20.20 +/- 0.14 mag and apparently hostless, at the coordinates: RA(J2000) = 11h 15m 09.30s (168.788748 deg) Dec(J2000) = +34d 26' 35.8" (+34.443280 deg) 14aiy, detected at r = 20.30 +/- 0.09 mag, coincident with the galaxy SDSS J114936.42+374417.3, at the coordinates: RA(J2000) = 11h 49m 36.47s (177.401968 deg) Dec(J2000) = +37d 44' 18.2" (+37.738379 deg) Due to the relative promptness of our first 10 observations, we were concerned that a bright (r <~ 14 mag) afterglow would have saturated on the P48 CCD and have been missed by our automated image subtraction pipeline. We therefore also visually inspected the 110 single-chip images from the first epoch of observations. We found no saturated objects that were absent from both the SDSS and the USNO-B1.0 catalogs. We also performed a semi-automated search over all of the P48 source extractions that contained saturated pixels. There were 6579 saturated objects, of which all were either present in the USNO-B1.0 catalog or clearly visible in archival SDSS images. The diagram http://www.its.caltech.edu/~lsinger/iptf/Fermi418277210.pdf shows the fifteen P48 fields (dark gray: the 10 prompt fields, light gray: the remaining 5) in relation to the Fermi GBM 1- and 2-sigma statistical+systematic contours.