TITLE: GCN CIRCULAR NUMBER: 18489 SUBJECT: LIGO/Virgo G194575: Swift observations of LSQ15bjb DATE: 15/10/27 14:19:38 GMT FROM: Phil Evans at U of Leicester P.A. Evans (U. Leicester), Frank Marshall (NASA/GSFC), J.A. Kennea (PSU), B. Sbarufatti (INAF-OAB/PSU), Scott Barthelmy (NASA/GSFC), Dave Burrows (PSU), Sergio Campana (INAF-OAB), Brad Cenko (NASA/GSFC), Neil Gehrels (NASA/GSFC), Paolo Giommi (ASI), John Nousek (PSU), Paul O'Brien (U. Leicester), Julian Osborne (U. Leicester), David Palmer (LANL), Matteo Perri (ASDC), Judy Racusin (NASA/GSFC), Mike Siegel (PSU), Gianpiero Tagliaferri (INAF-OAB) report on behalf of the Swift team: Swift performed follow-up observations of the rapidly-brightening optical transient LSQ15bjb reported by Rabinowitz et al (GCN Circ. 18473) inside the LIGO error region for trigger G194575. The observations began at 01:20 UT on October 27. No X-ray sources are found in the image. At the location of the La Silla-QUEST source there are no events recorded in 2ks of exposure time. The 3-sigma upper limit deduced from these data is 3.5e-3 ct/sec, corresponding to an approximate flux of 1.4e-13 erg/cm^2/s. UVOT took an exposure of 1370 s with the U filter starting at 01:20:05 UT, and a second exposure of 585 s with the U filter starting at 02:36:43. The source LSQ15bjb is detected with a preliminary u magnitude of 16.79 ± 0.07 in the UVOT photometric system (Breeveld et al. 2011, AIP Conf. Proce. 1358, 373) in the first exposure and 16.73 ± 0.07 in the second. We caution that the source is not well separated from the nearby galaxy. The magnitudes are not corrected for the Galactic extinction due to the reddening of E(B-V) = 0.03 in the direction of the source (Schlegel et al. 1998). This circular is an official product of the Swift team.