165 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
A Photon Splitting Cascade Model of Soft Gamma-Ray Repeaters
The spectra of soft gamma-ray repeaters (SGRs), with the exception of the
March 5, 1979 main burst, are characterized by high-energy cutoffs around 30
keV and low-energy turnovers that are much steeper than a Wien spectrum. Baring
(1995) found that the spectra of cascades due to photon splitting in a very
strong, homogeneous magnetic field can soften spectra and produce good fits to
the soft spectra of SGRs. Magnetic field strengths somewhat above the QED
critical field strength , where
G, is required to produce cutoffs at 30-40 keV. We have improved upon this
model by computing Monte Carlo photon splitting cascade spectra in a neutron
star dipole magnetic field, including effects of curved space-time in a
Schwarzschild metric. We investigate spectra produced by photons emitted at
different locations and observer angles. We find that the general results of
Baring hold for surface emission throughout most of the magnetosphere, but that
emission in equatorial regions can best reproduce the constancy of SGR spectra
observed from different bursts.Comment: 5 pages in LATEX using REVTEX aipbook.sty + 4 figures (uuencoded,
compressed postscript), to appear in the proceedings of the Third Huntsville
Workshop on Gamma-Ray Bursts, eds. C. Kouveliotou, M. S. Briggs and G. J.
Fishman (New York, AIP
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