Kavli Affiliate: Dheeraj R. Pasham
| First 5 Authors: Dheeraj R. Pasham, Michal Zajacek, C. J. Nixon, Eric R. Coughlin, Marzena Sniegowska
| Summary:
An accretion disk formed around a supermassive black hole (SMBH) after it
disrupts a star is expected to be initially misaligned with respect to the
black hole’s equatorial plane. This misalignment induces relativistic torques
(the Lense-Thirring effect) on the disk, causing the disk to precess at early
times, while at late times the disk aligns with the black hole and precession
terminates. Here, using high-cadence X-ray monitoring observations of a TDE, we
report the discovery of strong, quasi-periodic X-ray flux and temperature
modulations from a TDE. These X-ray modulations are separated by
17.0$^{+1.2}_{-2.4}$ days and persist for roughly 130 days during the early
phase of the TDE. Lense-Thirring precession of the accretion flow can produce
this X-ray variability, but other physical mechanisms, such as the
radiation-pressure instability, cannot be ruled out. Assuming typical TDE
parameters, i.e., a solar-like star with the resulting disk extending at-most
to so-called circularization radius, and that the disk precesses as a rigid
body, we constrain the disrupting black hole’s dimensionless spin parameter to
be 0.05<|a|<0.5.
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