69 research outputs found
On a Coherent Radioemission Mechanism in Quasars and in the Remains of Supernovae
Coherent radio emission mechanism in quasars and remains of supernova
The Eddington Luminosity Phase in Quasars: Duration and Implications
Non-steady and eruptive phenomena in quasars are thought to be associated
with the Eddington or super-Eddington luminous stage. Although there is no lack
in hypotheses about the total duration of such a stage, the latter remains
essentially unknown. We calculate the duration of quasar luminous phase in
dependence upon the initial mass of a newborn massive black hole (MBH) by
comparing the observed luminosity- and redshift distributions of quasars with
mass distribution of the central MBHs in normal galactic nuclei. It is assumed
that, at the quasar stage, each MBH goes through a single (or recurrent)
phase(s) of accretion with, or close to, the Eddington luminosity. The mass
distributions of quasars is found to be connected with that of MBHs residing in
normal galaxies by a one-to-one corrrespondence through the entire mass range
of the inferred MBHs if the accretion efficiency of mass-to-energy
transformation .Comment: 4 pages, 2 figures, uses aipproc.sty. To appear in "Cosmic
Explosions" (Proc. of the 10th Annual October Conference in Maryland, Eds.
S.S. Holt and W.W. Zhang
GRB Redshift Distribution is Consistent with GRB Origin in Evolved Galactic Nuclei
Recently we have elaborated a new cosmological model of gamma-ray burst (GRB)
origin (1998, ApJ 502, 192), which employs the dynamical evolution of central
dense stellar clusters in the galactic nuclei. Those clusters inevitably
contain a large fraction of compact stellar remnants (CSRs), such as neutron
stars (NSs) and stellar mass black holes (BHs), and close encounters between
them result in radiative captures into short-living binaries, with subsequent
merging of the components, thereby producing GRBs (typically at large distances
from the nucleus).
In the present paper, we calculate the redshift distribution of the rate of
GRBs produced by close encounters of NSs in distant galactic nuclei. To this
end, the following steps are undertaken: (i) we establish a connection between
the parameters of the fast evolving central stellar clusters (i.e. those for
which the time of dynamical evolution exceeds the age of the Universe) with
masses of the forming central supermassive black holes (SMBHs) using a
dynamical evolution model; (ii) we connect these masses with the inferred mass
distributions of SMBHs in the galactic nuclei and the redshift distribution of
quasars by assuming a certain `Eddington luminosity phase' in their activity;
(iii) we incorporate available observational data on the redshift distribution
of quasars as well as a recently found correlation between the masses of
galaxies and their central SMBHs. The resulting redshift distribution of the
GRB rate, which accounts for both fast and slowly evolving galactic nuclei is
consistent with that inferred from the BATSE data if the fraction of fast
evolving galactic nuclei is in the range .Comment: LaTeX, 4 pages (incl. 1 figure), to appear in "After the Dark Ages:
When Galaxies Were Young (the Universe at 2<z<5)", eds. S.S. Holt and E.P.
Smit
Post-Newtonian Theory for Precision Doppler Measurements of Binary Star Orbits
The determination of velocities of stars from precise Doppler measurements is
described here using relativistic theory of astronomical reference frames so as
to determine the Keplerian and post-Keplerian parameters of binary systems. We
apply successive Lorentz transformations and the relativistic equation of light
propagation to establish the exact treatment of Doppler effect in binary
systems both in special and general relativity theories. As a result, the
Doppler shift is a sum of (1) linear in terms, which include the
ordinary Doppler effect and its variation due to the secular radial
acceleration of the binary with respect to observer; (2) terms proportional to
, which include the contributions from the quadratic Doppler effect
caused by the relative motion of binary star with respect to the Solar system,
motion of the particle emitting light and diurnal rotational motion of
observer, orbital motion of the star around the binary's barycenter, and
orbital motion of the Earth; and (3) terms proportional to , which
include the contributions from redshifts due to gravitational fields of the
star, star's companion, Galaxy, Solar system, and the Earth. After
parameterization of the binary's orbit we find that the presence of
periodically changing terms in the Doppler schift enables us disentangling
different terms and measuring, along with the well known Keplerian parameters
of the binary, four additional post-Keplerian parameters, including the
inclination angle of the binary's orbit, . We briefly discuss feasibility of
practical implementation of these theoretical results, which crucially depends
on further progress in the technique of precision Doppler measurements.Comment: Minor changes, 1 Figure included, submitted to Astrophys.
Compressible hydromagnetic nonlinearities in the predecoupling plasma
The adiabatic inhomogeneities of the scalar curvature lead to a compressible
flow affecting the dynamics of the hydromagnetic nonlinearities. The influence
of the plasma on the evolution of a putative magnetic field is explored with
the aim of obtaining an effective description valid for sufficiently large
scales. The bulk velocity of the plasma, computed in the framework of the
LambdaCDM scenario, feeds back into the evolution of the magnetic power spectra
leading to a (nonlocal) master equation valid in Fourier space and similar to
the ones discussed in the context of wave turbulence. Conversely, in physical
space, the magnetic power spectra obey a Schroedinger-like equation whose
effective potential depends on the large-scale curvature perturbations.
Explicit solutions are presented both in physical space and in Fourier space.
It is argued that curvature inhomogeneities, compatible with the WMAP 7yr data,
shift to lower wavenumbers the magnetic diffusivity scale.Comment: 29 page
Gamma Ray Bursts from the Evolved Galactic Nuclei
A new cosmological scenario for the origin of gamma ray bursts (GRBs) is
proposed. In our scenario, a highly evolved central core in the dense galactic
nucleus is formed containing a subsystem of compact stellar remnants (CSRs),
such as neutron stars and black holes. Those subsystems result from the
dynamical evolution of dense central stellar clusters in the galactic nuclei
through merging of stars, thereby forming (as has been realized by many
authors) the short-living massive stars and then CSRs. We estimate the rate of
random CSR collisions in the evolved galactic nuclei by taking into account,
similar to Quinlan & Shapiro (1987), the dissipative encounters of CSRs, mainly
due to radiative losses of gravitational waves, which results in the formation
of intermediate short-living binaries, with further coalescence of the
companions to produce GRBs. We also consider how the possible presence of a
central supermassive black hole, formed in a highly evolved galactic nucleus,
influences the CSR binary formation. This scenario does not postulate ad hoc a
required number of tight binary neutron stars in the galaxies. Instead, it
gives, for the most realistic parameters of the evolved nuclei, the expected
rate of GRBs consistent with the observed one, thereby explaining the GRB
appearance in a natural way of the dynamical evolution of galactic nuclei. In
addition, this scenario provides an opportunity for a cosmological GRB
recurrence, previously considered to be a distinctive feature of GRBs of a
local origin only. We also discuss some other observational tests of the
proposed scenario.Comment: 25 pages, LATEX, uses aasms4.sty, accepted by Ap
On the X-ray Emission from Massive Star Clusters and their Evolving Superbubbles
The X-ray emission properties from the hot thermalized plasma that results
from the collisions of individual stellar winds and supernovae ejecta within
rich and compact star clusters are discussed. We propose a simple analytical
way of estimating the X-ray emission generated by super star clusters and
derive an expression that indicates how this X-ray emission depends on the main
cluster parameters. Our model predicts that the X-ray luminosity from the star
cluster region is highly dependent on the star cluster wind terminal speed, a
quantity related to the temperature of the thermalized ejecta.We have also
compared the X-ray luminosity from the SSC plasma with the luminosity of the
interstellar bubbles generated from the mechanical interaction of the high
velocity star cluster winds with the ISM.We found that the hard (2.0 keV - 8.0
keV) X-ray emission is usually dominated by the hotter SSC plasma whereas the
soft (0.3 keV - 2.0 keV) component is dominated by the bubble plasma. This
implies that compact and massive star clusters should be detected as point-like
hard X-ray sources embedded into extended regions of soft diffuse X-ray
emission. We also compared our results with predictions from the population
synthesis models that take into consideration binary systems and found that in
the case of young,massive and compact super star clusters the X-ray emission
from the thermalized star cluster plasma may be comparable or even larger than
that expected from the HMXB population.Comment: 24 pages, 8 figures, Accepted for publication in The Astrophysical
Journa
Primordial magnetic field and spectral distortion of cosmic background radiation
The role played by a primordial magnetic field during the pre-recombination
epoch is analysed through the cyclotron radiation (due to the free electrons)
it might produce in the primordial plasma. We discuss the constraint implied by
the measurement or lack thereof COBE on this primordial field.Comment: to appear in International Journal of Mod. Phy
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