189 research outputs found
The jet/disk connection in blazars
The new high energy data coming mainly from the Fermi and Swift satellites
and from the ground based Cerenkov telescopes are making possible to study not
only the energetics of blazar jets, but also their connection to the associated
accretion disks. Furthermore, the black hole mass of the most powerful objects
can be constrained through IR-optical emission, originating in the accretion
disks. For the first time, we can evaluate jet and accretion powers in units of
the Eddington luminosity for a large number of blazars. Firsts results are
intriguing. Blazar jets have powers comparable to, and often larger than the
luminosity produced by their accretion disk. Blazar jets are produced at all
accretion rates (in Eddington units), and their appearance depends if the
accretion regime is radiatively efficient or not. The jet power is dominated by
the bulk motion of matter, not by the Poynting flux, at least in the jet region
where the bulk of the emission is produced, at ~1000 Schwarzschild radii. The
mechanism at the origin of relativistic jets must be very efficient, possibly
more than accretion, even if accretion must play a crucial role. Black hole
masses for the most powerful jets at redshift ~3 exceed one billion solar
masses, flagging the existence of a very large population of heavy black holes
at these redshifts.Comment: 12 pages, 10 figures, invited contribution for the meeting: Plasmas
in the Laboratory and in the Universe: interactions, patterns, and
turbulence. Como, December 200
Coherent curvature radiation and Fast Radio Bursts
Fast radio bursts are extragalactic radio transient events lasting a few
milliseconds with a ~Jy flux at ~1 GHz. We propose that these properties
suggest a neutron star progenitor, and focus on coherent curvature radiation as
the radiation mechanism. We study for which sets of parameters the emission can
fulfil the observational constraints. Even if the emission is coherent, we find
that self-absorption can limit the produced luminosities at low radio
frequencies and that an efficient re-acceleration process is needed to balance
the dramatic energy losses of the emitting particles. Self-absorption limits
the luminosities at low radio frequency, while coherence favours steep
optically thin spectra. Furthermore, the magnetic geometry must have a high
degree of order to obtain coherent curvature emission. Particles emit photons
along their velocity vectors, thereby greatly reducing the inverse Compton
mechanism. In this case we predict that fast radio bursts emit most of their
luminosities in the radio band and have no strong counterpart in any other
frequency bands.Comment: 8 pages, 3 figures, 1 table. Accepted for publication in A&
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