TITLE: GCN CIRCULAR NUMBER: 18362 SUBJECT: LIGO/Virgo G184098: ongoing Pan-STARRS search for optical transients DATE: 15/09/24 13:29:47 GMT FROM: S. J. Smartt at Queens U Belfast S.J. Smartt, K. W. Smith, (Queenâ<80><99>s University Belfast), K. Chambers, M. Huber, E. Magnier, H. Flewelling, C. Waters, J. Tonry, A. Schultz, N. Primak (IfA, University of Hawaii), D. Young, D. Wright (Queenâ<80><99>s University Belfast), C. Stubbs (Harvard) Following our reports of Pan-STARRS pointing coordinates for the field of LIGO/Virgo G184098 and the search for transients, an update is provided here. The coordinates of 4 nights of observations are given on the GraceDB webpages. Images in i, z and y-band were taken on 2015-09-17, 19, 22, 23. The difference images were processed as described in Huber et al. (Atel 7153) and on the Pan-STARRS Survey for Transients (PSST) pages (http://star.pst.qub.ac.uk/ps1threepi/psdb/). We initially reported first night detections of PS15cbm, PS15cbj, PS15cbn (2015-09-17). However subsequent data show that only PS15cbm is real. The other two were not recovered in later images and are almost certainly instrumental ghosts. Over these four nights, we now have 5 objects which are detected in multiple nights and multiple filters (and different camera orientations) and are likely to be extragalactic transients (they are all associated with a galaxy in SDSS and PS1 reference images). Obj RA(J2000) Dec(J2000) mag z PS15cbm 08:49:19.85 +03:48:17.8 18.54(i) 0.059 PS15cci 09:13:22.76 +06:10:47.2 18.33(i) â<80>¦ PS15ccx 08:18:03.90 +04:18:04.2 19.42(z) â<80>¦ PS15ccv 08:55:23.07 +04:41:19.0 19.57(i) 0.071 PS15ccw 08:57:30.60 +04:31:56.1 19.33(i) 0.072 The mag is the discovery magnitude (AB system). The reported redshift is the spectroscopic redshift of the apparent host galaxy from SDSS DR12. The other two have no spectroscopic redshifts, but have detected host galaxies. >From the data in hand, all appear to be likely supernovae. The object furthest north-east (PS15cci) is close to the 90% confidence contour of the G182098 'LIB_skymap' GW localisation map. The others are outside this region but within the 'skyprobcc_cWBâ<80><99> map. Twilight restricted us pointing at the centre of the 'LIB_skymap' GW localisation map. Our survey area is slightly further south than the iPTF survey area (Singer et al. GCN 18337) and the J-GEM area (Morokuma et al. GCN 18361). Observations are continuing this week when the weather cooperates.