Long-term observations of X-ray sources: the Aquila-Serpens-Scutum region

Long-term (1969-1976) observations of galactic X-ray sources in the Aquila-Serpens-Scutum region are presented. Data were obtained by the 3-12 keV detector on the Vela 5B satellite. The time histories of nine sources were derived from sky maps of this confused region: Scutum X-1, 4U 1823 - 00, 4U 1915 05, Aquila X-1, Serpens X-1, 4U 1907 + 09, A1850 - 087, 4U 1901 + 03, and 4U 1957 + 11. These observations reveal new long-term variations for several sources. Aql X-1, which averages about one eruption per year, is shown to have an underlying cycle of 122-125 days, with an rms phase walk of 10 percent per cycle. A regular 199 day period is observed from the vicinity of 4U 1915 - 05. This period appears too long to reconcile with the standard model of that system as a low-mass binary with a 50 minute period. The OB system 4U 1907 + 09 shows a possible 41.6 day period, with substantial phase jitter. These variations are discussed as possible precessions in binary systems.