104 research outputs found
General relativistic polarized radiative transfer with inverse Compton scatterings
We present {\tt radpol} - a numerical scheme for integrating multifrequency
polarized radiative transfer equations along rays propagating in a curved
spacetime. The scheme includes radiative processes such as synchrotron
emission, absorption, Faraday rotation and conversion, and, for the first time,
relativistic Compton scatterings including effects of light polarization. The
scheme is fully covariant and is applicable to model radio--ray
emission and its polarization from, e.g., relativistic jets and accretion flows
onto black holes and other exotic objects described in alternative metric
theories and modeled semi-analytically or with time-dependent
magnetohydrodynamical simulations. We perform a few tests to validate the
implemented numerical algorithms that handle light polarization in curved
spacetime. We demonstrate application of the scheme to model broadband emission
spectra from a relativistically hot, geometrically thick coronal-like inflow
around a supermassive black hole where the disk model is realized in a general
relativistic magnetohydrodynamical simulation.Comment: 9 pages, 4 figures, accepted for publication in MNRA
What is the hard spectral state in X-ray binaries? Insights from GRRMHD accretion flows simulations and polarization of their X-ray emission
X-ray binaries (XRB) are known to exhibit different spectral states which are
associated with different black hole accretion modes. Recent measurments of
linear polarization of X-ray emission in X-ray binary Cygnus X-1 allow us to
test models for the hard state of accretion in a unique way. We show that
general relativistic radiative magnetohydrodynamic (GRRMHD) simulations of
accreting stellar black hole in a hard X-ray state are consisitent with the new
observational information. The state-of-the-art models of the hard state show
that the X-ray emission is predominantly produced by extended jets, away from
the central black hole with some contribution from hot corona near the black
hole. Our modeling results are supporting the idea that the strong correlations
between synchrotron and X-ray emission observed in many XRBs can be attributed
to the jet emission. In the presented framework, where first-principle models
have limited number of free parameters, the X-ray polarimetric observations put
constraints on the viewing angle of the accreting black hole system.Comment: 7 pages, 4 figures, invited contribution to a special issue of a
Springer Nature journal, comments are very welcom
General relativistic magnetohydrodynamical simulations of the jet in M87
(abridged) The connection between black hole, accretion disk, and radio jet
can be best constrained by fitting models to observations of nearby low
luminosity galactic nuclei, in particular the well studied sources Sgr~A* and
M87. There has been considerable progress in modeling the central engine of
active galactic nuclei by an accreting supermassive black hole coupled to a
relativistic plasma jet. However, can a single model be applied to a range of
black hole masses and accretion rates? Here we want to compare the latest
three-dimensional numerical model, originally developed for Sgr A* in the
center of the Milky Way, to radio observations of the much more powerful and
more massive black hole in M87. We postprocess three-dimensional GRMHD models
of a jet-producing radiatively inefficient accretion flow around a spinning
black hole using relativistic radiative transfer and ray-tracing to produce
model spectra and images. As a key new ingredient to these models, we allow the
proton-electron coupling in these simulations depend on the magnetic properties
of the plasma. We find that the radio emission in M87 is well described by a
combination of a two-temperature accretion flow and a hot single-temperature
jet. The model fits the basic observed characteristics of the M87 radio core.
The best fit model has a mass-accretion rate of Mdot approx 9x10^{-3} MSUN/YR
and a total jet power of P_j \sim 10^{43} erg/s. Emission at 1.3mm is produced
by the counter jet close to the event horizon. Its characteristic crescent
shape surrounding the black hole shadow could be resolved by future
millimeter-wave VLBI experiments. The model was successfully derived from one
for the supermassive black hole in center of the Milky Way by appropriately
scaling mass and accretion rate. This suggests the possibility that this model
could also apply to a larger range of low-luminosity black holes.Comment: 15 pages, 14 figures, accepted to Astronomy and Astrophysics, after
language proofs, with correct titl
Scale-invariant radio jets and varying black hole spin
Compact radio cores associated with relativistic jets are often observed in
both active galactic nuclei and X-ray binaries. Their radiative properties
follow some general scaling laws which primarily depend on their masses and
accretion rates. However, it has been suggested that the black hole spin can
also strongly influence the power and radio flux of these. Here, we attempt to
estimate the dependency of the radio luminosity of steady jets launched by
accretion disks on black hole mass, accretion rate and spin using numerical
simulations. We make use of 3D GRMHD simulations of accretion disks around
low-luminosity black holes in which the jet radio emission is produced by the
jet sheath. We find that the radio flux increases roughly by a factor of 6 as
the back hole spin increases from a~0 to a=0.98. This is comparable to the
increase in accretion power with spin, meaning that the ratio between radio jet
and accretion power is hardly changing. Although our jet spine power scales as
expected for the Blandford-Znajek process, the dependency of jet radio
luminosity on the black hole spin is somewhat weaker. Also weakly rotating
black holes can produce visible radio jets. The overall scaling of the radio
emission with black hole mass and accretion rate is consistent with the
scale-invariant analytical models used to explain the fundamental plane of
black hole activity. Spin does not introduce a significant scatter in this
model. The jet-sheath model can describe well resolved accreting systems, such
as SgrA* and M87, as well as the general scaling behavior of low-luminosity
black holes. Hence the model should be applicable to a wide range of radio jets
in sub-Eddington black holes. The black hole spin has an effect on the
production of visible radio jet, but it may not be the main driver to produce
visible radio jets. An extension of our findings to powerful quasars remains
speculative.Comment: 10 pages, 6 figures, A&A accepte
Accretion and outflow from a magnetized, neutrino cooled torus in the gamma ray burst central engine
Gamma Ray Bursts (GRB) are the extremely energetic transient events, visible
from the most distant parts of the Universe. They are most likely powered by
accretion on the hyper-Eddington rates that proceeds onto a newly born stellar
mass black hole. This central engine gives rise to the most powerful, high
Lorentz factor jets that are responsible for energetic gamma ray emission. We
investigate the accretion flow evolution in GRB central engine, using the 2D
MHD simulations in General Relativity. We compute the structure and evolution
of the extremely hot and dense torus accreting onto the fast spinning black
hole, which launches the magnetized jets. We calculate the chemical structure
of the disk and account for neutrino cooling. Our preliminary runs apply to the
short GRB case (remnant torus accreted after NS-NS or NS-BH merger). We
estimate the neutrino luminosity of such an event for chosen disk and central
BH massComment: 4 pages, 2 color figures; to appear in the conference proceedings
from High Energy Phenomena in Relativistic Outflows III Barcelona, (June 27 -
July 1, 2011); eds. J.M. Paredes, M. Rib\'o, F.A. Aharonian and G.E. Romer
Probing the accretion disk - jet connection via instabilities in the inner accretion flow. From microquasars to quasars
We present various instability mechanisms in the accreting black hole systems
which might indicate at the connection between the accretion disk and jet. The
jets observed in microquasars can have a persistent or blobby morphology.
Correlated with the accretion luminosity, this might provide a link to the
cyclic outbursts of the disk. Such duty-cycle type of behavior on short
timescales results from the thermal instability caused by the radiation
pressure domination. The same type of instability may explain the cyclic
radioactivity of the supermassive black hole systems. The somewhat longer
timescales are characteristic for the instability caused by the partial
hydrogen ionization. The distortions of the jet direction and complex
morphology of the sources can be caused by precession of the disk-jet axis.Comment: 2 pages, 2 figures; Proceedings of the 275 IAU Symposium "Jets at all
scales", Buenos Aires, 13-17.09.2010; eds. G. Romero, R. Sunyaev, T. Bellon
Observational appearance of inefficient accretion flows and jets in 3D GRMHD simulations: Application to Sgr~A*
Radiatively inefficient accretion flows (RIAFs) are believed to power
supermassive black holes (SMBH) in the underluminous cores of galaxies. Such
black holes are typically accompanied by flat-spectrum radio cores indicating
the presence of moderately relativistic jets. One of the best constrained RIAFs
is associated with the SMBH in the Galactic center, Sgr A*. Since the plasma in
RIAFs is only weakly collisional, the dynamics and the radiative properties of
these systems are very uncertain. Here we want to study the impact of varying
electron temperature on the appearance of accretion flows and jets. Using 3-D
GRMHD accretion flow simulations, we use ray tracing methods to predict spectra
and radio images of RIAFs allowing for different electron heating mechanisms in
the in- and outflowing parts of the simulations. We find that small changes in
the electron temperature can result in dramatic differences in the relative
dominance of jets and accretion flows. Application to Sgr A* shows that radio
spectrum and size of this source can be well reproduced with a model where
electrons are more efficiently heated in the jet. The X-ray emission is
sensitive to the electron heating mechanism in the jets and disk and therefore
X-ray observations put strong constraints on electron temperatures and geometry
of the accretion flow and jet. For Sgr A*, the jet model also predicts a
significant frequency-dependent core shift which could place independent
constraints on the model once measured accurately. We conclude that more
sophisticated models for electron distribution functions are crucial for
constraining GRMHD simulations with actual observations. For Sgr A*, the radio
appearance may well be dominated by the outflowing plasma. Nonetheless, at the
highest radio frequencies, the shadow of the event horizon should still be
detectable with future Very Long Baseline Interferometric observations.Comment: A&A accepted, 11 figures, 1 tabl
General relativistic magnetohydrodynamical -jet models for Sgr A*
The observed spectral energy distribution of an accreting supermassive black
hole typically forms a power-law spectrum in the Near Infrared (NIR) and
optical wavelengths, that may be interpreted as a signature of accelerated
electrons along the jet. However, the details of acceleration remain uncertain.
In this paper, we study the radiative properties of jets produced in
axisymmetric GRMHD simulations of hot accretion flows onto underluminous
supermassive black holes both numerically and semi-analytically, with the aim
of investigating the differences between models with and without accelerated
electrons inside the jet. We assume that electrons are accelerated in the jet
regions of our GRMHD simulation. To model them, we modify the electrons'
distribution function in the jet regions from a purely relativistic thermal
distribution to a combination of a relativistic thermal distribution and the
-distribution function. Inside the disk, we assume a thermal
distribution for the electrons. We calculate jet spectra and synchrotron maps
by using the ray tracing code {\tt RAPTOR}, and compare the synthetic
observations to observations of Sgr~A*. Finally, we compare numerical models of
jets to semi-analytical ones. We find that in the -jet models, the
radio-emitting region size, radio flux, and spectral index in NIR/optical bands
increase for decreasing values of the parameter, which corresponds to
a larger amount of accelerated electrons. The model with ,
(the percentage of electrons that are accelerated), and
observing angle fits the observed Sgr~A* emission in the
flaring state from the radio to the NIR/optical regimes, while ,
, and observing angle fit the upper
limits in quiescence.Comment: 17 pages, 16 figures, 1 tabl
- …