1,619 research outputs found
Theoretical interpretation of the HEAO-3 observations of Cygnus X-3 under the HEAO-3 Guest Investigator Program
A model of the galactic X-ray source Cygnus X-3 (Cyg X-3) is presented which deviates from previous models by positing that the X-rays originate in a jet rather than a binary system consiting of an ordinary star and a collapsed object. In the new model, the 4.8 hour period of Cyg X-3 is caused by variable absorption which occurs as the jet precesses. The primary role of the accretion disk corona (ADC) in modulating Cyg X-3 radiation is to make the observed intensity of a blob of material in a jet appear dimmer by absorption. The needed derivation of the positional dependence of the density of the ADC is freed of some complications by assuming that only the inner regions of the disk are precessing, with a period shorter than 4.8 hours. This model permits the secondary star to be a supergiant, as indicated by the luminosity of the system. The model is especially helpful in interpreting production of radio outbursts and very high energy gamma rays
Multi-waveband Emission Maps of Blazars
We are leading a comprehensive multi-waveband monitoring program of 34
gamma-ray bright blazars designed to locate the emission regions of blazars
from radio to gamma-ray frequencies. The "maps" are anchored by sequences of
images in both total and polarized intensity obtained with the VLBA at an
angular resolution of ~ 0.1 milliarcseconds. The time-variable linear
polarization at radio to optical wavelengths and radio to gamma-ray light
curves allow us to specify the locations of flares relative to bright
stationary features seen in the images and to infer the geometry of the
magnetic field in different regions of the jet. Our data reveal that some
flares occur simultaneously at different wavebands and others are only seen at
some of the frequencies. The flares are often triggered by a superluminal knot
passing through the stationary "core" on the VLBA images. Other flares occur
upstream or even parsecs downstream of the core.Comment: 5 pages, including 2 figures; to be published in Journal of
Astrophysics and Astronomy, as part of proceedings of the meeting
"Multiwavelength Variability of Blazars" held in Guangzhou, China, in
September 201
On the nature of an ejection event in the jet of 3C111
We present a possible scenario for the ejection of a superluminal component
in the jet of the Broad Line Radio Galaxy 3C111 in early 1996. VLBI
observations at 15 GHz discovered the presence of two jet features on scales
smaller than one parsec. The first component evolves downstream, whereas the
second one fades out after 1 parsec. We propose the injection of a perturbation
of dense material followed by a decrease in the injection rate of material in
the jet as a plausible explanation. This scenario is supported by 1D
relativistic hydrodynamics and emission simulations. The perturbation is
modeled as an increase in the jet density, without modifying the original
Lorentz factor in the initial conditions. We show that an increase of the
Lorentz factor in the material of the perturbation fails to reproduce the
observed evolution of this flare. We are able to estimate the lifetime of the
ejection event in 3C111 to be 36\pm7 days.Comment: Accepted for publication in Astronomy & Astrophysics Letter
Faraday Conversion in Turbulent Blazar Jets
Low () levels of circular polarization (CP) detected at radio
frequencies in the relativistic jets of some blazars can provide insight into
the underlying nature of the jet plasma. CP can be produced through linear
birefringence, in which initially linearly polarized emission produced in one
region of the jet is altered by Faraday rotation as it propagates through other
regions of the jet with varying magnetic field orientation. Marscher has begun
a study of jets with such magnetic geometries using the Turbulent Extreme
Multi-Zone (TEMZ) model, in which turbulent plasma crossing a standing shock in
the jet is represented by a collection of thousands of individual plasma cells,
each with distinct magnetic field orientations. Here we develop a radiative
transfer scheme that allows the numerical TEMZ code to produce simulated images
of the time-dependent linearly and circularly polarized intensity at different
radio frequencies. In this initial study, we produce synthetic polarized
emission maps that highlight the linear and circular polarization expected
within the model.Comment: 17 pages, 13 figures, accepted for publication in Ap
High-resolution polarization imaging of the Fermi blazar 3C 279
Ever since the discovery by the Fermi mission that active galactic nuclei (AGN) produce copious
amounts of high-energy emission, its origin has remained elusive. Using high-frequency radio
interferometry (VLBI) polarization imaging, we could probe the magnetic field topology of the
compact high-energy emission regions in blazars. A case study for the blazar 3C 279 reveals
the presence of multiple g -ray emission regions. Pass 8 Fermi-Large Area Telescope (LAT) data
are used to investigate the flux variations in the GeV regime; six g -ray flares were observed in
the source during November 2013 to August 2014. We use the 43 GHz VLBI data to study
the morphological changes in the jet. Ejection of a new component (NC2) during the first three
g -ray flares suggests the VLBI core as the possible site of the high-energy emission. A delay
between the last three flares and the ejection of a new component (NC3) indicates that highenergy
emission in this case is located upstream of the 43 GHz core (closer to the black hole).Accepted manuscrip
Expected level of self-Compton scattering in radio loud quasars
Radio-loud quasars usually contain parsec-scale nonthermal jets. The most compact emission region ('the core'), and perhaps some of the moving 'knots', are expected to be efficient producers of inverse Compton scattered X-rays and gamma-rays since many of the synchrotron photons will upscatter before escaping. Through multifrequency flux density observations and Very Long Baseline Interferometry (VLBI) measurements of angular sizes, one can predict the flux density of this self-Compton high-energy emission. It is not always the case that the brightest synchrotron sources are also the brightest X-ray and gamma-ray sources. Perhaps a better predictor of high-energy brightness is the ratio of hard X-ray to high-frequency radio emission. Using the synchrotron self-Compton relations, we predict the gamma-ray fluxes of several sources we expect to be detected by the Energetic Gamma Ray Experiment Telescope (EGRET). More accurate predictions will be made when we complete a program of contemporaneous radio-submillimeter and X-ray observations during the course of the EGRET all-sky survey
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