263 research outputs found
Cosmic rays from active galactic nuclei
Cosmic ray (CR) acceleration at the shock created by the expanding cocoons
around active galactic nuclei (AGNs) is studied. It is shown that above the
energy eV the overall energy spectrum of CRs, produced during the AGN
evolution and released in the intergalactic space, has the form , with , which extends up to
eV. It is concluded that cocoons shocks have to be
considered as a main source of extragalactic CRs, which together with Galactic
supernova remnants provide the observed CR spectrum.Comment: 9 pages, Accepted for publication in ApJ
Spectrum of cosmic rays, produced in supernova remnants
Nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova
remnants is employed to calculate CR spectra. The magnetic field in SNRs is
assumed to be significantly amplified by the efficiently accelerating nuclear
CR component. It is shown that the calculated CR spectra agree in a
satisfactory way with the existing measurements up to the energy eV.
The power law spectrum of protons extends up to the energy eV
with a subsequent exponential cutoff. It gives a natural explanation for the
observed knee in the Galactic CR spectrum. The maximum energy of the
accelerated nuclei is proportional to their charge number . Therefore the
break in the Galactic CR spectrum is the result of the contribution of
progressively heavier species in the overall CR spectrum so that at
eV the CR spectrum is dominated by iron group nuclei. It is shown that this
component plus a suitably chosen extragalactic CR component can give a
consistent description for the entire Galactic CR spectrum.Comment: 4 pages with emulateapj, 3 figures, accepted for publication in the
Astrophysical Journal Letter
Nonthermal and thermal emission from the supernova remnant RX J1713.7-3946
A nonlinear kinetic theory of cosmic ray (CR) acceleration in supernova
remnants (SNRs) is employed to investigate the properties of SNR RX
J1713.7-3946. Observations of the non-thermal radio and X-ray emission spectra
as well as the H.E.S.S. measurements of the very high energy gamma-ray emission
are used to constrain the astronomical and CR acceleration parameters of the
system. It is argued that RX J1713.7-3946 is a core collapse supernova (SN) of
type II/Ib with a massive progenitor, has an age of ~1600 yr and is at a
distance of ~1 kpc. It is in addition assumed that the CR
injection/acceleration takes place uniformly across the shock surface for this
kind of core collapse SNR. The theory gives a consistent description for all
the existing observational data, including the non-detection of thermal X-rays
and the spatial correlation of the X-ray and gamma-ray emission in the remnant.
Specifically it is shown that an efficient production of nuclear CRs, leading
to strong shock modification and a large downstream magnetic field strength B_d
~140 mkG can reproduce in detail the observed synchrotron emission from radio
to X-ray frequencies together with the gamma-ray spectral characteristics as
observed by the H.E.S.S. telescopes. The calculations are consistent with RX
J1713.7-3946 being an efficient source of nuclear cosmic rays.Comment: 6 pages, 4 figures, submitted to Astronomy and Astrophysic
Cosmic ray acceleration parameters from multi-wavelength observations. The case of SN 1006
The properties of the Galactic supernova remnant SN 1006 are theoretically
reanalysed. Nonlinear kinetic theory is used to determine the acceleration
efficiency of cosmic rays (CRs) in the supernova remnant SN 1006. The known
range of astronomical parameters and the existing measurements of nonthermal
emission are examined in order to define the values of the relevant physical
parameters which determine the CR acceleration efficiency. It is shown that the
parameter values -- proton injection rate, electron to proton ratio and
downstream magnetic field strength -- are determined with the appropriate
accuracy. In particular also the observed azimuthal variations in the gamma-ray
morphology agree with the theoretical expectation. These parameter values,
together with the reduction of the gamma-ray flux relative to a spherically
symmetric acceleration geometry, allow a good fit to the existing data,
including the recently detected TeV emission by H.E.S.S. SN 1006 represents the
first example where a high efficiency of nuclear CR production, required for
the Galactic CR sources, is consistently established.Comment: 10 pages, 6 figures, accepted for publication in A&
- …