932 research outputs found
Radiative Processes In Extragalactic Large-Scale Jets
About one thousand extragalactic large-scale jets are known, and a few tens
of them are confirmed sources of infrared, optical, or X-ray photons.
Multiwavelength emission comming directly from these outflows is always
non-thermal in origin. This fact constitutes a primary difficulty in extracting
unknown parameters of large-scale jets, since the non-thermal featureless
continua do not allow to infer undoubtfully (or even at all) bulk velocities
and composition of the radiating plasma. In addition, arcsecond spatial
resolution, limited sensitivity and narrow energy bands of the best
high-frequency telescopes like Spitzer, Hubble and Chandra, preclude precise
constraints on the spectral and morphological properties of the discussed
objects. Nevertheless, new multiwavelength observations have substantially
enriched our knowledge on extragalactic large-scale jets, in many aspects,
however, by means of challenging previous predictions and expectations. In this
short contribution I will concentrate on the following issue: what can be
learned by analyzing broad-band emission of the discussed objects about
particle acceleration processes acting thereby and about jet internal
parameters.Comment: 6 pages, 6 figures included. Proceedings of the Workshop
`Astrophysical Sources of High Energy Particles and Radiation', Torun, Jun.
200
Radio Loudness of AGNs: Host Galaxy Morphology and the Spin Paradigm
We investigate how the total radio luminosity of AGN-powered radio sources
depends on their accretion luminosity and the central black hole mass. We find
that AGNs form two distinct and well separated sequences on the radio-loudness
- Eddington-ratio plane. We argue that these sequences mark the real upper
bounds of radio-loudness of two distinct populations of AGNs: those hosted
respectively by elliptical and disk galaxies. Both sequences show the same
dependence of the radio-loudness on the Eddington ratio (an increase with
decreasing Eddington ratio), which suggests that another parameter in addition
to the accretion rate must play a role in determining the jet production
efficiency in active galactic nuclei, and that this parameter is related to
properties of the host galaxy. The revealed host-related radio dichotomy breaks
down at high accretion rates where the dominant fraction of luminous quasars
hosted by elliptical galaxies is radio quiet. We argue that the huge difference
between the radio-loudness reachable by AGNs in disc and elliptical galaxies
can be explained by the scenario according to which the spin of a black hole
determines the outflow's power, and central black holes can reach large spins
only in early type galaxies (following major mergers), and not (in a
statistical sense) in spiral galaxies.Comment: 7 pages, 4 figures included. Proceedings of the Workshop
`Extragalactic Jets: Theory and Observation from Radio to Gamma Ray',
Girdwood, May 200
Non-linear shock acceleration and high energy gamma rays from clusters of galaxies
Merger and accretion shocks in clusters of galaxies can accelerate particles
via first order Fermi process. Since this mechanism is believed to be
intrinsically efficient, shocks are expected to be modified by the backreaction
of the accelerated particles. Such a modification might induce appreciable
effects on the non--thermal emission from clusters and a suppression of the
heating of the gas at strong shocks. Here we consider in particular the gamma
ray emission and we discuss the capability of Cherenkov telescopes such as HESS
to detect clusters at TeV energies.Comment: 6 pages, to appear in the proceedings of the Gamma 2004 Symposium on
High Energy Gamma Ray Astronomy, Heidelberg, July 2004 (AIP Proceedings
Series
Electron Energy Distributions at Relativistic Shock Sites: Observational Constraints from the Cygnus A Hotspots
We report new detections of the hotspots in Cygnus A at 4.5 and 8.0 microns
with the Spitzer Space Telescope. Together with detailed published radio
observations and synchrotron self-Compton modeling of previous X-ray
detections, we reconstruct the underlying electron energy spectra of the two
brightest hotspots (A and D). The low-energy portion of the electron
distributions have flat power-law slopes (s~1.5) up to the break energy which
corresponds almost exactly to the mass ratio between protons and electrons; we
argue that these features are most likely intrinsic rather than due to
absorption effects. Beyond the break, the electron spectra continue to higher
energies with very steep slopes s>3. Thus, there is no evidence for the
`canonical' s=2 slope expected in 1st order Fermi-type shocks within the whole
observable electron energy range. We discuss the significance of these
observations and the insight offered into high-energy particle acceleration
processes in mildly relativistic shocks.Comment: 5 pages, 3 figures, in Extragalactic Jets: Theory and Observation
from Radio to Gamma Ray, Eds. T. A. Rector and D. S. De Youn
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