622 research outputs found
Cosmic Ray Origin, Acceleration and Propagation
This paper summarizes highlights of the OG3.1, 3.2 and 3.3 sessions of the
XXVIth International Cosmic Ray Conference in Salt Lake City, which were
devoted to issues of origin/composition, acceleration and propagation.Comment: To appear in the Summary-Rapporteur Volume of the 26th International
Cosmic Ray Conference, ed. B. L. Dingus (AIP, New York, 2000). Latex, 16
pages, no figures (Minor correction to text
Modelling Hard Gamma-Ray Emission From Supernova Remnants
The observation by the CANGAROO experiment of TeV emission from SN 1006, in
conjunction with several instances of non-thermal X-ray emission from supernova
remnants, has led to inferences of super-TeV electrons in these extended
sources. While this is sufficient to propel the theoretical community in their
modelling of particle acceleration and associated radiation, the anticipated
emergence in the next decade of a number of new experiments probing the TeV and
sub-TeV bands provides further substantial motivation for modellers. In
particular, the quest for obtaining unambiguous gamma-ray signatures of cosmic
ray ion acceleration defines a ``Holy Grail'' for observers and theorists
alike. This review summarizes theoretical developments in the prediction of
MeV-TeV gamma-rays from supernova remnants over the last five years, focusing
on how global properties of models can impact, and be impacted by, hard
gamma-ray observational programs, thereby probing the supernova remnant
environment. Properties of central consideration include the maximum energy of
accelerated particles, the density of the unshocked interstellar medium, the
ambient magnetic field, and the relativistic electron-to-proton ratio. Criteria
for determining good candidate remnants for observability in the TeV band are
identified.Comment: 10 pages, 2 figures, to appear in Proc. of Snowbird TeV Gamma-Ray
Workshop ed. B. L. Dingus (AIP, New York, 2000) (Replacement updates Fig. 2
and references
Photon Splitting in Magnetar Models of Soft Gamma Repeaters
The recent association of soft gamma repeaters (SGRs) with counterparts in
other wavebands has sparked much interest in these sources. One of the recent
models for these objects is that they originate in the environs of neutron
stars with fields much stronger than the quantum critical field
\teq{B_{cr}=4.413\times 10^{13}} Gauss. Near such neutron stars, dubbed
magnetars, the exotic quantum process of magnetic photon splitting becomes
prolific. Its principal effect is to degrade photon energies and thereby soften
gamma-ray spectra from neutron stars; it has recently been suggested that
splitting may be responsible for limiting the hardness of emission in SGRs, if
these sources originate in neutron stars with supercritical surface fields.
Seed photons in supercritical fields efficiently generate soft gamma-ray
spectra, typical of repeaters. In this paper, the influence of the curved
dipole field geometry of a neutron star magnetosphere on the photon splitting
rate is investigated. The dependence of the attenuation length on the location
and angular direction of the seed photons is explored.Comment: 5 pages including 3 encapsulated figures, as a compressed, uuencoded,
Postscript file. To appear in Proc. of the 1995 La Jolla workshop ``High
Velocity Neutron Stars and Gamma-Ray Bursts'' eds. Rothschild, R. et al.,
AIP, New Yor
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