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Todays Colloquium: Gamma-ray binaries as seen by VLBI arrays

Submitter: Javier Moldon
Description: Some galactic binary systems display a broadband and variable non-thermal spectral energy distribution (SED) from radio to gamma-rays, which is ideal to study high-energy processes on a periodic basis. This population of galactic sources has doubled in the recent years, and there are currently eight binary systems displaying high-energy (HE; > 100 MeV) and/or very-high-energy (VHE; > 100 GeV) gamma-ray emission. The population can be divided in gamma-ray binaries and gamma-ray emitting X-ray binaries, depending on the powering source of the relativistic particles producing the gamma-ray emission.

The wide range of different orbital periods and eccentricities provides a diversity of ambient conditions in which the physical processes take place. The diversity of systems, together with the repeatability of the conditions within each system, makes gamma-ray binaries excellent physical laboratories in which high energy particle acceleration, diffusion, absorption, and radiation mechanisms can be explored.

Gamma-ray binaries are known to form compact outflows of synchrotron-emitting particles up to distances of several AU. These radio outflows can easily reach projected angular separations of the order of milliarcseconds (mas), which are directly observable by means of Very Long Baseline Interferometry (VLBI) at radio wavelengths. The temporal and morphological properties of these VLBI structures can reveal the physical properties of the system and the nature of the source itself.
Copyright: Javier Moldon
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