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We present a comparative study of stellar winds in classical supergiant high mass X-ray binaries (SgXBs) and supergiant fast X-ray transients (SFXTs) based on the analysis of publicly available out-of-eclipse observations performed with Suzaku and XMM-Newton. Our data set includes 55 observations of classical SgXBs and 21 observations of SFXTs. We found that classical SgXBs are characterized by a systematically higher absorption and luminosity compared to the SFXTs, confirming the results of previous works in the literature. Additionally, we show that the equivalent width of the fluorescence Kα iron line in the classical SgXBs is significantly larger than that of the SFXTs (outside X-ray eclipses). Based on our current understanding of the physics of accretion in these systems, we conclude that the most likely explanation of these differences is ascribed to the presence of mechanisms inhibiting accretion most of the time in SFXTs, thereby leading to a much less efficient photoionization of the stellar wind compared to classical SgXBs. We do not find evidence for the previously reported anticorrelation between the equivalent width of the fluorescence iron line and the luminosity of SgXBs.

We present the timing and spectral properties of the transient Be/X-ray binary pulsar 3A 0535+262 during quiescence using three observations with the narrow field imaging instruments (NFI) of BeppoSAX. Assuming a distance of 2 kpc for this system, the 2-10 keV X-ray luminosities measured from the three observations are in the range of 1.5-4.0 $\times$ 10$^{33}$ erg s$^{-1}$, indicating a very low rate of accretion. We report the detection of pulsations at a very low luminosity of 2 $\times$ 10$^{33}$ erg s$^{-1}$ during one of the three observations, though at this accretion rate the system is expected to be in the centrifugally inhibited regime. The X-ray spectra for the unpulsed observations are best modeled as power law type while a combined model of power law and black-body is required to fit the pulsed spectrum., 13 pages, 6 figures, accepted in Astronomy and Astrophysics

We have investigated the orbital phase dependence of the X-ray spectrum of the High Mass X-ray Binary pulsar GX 301--2. Here we present the results from a spectral analysis of two sets of observations of GX 301--2 with the Rossi X-ray Timing Explorer (RXTE). Of particular interest are the variations of the absorption column density and the iron line flux along with other parameters of the spectral model with the orbital phase. We found that the X-ray spectrum can almost always be fitted with a partial covering absorption model. We have detected enhanced absorption near the periastron. However, the column density variation with orbital phase is not smooth, as is expected in a smooth stellar wind model. We discuss the results of the column density variation in the light of the two proposed models for GX 301-2, an equatorial disk emanating from the companion star Wray 977 and a gas stream following the neutron star. We also found that the iron K_alpha and K_beta line fluxes have peaks near the periastron and are well correlated with the continuum hard X-ray flux. The line equivalent width shows an interesting pattern with the column density, reasonably constant for low values of the column density and increasing rapidly beyond a certain value., Comment: 15 pages, 7 figures. accepted in Astronomy and Astrophysics

We present here results obtained from three BeppoSAX observations of the accretion-powered X-ray pulsar SMC X-1 carried out during the declining phases of its 40--60 days long super-orbital period. Timing analysis of the data clearly shows a continuing spin-up of the neutron star. Energy-resolved timing analysis shows that the pulse-profile of SMC X-1 is single peaked at energies less than 1.0 keV whereas an additional peak, the amplitude of which increases with energy within the MECS range, is present at higher energies. Broad-band pulse-phase-averaged spectroscopy of the BeppoSAX data, which is done for the first time since its discovery, shows that the energy spectrum in the 0.1--80 keV energy band has three components, a soft excess that can be modeled as a thermal black-body, a hard power-law component with a high-energy exponential cutoff and a narrow and weak iron emission line at 6.4 keV. Pulse-phase resolved spectroscopy indicates a pulsating nature of the soft spectral component, as seen in a few other binary X-ray pulsars, with a certain phase offset with respect to the hard power-law component. Dissimilar shape and phase of the soft and hard X-ray pulse profiles suggest a different origin of the soft and hard components., Comment: 8 Pages, 6 figures, Accepted for publication in A&A

We report results from two observations of the transient binary X-ray pulsar XTE J1946+274 with the Indian X-ray Astronomy Experiment (IXAE) made in September 18-30 1999 and June 28-July 7 2000. The pulsar has a ~80 days orbital period during which the X-ray intensity varies almost sinusoidally between intensity levels of 5 and 50 mCrab. The mid-time of the two observations with the IXAE are separated by an orbital phase of 0.56 and were in the decaying and rising parts of its orbital modulation, respectively. During both the observations, strong pulsations with 15.8 s period are detected in the 2-6 and 6-18 keV energy bands of IXAE. The pulse profiles in both the observations are double peaked and identical with a similar pulse fractions of ~30% in the two energy bands. The pulse periods and its local derivatives are obtained from the IXAE observations. The known pulse period history shows small deviations from an otherwise nearly constant spin-up trend of the pulsar since its discovery. If the measured local period derivatives are a sum of a nearly constant spin-up of the pulsar and effect of its orbital motion, it suggests that the orbit of this Be X-ray binary is eccentric. The RXTE-ASM light curve shows a continuous detection of 10 orbital modulation of the source since its discovery.