GCN Circular 24862

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.