We summarize five years of continuous monitoring of accretion-powered pulsars with the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray Observatory. Our 20-70 keV observations have determined or refined the orbital parameters of 13 binaries, discovered 5 new transient accreting pulsars, measured the pulsed flux history during outbursts of 12 transients (GRO J1744-28, 4U 0115+634, GRO J1750-27, GS 0834-430, 2S 1417-624, GRO J1948+32, EXO 2030+375, GRO J1008-57, A 0535+26, GRO J2058+42, 4U 1145-619 and A 1118-616), and also measured the accretion torque history of during outbursts of 6 of those transients whose orbital parameters were also known. We have also continuously measured the pulsed flux and spin frequency for eight persistently accreting pulsars (Her X-1, Cen X-3, Vela X-1, OAO 1657-415, GX 301-2, 4U 1626-67, 4U 1538-52, and GX 1+4). Because of their continuity and uniformity over a long baseline, BATSE observations have provided new insights into the long-term behavior of accreting magnetic stars. We have found that all accreting pulsars show stochastic variations in their spin frequencies and luminosities, including those displaying secular spin-up or spin-down on long time scales, blurring the conventional distinction between disk-fed and wind-fed binaries. Pulsed flux and accretion torque are strongly correlated in outbursts of transient accreting pulsars, but uncorrelated, or even anticorrelated, in persistent sources.Comment: LaTeX, psfig, 90 pages, 42 figures. To appear in Dec. 1997 ApJS, Vol 113, #

Using BATSE and RXTE observations from 1991 April to 2001 August, we have detected 71 outbursts from 82 periastron passages of EXO 2030+375, a 42 s transient X-ray pulsar with a Be star companion, including several outbursts from 1993 August to 1996 April, when the source was previously believed to be quiescent. Combining BATSE, RXTE, and EXOSAT data, we have derived an improved orbital solution. Applying this solution results in a smooth profile for the spin-up rate during the giant outburst and results in evidence for a correlation between the spin-up rate and observed flux in the brighter BATSE outbursts. Infrared and H measurements show a decline in the density of the circumstellar disk around the Be star. This decline is followed by a sudden drop in the X-ray flux and a turnover from a spin-up trend to spin-down in the frequency history. This is the first Be/X-ray binary that shows an extended interval, about 2.5 yr, in which the global trend is spin-down, but the outbursts continue. In 1995 the orbital phase of EXO 2030+375's outbursts shifted from peaking about 6 days after periastron to peaking before periastron. The outburst phase slowly recovered to peaking at about 2.5 days after periastron. We interpret this shift in orbital phase followed by a slow recovery as evidence of a global one-armed oscillation propagating in the Be disk. This is further supported by changes in the shape of the H profile, which are commonly believed to be produced by a reconfiguration of the Be disk. The truncated viscous decretion disk model provides an explanation for the long series of normal outbursts and the evidence of an accretion disk in the brighter normal outbursts. Longterm multiwavelength observations such as these clearly add considerably to our knowledge of Be/X-ray binaries and the relationship among optical, infrared, and X-ray observations.

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Aims. In this Letter we present results from INTEGRAL and RXTE observations of the spectral and timing behavior of the High Mass X-ray Binary A 0535+26 during its August/September 2005 normal (type I) outburst with an average flux F (5−100) keV ∼ 400 mCrab. The search for cyclotron resonance scattering features (fundamental and harmonic) is one major focus of the paper. Methods. Our analysis is based on data from INTEGRAL and RXTE Target of Opportunity Observations performed during the outburst. The pulse period is determined. X-ray pulse profiles in different energy ranges are analyzed. The broad band INTEGRAL and RXTE pulse phase averaged X-ray spectra are studied. The evolution of the fundamental cyclotron line at different luminosities is analyzed. Results. The pulse period P is measured to be 103.39315(5) s at MJD 53614.5137. Two absorption features are detected in the phase averaged spectra at E 1 ∼ 45 keV and E 2 ∼ 100 keV. These can be interpreted as the fundamental cyclotron resonance scattering feature and its first harmonic and therefore the magnetic field can be estimated to be B ∼ 4 × 10 12 G.