TITLE: GCN CIRCULAR NUMBER: 25485 SUBJECT: LIGO/Virgo S190814bv: CFHTphotometryof AT2019npv DATE: 19/08/27 08:05:00 GMT FROM: Xiaofeng Wang at Tsinghua University X. Wang (THU), S. Antier (APC), M. Coughlin (Caltech), W. Li (THU), X. Zhang (THU), J. Mo (THU), G. Xi (THU), J. Bai (Yunnan Obs), S. Basa (LAM), E. Bertin (IAP), M. Blazek (HETH/IAA-CSIC), Michel Boer (Artemis), A. Coleiro (APC), N. Christensen (Artemis), S. Ehgamberdiev (UBAI), D. A. Kann (HETH/IAA-CSIC), A. Klotz (IRAP), D. Coward (OzGrav-UWA), D. Corre (LL), J.G. Ducoin (LAL), B. Gendre (OzGrav-UWA), P. Hello (LAL), L. Hu (PMO), C. Lachaud (APC), X. Jiang (NAOC), N. Leroy (LAL), B. Li (PMO), W. Lin (THU), D. Mirzaqulov (UBAI), T. Sun (PMO), C. Thoene (HETH/IAA-CSIC), D. Turpin (NAOC), L. Wang (Texas University/PMO), A. de Ugarte Postigo (HETH/IAA-CSIC, DARK/NBI), X. Wu (PMO), H. Zhao (PMO), X. Zeng (XAO), J. J. Zhang (YNAO), J. C. Zhang (THU): Report on behalf of AOGOT (All-sky Observations of Gravitational Optical Transients) and Grandma joint collaborations: Using the MegaPrime/MegaCam instrument (1x1 deg FOV) at the Canada-France-Hawaii Telescope, we observed the candidate AT2019npv reported by Goldstein et al (GCN 25393) close to a galaxy at z=0.056 (Jonker et al, GCN 25454), which was a candidate electromagnetic counterpart of the GW event S190814bv (LIGO/Virgo Collaboration, GCN 25324, GCN. 25333). Multiple images were obtained with the CFHT for this object in g(210sx2), r(240sx2) and i(300sx2) bands beginning at 2019-08-24 13:08 UTC. Using references from the DECam Legacy Survey (DECaLS), we performed image differencing in g and r-bands, with a low significance detection in g-band and an r-band estimate of r_AB = 23.0+-0.05 mag (i-band has a significant detection, but the reference is not available and therefore the numbers are unreliable). This object has been ruled out by different spectroscopic observations and photometric archival analysis as being related to the LIGO/Virgo GW candidate (GCN25468, GCN25475, GCN25478). GCN OPS NOTE(27aug19): Per author's request, the last reference in the last sentence was changed from "GCN5478" to "GCN25478"; and C. Corre was added to the author list.]