Abstract
Hadrons accelerated to high energies in the accretion column of a binary X-ray pulsar can produce pions in collisions with accreting protons and ions. The pions decay promptly into charged particles and photons, giving rise to an electromagnetic cascade through pair and photon production processes in the strong magnetic field of the neutron star. We give a simplified analysis of this system for teragauss magnetic fields in the optically-thin limit, assuming that nonlinear interactions between the produced pairs and photons are small, and calculate photon spectra in the MeV range. The calculated spectra are found to depend strongly on energy and angle, and are exponentially truncated at energies determined by the γ — B pair production threshold, which is a function of the magnetic field strength and viewing angle with respect to the magnetic axis.
Gamma-ray observations of rotating magnetized neutron stars in the MeV range can provide a new method for determining (1) the magnetic field strength at the gamma-ray production site, and (2) the neutron star inclination angle. These possibilities are primarily due to γ — B pair attenuation processes in the accretion column, and are not restricted to the specific pion production model for gamma-ray emission proposed here. The Gamma Ray Observatory, with unprecedented sensitivity at MeV energies, should be able to test these ideas.
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Dermer, C.D. (1991). Pion production in strong magnetic fields: A model for gamma-ray emission from accreting X-ray pulsars. In: Zdziarski, A.A., Sikora, M. (eds) Relativistic Hadrons in Cosmic Compact Objects. Lecture Notes in Physics, vol 391. Springer, Berlin, Heidelberg. https://doi.org/10.1007/3-540-54789-4_57
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DOI: https://doi.org/10.1007/3-540-54789-4_57
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