TITLE: GCN CIRCULAR NUMBER: 25732 SUBJECT: LIGO/Virgo S190910h and S190910d: WHT photometry of ZTF candidates DATE: 19/09/12 06:26:28 GMT FROM: Giacomo Cannizzaro at SRON G. Cannizzaro (SRON/Radboud Univ), I. Pastor-Marazuela (API/ASTRON), P. Jonker (SRON/Radboud Univ), K. Maguire (TCD), M. Fraser (UCD), S. Brennan (UCD) and M Perez Torres (IAC) report on behalf of the GW@WHT collaboration: We performed optical photometry on the optical transients reported by the Zwicky Transient Facility (GCN 25722 and 25727) localised within the sky error region 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. We obtained the following magnitudes: Name rMag rMagErr gMag gMagErr ------------------------------------------------------- ZTF19abyheza 18.78 0.04 19.68 0.06 ZTF19abyiwiw 24.1 (L) ZTF19abyhhml 19.57 0.04 ZTF19abygvmp 18.81 0.05 19.045 0.06 ZTF19abymhyi 24.1 (L) 24.3 (L) ZTF19abyjcom 22.8 (L) ZTF19abyjcoo 21.4 (L) 22.5 (L) ZTF19abyjfiw 21.33 0.07 21.40 0.09 The photometry was obtained without performing image subtraction. With (L) we indicate 3-sigma limiting magnitudes. We note that ZTF19abyheza and ZTF19abyiwiw are within the sky localisation of gravitational wave trigger S190910d (GCN 25695).