TITLE: GCN CIRCULAR NUMBER: 24862 SUBJECT: LIGO/Virgo S190510g: Swift UVOT - no new counterpart candidates identified DATE: 19/06/20 13:54:26 GMT FROM: Paul Kuin at MSSL N. P. M. Kuin (UCL-MSSL), A. A. Breeveld (MSSL-UCL), C. Gronwall (PSU), F. E. Marshall (NASA/GSFC), S. R. Oates (Uni. of Warwick), M.J. Page (UCL-MSSL), M. de Pasquale (Istambul U), M. H. Siegel (PSU), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), S. D. Barthelmy (NASA/GSFC), A. P. Beardmore (U. Leicester), D. N. Burrows (PSU), S. Campana (INAF-OAB), S. B. Cenko (NASA/GSFC), G. Cusumano (INAF-IASF PA), V. D'Elia(ASDC), P. A. Evans (U. Leicester), P. Giommi (ASI), D. Hartmann (Clemson U.), J. A. Kennea (PSU), H. A. Krimm (NSF), A. Y. Lien (GSFC/UMBC), D. B. Malesani (DTU Space), A. Melandri (INAF-OAB), J. A. Nousek (PSU), P. T. O'Brien (U. Leicester), J. P. Osborne (U. Leicester), C. Pagani (U. Leicester), K. L. Page (U.Leicester), D.M. Palmer (LANL), M. Perri (ASDC), J. L. Racusin (NASA/GSFC), T. Sakamoto (AGU), B. Sbarufatti (INAF-OAB/PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu (PSU), and E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift team: Swift UVOT instrument started follow up observations of LVC event S190510g 121 minutes after the event until just over 3 days later, observing 977 fields in the highest probability region (Evans et al., GCN Circ. No. 24541). The UVOT approach for searching for the ultraviolet-optical counterpart has been described in Kuin et al. (GCN Circ. No. 24767). The limiting magnitude can vary but typically is 18.6th magnitude (Vega). The automated UVOT processing found 2836 galaxies using the GLADE catalog and flagged 121 counterpart candidates. Human inspection of these 121 candidates found no credible optical-ultraviolet source for the event, but 105 out of the 121 candidates were due to an unstable attitude or due to image artifacts from very bright sources. Neither did further inspection of the images of the galaxies lead to a candidate missed by the automated processing.