X-ray Transients in the Advanced LIGO/Virgo Horizon
  Advanced LIGO and Advanced Virgo will be all-sky monitors for merging compact
objects within a few hundred Mpc. Finding the electromagnetic counterparts to
these events will require an understanding of the transient sky at low
red-shift (z<0.1). We performed a systematic search for extragalactic, low
red-shift, transient events in the XMM-Newton Slew Survey. In a flux limited
sample, we found that highly-variable objects comprised 10% of the sample, and
that of these, 10% were spatially coincident with cataloged optical galaxies.
This led to 4x10^-4 transients per square degree above a flux threshold of
3x10^-12 erg cm-2 s-1 [0.2-2 keV] which might be confused with LIGO/Virgo
counterparts. This represents the first extragalactic measurement of the soft
X-ray transient rate within the Advanced LIGO/Virgo horizon. Our search
revealed six objects that were spatially coincident with previously cataloged
galaxies, lacked evidence for optical AGNs, displayed high luminosities around
10^43 erg s-1, and varied in flux by more than a factor of ten when compared
with the ROSAT All-Sky Survey. At least four of these displayed properties
consistent with previously observed tidal disruption events.
