2010A&A...514A..61B -
Astronomy and Astrophysics, volume 514, A61-61 (2010/5-1)
Optical depths for gamma-rays in the radiation field of a star heated by an external X-ray source in LMXBs. Application to Hercules X-1 and Scorpius X-1.
BEDNAREK W. and PABICH J.
Abstract (from CDS):
The surface of a low mass star inside a compact low mass X-ray binary system (LMXB) can be heated by an external X-ray source apparently caused by the accretion of mass 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 investigate 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 of the gamma-ray photons in the radiation field of such an 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 the interaction of electrons and γ-rays are quite similar to those found within high mass TeV γ-ray binaries such as LS 5039 and LSI 303 +61. However, because of differences in the soft radiation field, the expected γ-ray light curves can differ significantly between low mass and high mass X-ray binaries. As an example, we apply these 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 collide with a sufficient number of soft photon targets from the companion star to achieve efficient γ-ray production.
Abstract Copyright:
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Journal keyword(s):
binaries: close - gamma rays: general - radiation mechanisms: non-thermal
Simbad objects:
6
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