Ariel 5 Hard X-Ray Measurements of Galactic and Extragalactic X-Ray Sources

The paper surveys the hard X-ray measurements obtained from the Ariel-5 CsI crystal scintillator detector, 8 cm² area, 4 cm thick, f.w.h.m. 8⁰ and energy range 26 keV to 1.2 MeV. Implications arising from the prelaunch laboratory calibration of the instrument in connection with radioactivity corrections to previous satellite results are briefly mentioned. Various post-launch results are then discussed. Upper limits to the Coma cluster flux are given out to 800 keV and, together with radio data, yield a halo field [Note: See the image of page 521 for this formated text]lesssim 10^-12 T (10^-8 G). The hard flux from near the galactic centre is probably 60% from GCX and 40% from GX3 + 1. Crab Nebula data is consistent with an E^-2.1 differential power law for photon flux. Combined proportional counter and scintillator data on the transient A1118 - 61 near Cen X-3 and measurements on the very intense transient A0535 + 26 in Taurus are consistent with multi-layer sources with layer temperatures varying from 3 to 13 keV while Her X-1 during its 'on' state appears to shine by modified black-body radiation at 13 keV. The Cyg X-1 transition on 9 May, 1975 is examined in detail and although most variation in intensity occurred at [Note: See the image of page 521 for this formated text] lesssim 25 keV, some harder X-ray change in anti-phase with the soft photons appeared to occur. These changes are discussed in terms of an inverse-Compton photon acceleration model. The spectral shape of A0620 - 00 is considered in relation to the possibility that it is a black hole.