The European Space Agency's satellite COS-B
was dedicated to gamma-ray
astronomy in the energy range 50 MeV to 5 GeV and carried a
single experiment, a spark-chamber telescope: developed in
collaboration by six European institutes. The experiment became
operational on 1975 August 17 and was switched off on 1982 April 25
when on-board resources were exhausted. During this period, 65
observations, typically of a month duration, were performed. The
satellite was spin stabilized with the telescope axis along the spin
axis. Circular sky regions of about 40 degrees in diameter were
covered in each observation. The majority of the pointings were
distributed along the galactic equator, 15 observations were devoted
to regions at high (
20 degree) galactic latitudes. Several regions
of specific interest were repeatedly observed.
The highly eccentric polar orbit of COS-B with an apogee around
, chosen to maximize useful observation time while
allowing real-time data transmission, exposed the experiment to the
solar modulated interplanetary cosmic-ray flux. The unexpectedly long
operational life of the experiment, specifically of the spark-chamber,
was accompanied by a long-term degradation and by short-term
disturbances of its performances and consequently of the experimental
sensitivity. The variation and sensitivity of the instrumental
background were thoroughly investigated and integrated into the
database. The possible impact of their statistical and systematic
uncertainties must be considered in any type of analysis.