Abstract
Optical and near-infrared observations are compiled for the three gamma-ray binaries hosting Be stars: PSR B1259−63, LSI+61 303, and HESS J0632+057. The emissions from the Be disk are considered to vary according to the changes in its structure, some of which are caused by interactions with the compact object (e.g., tidal forces). Due to the high eccentricity and large orbit of these systems, the interactions—and, hence the resultant observables—depend on the orbital phase. To explore such variations, multi-band photometry and linear polarization were monitored for the three considered systems, using two 1.5 m-class telescopes: IRSF at the South African Astronomical Observatory and Kanata at the Higashi–Hiroshima Observatory.
Highlights
Gamma-ray binaries are the group of X-ray binaries emitting strong, high-energy (0.1–100 GeV) and very high-energy (>100 GeV) gamma-rays [1]
In the case that the compact object is the rotation-powered pulsar, when the pulsar wind collides with the stellar winds and/or the Balmer lines from its circumstellar disk (Be disk), particle acceleration is thought to occur at the shock region, where non-thermal emissions increase: this is the case considered in a pulsar-wind model
In the system where mass is transferred from the stellar wind and/or the Be disk to the compact object, sufficient mass transfer leads to jet formation, such that particle acceleration occurs
Summary
Gamma-ray binaries are the group of X-ray binaries emitting strong, high-energy (0.1–100 GeV) and very high-energy (>100 GeV) gamma-rays [1]. Companion massive stars dominate the emissions from the binaries in the optical and near-infrared bands. In a gamma-ray binary, the relativistic particles from the compact object interact with the photon field and the low-density fast outflow (wind), emitting UV radiation from the massive star. In the case that the compact object is the rotation-powered pulsar, when the pulsar wind collides with the stellar winds and/or the Be disk, particle acceleration is thought to occur at the shock region, where non-thermal emissions increase: this is the case considered in a pulsar-wind model. In the system where mass is transferred from the stellar wind and/or the Be disk to the compact object, sufficient mass transfer leads to jet formation, such that particle acceleration occurs (microquasar model). The stellar wind and/or the Be disk play important roles in the mass/plasma distribution, photon field, and other structures determining binary interactions
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