TITLE: GCN CIRCULAR NUMBER: 25417 SUBJECT: LIGO/Virgo S190814bv: Further Pan-STARRS observations and transient sources DATE: 19/08/20 21:44:10 GMT FROM: Stephen Smartt at Queen's U/Belfast S. Srivastav (QUB), M. Huber (IfA), S. J. Smartt, K. W. Smith (QUB), K. Chambers (IfA), D. R. Young, O. McBrien, J. Gillanders, D. O'Neil, P. Clark, S. Sim (QUB), T. de Boer, J. Bulger, J. Fairlamb, C.-C. Lin, T. Lowe, E. Magnier A. Schultz, R. J. Wainscoat, M. Willman, (IfA, University of Hawaii) A. Rest (STScI), C. Stubbs (Harvard) We report further observations of the LALInference skymap of the NSBH event S190814bv (The LIGO Scientific Collaboration and the Virgo Collaboration, GCN 25324, 25333) with the Pan-STARRS1 telescope (Chambers et al. 2016 arXiv :161205560C, Huber et al. GCN25356). Images were taken in the PS1 z-band between 2019-08-18 11:03:19 UT and 2019-08-18 14:54:11 UT (58713.46 - 58713.62). A sequence of 53 x 240 sec dithered exposures was taken covering the central (approximately) 50% probability region. Given the moon position, and the time lapsed after s190814bv, and the low probability of a bright transient at this epoch, we made the choice to focus on the central part of the skymap, with extra depth and one filter. The 240s sec exposures were combined into a single epoch stack, covering the GPC1 camera chip gaps. The images were processed with the IPP (Magnier et al. 2016, arXiv:1612.05240) and difference images for the co-added stacks were produced using the Pan-STARRS1 Science Consortium 3Pi data to detect transient objects. The median 5-sigma depth of the stacked sky cells was z < 21.6 (AB mag). We may be able to significantly improve on depth by collecting a deep reference frame during the next lunation. Standard filtering procedures, combined with a machine learning algorithm (Wright et al. 2015, MNRAS, 449, 451) were applied 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). Given the extra depth compared to our first epoch (z < 20.4) on 2019-08-15 12:40:37 UT (58710.5282 ; see Huber et al. GCN 25356), we detected a significant number of fainter new transients, given in the table below. Examining potential host galaxies, and the weak constraints we have from earlier epoch data, we do not find a source that appears consistent with being a candidate for the counterpart to s190814bv. All candidates have been registered on the IAU TNS. We recovered several of the DECam GROWTH and DESGW transients (e.g. those reported in Goldstein et al. GCN 25393, Herner et al. GCN 25398 and related GCNs). We find that the combination of photometric evolution and redshift constraints (through possible hosts) leaves no obvious counterpart candidate for the objects in common. Name | TNS Name | RA (J2000) | Dec (J2000) | Disc MJD | z Mag err PS19epz | AT2019nuw | 00:50:26.34 | -25:52:57.8 | 58713.54 | 21.85 0.24 PS19eqa | AT2019nux | 00:50:21.01 | -23:42:46.7 | 58713.54 | 21.75 0.20 PS19eqc | AT2019nuz | 00:49:52.26 | -25:31:25.6 | 58713.54 | 21.89 0.22 PS19eqd | AT2019nva | 00:52:43.39 | -23:37:54.0 | 58713.54 | 21.49 0.18 PS19eqe | AT2019nvb | 00:46:51.16 | -25:25:39.3 | 58713.54 | 21.72 0.22 PS19eqf | AT2019nvc | 00:52:18.32 | -26:19:42.0 | 58713.54 | 21.31 0.18 PS19eqg | AT2019nvd | 00:55:42.30 | -24:41:50.2 | 58713.54 | 21.47 0.17 PS19eqh | AT2019nve | 00:56:05.51 | -24:38:26.3 | 58713.54 | 21.30 0.15 PS19eqo | AT2019nvr | 00:48:16.08 | -25:28:14.9 | 58713.54 | 20.89 0.13 PS19eqp | AT2019nvs | 00:52:37.75 | -26:11:41.4 | 58713.55 | 21.44 0.24