Published online by Cambridge University Press: 12 April 2016
Nine years of rocket and balloon observations, considerably enhanced in the last few months by the survey experiment on the Uhuru satellite, have revealed a large number – now approaching 100 – of cosmic x-ray sources, remarkable in both their luminosities (Lx= 1036–1046 ergs s-1) and apparent variety. Spectral data, expected eventually to be of crucial importance in revealing the emission processes and dynamics of individual sources, have been of generally inadequate quality to date (e.g. Figure 1).