  We aimed to detect a supernova (SN) shock breakout (SBO) with observations in
time domain. The SBO marks the first escape of radiation from the blast wave
that breaks through the photosphere of the star and launches the SN ejecta, and
peaks in the ultraviolet and soft X-ray bands. The detection of a SBO allows
determining the onset of the explosion with an accuracy from a few hours to a
few seconds. Using the XRT and UVOT instruments onboard the Swift satellite we
carried out a weekly cadenced, six months lasting monitoring of seven nearby
(distance <50 Mpc) galaxies, namely NGC1084, NGC2207/IC2163, NGC2770,
NGC4303/M61, NGC3147, NGC3690, NGC6754. We searched for variable/transient
sources in the collected data. We found no evidence for a SN SBO event, but we
discovered five objects located within the light of the sample galaxies that
are variable in the X-ray and/or in the UV. Our sample galaxies are within the
Universe volume that will be reached by the forthcoming advanced gravitational
waves (GW) detectors (a-LIGO/a-Virgo), thus this work provides an example on
how to carry out Swift surveys useful to detect the GW signal from SNe, and to
detect counterparts to GW triggers.
