Title:
Late-time X-ray observations of tidal disruption flares:
the relation between the optical and X-ray emission and prospects for 
BH spin measurements

Abstract:
Many tidal disruption events (TDEs) are currently discovered by
optical transient surveys and this number is expected to
grow. Similarly, the eROSITA satellite is expected to discover many
TDEs in X-rays. The origin of the optical emission and why some TDEs
are bright in optical, or optical and X-rays, whereas others are found
only in X-rays or optical remains unknown. The optical light could be
caused by reprocessing of X-ray emission from a compact accretion
disk. Or alternatively, the optical emission could be powered by the
kinetic energy of the stellar debris streams liberated in inter-stream
shocks. Late-time observations will help to address these questions,
because after a few years our view to the accretion disk should be
un-obscured. Our late-time Chandra X-ray detections of several TDEs
that went undetected in X-rays during the initial optical flares
corroborate the picture of the late time presence of an accretion disk
suggested by van Velzen et al. 2019. Late-time X-ray observations of
TDEs opens the possibility for detailed modeling of the soft X-ray
emission as thermal disc emission allow us to determine the SMBH spin.
Furthermore, we will discuss the scenario we proposed where typically
the X-ray bright phase follows the optical bright phase. This
suggested picture can be checked using future optical and X-ray survey
data.