TITLE: GCN CIRCULAR NUMBER: 25730 SUBJECT: LIGO/Virgo S190910h: WHT spectroscopy of ZTF19abygvmp/AT2019pzg DATE: 19/09/12 02:05:38 GMT FROM: Giacomo Cannizzaro at SRON p.p1 {margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica} p.p2 {margin: 0.0px 0.0px 0.0px 0.0px; font: 12.0px Helvetica; min-height: 14.0px} G. Cannizzaro (SRON/Radboud Univ), I. Pastor-Marazuela (API/ASTRON), P. Jonker (SRON/Radboud Univ), K. Maguire (TCD), M. Fraser (UCD) report on behalf of the GW@WHT collaboration: We obtained optical spectroscopy of ZTF19abygvmp/AT2019pzg (GCN 25727) an optical transient within the sky localisation of the gravitational wave trigger S190910h (GCN 25707) with the ACAM instrument mounted on the William Herschel Telescope located at the Roque de Los Muchachos Observatory, La Palma, Spain. The spectrum is dominated by the host galaxy light and shows a strong emission line compatible with Halpha at redshift z=0.049 (219 Mpc), confirming its location spectroscopically within the most up-to-date distance range based on the GW signal of S190910h of 241 +- 89 Mpc.