14,499 research outputs found
Cohort profile: the DASH (determinants of adolescent social well-being and health) study, an ethnically diverse cohort
No abstract available
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
Pair production rates in mildly relativistic, magnetized plasmas
Electron-positron pairs may be produced by either one or two photons in the presence of a strong magnetic field. In magnetized plasmas with temperatures kT approximately sq mc, both of these processes may be important and could be competitive. The rates of one-photon and two-photon pair production by photons with Maxwellian, thermal bremsstrahlung, thermal synchrotron and power law spectra are calculated as a function of temperature or power law index and field strength. This allows a comparison of the two rates and a determination of the conditions under which each process may be a significant source of pairs in astrophysical plasmas. It is found that for photon densities n(gamma) or = 10 to the 25th power/cu cm and magnetic field strengths B or = 10 to the 12th power G, one-photon pair production dominates at kT approximately sq mc for a Maxwellian, at kT approximately 2 sq mc for a thermal bremsstrahlung spectrum, at all temperatures for a thermal synchrotron spectrum, and for power law spectra with indices s approximately 4
High Energy Neutrinos and Photons from Curvature Pions in Magnetars
We discuss the relevance of the curvature radiation of pions in strongly
magnetized pulsars or magnetars, and their implications for the production of
TeV energy neutrinos detectable by cubic kilometer scale detectors, as well as
high energy photons.Comment: 19 pages, 4 figures, to appear in JCA
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