TITLE: GCN CIRCULAR NUMBER: 17079 SUBJECT: GRB 141118A: iPTF Optical Observations DATE: 14/11/21 07:37:46 GMT FROM: Leo Singer at CIT/PTF L. P. Singer (Caltech), M. M. Kasliwal (Carnegie Observatories/Princeton), V. B. Bhalerao (IUCAA), and S. B. Cenko (NASA/GSFC) report on behalf of the intermediate Palomar Transient Factory (iPTF) collaboration: We searched for optical counterparts of GRB 141118A (GCN 17073, Hurley et al.; GCN 17074, Golenetskii et al.) using the Palomar 48-inch Oschin telescope (P48). At about 18 hours after the burst, we began imaging 20 fields spanning an area of 145 deg2, covering most of the 1-sigma statistical+systematic region of the final Fermi GBM localization (Fermi trigger 438020153 / 141118678). Based on the GBM localization, we estimate a 77% chance that these fields contain the true location of the source. Coincidentally, we estimate the same containment probability based on the IPN error box. Sifting through candidate variable sources using image subtraction and standard iPTF vetting procedures, we detect the optical transient iPTF14hvs, at the coordinates: RA(J2000) = 10h 26m 05.29s (156.522055 deg) Dec(J2000) = +18d 34' 08.6" (+18.569044 deg) This position is just inside the error box. It is also in the outskirts of the galaxy SDSS J102605.09+183411.6, which has a photoZ of ~0.1. In host- subtracted P48 photometry, we find marginal evidence that the source faded: +18.41 hours: R = 19.92 +/- 0.14 +19.06 hours: R = 20.03 +/- 0.08 Times are relative to the GBM trigger. Magnitudes are in the Mould R filter and in the AB system, calibrated with respect to point sources in SDSS as described in Ofek et al. (2012, http://dx.doi.org/10.1086/664065). We obtained a series of spectra of iPTF14hvs with the Gemini Multi-Object Spectrograph mounted on the 8 m Gemini North telescope beginning at 15:21 UT on 2014 Nov 11. The spectra cover the wavelength range of 3900-9200 A. Cross-correlation with a library of supernova spectra using the ``Supernova Identification'' code (SNID; Blondin and Tonry 2007, ApJ 666, 1024) indicates the source is a type Ia supernova several weeks past maximum light at z ~ 0.11. Spatially offset from the transient location we identify narrow emission lines of H-alpha, [N II], and [S II] at a common redshift of z = 0.108. We conclude that iPTF14hvs is not related to the GRB. The diagram http://www.its.caltech.edu/~lsinger/iptf/Fermi438020153.pdf shows our P48 fields and the location of the optical transient in relation to the Fermi GBM 1- and 2-sigma statistical+systematic contours and the IPN annulus. We thank the IPN team for promptly sharing their analysis.