{
  "bibcode": "2015GCN.17415....1S",
  "body": "L. P. Singer (NASA/GSFC), M. M. Kasliwal (Carnegie Observatories/Princeton),\nand S. B. Cenko (NASA/GSFC) report on behalf of the intermediate Palomar\nTransient Factory (iPTF) collaboration:\n\nFermi detected GRB 150206B (Fermi trigger 444908790 / bn150206407) at\n2015-02-06 09:46:27.48. At 2015-02-06 10:23:45, 37 minutes after the\nburst, we began searching for optical counterparts using the Palomar\n48-inch Oschin telescope (P48).\n\nWe imaged 20 fields covering an area of 144 deg^2 mostly inside the\n1-sigma statistical+systematic region of the final Fermi GBM localization.\nWe estimate a 51% prior probability that these fields contain the true\nlocation of the source. Sifting through candidate variable sources using\nimage subtraction and standard iPTF vetting procedures, we detected the\nfollowing optical transient candidates:\n\niPTF15gz, at the coordinates:\n  RA(J2000)  =  13h 47m 18.31s (206.826292 deg)\n  Dec(J2000) = +55d 38' 33.7\"  (+55.642694 deg)\nNo source is visible at this position in archival SDSS and iPTF images.\nThe following P48 photometry is suggestive of fading:\n  +116.7 min:   R = 20.25 +/- 0.13\n  +160.7 min:   R = 20.54 +/- 0.19\n\niPTF15hb, at the coordinates:\n  RA(J2000)  =  14h 07m 09.34s (211.788915 deg)\n  Dec(J2000) = +63d 02' 20.6\"  (+63.039047 deg)\nThis position is near the galaxy SDSS J140709.19+630218.3, with photoZ ~ 0.2\nsuggesting an absolute magnitude of M_R ~ -21, consistent with typical\noptical afterglows. We report the following photometry:\n  +98.20 min:   R = 18.94 +/- 0.05\n  +142.2 min:   R = 18.87 +/- 0.04\n  +186.3 min:   R = 19.00 +/- 0.04\n\niPTF15gv, at the coordinates:\n  RA(J2000)  =  14h 15m 28.31s (213.867960 deg)\n  Dec(J2000) = +58d 24' 47.8\"  (+58.413284 deg)\nThis coincides with the galaxy SDSS J141527.96+582447.9, with photoZ ~ 0.085,\nsuggesting M_R ~ -18. Although this is fainter than a typical optical\nafterglow, the source is rapidly fading:\n  +125.3 min:   19.89 +/- 0.07\n  +169.3 min:   20.33 +/- 0.11\nwhich fits a power law relative to the time of the burst, F_nu ~ t^-alpha,\nwith alpha = 1.3 +/- 0.4.\n\nTimes are relative to the GBM trigger. Magnitudes are in the Mould R\nfilter and in the AB system, calibrated with respect to point sources in\nSDSS as described in Ofek et al. (2012, http://dx.doi.org/10.1086/664065).\n\nThere were several other optical candidates in these fields; all of the\ncandidates listed below are coincident with galaxies of known redshift in\nSDSS, by which association we infer absolute magnitudes of M_R ~ -19,\ntypical of type Ia supernovae but not long GRB optical afterglows (see\nSection 2.4 of Singer et al. 2015, http://arxiv.org/abs/1501.00495, and\nreferences therein). These are:\n\niPTF15ha, at the coordinates:\n  RA(J2000)  =  14h 03m 11.73s (210.798855 deg)\n  Dec(J2000) = +64d 22' 19.3\"  (+64.372029 deg)\n\niPTF15gu, at the coordinates:\n  RA(J2000)  =  14h 29m 11.95s (217.299810 deg)\n  Dec(J2000) = +56d 59' 21.4\"  (+56.989264 deg)\n\niPTF15gy, at the coordinates:\n  RA(J2000)  =  14h 47m 18.26s (221.826083 deg)\n  Dec(J2000) = +54d 36' 30.6\"  (+54.608492 deg)\n\niPTF15gx, at the coordinates:\n  RA(J2000)  =  15h 03m 42.64s (225.927684 deg)\n  Dec(J2000) = +54d 48' 03.1\"  (+54.800849 deg)\n\nFurther observations of iPTF15gz, iPTF15hb, and iPTF15gv, are encouraged\nto determine if one of the three is associated with the GRB.\n\nThe diagram http://www.its.caltech.edu/~lsinger/iptf/Fermi444908790.pdf\nshows the locations of our candidates and the P48 fields in relation to\nthe Fermi GBM 1- and 2-sigma statistical+systematic contours.",
  "circularId": 17415,
  "createdOn": 1423256792000,
  "email": "leo.p.singer@nasa.gov",
  "subject": "GRB 150206B: iPTF Optical Observations",
  "submitter": "Leo Singer at GSFC/iPTF  <leo.p.singer@nasa.gov>",
  "eventId": "GRB 150206B"
}