TITLE: GCN CIRCULAR NUMBER: 21488 SUBJECT: LIGO/Virgo G297595: Pan-STARRS coverage and transients over the first 5hrs DATE: 17/08/15 16:11:56 GMT FROM: S. J. Smartt at Queens U Belfast K. C. Chambers (IfA), K. W. Smith (QUB), M. E. Huber (IfA), S. J. Smartt, D. R. Young (QUB), M. Coughlin (Harvard), T.-W. Chen (MPE), L. Denneau, H. Flewelling, A. Heinze, E. Kankare (QUB), T. Lowe, E. A. Magnier (IfA), A. Rest (STScI), B. Stalder (IfA), A. S. B. Schultz, C. W. Stubbs (Harvard) J. Tonry, C. Waters, R. J. Wainscoat, H. Weiland, M. Willman (IfA), D. E. Wright (QUB) Following Katsavounidis et al. (GCN 21474), we report Pan-STARRS imaging observations of the skymap (bayestar.fits) of G297595, a GW source with event time 2017/08/14 10:30:43.526780 == MJD 57979.43800378 We covered around 60 square degrees on the first night following the release of the G297595 alert. We began taking data at 2017-08-14.564 UT (57979.564; 3hrs after the event detection, and 2.5hrs after the alert). We estimate that this first night of data coverage corresponds to a probability of containing the source of around 60%, (based on the bayestar.fits map; Singer et al. 2016, ApJL 829, 15). Our coverage map will be posted on GraceDB. Note that we could not go below dec=-48, and did not cover the most southern part of the skymap. Images were taken in the Pan-STARRS i-band filter in a series of overlapping 45s exposures, with typically 4-6 images at each position. Difference images were produced by subtracting the Pan-STARRS1 3Pi reference image from these separate 45s exposures (Chambers et al. arXiv:1612.05560, and available at http://panstarrs.stsci.edu). At airmass of 2.8 to 2.3, we reach i ~ 21 in the individual exposures. Using techniques discussed in Smartt et al. (2016, MNRAS, 462, 4094), we have located and vetted transients with quality filters and a machine learning algorithm on the difference images. Obvious variable sources which are likely AGN/QSOs or variable stars have, as far as possible, been removed from this transient list through catalogue matching. We found 6 objects that are likely astrophysical transients, but all 6 are close to or coincident with the cores of resolved galaxies. The difference images are good quality and these are likely real, but may be AGN activity. Given the recent interest in nuclear transients and their nature we report them here for follow-up. The “prob countour” gives the bayestar.fits map probability which contains the transient. We found no SN-like, or GRB-afterglow like candidates which are associated with a galaxy and offset from the core, and similarly no orphan hostless transients to a limit of i ~ 21. Some of the following transients could be nuclear supernovae but have no measurable offsets. name ra dec mjd disc mag prob contour Notes PS17edg 02:51:44.91 -39:39:29.0 57979.568 20.29 i 70 1 PS17edm 02:54:18.07 -41:31:25.8 57979.576 20.62 i 40 2 PS17edh 02:54:07.09 -41:37:31.8 57979.576 18.36 i 40 3 PS17edn 02:55:45.77 -40:40:17.4 57979.576 20.78 i 50 4 PS17edl 02:52:48.23 -41:25:51.3 57979.578 20.51 i 40 5 PS17edj 02:30:45.31 -45:07:02.1 57979.587 18.39 i 90 6 1. The transient is associated with APMUKS(BJ) B024948.84-395146.3; a 20.03 mag galaxy found in the NED catalogue. It's located 0.34" S, 0.30" W from the galaxy centre. 2. The transient is associated with LCRS B025225.0-414335; a 18.86 mag galaxy found in the NED catalogue. It's located 0.3" from the galaxy core. 3. The transient is associated with LCRS B025214.1-414941; a 17.26 mag galaxy found in the NED catalogue. It's located 0.3" (0.7 Kpc) from the galaxy core. A host z=0.146 implies a transient M = -20.85. 4. The transient is associated with 02554579-4040171 ; a J=16.85 mag stellar source found in the 2MASS PSC catalogue. It's located 0.4" from the source core. The object appears slightly extended in the PS1 images and is likely a galaxy. 5. The transient is associated with 02524824-4125517 ; a J=16.72 mag stellar source found in the 2MASS PSC catalogue. It's located 0.4" from the source core. The object appears slightly extended in the PS1 images and is likely a galaxy. 6. The transient is synonymous with LCRS B022852.4-452018; a 18.45 mag galaxy found in the NED catalogue. It's located 0.2" (0.5 Kpc) from the galaxy core. A host z=0.143 implies a transient M = -20.56.