331 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
10 years of VLBA-BU-BLAZAR monitoring: relationship between gamma-ray and millimeter-wave events in blazar jets
https://fermi.gsfc.nasa.gov/science/mtgs/symposia/2018/program/wed/Alan_Marscher.pdfPublished versio
Behind the scenes: doing science across the spectrum
Summary of observations of blazars from radio through gamma-ray wavelengths, and their interpretation in terms of relativistic jets of ultra-high-energy particles and magnetic fields, powered by super-massive black holes at the centers of galaxieshttps://fermi.gsfc.nasa.gov/fermi10/fridays/03162018.htmlPublished versio
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
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
Hard gamma ray emission from blazars
The gamma-ray emission expected from compact extragalactic sources of nonthermal radiation is examined. The highly variable objects in this class should produce copious amounts of self-Compton gamma-rays in the compact relativistic jet. This is shown to be a likely interpretation of the hard gamma-ray emission recently detected from the quasar 3C 279 during a period of strong nonthermal flaring at lower frequencies. Ways of discriminating between the self-Compton model and other possible gamma-ray emission mechanisms are discussed
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