Kavli Affiliate: Dheeraj R. Pasham
| First 5 Authors: Yukta Ajay, Dheeraj R. Pasham, Thomas Wevers, Eric R. Coughlin, Francesco Tombesi
| Summary:
ASASSN-14li is a low-redshift ($z= 0.0206$) tidal disruption event (TDE) that
has been studied extensively across the entire electromagnetic spectrum, and
has provided one of the most sensitive measurements of a TDE to-date. Its X-ray
spectrum is soft and thermal (kT$sim$ 0.05 keV) and shows a residual broad
absorption-like feature between 0.6-0.8 keV, which can be associated with a
blue-shifted O VII (rest-frame energy 0.57 keV) resulting from an ultrafast
outflow (UFO) at early times (within 40 days of optical discovery). By
carefully accounting for pile-up and using precise XSTAR photo-ionization table
models, we analyze the entire archival X-ray data from XMM-Newton and track the
evolution of this absorption feature for $sim$4.5 years post disruption. Our
main finding is that, contrary to the previous literature, the absorption
feature is transient and intermittent. Assuming the same underlying physical
basis (i.e. outflows) for the recurring absorption feature in ASASSN-14li, the
outflow is seen to disappear and reappear multiple times during the first
$sim$2 years of its evolution. No observable spectral imprint is detected
thereafter. While theoretical studies suggest the launch of outflows in the
early phases of the outburst during the super-Eddington regime, the outflow’s
intermittent behavior for multiple years after disruption is unusual. We
discuss this peculiar behavior within the context of varying inner disk
truncation, radiation pressure, and magnetically-driven outflow scenarios.
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