Rowell, G.2010-07-082010-07-082009Astronomy and Astrophysics: a European journal, 2009; 508(3):1135-11400004-63611432-0746http://hdl.handle.net/2440/59387Context: High energy particles reside in the relativistic jets of microquasars, making them possible sources of very high energy radiation (VHE, >100 GeV). Detecting this emission would provide a new handle on jet physics. Aims: Observations of the microquasar GRS 1915+105 with the HESS telescope array were undertaken in 2004–2008 to search for VHE emission. Methods: Stereoscopic imaging of Cherenkov radiation from extensive air showers is used to reconstruct the energy and direction of the incident gamma rays. Results: There is no evidence for a VHE gamma-ray signal either from the direction of themicroquasar or its vicinity. An upper limit of ph cm-2 s-1 (99.9% confidence level) is set on the photon flux above 410 GeV, equivalent to a VHE luminosity of 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-ray binaries. 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 acceleration in 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 produced by GRS 1915+105, but the emission is highly time-dependent.en© ESO 2009X-rays: binariesX-rays: individuals: GRS 1915+105gamma rays: observationsJournal article002009452010.1051/0004-6361/2009133890002730573000072-s2.0-7284910629236287Rowell, G. [0000-0002-9516-1581]