GCN Circular 24305

Aaron Tohuvavohu (PSU), Phil Evans (U. Leicester), Mike Siegel (PSU),
Frank Marshall (NASA GSFC), Brad Cenko (NASA GSFC) and Jamie Kennea
(PSU) report on behalf of the Swift Gravitational Wave Galaxy Survey
(SGWGS) team

The position of the potential Swift/UVOT counterpart (Breeveld et
al. GCN. 24296) to the LIGO/Virgo S190425z trigger (LIGO/Virgo
Collaboration GCN. 24168)  was imaged by the Neil Gehrels Swift
Observatory on 2018, October 21/22 UT with the Swift
Ultraviolet/Optical Telescope in the u and uvw1 filters for a total
1.2 ks of exposure as part of the Swift Gravitational Wave Galaxy
Survey (PI Tohuvavohu). Examining the image we do not detect any
source at the position of the counterpart candidate to a 5-sigma
limiting magnitude of ~21 mag in U-band, corresponding to  ~ -14 mag
at the distance of the associated host galaxies (~100 Mpc).  These
magnitudes are in the AB system and are not corrected for Galactic
extinction in the direction of the event.

The Swift Gravitational Wave Galaxy Survey is a 5 Million second
pre-imaging survey of the ~14,000 most likely host galaxies for BNS
mergers within ~100 Mpc. It is performed in the  u and uvw1 bands and
with XRT in the Photon Counting mode. It is currently ~43%
complete. When complete it will cover 41.2% of the integrated B-band
luminosity within 100 Mpc down to ~21 mag in u and uvw1 and
~5 �� 10 ���13 erg cm ���2 s ���1 in the X-rays (0.3 - 10 keV).