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Register a new userPhase Variation in the Pulse Profile of SMC X-1
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J. Neilsen
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We present the results of timing and spectral analysis of X-ray high state observations of the high-mass X-ray pulsar SMC X-1 with Chandra, XMM-Newton, and ROSAT, taken between 1991 and 2001. The source has L_X ~ 3-5 x 10^38 ergs/s, and the spectra can be modeled as a power law plus blackbody with kT_BB ~ 0.18 keV and reprocessed emission radius R_BB ~ 2 x 10^8 cm, assuming a distance of 60 kpc to the source. Energy-resolved pulse profiles show several distinct forms, more than half of which include a second pulse in the soft profile, previously documented only in hard energies. We also detect significant variation in the phase shift between hard and soft pulses, as has recently been reported in Her X-1. We suggest an explanation for the observed characteristics of the soft pulses in terms of precession of the accretion disk.
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The high mass X-ray binary Cep X-4, during its 2014 outburst, showed evidence for an asymmetric cyclotron line in its hard X-ray spectrum. The 2014 spectrum provides one of the clearest cases of an asymmetric line profile among all studied sources with Cyclotron Resonance Scattering Features (CRSF). We present a phase-resolved analysis of NuSTAR and Suzaku data taken at the peak and during the decline phases of this outburst. We find that the pulse-phased resolved spectra are well-fit by a single, symmetric cyclotron feature. The fit parameters vary strongly with pulse phase: most notably the central energy and depth of the cyclotron feature, the slope of the power-law component, and the absorbing column density. We synthesise a phase averaged spectrum using the best-fit parameters for these individual pulse phases, and find that this combined model spectrum has a similar asymmetry in the cyclotron features as discovered in phase-averaged data. We conclude that the pulse phase resolved analysis with simple symmetric line profiles when combined can explain the asymmetry detected in the phase-averaged data.
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.
The High Mass X-ray Binaries (HMXRBs) SMC X-1 and 4U1700-37 have been observed with FUSE to study the effect of the X-ray source on the stellar wind of the primary. In both systems phase dependent changes in the wind lines have been observed, indicating the creation of a X-ray ionization zone in the stellar wind. The high X-ray luminosity of SMC X-1 ionizes much of the wind and leaves a Stromgren zone. This disrupts the resonance-line acceleration of the wind in portions of the orbit, quencing the wind and disrupting the mass flow. A similar but less dramatic effect was found for the first time in 4U1700-37. This so-called Hatchett-McCray (HM) effect had been predicted for 4U1700-37, but was not previously detected.
We have observed a complex and continuous change in the integrated pulse profile of PSR B2217+47, manifested as additional components trailing the main peak. These transient components are detected over 6 years at $150$ MHz using the LOw Frequency ARray (LOFAR), but they are not seen in contemporaneous Lovell observations at $1.5$ GHz. We argue that propagation effects in the ionized interstellar medium (IISM) are the most likely cause. The putative structures in the IISM causing the profile variation are roughly half-way between the pulsar and the Earth and have transverse radii $R sim 30$ AU. We consider different models for the structures. Under the assumption of spherical symmetry, their implied average electron density is $overline{n}_e sim 100$ cm$^{-3}$. Since PSR B2217+47 is more than an order of magnitude brighter than the average pulsar population visible to LOFAR, similar profile variations would not have been identified in most pulsars, suggesting that subtle profile variations in low-frequency profiles might be more common than we have observed to date. Systematic studies of these variations at low frequencies can provide a new tool to investigate the proprieties of the IISM and the limits to the precision of pulsar timing.
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.
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