Abstract
Three gamma-ray binaries, namely PSR B1259–63, HESS J0632+057 and LS I +61 303, contain compact objects orbiting around massive Be stars. Around periastron passage the compact objects should produce significant changes in the structure of the Be disks due to gravitational forces and eventually by ram pressure from the putative pulsar wind. Indeed, variability in the Hα emission line has been detected in all these systems, and optical periodic variability has been detected in one of them. However, there is lack of a systematic monitoring with accurate photometry, which could be used to constrain the shape of the disk during the periastron passage. This information is important to build accurate physical models to explain the broadband spectral energy distribution of these sources. Here we present an ongoing program to monitor the optical photometry of gamma-ray binaries and show preliminary results for the case of LS I +61 303.
Highlights
Gamma-ray binaries are systems that comprise a young massive star and a compact object that display non-thermal emission dominated by MeV-GeV photons
In a gamma-ray binary containing a Be star the circumstellar disk is perturbed around periastron passage, due to both the gravitational forces induced by the compact object and the ram pressure of the expected relativistic pulsar wind
LS I +61 303 is a gamma-ray binary composed by an optical star (V ∼ 10.8) with spectral type B0 Ve and a compact companion orbiting in a highly eccentric orbit with a period of 26.4960 day known from decades of radio outburst data.[3]
Summary
Gamma-ray binaries are systems that comprise a young massive star and a compact object that display non-thermal emission dominated by MeV-GeV photons. In a gamma-ray binary containing a Be star the circumstellar disk is perturbed around periastron passage, due to both the gravitational forces induced by the compact object and the ram pressure of the expected relativistic pulsar wind. LS I +61 303 is a gamma-ray binary composed by an optical star (V ∼ 10.8) with spectral type B0 Ve and a compact companion orbiting in a highly eccentric orbit with a period of 26.4960 day known from decades of radio outburst data.[3] In Ref. 4 it was found an orbital solution that supports an eccentricity of e = 0.72 ± 0.15. Variable flux modulated with the orbital period has been detected in TeV,[5] X-rays, optical photometry, Hα spectroscopy, and radio (see Ref. 3 and references therein). In Ref. 4 the orbital ephemeris were estimated, and the radio lightcurve maxima was found at ∼0.3–0.4 orbital phases passed periastron, which takes place at orbital phase 0.23
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