The seminar will be held online

1) Speaker: Hiroki Yoneda (RIKEN, Saitama, Japan).

Title: “Mystery of the strong MeV gamma-ray emission from gamma-ray binary systems — magnetars in disguise?”

Abstract: From the middle of the 2000s, a new class of compact binary systems is established, so-called gamma-ray binary systems. They show non-thermal emission peaking above 1 MeV in their SEDs, which is completely different from X-ray binaries. This feature indicates that efficient particle acceleration takes place in these binaries. Although several models have been proposed e.g. microquasar model or pulsar wind model, the physical mechanism of their activities is still unclear. In this seminar, I will explain the latest result of the spectral analysis of one of the brightest gamma-ray binaries, LS 5039, and the dominant MeV gamma-ray component indicates a more efficient acceleration than Fermi acceleration. Next, I will explain a new possibility that some of the gamma-ray binaries may contain magnetars, which is stimulated by hints of pulsation in hard X-rays. Finally, I will discuss future prospects by referring to ongoing MeV gamma-ray missions.