We present results from quantitative modeling and spectral analysis of the high mass X-ray binary system Vela X-1 obtained with the Chandra High Energy Transmission Grating Spectrometer. The observations cover three orbital phase ranges within a single binary orbit. The spectra exhibit emission lines from H-like and He-like ions driven by photoionization, as well as fluorescent emission lines from several elements in lower charge states. The properties of these X-ray lines are measured with the highest accuracy to date. In order to interpret and make full use of the high-quality data, we have developed a simulator, which calculates the ionization and thermal structure of a stellar wind photoionized by an X-ray source, and performs Monte Carlo simulations of X-ray photons propagating through the wind. The emergent spectra are then computed as a function of the viewing angle accurately accounting for photon transport in three dimensions including dynamics. From comparisons of the observed spectra with results from the simulator, we are able to find the ionization structure and the geometrical distribution of material in the stellar wind of Vela X-1 that can reproduce the observed spectral line intensities and continuum shapes at different orbital phases remarkably well. We find that the stellar wind profile can be represented by a CAK-model with a star mass loss rate of (1.5-2.0) ×10 −6 M ⊙ yr −1 , assuming a terminal velocity of 1100 km s −1 . It is found that a large fraction of X-ray emission lines from highly ionized ions are formed in the region between the neutron star and the companion star. We also find that the fluorescent X-ray lines must be produced in at least three distinct regions -(1) the extended stellar wind, (2) reflection off the stellar photosphere, and (3) in a distribution of dense material partially covering and possibly trailing the neutron star, which may be associated with an accretion wake. Finally, from detailed analysis of the emission line profiles, we demonstrate that the stellar wind dynamics is affected by X-ray photoionization.

The Ginga X-ray spectra of the two binary X-ray pulsars, 4U 1907]09 and Vela X-1, were analyzed for e †ects due to electron cyclotron resonance. For this purpose, a new continuum spectral model, called NPEX, was developed. The NPEX model, combined with the classical cyclotron scattering line proÐle, was Ðrst tested against the Ginga spectra (typically in 2È50 keV) of Her X-1, 4U 0115]63, 4U 1538[52, X0331]53, and Cep X-4 and was conÐrmed to reproduce successfully their overall spectra including the previously known cyclotron resonance features. Through application of the same model to the pulsephaseÈaveraged and phase-resolved Ginga spectra, it was conÐrmed that 4U 1907]09 and Vela X-1 exhibit fundamental cyclotron resonances at D20 and D25 keV, respectively. The data for both objects are also consistent with the presence of the second-harmonic resonances, which were discovered with hard X-ray experiments. Including these two examples, the cyclotron resonance e †ects are now established in about a dozen binary X-ray pulsars. Their surface magnetic Ðeld strengths, implied by their resonance energies, apparently distribute over a narrow range of (1È4) ] 1012 G. Although the fewer number of higher Ðeld objects may be an instrumental selection e †ect, the lack of objects with magnetic Ðelds of (0.2È1) ] 1012 G is concluded to be real. A limited number of ASCA data are utilized to reinforce this conclusion. These results suggest that the magnetic Ðeld of binary X-ray pulsars do not decay signiÐcantly at least in D108 yr.

High-sensitivity wide-band X-ray spectroscopy is the key feature of the Suzaku X-ray observatory, launched on 2005 July 10. This paper summarizes the spacecraft, in-orbit performance, operations, and data processing that are related to observations. The scientific instruments, the high-throughput X-ray telescopes, X-ray CCD cameras, non-imaging hard X-ray detector are also described.