387 research outputs found
An accretion disc with magnetic outflows triggered by a sudden mass accretion event in changing-look active galactic nucleus 1ES 1927+654
1ES 1927+654 was known as a type 2 Seyfert galaxy, which exhibited drastic
variability recently in ultraviolet (UV)/optical and X-ray bands. An UV/optical
outburst was observed in the end of 2017, and it reached the peak luminosity
days later. The high-cadence observations showed a rapid X-ray flux
decline with complete disappearance of the power-law hard X-ray component when
the soft X-ray thermal emission reached its lowest level about days after
the UV/optical peak. The power law X-ray component reappeared with thermal
X-ray emission brightening from its lowest flux within next 100~days. We
assume an episodic accretion event taking place in the outer region of the disc
surrounding a central black hole (BH), which is probably due to a red giant
star tidally disrupted by the BH. The inner thin disc with corona is completely
swept by the accretion event when the gas reaches the innermost circular stable
orbit. The field threading the disrupted star is dragged inwards by the disc
formed after the tidal disruption event, which accelerates outflows from the
disc. The disc dimmed since a large fraction of the energy released in the disc
is tapped into the outflows. The accretion rate of the episodic accretion event
declines, and ultimately it turns out to be a thin disc, which is inefficient
for field advection, and the outflows are switched off. A thin disc with corona
reappears later after the outburst.Comment: 11 pages, accepted by MNRA
Strongly enhanced light-matter interaction in a hybrid photonic-plasmonic resonator
We propose a hybrid photonic-plasmonic resonant structure which consists of a
metal nanoparticle (MNP) and a whispering gallery mode (WGM) microcavity. It is
found that the hybrid mode enables a strong interaction between the light and
matter, and the single-atom cooperativity is enhanced by more than two orders
of magnitude compared to that in a bare WGM microcavity. This remarkable
improvement originates from two aspects: (1) the MNP offers a highly enhanced
local field in the vicinity of an emitter, and (2), surprisingly, the
high-\textit{Q} property of WGMs can be maintained in the presence of the MNP.
Thus the present system has great advantages over a single microcavity or a
single MNP, and holds great potential in quantum optics, nonlinear optics and
highly sensitive biosening.Comment: 5 pages, 4 figure
Testing wind as an explanation for the spin problem in the continuum-fitting method
The continuum-fitting method is one of the two most advanced methods of
determining the black hole spin in accreting X-ray binary systems. There are,
however, still some unresolved issues with the underlying disk models. One of
them manifests as an apparent decrease in spin for increasing source
luminosity. Here, we perform a few simple tests to establish whether outflows
from the disk close to the inner radius can address this problem. We employ
four different parametric models to describe the wind and compare these to the
apparent decrease in spin with luminosity measured in the sources LMC~X-3 and
GRS~1915+105. Wind models in which parameters do not explicitly depend on the
accretion rate cannot reproduce the spin measurements. Models with mass
accretion rate dependent outflows, however, have spectra that emulate the
observed ones. The assumption of a wind thus effectively removes the artifact
of spin decrease. This solution is not unique; the same conclusion can be
obtained with a truncated inner disk model. To distinguish among valid models,
high resolution X-ray data and a realistic description of the Comptonization in
the wind will be needed.Comment: 14 pages, 11 figures, accepted by Ap
Corrections to Estimated Accretion Disk Size due to Color Correction, Disk Truncation and Disk Wind
We consider three corrections to the disk sizes estimated at a given
frequency using accretion models. They are due to a color correction, a disk
truncation at an inner radius larger than the innermost stable circular orbit,
and disk winds, which we apply to the standard disk model. We apply our results
to the estimates of the disk sizes based on microlensing. We find these three
effects combined can explain the long-standing problem of the disk sizes from
microlensing being larger than those estimated using the standard disk model
(i.e., that without accounting for the above effects). In particular, an
increase of the color correction with the increasing temperature can lead to a
strong increase of the half-light radius even if this correction is close to
unity at the temperature corresponding to an observed frequency. Our proposed
formalism for calculating the half-light radius also resolves the long-standing
issue of discrepancies between the disk size estimates based on the accretion
rate and on the observed flux.Comment: ApJL, in pres
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