135 research outputs found
A lower bound on the local extragalactic magnetic field
Assuming that the hard gamma-ray emission of Cen A is a result of synchrotron
radiation of ultra-relativistic electrons, we derive a lower bound on the local
extragalactic magnetic field, G. This result is consistent with
(and close to) upper bounds on magnetic fields derived from consideration of
cosmic microwave background distortions and Faraday rotation measurements.Comment: Includes extensive discussion of particle acceleration above 10^20 eV
in the hot spot-like region of Cen
Isothermal Plasma Wave Properties of the Schwarzschild de-Sitter Black Hole in a Veselago Medium
In this paper, we study wave properties of isothermal plasma for the
Schwarzschild de-Sitter black hole in a Veselago medium. We use ADM 3+1
formalism to formulate general relativistic magnetohydrodynamical (GRMHD)
equations for the Schwarzschild de-Sitter spacetime in Rindler coordinates.
Further, Fourier analysis of the linearly perturbed GRMHD equations for the
rotating (non-magnetized and magnetized) background is taken whose determinant
leads to a dispersion relation. We investigate wave properties by using
graphical representation of the wave vector, the refractive index, change in
refractive index, phase and group velocities. Also, the modes of wave
dispersion are explored. The results indicate the existence of the Veselago
medium.Comment: 24 pages, 12 figures, accepted for publication in Astrophys. Space
Sci. arXiv admin note: text overlap with arXiv:1101.0884 and arxiv:1007.285
Energy and Flux Measurements of Ultra-High Energy Cosmic Rays Observed During the First ANITA Flight
The first flight of the Antarctic Impulsive Transient Antenna (ANITA)
experiment recorded 16 radio signals that were emitted by cosmic-ray induced
air showers. For 14 of these events, this radiation was reflected from the ice.
The dominant contribution to the radiation from the deflection of positrons and
electrons in the geomagnetic field, which is beamed in the direction of motion
of the air shower. This radiation is reflected from the ice and subsequently
detected by the ANITA experiment at a flight altitude of 36km. In this paper,
we estimate the energy of the 14 individual events and find that the mean
energy of the cosmic-ray sample is 2.9 EeV. By simulating the ANITA flight, we
calculate its exposure for ultra-high energy cosmic rays. We estimate for the
first time the cosmic-ray flux derived only from radio observations. In
addition, we find that the Monte Carlo simulation of the ANITA data set is in
agreement with the total number of observed events and with the properties of
those events.Comment: Added more explanation of the experimental setup and textual
improvement
Radiation fields of disk, BLR and torus in quasars and blazars: implications for gamma-ray absorption
The radiation fields external to the jets and originating from within a few
parsecs from the black hole, are discussed in this paper. They are the direct
radiation from an accretion disk in symbiosis with jets, the radiation field
from the broad line region (BLR) surrounding the accretion disk, and the
infrared radiation from a dusty torus. The jet/disk symbiosis modifies the
energetics in the central parsec of AGN such that for a given accretion rate, a
powerful jet would occur at the expense of the disk luminosity, and
consequently the disk would less efficiently ionize the BRL clouds or heat the
dust in the torus, thereby affecting potentially important target photon fields
for interactions of gamma-rays, accelerated electrons and protons along the
jet.
Motivated by unification schemes of active galactic nuclei, we briefly review
the evidence for the existence of broad line regions and small-scale dust tori
in BL Lacs and Fanaroff-Riley Class I (FR-I) radio galaxies. We propose that an
existing jet-accretion disk symbiosis can be extrapolated to provide a large
scale-symbiosis between other important dusty constituents of the blazar/FR-I
family. In the present paper, we discuss in the context of this symbiosis
interactions of GeV and TeV gamma-rays produced in the jet with the various
radiation fields external to the jet in quasars and blazars, taking account the
anisotropy of the radiation.Comment: 27 pages, 12 figures. submitted to Astroparticle Physic
Light Therapy for Cancer-Related Fatigue in (Non-)Hodgkin Lymphoma Survivors: Results of a Randomized Controlled Trial
A new estimate of the extragalactic radio background and implications for ultra-high-energy gamma-ray propagation
We make a new estimate of the extragalactic radio background down to kHz
frequencies based on the observed luminosity functions and radio spectra of
normal galaxies and radio galaxies. We have constructed models for the spectra
of these two classes of objects down to low frequencies based on observations
of our Galaxy, other normal galaxies and radio galaxies. We check that the
models and evolution of the luminosity functions give source counts consistent
with data and calculate the radio background expected from kHz to GHz
frequencies.
The motivation for this calculation is that the propagation of ultra-high
energy gamma-rays in the universe is limited by photon-photon pair production
on the radio background. Electromagnetic cascades involving photon-photon pair
production and subsequent synchrotron radiation in the intergalactic magnetic
field may develop. Such gamma-rays may be produced in acceleration sites of
ultra-high energy cosmic rays, as a result of interactions with the microwave
background, or emitted as a result of decay or annihilation of topological
defects. We find that photon-photon pair production on the radio background
remains the dominant attenuation process for gamma-rays from
GeV up to GUT scale energies.Comment: LaTeX, 21 pages, including 10 postscript figures, tar'd and gzip'
Fauna of mosquitoes (Diptera: Culicidae) in Goytacazes National Forest and surrounding area, State of EspĂrito Santo, Southeastern Brazil
The global atmospheric electrical circuit and climate
Evidence is emerging for physical links among clouds, global temperatures, the global atmospheric electrical circuit and cosmic ray ionisation. The global circuit extends throughout the atmosphere from the planetary surface to the lower layers of the ionosphere. Cosmic rays are the principal source of atmospheric ions away from the continental boundary layer: the ions formed permit a vertical conduction current to flow in the fair weather part of the global circuit. Through the (inverse) solar modulation of cosmic rays, the resulting columnar ionisation changes may allow the global circuit to convey a solar influence to meteorological phenomena of the lower atmosphere. Electrical effects on non-thunderstorm clouds have been proposed to occur via the ion-assisted formation of ultra-fine aerosol, which can grow to sizes able to act as cloud condensation nuclei, or through the increased ice nucleation capability of charged aerosols. Even small atmospheric electrical modulations on the aerosol size distribution can affect cloud properties and modify the radiative balance of the atmosphere, through changes communicated globally by the atmospheric electrical circuit. Despite a long history of work in related areas of geophysics, the direct and inverse relationships between the global circuit and global climate remain largely quantitatively unexplored. From reviewing atmospheric electrical measurements made over two centuries and possible paleoclimate proxies, global atmospheric electrical circuit variability should be expected on many timescale
The Antarctic Impulsive Transient Antenna Ultra-high Energy Neutrino Detector Design, Performance, and Sensitivity for 2006-2007 Balloon Flight
We present a detailed report on the experimental details of the Antarctic
Impulsive Transient Antenna (ANITA) long duration balloon payload, including
the design philosophy and realization, physics simulations, performance of the
instrument during its first Antarctic flight completed in January of 2007, and
expectations for the limiting neutrino detection sensitivity. Neutrino physics
results will be reported separately.Comment: 50 pages, 49 figures, in preparation for PR
How to move ionized gas: an introduction to the dynamics of HII regions
This review covers the dynamic processes that are important in the evolution
and structure of galactic HII regions, concentrating on an elementary
presentation of the physical concepts and recent numerical simulations of HII
region evolution in a non-uniform medium.
The contents are as follows:
(1) The equations (Euler equations; Radiative transfer; Rate equations; How
to avoid the dynamics; How to avoid the atomic physics).
(2) Physical concepts (Static photoionization equilibrium; Ionization front
propagation; Structure of a D-type front; Photoablation flows; Other
ingredients - Stellar winds, Radiation pressure, Magnetic fields,
Instabilities).
(3) HII region evolution (Early phases: hypercompact and ultracompact
regions; Later phases: compact and extended regions; Clumps and turbulence).Comment: To be published as a chapter in 'Diffuse Matter from Star Forming
Regions to Active Galaxies' - A volume Honouring John Dyson. Eds. T. W.
Harquist, J. M. Pittard and S. A. E. G. Falle. 25 pages, 7 figures. Some
figures degraded to meet size restriction. Full-resolution version available
at http://www.ifront.org/wiki/Dyson_Festschrift_Chapte
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