Observations of γ-ray Bursts and Solar Flares with Granat

Abstract

The Granat observatory was launched into a high apogee orbit on 1989 December 1 by a PROTON launcher. The initial Granat orbit had an apogee close to 200000 km and a perigee of 2000 km with an orbital period of 4 days. The satellite is entering the radiation belts for a few hours every orbit. Due to orbital evolution the perigee increased and the apogee decreased with time. After about 1.5 years of operation the perigee increased up to 20000 km. This has put the satellite completely outside of the proton radiation belts which makes the detector activation during the perigee passage negligible. Moreover, the satellite orbit is outside of the magnetosphere during the most parts of the mission. This makes such an orbit very attractive for high energy astrophysics missions which require low background level in order to achieve high sensitivity, and makes it essential for the investigation of the high energy transient phenomena such as cosmic γ-ray bursts and solar flares.