TITLE: GCN CIRCULAR NUMBER: 24296 SUBJECT: LIGO/Virgo S190425z: Transient found in Swift/UVOT counterpart search DATE: 19/04/27 18:38:54 GMT FROM: Mike Siegel at PSU/Swift MOC LIGO/Virgo S190425z: Transient found in Swift/UVOT counterpart search A. A. Breeveld (MSSL-UCL), N. P. M. Kuin (UCL-MSSL), F. E. Marshall (NASA/GSFC), P. Brown (TAMU), S. R. Oates (Uni. of Warwick), M. H. Siegel (PSU), M. de Pasquale (Uni. of Istanbul), S. D. Barthelmy (NASA/GSFC), A. Y. Lien (GSFC/UMBC), D. M. Palmer (LANL), T. Sakamoto (AGU), A. P. Beardmore (U. Leicester), D. N. Burrows (PSU), S. Campana (INAF-OAB), S. B. Cenko (NASA/GSFC), G. Cusumano (INAF-IASF PA), A. D'Ai (INAF-IASFPA), P. D'Avanzo (INAF-OAB), V. D'Elia(ASDC), S. Emery (UCL-MSSL), P. A. Evans (U. Leicester), P. Giommi (ASI), C. Gronwall (PSU), D. Hartmann (Clemson U.), J. A. Kennea (PSU), H. A. Krimm (NSF), A. Melandri (INAF-OAB), B. Mingo (U. Leicester), J. A. Nousek (PSU), P. T. O'Brien (U. Leicester), J. P. Osborne (U. Leicester), C. Pagani (U. Leicester), K. L. Page (U.Leicester), M. Perri (ASDC), J. L. Racusin (NASA/GSFC), B. Sbarufatti (INAF-OAB/PSU), G. Tagliaferri (INAF-OAB), A. Tohuvavohu (PSU), E. Troja (NASA/GSFC/UMCP) report on behalf of the Swift team: We report a candidate transient found in the UVOT search results of the LVC event S190425z (LIGO/VIRGO Collaboration GCN Circ. 24168). On 2019-04-26 at 18:49:22 UT Swift UVOT took a 66.8 s exposure in the u band with exposure ID uu577997367I (target ID 07016575) which shows a new source when compared with archived DSS images. The new source is not listed in the Gaia DR1, 2MASS or GSC2.3 catalogs or Pan-STARRS and is not listed as a minor planet. The position is: RA = 255.5800 deg Dec = -12.48562 deg which is RA=17:02:19.2, Dec=-12:29:08.2 (J2000). The magnitude using the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proc. 1358, 373) is u=17.74 +/- 0.18 mag (Vega). No source is found at this position in the XRT, with a 3-sigma upper limit of 5.8 x 10^-2 ct s^-1, which corresponds to a 0.3-10 keV observed flux of 2.5 x 10^-11 erg cm^-2 s^-1. At this position, the distance estimate from the LALInference sky map has a mean of 132 Mpc with a sigma of 35 Mpc. There is a bright galaxy in the 2MPZ catalogue (Bilicki et al., 2014) 2MPZ J17021587-1228210 at 68 arcsec (z = 0.022, D = 99 Mpc, abs K magnitude = 12.4), which is 33 kpc away in projection. A second galaxy, 2MPZ J17020235-1229511 lies 250 arcsec away from the UVOT position. This galaxy has a distance of 106 Mpc in the 2MPZ catalogue so the projected offset is 128 kpc. At the distance of these galaxies, the absolute U magnitude would be -17.3, which is brighter than AT 2017gfo at t ~ 2 days. This circular is an official product of the Swift team.