168 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 and Pair Conversion in Strong Magnetic Fields
The magnetospheres of neutron stars provide a valuable testing ground for
as-yet unverified theoretical predictions of quantum electrodynamics (QED) in
strong electromagnetic fields. Exhibiting magnetic field strengths well in
excess of a TeraGauss, such compact astrophysical environments permit the
action of exotic mechanisms that are forbidden by symmetries in field-free
regions. Foremost among these processes are single-photon pair creation, where
a photon converts to an electron-positron pair, and magnetic photon splitting,
where a single photon divides into two of lesser energy via the coupling to the
external field. The pair conversion process is exponentially small in weak
fields, and provides the leading order contribution to vacuum polarization. In
contrast, photon splitting possesses no energy threshold and can operate in
kinematic regimes where the lower order pair conversion is energetically
forbidden. This paper outlines some of the key physical aspects of these
processes, and highlights their manifestation in neutron star magnetospheres.
Anticipated observational signatures include profound absorption turnovers in
pulsar spectra at gamma-ray wavelengths. The shapes of these turnovers provide
diagnostics on the possible action of pair creation and the geometrical locale
of the photon emission region. There is real potential for the first
confirmation of strong field QED with the new GLAST mission, to be launched by
NASA in 2008. Suppression of pair creation by photon splitting and its
implications for pulsars is also discussed.Comment: 18 pages, 3 embedded figures, invited review, to appear in Proc.
CASYS '07 Conference "Computing Anticipatory Systems," eds. D. Dubois, et al.
(AIP Conf. Proc., New York, 2008
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