Astrophys. J., 897, 80-80 (2020/July-1)
Continuum-fitting the X-ray spectra of tidal disruption events.
WEN S., JONKER P.G., STONE N.C., ZABLUDOFF A.I. and PSALTIS D.
Abstract (from CDS):
We develop a new model for X-ray emission from tidal disruption events (TDEs), applying stationary general relativistic "slim disk" accretion solutions to supermassive black holes (SMBHs) and then ray-tracing the photon trajectories from the image plane to the disk surface, including gravitational redshift, Doppler, and lensing effects self-consistently. We simultaneously and successfully fit the multi-epoch XMM-Newton X-ray spectra for two TDEs: ASASSN-14li and ASASSN-15oi. We test explanations for the observed, unexpectedly slow X-ray brightening of ASASSN-15oi, including delayed disk formation and variable obscuration by a reprocessing layer. We propose a new mechanism that better fits the data: a "slimming disk" scenario in which accretion onto an edge-on disk slows, reducing the disk height and exposing more X-rays from the inner disk to the sightline over time. For ASASSN-15oi, we constrain the SMBH mass to 4.0–3.1+2.5×106M☉. For ASASSN-14li, the SMBH mass is 10–7+1×106M☉, and the spin is >0.3. For both TDEs, our fitted masses are consistent with independent estimates; for ASASSN-14li, application of the external mass constraint narrows our spin constraint to >0.85. The mass accretion rate of ASASSN-14li decays slowly, as ∝t–1.1, perhaps due to inefficient debris circularization. Over ≃1100 days, its SMBH has accreted ΔM ≃ 0.17M☉, implying a progenitor star mass of >0.34M☉, i.e., no "missing energy problem." For both TDEs, the hydrogen column density declines to the host galaxy plus Milky Way value after a few hundred days, suggesting a characteristic timescale for the depletion or removal of obscuring gas.
© 2020. The American Astronomical Society. All rights reserved.
Tidal disruption - X-ray transient sources - Accretion - Black hole physics - Supermassive black holes
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