Cos-B devoted a significant fraction of its lifetime to the search for emission from the Cygnus X-3. the 4.8h X-ray pulsar and possible UHE gamma-ray emitter. Cygnus X-3 was reported to have been seen pulsating in 100 MeV gamma rays by SAS 2 in 1972 (Ref.15). Despite devoting about 300d (in excess of 10% of intire mission) at several epochs to viewing Cygnus X-3, no point-like emission was observed and no 4.8 hr gamma variability of the field was detected, as shown in the combined data (Ref.16) in Figure 7. To avoid a conflict with the SAS 2 data it can only be concluded that the emission is time variable, having turned off prior to the launch of Cos-B.
Her X-1 and Vela X-1 are two systems which are believed to emit UHE gamma rays. Her X-1 could not be viewed by Cos-B but Vela X-1 appeared many times in the field of view. However, no gamma ray signal, pulsed or otherwise, could be detected from this field.