329 research outputs found
Dependence of the optical continuous spectrum of quasars on their red-shift
Dependence of optical continuous spectrum of quasi-stellar sources on red shif
An Induction Accelerator of Cosmic Rays on the Axis of an Accretion Disk
The structure and magnitude of the electric field created by a rotating
accretion disk with a poloidal magnetic field is found for the case of a vacuum
approximation along the axis. The accretion disk is modeled as a torus filled
with plasma and the frozen-in magnetic field. The dimensions and location of
the maximum electric field are found, as well as the energy of the accelerated
particles. The gravitational field is assumed to be weak.Comment: 10 pages, 4 figure
Radio astronomical space system of aperture synthesis: Filling of the spatial frequency spectrum
The information potential of radio astronomical space systems of aperture synthesis is examined. Ground based and space radio telescopes are included
Synchrotron aging and the radio spectrum of SN 1993J
We combine the GMRT low frequency radio observations of SN 1993J with the VLA
high frequency radio data to get a near simultaneous spectrum around day 3200
since explosion. The low frequency measurements of the supernova determine the
turnover frequency and flux scale of the composite spectrum and help reveal a
steepening in the spectral index, , in the optically
thin part of the spectrum. This is the first observational evidence of a break
in the radio spectrum of a young supernova. We associate this break with the
phenomenon of synchrotron aging of radiating electrons. From the break in the
spectrum we calculate the magnetic field in the shocked region independent of
the equipartition assumption between energy density of relativistic particles
and magnetic energy density. We determine the ratio of these two energy
densities and find that this ratio is in the range: . We also predict the nature of the evolution of the synchrotron break
frequency with time, with competing effects due to diffusive Fermi acceleration
and adiabatic expansion of the radiative electron plasma.Comment: 12 pages, 2 figures. Accepted for publication in ApJ
New analytic models of traversable wormholes
The analytic solution of the general relativity equations for spherically
symmetric wormholes are given. We investigate the special case of a
"traversable" wormhole i.e., one allowing the signal to pass through it. The
energy-momentum tensor of wormhole matter is represented as a superposition of
a spherically symmetric magnetic field and dust matter with negative matter
density. The dynamics of the model are investigated. We discuss both the
solution of the equation with a Lambda-term and without it. Superposing enough
dust matter, a magnetic field, and a Lambda-term can produce a static solution,
which turns out to be a spherical Multiverse model with an infinite number of
wormholes connected spherical universes. Corresponding solution can be static
and dynamic.Comment: 15 pages, 2 figure
Magnetically-dominated jets inside collapsing stars as a model for gamma-ray bursts and supernova explosions
It has been suggested that magnetic fields play a dynamically-important role
in core-collapse explosions of massive stars. In particular, they may be
important in the collapsar scenario for gamma-ray bursts (GRB), where the
central engine is a hyper-accreting black hole or a millisecond magnetar. The
present paper is focussed on the magnetar scenario, with a specific emphasis on
the interaction of the magnetar magnetosphere with the infalling stellar
envelope. First, the ``Pulsar-in-a-Cavity'' problem is introduced as a paradigm
for a magnetar inside a collapsing star. The basic set-up of this fundamental
plasma-physics problem is described, outlining its main features, and simple
estimates are derived for the evolution of the magnetic field. In the context
of a collapsing star, it is proposed that, at first, the ram pressure of the
infalling plasma acts to confine the magnetosphere, enabling a gradual build-up
of the magnetic pressure. At some point, the growing magnetic pressure
overtakes the (decreasing) ram pressure of the gas, resulting in a
magnetically-driven explosion. The explosion should be highly anisotropic, as
the hoop-stress of the toroidal field, confined by the surrounding stellar
matter, collimates the magnetically-dominated outflow into two beamed
magnetic-tower jets. This creates a clean narrow channel for the escape of
energy from the central engine through the star, as required for GRBs. In
addition, the delayed onset of the collimated-explosion phase can explain the
production of large quantities of Nickel-56, as suggested by the GRB-Supernova
connection. Finally, the prospects for numerical simulations of this scenario
are discussed.Comment: Invited paper in the "Physics of Plasmas" (May 2007 special issue),
based on an invited talk at the 48th Annual Meeting of the APS Division of
Plasma Physics (Oct. 30 - Nov. 3, 2006, Philadelphia, PA); 24 pages, 7
figure
Magnetic fields in AGNs and microquasars
Observations of AGNs and microquasars by ASCA, RXTE, Chandra and XMM-Newton
indicate the existence of wide X-ray emission lines of heavy ionized elements
in their spectra. The emission can arise in the inner parts of accretion discs
where the effects of General Relativity (GR) must be counted, moreover such
effects can dominate. We describe a procedure to estimate an upper limit of the
magnetic fields in the regions where X-ray photons are emitted. We simulate
typical profiles of the iron line in the presence of a magnetic
field and compare them with observational data. As an illustration we find Gs for Seyfert galaxy MCG--6--30--15. Using the perspective
facilities of measurement devices (e.g. Constellation-X mission) a better
resolution of the blue peak structure of iron line will allow to
find the value of the magnetic fields if the latter are high enough.Comment: 9 pages, 6 figures, submitted to MNRA
Ultraviolet HST Observations of the Jet in M87
We present new ultraviolet photometry of the jet in M87 obtained from HST
WFPC2 imaging. We combine these ultraviolet data with previously published
photometry for the knots of the jet in radio, optical, and X-ray, and fit three
theoretical synchrotron models to the full data set. The synchrotron models
consistently overpredict the flux in the ultraviolet when fit over the entire
dataset. We show that if the fit is restricted to the radio through ultraviolet
data, the synchrotron models can provide a good match to the data. The break
frequencies of these fits are much lower than previous estimates. The implied
synchrotron lifetimes for the bulk of the emitting population are longer than
earlier work, but still much shorter than the estimated kinematic lifetimes of
the knots. The observed X-ray flux cannot be successfully explained by the
simple synchrotron models that fit the ultraviolet and optical fluxes. We
discuss the possible implications of these results for the physical properties
of the M87 jet. We also observe increased flux for the HST-1 knot that is
consistent with previous results for flaring. This observation fills in a
significant gap in the time coverage early in the history of the flare, and
therefore sets constraints on the initial brightening of the flare.Comment: 14 pages, 2 figures, Accepted for publication in ApJ, changed
lightcurve and caption in Figure
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