21 research outputs found
Static configurations and evolution of higher dimensional brane-dilaton black hole system
Static configurations and a dynamical evolution of the system composed of a
higher-dimensional spherically symmetric dilaton black hole and the
Dirac-Goto-Nambu brane were investigated. The studies were conducted for three
values of the dilaton coupling constant, describing the uncoupled case, the
low-energy limit of the string theory and dimensionally reduced Klein-Kaluza
theories. When the black hole is nonextremal, two types of static
configurations are observed, a brane which intersects the black hole horizon
and a brane not having any common points with the accompanying black hole. As
the number of spacetime dimensions increases, the brane bend in the vicinity of
the black hole disappears closer to its horizon. Dynamical evolution of the
system results in an expulsion of the black hole from the brane. It proceeds
faster for bigger values of the bulk spacetime dimension and thicker branes.
The value of the dilatonic coupling constant does not influence neither the
static configurations nor the dynamical behavior of the examined nonextremal
system. In the extremal dilaton black hole case one obtains expulsion of the
brane which is independent on the spacetime dimensionality and the value of the
coupling constant. Dynamical studies of the configurations in the extremal case
reveal that the course of evolution of the system is similar to the nonextremal
one, except for a slightly earlier expulsion of the black hole from the brane.Comment: 23 pages, 7 figure
Comment on Viscous Stability of Relativistic Keplerian Accretion Disks
Recently Ghosh (1998) reported a new regime of instability in Keplerian
accretion disks which is caused by relativistic effects. This instability
appears in the gas pressure dominated region when all relativistic corrections
to the disk structure equations are taken into account. We show that he uses
the stability criterion in completely wrong way leading to inappropriate
conclusions. We perform a standard stability analysis to show that no unstable
region can be found when the relativistic disk is gas pressure dominated.Comment: 9 pages, 4 figures, uses aasms4.sty, submitted for ApJ Letter
On the origin of X-ray spectra in luminous blazars
Gamma-ray luminosities of some quasar-associated blazars imply jet powers
reaching values comparable to the accretion power even if assuming very strong
Doppler boosting and very high efficiency of gamma-ray production. With much
lower radiative efficiencies of protons than of electrons, and the recent
reports of very strong coupling of electrons with shock-heated protons
indicated by Particle-in-Cell (PIC) simulations, the leptonic models seem to be
strongly favored over the hadronic ones. However, the electron-proton coupling
combined with the ERC (External-Radiation-Compton) models of gamma-ray
production in leptonic models predict extremely hard X-ray spectra, with energy
indices about 0. This is inconsistent with the observed 2-10 keV slopes of
blazars, which cluster around an index value of 0.6. This problem can be
resolved by assuming that electrons can be cooled down radiatively to
non-relativistic energies, or that blazar spectra are entirely dominated by the
SSC (Synchrotron-Self Compton) component up to at least 10 keV. Here, we show
that the required cooling can be sufficiently efficient only at distances r <
0.03pc. SSC spectra, on the other hand, can be produced roughly co-spatially
with the observed synchrotron and ERC components, which are most likely located
roughly at a parsec scale. We show that the dominant SSC component can also be
produced much further than the dominant synchrotron and ERC components, at
distances larger than 10 parsecs. Hence, depending on the spatial distribution
of the energy dissipation along the jet, one may expect to see
gamma-ray/optical events with either correlated or uncorrelated X-rays. In all
cases the number of electron-positron pairs per proton is predicted to be very
low. The direct verification of the proposed SSC scenario requires sensitive
observations in the hard X-ray band which is now possible with the NuSTAR
satellite.Comment: 19 pages, 1 figure, accepted for publication in Ap
Evolution of a Self-interacting Scalar Field in the spacetime of a Higher Dimensional Black Hole
In the spacetime of n-dimensional static charged black hole we examine the
mechanism by which the self-interacting scalar hair decay. It is turned out
that the intermediate asymptotic behaviour of the self-interacting scalar field
is determined by an oscilatory inverse power law. We confirm our results by
numerical calculations.Comment: RevTex, 6 pages, 8 figures, to be published in Phys.Rev.D1
Thick Domain Walls in AdS Black Hole Spacetimes
Equations of motion for a real self-gravitating scalar field in the
background of a black hole with negative cosmological constant were solved
numerically. We obtain a sequence of static axisymmetric solutions representing
thick domain wall cosmological black hole systems, depending on the mass of
black hole, cosmological parameter and the parameter binding black hole mass
with the width of the domain wall. For the case of extremal cosmological black
hole the expulsion of scalar field from the black hole strongly depends on it.Comment: 20 pages, 19 figures, accepted for publication in Phys. Rev.
Decay of Dirac Massive Hair in the Background of Spherical Black Hole
The intermediate and late-time behaviour of massive Dirac hair in the static
spherically symmetric black hole spacetime was studied. It was revealed that
the intermediate asymptotic pattern of decay of massive Dirac spinor hair is
dependent on the mass of the field under consideration as well as the multiple
number of the wave mode. The long-lived oscillatory tail observed at timelike
infinity in the considered background decays slowly as t^{-5/6}.Comment: 8 pages, 5 figures, RevTex, to be published in Phys.Rev.D1
3C454.3 reveals the structure and physics of its 'blazar zone'
Recent multi-wavelength observations of 3C454.3, in particular during its
giant outburst in 2005, put severe constraints on the location of the 'blazar
zone', its dissipative nature, and high energy radiation mechanisms. As the
optical, X-ray, and millimeter light-curves indicate, significant fraction of
the jet energy must be released in the vicinity of the millimeter-photosphere,
i.e. at distances where, due to the lateral expansion, the jet becomes
transparent at millimeter wavelengths. We conclude that this region is located
at ~10 parsecs, the distance coinciding with the location of the hot dust
region. This location is consistent with the high amplitude variations observed
on ~10 day time scale, provided the Lorentz factor of a jet is ~20. We argue
that dissipation is driven by reconfinement shock and demonstrate that X-rays
and gamma-rays are likely to be produced via inverse Compton scattering of
near/mid IR photons emitted by the hot dust. We also infer that the largest
gamma-to-synchrotron luminosity ratio ever recorded in this object - having
taken place during its lowest luminosity states - can be simply due to weaker
magnetic fields carried by a less powerful jet.Comment: 19 pages, 3 figures, accepted for publication in Ap
Dynamical Collapse of Charged Scalar Field in Phantom Gravity
We investigated the problem of the dynamical collapse of a self-gravitating
complex charged scalar field in Einstein-Maxwell-dilaton theory with a phantom
copuling for the adequate fields in the system under consideration. We also
considered two simplifications of it, i.e., the separate collapses of phantom
Maxwell and phantom scalar fields under the influence of Einstein gravity. One
starts with the regular spacetime and leads the evolution through the formation
of the horizons and the final singularity. We discuss the structures of
spacetimes emerging in the process of the dynamical collapse and comment on the
role of the considered fields in its course.Comment: 15 pages, RevTex, 18 figures, to be published in Phys.Rev.D1