9,883 research outputs found
The central engine of quasars and AGNs: A relativistic proton radiative shock
Active galactic nuclei (AGNs) and quasars (QSOs) appear to emit roughly equal energy per decade from radio to gamma-ray energies (e.g. Ramaty and Ligenfelter 1982). This argues strongly for a nonthermal radiation mechanism (see Rees 1984). In addition, statistical studies have indicated that the spectra of these objects in the IR-UV and 2 to 50 keV X-ray band, can be fitted very well with power laws of specific indices. These spectral indices do not seem to depend on the luminosity or morphology of the objects (Rothschild et al. 1983; Malkan 1984), and any theory should account for them in a basic and model independent way. If shocks accelerate relativistic protons via the first-order Fermi mechanism (e.g. Axfor 1981), the radiating electrons can be produced as secondaries throughout the source by proton-proton (p-p) collisions and pion decay, thus eliminating Compton losses (Protheroe and Kazanas 1983). As shown by Kazanas (1984), if relativistic electrons are injected at high energies, e+-e- pair production results in a steady state electron distribution that is very similar to that observed in AGNs, independent of the details of injection and the dynamics of the source. The conditions required by this mechanism are met in the shock model of Eichler (1984) and Ellison and Eichler (1984) which allows the self-consistent calculation of the shock acceleration efficiency
Relativistic cosmic ray spectra in the full non-linear theory of shock acceleration
The non-linear theory of shock acceleration was generalized to include wave dynamics. In the limit of rapid wave damping, it is found that a finite ave velocity tempers the acceleration of high Mach number shocks and limits the maximum compression ratio even when energy loss is important. For a given spectrum, the efficiency of relativistic particle production is essentially independent of v sub Ph. For the three families shown, the percentage of kinetic energy flux going into relativistic particles is (1) 72%, 2) 44%, and (3) 26% (this includes the energy loss at the upper energy cuttoff). Even small v sub ph, typical of the HISM, produce quasi-universal spectra that depend only weakly on the acoustic Mach number. These spectra should be close enough to e(-2) to satisfy cosmic ray source requirements
Corequake and shock heating model of the 5 March 1979 gamma ray burst
Ramatry, et al. proposed a model to account for the 5 March 1979 gamma ray burst in terms of a neutron star corequake and subsequent shock heating of the neutron star atmosphere. This model is extended by examining the overall energetics and characteristics of these shocks, taking into account the e(+)-e(-) pair production behind the shock. The effects of a dipole magnetic field in the shock jump conditions are also examined and it is concluded that the uneven heating produced by such a field can account for the temperature difference between pole and equator implied by the pulsating phase of the burst. The overall energetics and distribution of energy between e(+)-(-) pairs and photons appears to be in agreement with observations if this event is at a distance of 55 kpc as implied by its association with the Large Magellanic Cloud
Cosmic rays in the 10(16) to 10(19) eV range from pulsars
The flux is calculated of cosmic rays (CRs) produced by a distribution of pulsars that are: (1) born with rapid rotation rates, (2) slow down as they evolve, and (3) produce energetic nuclei with a characteristic energy proportional to their rotation rates. It is found that, for energy independent escape from the disk of the galaxy, the predicted spectrum will be essentially what is observed between approx 10 to the 16th power to 10 to the 19 power eV if the slow down law as inferred for radio pulsars can be extrapolated to young pulsars with shorter periods
First-order shock acceleration in solar flares
The first order Fermi shock acceleration model is compared with specific observations where electron, proton, and alpha particle spectra are available. In all events, it is found that a single shock with a compression ratio as inferred from the low energy proton spectra can reasonably produce the full proton, electron, and alpha particle spectra. The model predicts that the acceleration time to a given energy will be approximately equal for electrons and protons and, for reasonable solar parameters, can be less than 1 sec to 100 MeV
Acceleration Rates and Injection Efficiencies in Oblique Shocks
The rate at which particles are accelerated by the first-order Fermi
mechanism in shocks depends on the angle, \teq{\Tbone}, that the upstream
magnetic field makes with the shock normal. The greater the obliquity the
greater the rate, and in quasi-perpendicular shocks rates can be hundreds of
times higher than those seen in parallel shocks. In many circumstances
pertaining to evolving shocks (\eg, supernova blast waves and interplanetary
traveling shocks), high acceleration rates imply high maximum particle energies
and obliquity effects may have important astrophysical consequences. However,
as is demonstrated here, the efficiency for injecting thermal particles into
the acceleration mechanism also depends strongly on obliquity and, in general,
varies inversely with \teq{\Tbone}. The degree of turbulence and the resulting
cross-field diffusion strongly influences both injection efficiency and
acceleration rates. The test particle \mc simulation of shock acceleration used
here assumes large-angle scattering, computes particle orbits exactly in
shocked, laminar, non-relativistic flows, and calculates the injection
efficiency as a function of obliquity, Mach number, and degree of turbulence.
We find that turbulence must be quite strong for high Mach number, highly
oblique shocks to inject significant numbers of thermal particles and that only
modest gains in acceleration rates can be expected for strong oblique shocks
over parallel ones if the only source of seed particles is the thermal
background.Comment: 24 pages including 6 encapsulated figures, as a compressed,
uuencoded, Postscript file. Accepted for publication in the Astrophysical
Journa
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