Continuum-Fitting the X-ray Spectra of Tidal Disruption Events. (arXiv:2003.12583v1 [astro-ph.HE])
<a href="http://arxiv.org/find/astro-ph/1/au:+Wen_S/0/1/0/all/0/1">Sixiang Wen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jonker_P/0/1/0/all/0/1">Peter G. Jonker</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Stone_N/0/1/0/all/0/1">Nicholas C. Stone</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zabludoff_A/0/1/0/all/0/1">Ann I. Zabludoff</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Psaltis_D/0/1/0/all/0/1">Dimitrios Psaltis</a>
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-{it 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 $4.0^{+2.5}_{-3.1} times
10^6M_odot$. For ASASSN-14li, the SMBH mass is $10^{+1}_{-7}times
10^6M_odot$ and the spin is $0.998^{+0}_{-0.7}$. 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
$0.998^{+0}_{-0.15}$. The mass accretion rate of ASASSN-14li decays slowly, as
$propto t^{-1.1}$, perhaps due to inefficient debris circularization. Over
$approx$1100 days, its SMBH has accreted $Delta M approx 0.17 M_odot$,
implying a progenitor star mass of $> 0.34 M_odot$, 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.
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-{it 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 $4.0^{+2.5}_{-3.1} times
10^6M_odot$. For ASASSN-14li, the SMBH mass is $10^{+1}_{-7}times
10^6M_odot$ and the spin is $0.998^{+0}_{-0.7}$. 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
$0.998^{+0}_{-0.15}$. The mass accretion rate of ASASSN-14li decays slowly, as
$propto t^{-1.1}$, perhaps due to inefficient debris circularization. Over
$approx$1100 days, its SMBH has accreted $Delta M approx 0.17 M_odot$,
implying a progenitor star mass of $> 0.34 M_odot$, 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.
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