Ariel 5 hard X-ray measurements of galactic and extragalactic X-ray sources

Abstract

The paper surveys the hard X-ray measurements obtained from the Ariel-5 CsI crystal scintillator detector, 8 cm 2 area, 4 cm thick, f. w. h. m. 8 0 and energy range 26 keV to 1.2 MeV. Implications arising from the pre-launch 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 <̃ 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 <̃ 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.