HESS upper limits on very high energy gamma-ray emissionfrom the microquasar GRS 1915+105

摘要

Aims. Observations of the microquasar GRS 1915+105 with the HESS telescope array were undertaken in 2004-2008 to search for VHE emission.Wethods. Stereoscopic imaging of Cherenkov radiation from extensive air showers is used to reconstruct the energy and direction of the incidentWilma rays.Results. There is no evidence for a VHE gamma-ray signal either from the direction of the microquasar or its vicinity. An upper limit of 6.1 x10-13 ph cm -2 s-1 (99.9 confidence level) is set on the photon flux above 410 GeV, equivalent to a VHE luminosity of -1034 erg s-1 at 11 kpc.Conclusions. The VHE to X-ray luminosity ratio in GRS 1915+105 is at least four orders of magnitude lower than the ratio observed in gamma-rayinaries. The VHE radiative efficiency of the compact jet is less than 0.01 based on its estimated total power of 1038 erg s-1. Particle accelerationIn GRS 1915+105 is not efficient at high energies and/or the magnetic field is too strong. It is also possible that VHE gamma-rays are producedGRS 1915+105, but the emission is highly time-dependent.