HEAO 1 observations of the X-ray pulsar 4U 1626-67

Abstract

Results are reported for an observation of the 7-s pulsar 4U 1626-67 with the A-2 experiment on HEAO 1. The phase-averaged X-ray spectrum between 0.7 and 60 keV is complex, as are the constituent spectra, which change radically as a function of pulse phase. Included in this spectral change is the sudden appearance and subsequent decay of a continuum or emission feature with a mean energy of 19 keV, which contains about one-half the power in this spectral range. Pulse-timing results include a new determination of the pulse period and a factor of 8 reduction in the upper limit for the light travel time for orbital periods between 1 and 7 hours. These findings are discussed and compared with the general nature of pulsar spectra.