TITLE: GCN CIRCULAR NUMBER: 18995 SUBJECT: GRB 160206B: iPTF P48 Observations and Optical Transient Candidates DATE: 16/02/06 18:02:12 GMT FROM: Leo Singer at GSFC/iPTF L. P. Singer (NASA/GSFC), S. B. Cenko (NASA/GSFC), M. M. Kasliwal (Caltech), and V. Bhalerao (IUCAA) report on behalf of a larger collaboration: Fermi GBM detected GRB 160206B (trigger 476446756 / bn160206430) at 2016-02-06 10:19:12.43. At 10:29:40, about 10 minutes after the burst, we began searching for optical counterparts using the Palomar 48-inch Oschin telescope (P48). We imaged 114 fields covering an area of 379 deg^2 and covering most of the 2-sigma statistical+systematic region of the final Fermi GBM localization. We estimate a 84% prior probability that these fields contain the true location of the source. Sifting through candidate variable sources using image subtraction and standard iPTF vetting procedures, we detected the following optical transient candidates: name RA Dec mag t Notes ---------------------------------------------------------------------------- Hosts with spectroscopic redshifts ---------------------------------------------------------------------------- iPTF16ca 181.162415 +45.059301 19.97 +2.39 z=0.190, host is an X-ray source iPTF16ce 188.768138 +47.301857 20.27 +2.81 z=0.131 iPTF16ch 189.333005 +51.432720 20.70 +1.82 z=0.120 iPTF16cc 187.973175 +45.076476 19.12 +2.73 z=0.062, poor subtraction in interacting host galaxy iPTF16cl 170.605169 +59.384422 20.12 +1.79 z=0.051 iPTF16cd 187.947490 +47.927964 19.48 +1.39 z=0.030 ---------------------------------------------------------------------------- Hosts with photometric redshifts ---------------------------------------------------------------------------- iPTF16cg 175.872772 +50.316844 19.65 +2.30 z=0.31 iPTF16ci 180.780807 +53.977868 19.49 +1.73 z=0.27 iPTF16ck 193.756732 +57.354180 20.42 +2.93 z=0.19 iPTF16cf 197.002541 +48.632699 20.05 +2.08 z=0.13 iPTF16bx 116.788070 +22.170396 19.20 -1.32 z=0.09 Times are in hours since 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). Further observations of the above candidates are encouraged to determine their nature and if one of them is the optical afterglow of the GRB. We have scheduled additional imaging of the P48 fields tonight. The diagram http://asd.gsfc.nasa.gov/Brad.Cenko/Fermi476446756.pdf shows the locations of our candidates and the P48 fields in relation to the Fermi GBM 1-, 2-, and 3-sigma statistical+systematic contours.