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arXiv · 1001.5385

Optical depths for gamma-rays in the radiation field of a star heated by external X-ray source in LMXBs: Application to Her X-1 and Sco X-1

W. Bednarek·J. Pabich
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Abstract

The surface of a low mass star inside a compact low mass X-ray binary system (LMXB) can be heated by the external X-ray source which may appear due to the accretion process onto a companion compact object (a neutron star or a black hole). As a result, the surface temperature of the star can become significantly higher than it is in the normal state resulting from thermonuclear burning. We wonder whether high energy electrons and gamma-rays, injected within the binary system, can efficiently interact with this enhanced radiation field. To decide this, we calculate the optical depths for the gamma-ray photons in the radiation field of such irradiated star as a function of the phase of the binary system. Based on these calculations, we conclude that compact low mass X-ray binary systems may also become sources of high energy gamma-rays since conditions for interaction of electrons and gamma-rays are quite similar to these ones observed within the high mass TeV gamma-ray binaries such as LS 5039 and LSI 303 +61. However, due to differences in the soft radiation field, the expected gamma-ray light curves can significantly differ between low mass and high mass X-ray binaries. As an example, we apply such calculations to two well known LMXBs: Her X-1 and Sco X-1. It is concluded that electrons accelerated to high energies inside these binaries should find enough soft photon target from the companion star for efficient gamma-ray production.

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W. Bednarek, J. Pabich. 2010-01-29. Optical depths for gamma-rays in the radiation field of a star heated by external X-ray source in LMXBs: Application to Her X-1 and Sco X-1. https://doi.org/10.1051/0004-6361/200913391

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