Kavli Affiliate: Luis C. Ho
| First 5 Authors: Ruancun Li, Luis C. Ho, Claudio Ricci, Benny Trakhtenbrot,
| Summary:
The properties of slim accretion disks, while crucial for our understanding
of black hole growth, have yet to be studied extensively observationally. We
analyze the multi-epoch broad-band spectral energy distribution of the
changing-look active galactic nucleus 1ES 1927+654 to derive the properties of
its complex, time-dependent accretion flow. The accretion rate decays as
$dot{M} propto t^{-1.53}$, consistent with the tidal disruption of a $1.1,
M_odot$ star. Three components contribute to the spectral energy distribution:
a central overheated zone resembling a slim disk, an outer truncated thin disk,
and a hot corona. Photon trapping in the slim disk triggered by the high
initial $dot{M}$ was characterized by a low radiation efficiency ($3%$),
which later more than doubled ($8%$) after $dot{M}$ dropped sufficiently low
for the disk to transition to a geometrically thin state. The blackbody
temperature profile $T propto R^{-0.60}$ for the inner overheated zone matches
the theoretical expectations of a slim disk, while the effective temperature
profile of $T propto R^{-0.69}$ for the outer zone is consistent with the
predictions of a thin disk. Both profiles flatten toward the inner boundary of
the disk as a result of Compton cooling in the corona. Our work presents
compelling observational evidence for the existence of slim accretion disks and
elucidates the key parameters governing their behavior, paving the way for
further exploration in this area.
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