333 research outputs found
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
Intermittent activity of radio sources. Accretion instabilities and jet precession
We consider the radiation pressure instability operating on short timescales
10^3 - 10^6 years in the accretion disk around a supermassive black hole as the
origin of the intermittent activity of radio sources. We test whether this
instability can be responsible for short ages (<10^4 years) of Compact Steep
Spectrum sources measured by hot spots propagation velocities in VLBI
observations and statistical overabundance of Gigahertz Peaked Spectrum
sources.The implied timescales are consistent with the observed ages of the
sources. We aslo discuss possible implications of the intermittent activity on
the complex morphology of radio sources, such as the quasar 1045+352, dominated
by a knotty jet showing several bends. It is possible that we are whitnessing
an ongoing jet precession in this source due to internal instabilities within
the jet flow.Comment: 2 pages, 1 figure, Proceedings of the 275 IAU Symposium "Jets at all
scales", Buenos Aires, 13-17.09.2010; eds. G. Romero, R. Sunyaev, T. Bellon
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