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We present the broadband X-ray spectrum of Cyg X-1 in the low/hard state as observed by the instruments on board BeppoSAX. The spectrum spans from 0.1 to 200 keV, allowing the total accretion luminosity to be observed rather than extrapolated, corresponding to D2% of the Eddington limit for a 10 black hole. The broad bandpass allows us to determine the continuum shape with great accuracy. M _ Simple models of Compton upscattering of seed photons from the accretion disk do not adequately match the spectrum. At low energies an additional continuum component is required, giving a complex soft excess which extends up to D4 keV, in line with previous results from ASCA. Moreover, we clearly detect a reÑected component from the accretion disk that is smeared, probably because of relativistic and Doppler e †ects. The reÑecting material is not strongly ionized and does not subtend a large solid angle as seen from the corona ()/2n D 0.1È0.3). The estimated inner radius of the disk, which depends on the inclination of the system, is most probably between 10 and 70 gravitational radii An unsmeared (R g ). reprocessed component, probably originating from the companion star or the outer disk, could also be present. In this case, the inner radius of the disk, as inferred from the smeared reÑection, is smaller, between and 6R g 20R g .

We study the timing properties of the bursting atoll source 4U 1728-34 as a function of its position in the X-ray color-color diagram. In the island part of the color-color diagram (corresponding to the hardest energy spectra), the power spectrum of 4U 1728-34 shows several features such as a band limited noise component present up to a few tens of Hz, a low-frequency quasi-periodic oscillation (LFQPO) at frequencies between 20 and 40 Hz, a peaked noise component around 100 Hz, and one or two QPOs at kHz frequencies. In addition to these, in the lower banana (corresponding to softer energy spectra) we also find a very low frequency noise (VLFN) component below ~ 1 Hz. In the upper banana (corresponding to the softest energy spectra), the power spectra are dominated by the VLFN, with a peaked noise component around 20 Hz. We find that the frequencies of the kHz QPOs are well corre lated with the position in the X-ray color-color diagram. For the frequency of the LFQPO and the break frequency of the broadband noise component, the relation appears more complex. Both of these frequencies increase when the frequency of the upper kHz QPO increases from 400 to 900 Hz, but at this frequency a jump in the values of the parameters occurs. We interpret this jump in terms of the gradual appearance of a QPO at the position of the break at high inferred mass accretion rate, while the previous LFQPO disappears. Simultaneously, another kind of noise appears with a break frequency of ~7 Hz, similar to the NBO of Z sources. The 100 Hz peaked noise does not seem to correlate with the position of the source in the color-color diagram but remains relatively constant in frequency. This com ponent may be similar to several 100 Hz QPOs observed in black hole binaries.

We report spectral and temporal analysis of the X-ray pulsar Centaurus X-3 out of eclipse observed by BeppoSAX. The broadband spectrum (0.12È100 keV) is well described by an absorbed power law modiÐed by a high-energy rollover at D14 keV (e-folding energy D8 keV) plus an iron emission line at D6.7 keV. A soft excess below 1 keV is also present. Interpreted as a blackbody (kT^0.1 keV), it corresponds to 58% of the total unabsorbed Ñux. This component seems to originate from reprocessing of the primary radiation by an opaque shell located at the magnetosphere. An absorption feature at D30 keV is also present. Interpreted as a cyclotron line, after correction for gravitational redshift, this corresponds to a surface magnetic Ðeld of D3.5 ] 1012 G. Phase-resolved spectroscopy reveals a variation by about 8 keV of the cyclotron resonance energy along the pulse proÐle. In particular, the line energy decreases from D36 to D28 keV along the peak, starting from the ascent. The asymmetric variations of the cyclotron line energy can be explained by assuming an o †set of the dipolar magnetic Ðeld with respect to the neutron star center. The spectral results are discussed in terms of emission from magnetic caps, where Comptonization of soft photons occurs. The soft photons could come from either magnetically resonant double Compton scattering or from illumination of the polar cap by the primary radiation reprocessed at the magnetospheric surface, a feedback mechanism similar to that proposed for the formation of black hole spectra.

We report on a 63-ks long XMM-Newton observation of the accreting millisecond pulsar SAX J1808.4-3658 during the latest X-ray outburst which started on September 21st 2008. The pn spectrum shows a highly significant emission line in the energy band where the iron K-α line is expected, and which we identify as emission from neutral (or mildly ionized) iron. The line profile appears to be quite broad (more than 1 keV FWHM) and asymmetric; the most probable explanation for this profile is Doppler and relativistic broadening from the inner accretion disc. From a fit with a diskline profile we find an inner radius of the disc of 8.7+3.7 −2.7 Rg, corresponding to 18.0 +7.6 −5.6 km for a 1.4 M⊙ neutron star. The disc therefore appears truncated inside the corotation radius (31 km for SAX J1808.4-3658) in agreement with the fact that the source was still showing pulsations during the XMM-Newton observation.