17 research outputs found
Constraints on the black hole spin in the quasar SDSS J094533.99+100950.1
The spin of the black hole is an important parameter which may be responsible
for the properties of the inflow and outflow of the material surrounding a
black hole. Broad band IR/optical/UV spectrum of the quasar SDSS
J094533.99+100950.1 is clearly disk-dominated, with the spectrum peaking up in
the observed frequency range. Therefore, disk fitting method usually used for
Galactic black holes can be used in this object to determine the black hole
spin. We develop the numerical code for computing disk properties, including
radius-dependent hardening factor, and we apply the ray-tracing method to
incorporate all general relativity effects in light propagation. We show that
the simple multicolor disk model gives a good fit, without any other component
required, and the disk extends down to the marginally stable orbit. The best
fit accretion rate is 0.13, well below the Eddington limit, and the black hole
spin is moderate, 0.3. The contour error for the fit combined with the
constraints for the black hole mass and the disk inclination gives a constraint
that the spin is lower than 0.8. We discuss the sources of possible systematic
errors in the parameter determinations
Current Status of Simulations
As the title suggests, the purpose of this chapter is to review the current
status of numerical simulations of black hole accretion disks. This chapter
focuses exclusively on global simulations of the accretion process within a few
tens of gravitational radii of the black hole. Most of the simulations
discussed are performed using general relativistic magnetohydrodynamic (MHD)
schemes, although some mention is made of Newtonian radiation MHD simulations
and smoothed particle hydrodynamics. The goal is to convey some of the exciting
work that has been going on in the past few years and provide some speculation
on future directions.Comment: 15 pages, 14 figures, to appear in the proceedings of the ISSI-Bern
workshop on "The Physics of Accretion onto Black Holes" (8-12 October 2012
Two eclipsing ultraluminous X-ray sources in M51
We present the discovery, from archival Chandra and XMM-Newton data, of X-ray eclipses in two ultraluminous X-ray sources (ULXs), located in the same region of the galaxy M51: CXOM51 J132940.0+471237 (ULX-1, for simplicity) and CXOM51 J132939.5+471244 (ULX-2). Three eclipses were detected for ULX-1 and two for ULX-2. The presence of eclipses puts strong constraints on the viewing angle, suggesting that both ULXs are seen almost edge-on and are certainly not beamed toward us. Despite the similar viewing angles and luminosities ( erg s-1 in the 0.3-8 keV band for both sources), their X-ray properties are different. ULX-1 has a soft spectrum, well fitted by Comptonization emission from a medium with electron temperature . ULX-2 is harder, well fitted by a slim disk with -1.8 keV and normalization consistent with a ~10 M o black hole. ULX-1 has a significant contribution from multi-temperature thermal-plasma emission ( erg s-1). About 10% of this emission remains visible during the eclipses, proving that the emitting gas comes from a region slightly more extended than the size of the donor star. From the sequence and duration of the Chandra observations in and out of eclipse, we constrain the binary period of ULX-1 to be either days, or ˜12.5-13 days. If the donor star fills its Roche lobe (a plausible assumption for ULXs), both cases require an evolved donor, most likely a blue supergiant, given the young age of the stellar population in that Galactic environment. © 2016. The American Astronomical Society. All rights reserved
Spectropolarimetry of high-redshift obscured and red quasars
Spectropolarimetry is a powerful technique that has provided critical support
for the geometric unification model of local active galactic nuclei. In this
paper, we present optical (rest-frame UV) Keck spectropolarimetry of five
luminous obscured (Type 2) and extremely red quasars (ERQs) at z~2.5. Three
objects reach polarization fractions of >10% in the continuum. We propose a
model in which dust scattering is the dominant scattering and polarization
mechanism in our targets, though electron scattering cannot be completely
excluded. Emission lines are polarized at a lower level than is the continuum.
This suggests that the emission-line region exists on similar spatial scales as
the scattering region. In three objects we detect an intriguing 90 degree swing
in the polarization position angle as a function of line-of-sight velocity in
the emission lines of Ly-alpha, CIV and NV. We interpret this phenomenon in the
framework of a geometric model with an equatorial dusty scattering region in
which the material is outflowing at several thousand km/sec. Emission lines may
also be scattered by dust or resonantly. This model explains several salient
features of observations by scattering on scales of a few tens of pc. Our
observations provide a tantalizing view of the inner region geometry and
kinematics of high-redshift obscured and extremely red quasars. Our data and
modeling lend strong support for toroidal obscuration and powerful outflows on
the scales of the UV emission-line region, in addition to the larger scale
outflows inferred previously from the optical emission-line kinematics.Comment: 26 pages, MNRAS, in pres