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Register a new userSpectral evolution of the supergiant HMXB IGR J16320-4751 along its orbit using XMM-Newton
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Authors
Federico Garcia
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The INTEGRAL satellite has revealed a previously hidden population of absorbed high-mass X-ray binaries (HMXBs) hosting supergiant (SG) stars. Among them, IGR J16320-4751 is a classical system intrinsically obscured by its environment, with a column density of ~10$^{23}$ cm$^{-2}$, composed by a neutron star (NS, spin period ~1300 s), accreting matter from the stellar wind of an O8I star, with an orbital period of ~9 d. We analyzed all archival XMM-Newton and Swift/BAT observations, performing a detailed temporal and spectral analysis of its X-ray emission. XMM-Newton light curves show high-variability and flaring activity on several timescales. In one observation we detected two short and bright flares where the flux increased by a factor of ~10 for ~300 s, with similar behavior in the soft and hard X-ray bands. By inspecting the 4500-day light curves of the Swift/BAT data, we derived a refined period of 8.99$pm$0.01 days. The XMM-Newton spectra are characterized by a highly absorbed continuum and a Fe absorption edge at ~7 keV. We fitted the continuum with a thermally Comptonized model, and the emission lines with 3 narrow Gaussian functions using two absorption components, to take into account both the interstellar medium and the intrinsic absorption. We derived the column density at different orbital phases, showing its clear modulation. We also show that the flux of the Fe K$alpha$ line is correlated with the NH column, suggesting a link between absorbing and fluorescent matter that, together with the orbital modulation, points towards the SG wind as the main contributor to both continuum absorption and Fe K$alpha$ emission. Assuming a simple model for the SG wind we were able to explain the orbital modulation of the absorption column density, Fe K$alpha$ emission, and the high-energy Swift/BAT flux, allowing us to constrain the geometrical parameters of the binary system.
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We report a discovery of strong modulations of the X-ray flux detected from IGR J16320-4751 = AX J1631.9-4752 with a period of P~1300 sec. We reanalyzed the data of an XMM-Newton ToO performed soon after the discovery of the source by INTEGRAL and found the modulation at a period of P=1309+/-40 sec with a high significance. Modulations of the source flux with two possible periods of ~1300 and ~1500 sec were identified in the ASCA archival data. It is very likely that the modulation can be interpreted as X-ray pulsations, favouring a pulsar as the compact object in IGR/AX J16320-4752. Thus for the moment this source became the fourth source from a new class of highly absorbed binary systems for which the pulsations are observed.
We present the results of combined INTEGRAL and XMM-Newton observations of the supergiant fast X-ray transient (SFXT) IGR J17354$-$3255. Three XMM-Newton observations of lengths 33.4 ks, 32.5 ks and 21.9 ks were undertaken, the first an initial pointing to identify the correct source in the field of view and the latter two performed around periastron. Simultaneous INTEGRAL observations across $sim66%$ of the orbital cycle were analysed but the source was neither detected by IBIS/ISGRI nor by JEM-X. The XMM-Newton light curves display a range of moderately bright X-ray activity but there are no particularly strong flares or outbursts in any of the three observations. We show that the spectral shape measured by XMM-Newton can be fitted by a consistent model throughout the observation, suggesting that the observed flux variations are driven by obscuration from a wind of varying density rather than changes in accretion mode. The simultaneous INTEGRAL data rule out simple extrapolation of the simple powerlaw model beyond the XMM-Newton energy range.
We report on a 12 hr XMM-Newton observation of the supergiant High-Mass X-ray Binary IGR J16207-5129. This is only the second soft X-ray (0.4-15 keV, in this case) study of the source since it was discovered by the INTEGRAL satellite. The average energy spectrum is very similar to those of neutron star HMXBs, being dominated by a highly absorbed power-law component with a photon index of 1.15. The spectrum also exhibits a soft excess below 2 keV and an iron Kalpha emission line at 6.39+/-0.03 keV. For the primary power-law component, the column density is 1.19E23 cm^-2, indicating local absorption, likely from the stellar wind, and placing IGR J16207-5129 in the category of obscured IGR HMXBs. The source exhibits a very high level of variability with an rms noise level of 64%+/-21% in the 0.0001 to 0.05 Hz frequency range. Although the energy spectrum suggests that the system may harbor a neutron star, no pulsations are detected with a 90% confidence upper limit of 2% in a frequency range from 0.0001 to 88 Hz. We discuss similarities between IGR J16207-5129 and other apparently non-pulsating HMXBs, including other IGR HMXBs as well as 4U 2206+54 (but see arXiv:0812.2365) and 4U 1700-377.
We report on the results of a NuSTAR observation of the Supergiant Fast X-ray Transient pulsar IGRJ11215-5952 during the peak of its outburst in June 2017. IGRJ11215-5952 is the only SFXT undergoing strictly periodic outbursts, every 165 days. NuSTAR caught several X-ray flares, spanning a dynamic range of 100, and detected X-ray pulsations at 187.0 s, consistent with previous measurements. The spectrum from the whole observation is well described by an absorbed power-law (with a photon index of 1.4) modified, above 7 keV, by a cutoff with an e-folding energy of 24 keV. A weak emission line is present at 6.4 keV, consistent with Kalpha emission from cold iron in the supergiant wind. The time-averaged flux is 1.5E-10 erg/cm2/s (3-78 keV, corrected for the absorption), translating into an average luminosity of about 9E35 erg/s (1-100 keV, assuming a distance of 6.5 kpc). The NuSTAR observation allowed us to perform the most sensitive search for cyclotron resonant scattering features in the hard X-ray spectrum, resulting in no significant detection in any of the different spectral extractions adopted (time-averaged, temporally-selected, spin-phase-resolved and intensity-selected spectra). The pulse profile showed an evolution with both the energy (3-12 keV energy range compared with 12-78 keV band) and the X-ray flux: a double peaked profile was evident at higher fluxes (and in both energy bands), while a single peaked, sinusoidal profile was present at the lowest intensity state achieved within the NuSTAR observations (in both energy bands). The intensity-selected analysis allowed us to observe an anti-correlation of the pulsed fraction with the X-ray luminosity. The pulse profile evolution can be explained by X-ray photon scattering in the accreting matter above magnetic poles of a neutron star at the quasi-spherical settling accretion stage.
We present the results of a 500 ksec long XMM-Newton observation and a 120 ksec long quasi-simultaneous Chandra observation of the Narrow Line Seyfert 1 galaxy 1H0707-495 performed in 2010 September. Consistent with earlier results by Fabian et al. (2009) and Zoghbi et al. (2010), the spectrum is found to be dominated by relativistically broadened reflection features from an ionised accretion disc around a maximally rotating black hole. Even though the spectra changed between this observation and earlier XMM-Newton observations, the physical parameters of the black hole and accretion disc (i.e., spin and inclination) are consistent between both observations. We show that this reflection spectrum is slightly modified by absorption in a mildly relativistic, highly ionised outflow which changed velocity from around 0.11c to 0.18c between 2008 January and 2010 September. Alternative models, in which the spectral shape is dominated by absorption, lead to spectral fits of similar quality, however, the parameters inferred for the putative absorber are unphysical.
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