Abstract for Proposal 094195
Ultra-fast outflows and their potential for feedback in tidal disruption events
Tidal disruption events (TDEs) can probe accretion and ejection processes
at high mass accretion rates in SMBHs. One outstanding puzzle is the
current dearth of powerful accretion disk winds that are expected to
be launched during near- or super-Eddington accretion. Answering this
question is relevant for our understanding of galaxy evolution, as such
outflows may significantly affect the gas in dormant nuclei. Our recent
discovery and detailed modeling of a new ultra-fast outflows (UFOs)
reveals a large spread in their properties, and implies that they may be
more powerful than previously observed. We aim to characterize in detail
2 new TDE UFOs at high and low mass accretion rates, to establish the
typical energy injection budget by TDEs and their potential to influence
the host galaxy.
Details on Observing Strategy and Trigger Criteria
We will trigger the first XMM epoch at the moment that we find evidence
for the presence of an ultra-fast outflow (i.e. emission/absorption
features superimposed on the continuum emission) in X-ray spectra
from other X-ray observatories (NICER / Swift). The typical 3-4 week
turn-around time of XMM is sufficient for our purposes; this will enable
studying variability in the UFO on those timescales at early times.
A second XMM-Newton observation will be triggered at late times, around
500+-200 days after peak X-ray luminosity. Both TDEs that showed UFOs in
their evolution have been X-ray bright (i.e. detectable by Swift/XRT)
for ~700 days, and both still showed a UFO around 500 days. Swift/XRT
monitoring on a ~monthly basis will be used to monitor the long-term
X-ray evolution of the TDE. These observations will be requested as
regular ToO Swift triggers. If it becomes clear that the TDE is declining
faster than expected, we will trigger the second observation earlier
than 500 days but as late as possible, informed by the Swift monitoring
(typical 3sigma Swift/XRT sensitivity is around 10^{-13} erg cm^{-2}
s^{-1}, so an XRT detection will ensure that the XMM-Newton observation
yields >5000 photons).