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Register a new userPhotoionized Lines in the X-ray Spectra of SMC X-1
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We present a detailed spectral analysis of Chandra/ACIS-S CC mode observations of the massive X-ray binary system SMC X-1. The system was observed during both the high and low X-ray states of the roughly 60-day superorbital period. The continuum spectra during both states are well represented by a power law with photon index $alpha$=0.9 and a blackbody of kT = 0.15keV. The high state spectra are dominated by the continuum and independent of orbital phase whereas the low state spectra show a strong orbital dependence as well as line emission from O, Ne, Mg, Fe, and Si. This is consistent with the states attributed to disk precession: during the high state X-ray emission is dominated by the compact source which is abrubtly eclipsed and during the low state the compact object is hidden by the disk and a larger, less luminous scattering region is responsible for the X-ray emission. A prominent Ne IX feature places a stringent limit (Log $xi$ = 2.0-2.5) on the ionization parameter which constrains the wind dynamics of the system. The Fe line fluxes are related linearly to the blackbody fluxes indicating that both originate in the same region or are excited by the same mechanism. There is evidence for structure in the Fe-line that cannot be fully resolved by the current observations. The pulse period measured during our observations, 0.7057147$pm$0.00000027s shows that the uninterrupted spin-up trend of SMC X-1 continues. We discuss the implications of our results for models of SMC X-1.
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We present results from quantitative modeling and spectral analysis of the high mass X-ray binary Vela X-1 obtained with the Chandra HETGS. 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. 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 the simulation results, we are able to find the ionization structure and the geometrical distribution of material in Vela X-1 that can reproduce the observed spectral line intensities and continuum shapes at different orbital phases remarkably well. 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 lines, we demonstrate that the stellar wind is affected by X-ray photoionization.
(Shortened) Ultraviolet observations of the black hole X-ray binary Cygnus X-1 were obtained using the STIS on HSTubble. We detect P Cygni line features show strong, broad absorption components when the X-ray source is behind the companion star and noticeably weaker absorption when the X-ray source is between us and the companion star. We fit the P Cygni profiles using the SEI method applied to a spherically symmetric stellar wind subject to X-ray photoionization from the black hole. The Si IV doublet provides the most reliable estimates of the parameters of the wind and X-ray illumination. The velocity $v$ increases with radius $r$ according to $v=v_infty(1-r_star/r)^beta$, with$betaapprox0.75$ and $v_inftyapprox1420$ km s$^{-1}$.The microturbulent velocity was $approx160$ km s$^{-1}$. Our fit implies a ratio of X-ray luminosity to wind mass-loss rate of L$_{X,38}/dot M_{-6} approx 0.33$, measured at $dot M_{-6}$ = 4.8. Our models determine parameters that may be used to estimate the accretion rate onto the black hole and independently predict the X-ray luminosity. Our predicted L$_x$ matches that determined by contemporaneous RXTE ASM remarkably well, but is a factor of 3 lower than the rate according to Bondi-Hoyle-Littleton spherical wind accretion. We suggest that some of the energy of accretion may go into powering a jet.
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.
We present the detection of new cometary X-ray emission lines in the 1.0 to 2.0 keV range using a sample of comets observed with the Chandra X-ray observatory and ACIS spectrometer. We have selected 5 comets from the Chandra sample with good signal-to-noise spectra. The surveyed comets are: C/1999 S4 (LINEAR), C/1999 T1 (McNaught-Hartley), 153P/2002 (Ikeya-Zhang), 2P/2003 (Encke), and C/2008 8P (Tuttle). We modeled the spectra with an extended version of our solar wind charge exchange (SWCX) emission model (Bodewits et al. 2007). Above 1 keV, we find Ikeya-Zhang to have strong emission lines at 1340 and 1850 eV that we identify as being created by solar wind charge exchange lines of Mg XI and Si XIII, respectively, and weaker emission lines at 1470, 1600, and 1950 eV formed by SWCX of Mg XII, Mg XI, and Si XIV, respectively. The Mg XI and XII and Si XIII and XIV lines are detected at a significant level for the other comets in our sample (LS4, MH, Encke, 8P), and these lines promise additional diagnostics to be included in SWCX models. The silicon lines in the 1700 to 2000 eV range are detected for all comets, but with the rising background and decreasing cometary emission, we caution these detections need further confirmation with higher resolution instruments.
We have investigated the composition and distribution of the wind of Sk 160, the supergiant companion of the X-ray star SMC X-1, by comparing an X-ray spectrum of the source, obtained with the ASCA observatory, during an eclipse with the computed spectra of reprocessed radiation from circumstellar matter with various density distributions. We show that the metal abundance in the wind of Sk 160 is no greater than a few tenths of solar, as has been determined for other objects in the Magellanic Clouds. We also show that the observed X-ray spectrum is not consistent with the density distributions of circumstellar matter of the spherically symmetric form derived for line-driven winds, nor with the density distribution derived from a hydrodynamic simulation of the X-ray perturbed and line-driven wind by Blondin & Woo (1995).
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