{
  "bibcode": "2015GCN.18497....1S",
  "body": "L. P. Singer (NASA/GSFC), M. M. Kasliwal (Caltech), R. Ferretti\n(Stockholm), S. B. Cenko (NASA/GSFC), T. Barlow (Caltech), Y. Cao\nCaltech), R. Laher (IPAC), and J. Rana (IUCAA) report on behalf of the\nintermediate Palomar Transient Factory (iPTF) collaboration:\n\nWe have performed tiled observations of LIGO/Virgo G194575 using the\nPalomar 48-inch Oschin telescope (P48). The anti-sun probability island\nfrom the BAYESTAR localization was observable from Palomar for most of the\nnight and weather conditions were good. Starting at 2015-10-23 03:26 UTC,\nabout 14 hours after the GW trigger, we imaged 160 fields spanning 1114\ndeg2. We estimate a 17% prior probability that these fields contain the\ntrue location of the source.\n\nSifting through candidate variable sources using image subtraction by both\nour NERSC and IPAC pipelines, and applying standard iPTF vetting\nprocedures, we flagged the following optical transient candidates for\nfurther follow-up:\n\n   name       RA       Dec     time  mag \n--------- --------- --------- ----- -----\niPTF15dkm 354.32375  -3.53254 03:39 18.66\niPTF15dlc  16.14909  -2.54011 08:15 16.17\niPTF15dld  14.55532  -3.66397 08:15 18.50\niPTF15dlj  19.76198 +10.00134 09:22 18.14\niPTF15dln  14.58195  +7.23471 09:15 18.81\niPTF15dmk  21.22653  +0.61874 10:58 19.60\niPTF15dmn   7.23638 -11.40550 09:07 18.37\niPTF15dmq 353.87809  +6.45032 04:36 18.64\niPTF15dni  21.26675  -4.70845 10:23 17.72\niPTF15dkv   7.77118  -2.65228 07:08 18.84\niPTF15dkn 357.54623  +0.09660 05:34 19.17\niPTF15dkk 357.57171  -3.16660 05:38 19.43\niPTF15dnh  14.90946 -14.19912 10:01 19.45\niPTF15dlb  16.18149  +2.06164 08:25 19.21 = (PS15byt)\niPTF15dmv  21.02204 -10.50270 10:20 19.85\niPTF15dkt   7.20239  -2.70993 07:08 18.05 = (PS15coc)\niPTF15dmt  97.71723 +39.31086 13:01 19.17\niPTF15dmu  22.59586  -4.41018 10:25 19.35\niPTF15dms  98.41981 +37.30400 13:00 19.97\niPTF15dmp  16.28538  -9.74387 09:59 20.05\niPTF15dmf  15.40890  -3.94111 08:15 18.48\niPTF15dmb  18.31767  -6.51451 10:09 19.45\niPTF15dlz  22.25290  -4.36629 10:25 19.22\niPTF15dlv  20.54769  -2.00612 10:26 19.18\niPTF15dlu  22.85842  -8.89533 10:21 19.40\niPTF15dlr  18.56416  +3.32916 10:03 19.14 (= PS1-14aen)\niPTF15dlp  15.49983  +9.50920 09:14 19.11\niPTF15dlg   3.68611 -11.70795 09:05 19.10\niPTF15dla  14.73492  +1.74302 08:25 18.28\niPTF15dkj 359.67964  -7.68101 05:41 19.47\niPTF15dku   2.86523  -6.42730 07:11 17.74 (= LSQ15bjb, PS15cog)\niPTF15dmr   6.96306 -11.47793 09:05 18.82 (= PS15bww)\niPTF15dmj  21.09391  +3.58754 11:02 16.10 (= PS15cku)\niPTF15dls  19.93774  +4.08302 10:03 19.34\niPTF15dlo  18.11055  +5.07488 09:26 19.17\niPTF15dlm  15.73540  +5.54822 09:17 18.90\niPTF15dll  16.22272  +4.76531 09:17 17.63 (= PS15byu)\niPTF15dli  18.13482 +10.49597 09:22 19.68 (= PS15buq)\niPTF15dlk  17.44493 +13.30794 09:21 16.34\niPTF15dko   3.41903  +8.90473 06:51 19.34\niPTF15dma  22.39782 -15.50700 10:16 19.93\niPTF15dlx  22.44977 -15.14902 10:16 19.39\n\nWhere relevant, we have given equivalent designations by Pan-STARRS\n(Smartt et al., GCN 18451, GCN 18484) and La Silla-QUEST (Rabinowitz et\nal., GCN 18473).\n\nThe following sources are coincident with galaxies with redshifts\n(spectroscopic or photometric) < 0.1: iPTF15dkm, iPTF15dlc, iPTF15dld,\niPTF15dlj, iPTF15dln, iPTF15dmn, iPTF15dni, iPTF15dkv, iPTF15dkn,\niPTF15dkk, iPTF15dnh.\n\niPTF15dlc may be a variable star superimposed on a nearby galaxy.\n\niPTF15dni appeared to fade by 0.5 mag in one day, but its position in the\nnucleus of its host galaxy makes the host-subtracted photometry\nquestionable. We will obtain further follow-up to confirm the fading.\n\niPTF15dmk and iPTF15dmq lacked any plausible host galaxy or quiescent\ncounterpart in SDSS or archival iPTF images, but showed no significant\nintra-night photometric evolution.\n\niPTF15dlb (our designation of PS15byt) is a known nova in the galaxy IC\n1613 (Williams & Darnley, ATel #8061).\n\nThe following candidates coincided with galaxies with redshifts > 0.1:\niPTF15dmv, iPTF15dkt.\n\nThe following sources had no known redshift but showed unremarkable\nphotometric evolution: iPTF15dmt, iPTF15dmu, iPTF15dms, iPTF15dmp,\niPTF15dmf, iPTF15dmb, iPTF15dlz, iPTF15dlv, iPTF15dlu, iPTF15dlr,\niPTF15dlp, iPTF15dlg, iPTF15dla, iPTF15dkj.\n\nThe following sources were previously known SNe or AGNs: iPTF15dku,\niPTF15dmr, iPTF15dmj, iPTF15dls, iPTF15dlo, iPTF15dlm, iPTF15dll,\niPTF15dli, iPTF15dlk, iPTF15dko.\n\niPTF15dku is our designation for LSQ15bjb. We report the following\nadditional photometry:\n  -377.25 days: R < 20.21\n    +0.71 days: R = 18.62 +/- 0.13\n    +1.71 days: R = 18.15 +/- 0.15\n\nIn summary, we encourage further follow-up of iPTF15dkm, iPTF15dld,\niPTF15dlj, iPTF15dln, iPTF15dmn, iPTF15dni, iPTF15dkv, iPTF15dkn,\niPTF15dkk, iPTF15dnh, iPTF15dmk, iPTF15dmq.\n\nPositions are stated in the ICRS. Times are in UTC. Magnitudes are based\non image subtraction; they are in the Mould R filter and in the AB system,\ncalibrated with respect to point sources in SDSS as described in Ofek et\nal. (2012, http://dx.doi.org/10.1086/664065).\n\nThe diagram https://gracedb.ligo.org/apiweb/events/G194575/files/iptf.pdf\nshows the locations of our candidates and the P48 fields in relation to\nthe LIGO/Virgo localization.",
  "circularId": 18497,
  "createdOn": 1445978732000,
  "email": "leo.p.singer@nasa.gov",
  "eventId": "LIGO/Virgo G194575",
  "subject": "LIGO/Virgo G194575: iPTF Optical Transient Candidates",
  "submitter": "Leo Singer at NASA/GSFC  <leo.p.singer@nasa.gov>"
}