TeV and MeV gamma-rays from binary systems

Abstract

We report the third consecutive detection of Vela X-1 as a source of VHE gamma-rays ( E_γ > 1 TeV) with a 99.92 % significance. The pulsed emission shows a broad sinusoidal light curve at a period similar to the X-ray value, with a large negative period derivative over the 60 days of observation. We also report our observations on Cen X-3 in which we were able to confirm the orbitally modulated, pulsed VHE gamma-ray emission from Cen X-3 at the 2σ level. Finally, the possible detection of stable material at one of the Lagrangian points in the system PSR1957+20 is reported. We found indications from VHE gamma-ray data (at the 3σ level) of a DC enhancement at the L4 Lagrangian point. This indication was then independently confirmed at the 99.9% level from COS-B data. This enhancement of radiation in the binary orbit may indicate the existence of stable material with a column density of about 50 g/cm ² at the Lagrangian point L4.