共查询到20条相似文献,搜索用时 46 毫秒
1.
We explore an accretion model for low luminosity AGN (LLAGN) that attributes the low radiative output to a low mass accretion
rate,
, rather than a low radiative efficiency. In this model, electrons are assumed to drain energy from the ions as a result of
collisionless plasma microinstabilities. Consequently, the accreting gas collapses to form a geometrically thin disk at small
radii and is able to cool before reaching the black hole. The accretion disk is not a standard disk, however, because the
radial disk structure is modified by a magnetic torque which drives a jet and which is primarily responsible for angular momentum
transport. We also include relativistic effects. We apply this model to the well known LLAGN M87 and calculate the combined
disk-jet steady-state broadband spectrum. A comparison between predicted and observed spectra indicates that M87 may be a
maximally spinning black hole accreting at a rate of ∼10−3
M
⊙ yr−1. This is about 6 orders of magnitude below the Eddington rate for the same radiative efficiency. Furthermore, the total jet
power inferred by our model is in remarkably good agreement with the value independently deduced from observations of the
M87 jet on kiloparsec scales. 相似文献
2.
We explore an accretion model for low luminosity AGN (LLAGN) that attributes the low radiative output to a low mass accretion
rate,
, rather than a low radiative efficiency. In this model, electrons are assumed to drain energy from the ions as a result of
collisionless plasma microinstabilities. Consequently, the accreting gas collapses to form a geometrically thin disk at small
radii and is able to cool before reaching the black hole. The accretion disk is not a standard disk, however, because the
radial disk structure is modified by a magnetic torque which drives a jet and which is primarily responsible for angular momentum
transport. We also include relativistic effects. We apply this model to the well known LLAGN M87 and calculate the combined
disk-jet steady-state broadband spectrum. A comparison between predicted and observed spectra indicates that M87 may be a
maximally spinning black hole accreting at a rate of ∼10−3
M
⊙ yr−1. This is about 6 orders of magnitude below the Eddington rate for the same radiative efficiency. Furthermore, the total jet
power inferred by our model is in remarkably good agreement with the value independently deduced from observations of the
M87 jet on kiloparsec scales.
* This paper has previously been published in Astrophysics and Space Science, vol. 310:3–4. 相似文献
3.
The measurements of pulsar frequency second derivatives have shown that they are 102−106 times larger than expected for standard pulsar spin-down law, and are even negative for about half of pulsars. We explain
these paradoxical results on the basis of the statistical analysis of the rotational parameters ν,
and
of the subset of 295 pulsars taken mostly from the ATNF database. We have found a strong correlation between
and
for both
and
, as well as between ν and
. We interpret these dependencies as evolutionary ones due to
being nearly proportional to the pulsars’ age. The derived statistical relations as well as “anomalous” values of
are well described by assuming the long-time variations of the spin-down rate. The pulsar frequency evolution, therefore,
consists of secular change of ν
ev(t),
and
according to the power law with n≈5, the irregularities, observed within a timespan as a timing noise, and the variations on the timescale larger than that—several
decades.
This work has been supported by the Russian Foundation for Basic Research (grant No 04-02-17555), Russian Academy of Sciences
(program “Evolution of Stars and Galaxies”), and by the Russian Science Support Foundation. The authors would also like to
thank the anonymous referee for valuable comments. 相似文献
4.
Using Damour-Ruffini’s and Hamilton-Jacobi’s methods, Hawking radiation from a Vaidya black hole is investigated. Due to non-stationary
black holes, the event horizon r
H
and the entropy S are all related to both the mass m(υ) and
. When the back-reaction of particles’s energy to space-time is considered, we get the emission probability. It is found that
the result is different from that of the stationary Schwarzschild black hole, because
is the function of mass m(υ).
相似文献
5.
We explore self-similar hydrodynamic evolution of central voids embedded in an isothermal gas of spherical symmetry under
the self-gravity. More specifically, we study voids expanding at constant radial speeds in an isothermal gas and construct
all types of possible void solutions without or with shocks in surrounding envelopes. We examine properties of void boundaries
and outer envelopes. Voids without shocks are all bounded by overdense shells and either inflows or outflows in the outer
envelope may occur. These solutions, referred to as type
void solutions, are further divided into subtypes
and
according to their characteristic behaviours across the sonic critical line (SCL). Void solutions with shocks in envelopes
are referred to as type
voids and can have both dense and quasi-smooth edges. Asymptotically, outflows, breezes, inflows, accretions and static outer
envelopes may all surround such type
voids. Both cases of constant and varying temperatures across isothermal shock fronts are analyzed; they are referred to as
types
and
void shock solutions. We apply the ‘phase net matching procedure’ to construct various self-similar void solutions. We also
present analysis on void generation mechanisms and describe several astrophysical applications. By including self-gravity,
gas pressure and shocks, our isothermal self-similar void (ISSV) model is adaptable to various astrophysical systems such
as planetary nebulae, hot bubbles and superbubbles in the interstellar medium as well as supernova remnants.
相似文献
6.
M. G. Abrahamyan 《Astrophysics》2009,52(1):119-131
The nonlinear dynamics of a rotating jet is examined following its ejection from a compact gravitating object by a vortex
mechanism. A scenario is described in which a dense stream expands and is subsequently transformed into a nonstationary vortex
consisting of a cylindrical core and a “sheath.” At this stage of development, a converging radial flow of matter in the differentially
rotating nonuniform sheath collimates the jet and speeds up the rotation of the core, as well as the flow of matter along
the jet, in accordance with a power law or “explosive” instability, until the velocity discontinuity at the surface of the
core approaches the sound speed. Flows of this type have low energy dissipation and can serve as unique channels for the acceleration
and collimation of jet eruptions from young stars, active galactic nuclei, and quasars.
Translated from Astrofizika, Vol. 52, No. 1, pp. 135–145 (February 2009). 相似文献
7.
Maxim Lyutikov 《Astrophysics and Space Science》1998,264(1-4):411-421
A theory of pulsar radio emission generation, in which the observed waves are produced directly by the maser-type plasma instabilities
on the anomalous cyclotron-Cherenkov resonance
and the Cherenkov-drift resonance
, is capable of explaining the main observational characteristics of pulsar radio emission. The instabilities are due to the
interaction of the fast particles of the primary beam and from the tail of the distribution with the normal modes of a strongly
magnetized one-dimensional electron-positron plasma. The waves emitted at these resonances are vacuum-like electromagnetic
waves that may leave the magnetosphere directly. The cyclotron-Cherenkov instability is responsible for core emission pattern
and the Cherenkov-drift instability produces conal emission. The conditions for the development of the cyclotron-Cherenkov
instability are satisfied for the both typical and millisecond pulsars provided that the streaming energy of the bulk plasma
is not very high γ
p
= 5 ÷ 10. In a typical pulsar the cyclotron-Cherenkov and Cherenkov-drift resonances occur in the outer parts of magnetosphere
at r
res
≈ 109cm. This theory can account for various aspects of pulsar phenomenology including the morphology of the pulses, their polarization
properties and spectral behavior.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
8.
Qiuhe Peng 《Astrophysics and Space Science》1989,154(2):271-279
Both the critical content
c
( N
m
/N
B
, whereN
m
,N
B
are the total numbers of monopoles and nucleons, respectively, contained in the object), and the saturation content
s
of monopoles in a rotating relativistic object are found in this paper. The results are:
相似文献
9.
10.
In this paper we have considered the Universe to be filled with Modified Gas and the Cosmological Constant Λ to be time-dependent
with or without the Gravitational Constant G to be time-dependent. We have considered various phenomenological models for Λ, viz.,
and
. Using these models it is possible to show the accelerated expansion of the Universe at the present epoch. Also we have shown
the natures of G and Λ over the total age of the Universe. Using the statefinder parameters we have shown the diagrammatical representation
of the evolution of the Universe starting from radiation era to ΛCDM model. 相似文献
11.
V. V. Ivanov 《Astrophysics》2009,52(1):24-39
This is a discussion of V. A. Ambartsumyan’s studies of the mean number of scatterings for photons in scattering media and
of further work and development in this area, especially at Ambartsumyan’s St. Petersburg school. The following questions
are discussed briefly: (a) the traditional method for calculating the number of scatterings from the source function and critiques
of this method. (b) The equation for the number N(τ; τ0 ) of scatterings for a photon born at optical depth τ in a plane layer of optical thickness τ0 and its use for calculating the number of scatterings, averaged over the entire ensemble of photons for a medium with arbitrary internal sources. These questions
are first considered for the case of monochromatic scattering, and then for scattering in a spectral line with complete frequency
redistribution (CFR). (c) The mean path length for a resonance line photon in a scattering medium with CFR and continuum absorption: the basic equations and asymptotic
behavior of an optically thick layer. (d) A review of calculations of and in media that are so thick that the CFR approximation breaks down and the effects of partial frequency redistribution (PFR)
become dominant. The presentation is at a semiquantitative level in many parts of this paper, with stress on physical significance
rather than the mathematics, through the use of approximate and asymptotic solutions.
Translated from Astrofizika, Vol. 52, No. 1, pp. 29–45 (February 2009). 相似文献
12.
M. S. Wheatland 《Solar physics》2009,255(2):211-227
A Monte Carlo approach to solving a stochastic-jump transition model for active-region energy (Wheatland and Glukhov: Astrophys. J.
494, 858, 1998; Wheatland: Astrophys. J.
679, 1621, 2008) is described. The new method numerically solves the stochastic differential equation describing the model, rather than the
equivalent master equation. This has the advantages of allowing more efficient numerical solution, the modeling of time-dependent
situations, and investigation of details of event statistics. The Monte Carlo approach is illustrated by application to a
Gaussian test case and to the class of flare-like models presented in Wheatland (Astrophys. J.
679, 1621, 2008), which are steady-state models with constant rates of energy supply, and power-law distributed jump transition rates. These
models have two free parameters: an index (δ), which defines the dependence of the jump transition rates on active-region energy, and a nondimensional ratio (
) of total flaring rate to rate of energy supply. For
the nondimensional mean energy
of the active-region satisfies
, resulting in a power-law distribution of flare events over many decades of energy. The Monte Carlo method is used to explore
the behavior of the waiting-time distributions for the flare-like models. The models with δ≠0 are found to have waiting times that depart significantly from simple Poisson behavior when
. The original model from Wheatland and Glukhov (Astrophys. J.
494, 858, 1998), with δ=0 (i.e., no dependence of transition rates on active-region energy), is identified as being most consistent with observed flare statistics. 相似文献
13.
We investigate static, spherical configurations of cold catalized matter in the Einstein-Cartan theory of gravitation. Assuming that density of spin is proportional to the number density of baryonsn and using an equation of state of a degenerate, relativistic Fermi gas, we numerically integrated the relativistic equation of equilibrium. We have also studied the stability of those configurations. Configurations with central number densityn
c
such that
where
is the effective pressure, are very similar to general relativistic configurations with the same central density. In the Einstein-Cartan theory there exists another disjoint family of equilibrium configurations for which
but
. Those configurations have very small masses 10–6 g and raddi 10–34 cm and are unstable.Supported in part by Research Grant MR-I-7. 相似文献
14.
In this work, we shall confine ourselves to solve analytically the integrals called
,
for the two components of albedo radiation pressure on an Earth’s satellite. When the Earth’s albedo is variable, as far as
we know, this case has not been dealt with analytically. We shall solve these two integrals when the satellite’ horizon is
illuminated and when the sun lies on the equator. This approach will facilitate the evaluation of the mentioned two equations.
We will also compare our results with previous works obtained numerically. 相似文献
15.
Markus Ackermann 《Astrophysics and Space Science》2007,309(1-4):421-427
The AMANDA-II telescope, operated by the IceCube collaboration, is currently the world’s most sensitive telescope to fluxes
of neutrinos from individual sources. A data sample of 4282 neutrino induced events collected in 1001 days of detector livetime
during the years 2000–2004 have now been analyzed looking for a neutrino signal from point-like sources. A sensitivity to
fluxes of
of d
Φ/dE=1.0×10−10(E/TeV)−2 TeV−1 cm−2s−1 was reached in the energy range between 1.7 TeV and 2.4 PeV. So far no statistically significant localized excess of events
over the background of atmospheric neutrinos has been found, which would be ascribed to a neutrino source. However, the flux
upper limits derived from the non-observation of a signal are comparable to observed fluxes of high energy gamma rays from
blazars and within the range of current models for neutrino emission from selected sources. Possible constraints on these
models are discussed.
相似文献
16.
17.
We report on 10 yr of monitoring of the 8.7-s Anomalous X-ray Pulsar 4U 0142+61 using the Rossi X-Ray Timing Explorer (RXTE). This pulsar exhibited stable rotation from 2000 until February 2006: the RMS phase residual for a spin-down model which
includes ν,
, and
is 2.3%. We report a possible phase-coherent timing solution valid over a 10-yr span extending back to March 1996. A glitch
may have occurred between 1998 and 2000, but it is not required by the existing data. We also report that the source’s pulse
profile has been evolving in the past 6 years, such that the dip of emission between its two peaks has been getting shallower
since 2000, almost as if the profile is recovering to its pre-2000 morphology, in which there was no clear distinction between
the peaks. These profile variations are seen in the 2–4 keV band but not in 6–8 keV. Finally, we present the pulsed flux time
series of the source in 2–10 keV. There is evidence of a slow but steady increase in the source’s pulsed flux since 2000.
The pulsed flux variability and the narrow-band pulse profile changes present interesting challenges to aspects of the magnetar
model.
This work was supported by the Natural Sciences and Engineering Research Council (NSERC) PGSD scholarship to R.D. F.P.G. holds
a National Research Council Research Associateship Award at NASA Goddard Space Flight Center. Additional support was provided
by NSERC Discovery Grant Pgpin 228738-03 NSERC Steacie Supplement Smfsu 268264-03, FQRNT, CIAR, and CFI. V.M.K. is a Canada
Research Chair. 相似文献
18.
The modulational instability of the weakly nonlinear longitudinal Langmuir as well as the transverse electromagnetic waves, propagation in the relativistic plasma without the static fields is described. The nonlinear Schrödinger equation taking account of the nonlinear Landau damping for these waves has been derived by means of the relativistic Vlasov and Maxwell equations. The plasma with the weakly relativistic temperature and that with an ultrarelativistic one has been investigated. In the first case, for the electron-proton plasma with the temperature more than 2.3 KeV we found the regional change of the wave numbers for which the soliton of two types, subsonic and supersonic, can exist. The soliton of the transverse waves can exist when the group velocity of the waves is between the thermal velocity of the electron and ion and the length of the linear waves is less than 2c/
pi
.In the second case the regions of the wave numbers, with the solitons of the Langmuir and transverse waves have been determined.The nonlinear waves in the electron-positron plasma and the waves with the phase velocity, which is about the light one, are also considered in the following paper. 相似文献
19.
B. G. Piner S. C. Unwin A. E. Wehrle P. G. Edwards A. L. Fey K. A. Kingham 《New Astronomy Reviews》1999,43(8-10)
We have produced 22 VLBI images of the TeV blazar Markarian 421 at 11 epochs, including a Space VLBI observation with the HALCA satellite. We measure the speeds of the three innermost jet components to be 0.64±0.33, 0.48±0.09, and 0.06±0.09c (H0=65 km s−1 Mpc−1). Interpretation of these subluminal speeds in terms of the high Doppler factor demanded by the TeV observations is discussed. 相似文献
20.
Xinwu Cao 《Monthly notices of the Royal Astronomical Society》2002,332(4):999-1004
We consider the power of a relativistic jet accelerated by the magnetic field of an accretion disc. It is found that the power extracted from the disc is mainly determined by the field strength and configuration of the field far from the disc. Comparing it with the power extracted from a rotating black hole, we find that the jet power extracted from a disc can dominate over that from the rotating black hole. However, in some cases, the jet power extracted from a rapidly rotating hole can be more important than that from the disc, even if the poloidal field threading the hole is not significantly larger than that threading the inner edge of the disc. The results imply that the radio-loudness of quasars may be governed by its accretion rate, which might be regulated by the central black hole mass. It is proposed that the different disc field generation mechanisms might be tested against observations of radio-loud quasars if their black hole masses are available. 相似文献
|