TITLE: GCN CIRCULAR NUMBER: 26839 SUBJECT: LIGO/VIRGO S200115j: No obvious candidates from Pan-STARRS2 observations DATE: 20/01/21 15:55:18 GMT FROM: Shubham Srivastav at QUB S. Srivastav, S. J Smartt (QUB), M. Huber (IfA, Univ. of Hawaii), K. W. Smith (QUB), K. Chambers, A. Schulz (IfA), D. R. Young, O. McBrien, J. Gillanders, D. O'Neil, P. Clark, S. Sim (QUB), T. de Boer, J. Bulger, J. Fairlamb, M. Huber, C.-C. Lin, T. Lowe, E. Magnier, R. J. Wainscoat, M. Willman (IfA, Univ. of Hawaii), T.-W, Chen (Stockholm), A. Rest (STScI), C. Stubbs (Harvard) We report observations of the skymap of the mass gap event S200115j (LVC, GCN 26759). We targeted one of the eastern lobes in the Lal Inference probability region (RA ~ 3 hr) with the Pan-STARRS2 telescope. The images were obtained in the w-band (Tonry et al. 2012, ApJ 750, 99). A sequence of quads (4 x 45 sec) was taken at each pointing position during the nights of 2020-01-18 and 2020-01-19. The images were processed with the IPP (Magnier et al. 2016,arXiv:1612.05240) and difference images were produced using the Pan-STARRS1 Science Consortium 3Pi images as reference frames. Transient candidates were run through our standard filtering procedures, combined with a machine learning algorithm (Wright et al. 2015, MNRAS, 449, 451) and all candidates were spatially cross-matched with known minor planets, and major star, galaxy, AGN and multi-wavelength catalogues (as described in Smartt et al. 2016, MNRAS, 462 4094). We report the following transients within the 90% contour of the skymap. All the candidates are offset from a clear galaxy. PS20ev and PS20fr have spectroscopic host redshifts (from NED), while the rest have photometric redshifts from GLADE or SDSS. The GW event was reported by LVC on MJD 58863.18. Name TNS Name RA (J2000) Dec (J2000) Disc. MJD Disc. Mag redshift PS20ev AT2020ait 02:36:56.51 -02:12:03.5 58866.30 20.23 0.0701 (s) PS20fs AT2020ajy 02:53:21.00 +03:23:17.4 58866.32 21.46 0.301 (p) PS20fo AT2020ajw 02:25:53.75 -03:13:04.6 58866.30 19.90 0.138 (p) PS20fr AT2020ajx 02:25:23.51 -07:50:15.5 58866.30 20.42 0.0538 (s) PS20fu AT2020ajz 02:49:02.17 +04:59:11.6 58866.30 21.16 - PS20fv AT2020aka 02:37:24.50 -01:09:20.1 58867.26 19.91 0.142 (p) PS20fw AT2020akb 03:10:05.41 +05:59:16.4 58867.32 21.05 0.098 (p) PS20fx AT2020akc 02:52:35.05 +07:15:11.9 58866.30 20.89 - Only PS20fs (AT2020ajy) shows a ~0.5 mag rise, the other transients show a flat w-band light curve. There are no obvious candidates that show rapid fading. The LVC distance of 332 +/- 78 Mpc corresponds to 0.06 < z < 0.09 (for Ho = 70). We also recover the following transients discovered by the ATLAS and ZTF surveys after the GW event. Our photometry does not indicate any unusual rise or fade. Source TNS Name RA (J2000) Dec (J2000) MJD PS2 Mag redshift ATLAS AT2020afo 02:27:31.13 -01:06:41.6 58867.26 18.61 0.0857 (s) ZTF AT2020agw 02:34:02.13 -04:26:44.3 58866.30 20.62 - ZTF AT2020aeo 02:59:39.07 +06:41:11.2 58867.25 20.89 -