A Sequence of Outbursts from the Transient X-Ray Pulsar GS 0834-430

Abstract

GS 0834-430, a 12.3 s accretion-powered pulsar, has been observed in seven outbursts with the BATSE large-area detectors on the Compton Gamma Ray Observatory. The first five outbursts observed by BATSE occurred at intervals of about 107 days, while the final two outbursts were separated by about 140 days. The photon energy spectrum, measured by Earth occultation in the 20-100 keV band, can be fitted by a power law with photon index α ≈ -3.7 or by an exponential spectrum with temperature kT ≈ 15 keV, with some variations within outbursts. The source has a low pulse fraction, ≾ 0.15 in the 20-50 keV band. We have observed significant temporal and energy-dependent variations in epoch folded pulse profiles. Because the intrinsic torque effects for this system are at least comparable to orbital effects, pulse timing analysis did not produce a unique orbital solution. However, confidence regions for the orbital elements yielded the following 1 σ limits: orbital period P_(orb) = 105.8 ± 0.4 days and eccentricity 0.10 ≾ e ≾ 0.17. GS 0834-430 is most likely a Be/X-ray binary.