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تسجيل مستخدم جديدDiscovery of long-term superorbital periodicities in the pseudo-transient LMXBs: IGR J17098-3628 and EXO0748-676
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M.M. Kotze
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Long-term monitoring of the recently discovered X-ray transient, IGR J17098-3628, by the All Sky Monitor on board the Rossi X-ray Timing Explorer, has shown that it displays a long term (~163d) quasi-periodic modulation in the data spanning its active state (i.e. approximately MJD 53450-54200). Furthermore, this light-curve is not typical of classical soft X-ray transients, in that J17098-3628 has remained active since its initial discovery, and may be more akin to the pseudo-transient EXO0748-676, which is now classified as a persistent Low Mass X-ray Binary. However, EXO0748-676 recently entered a more active phase (since approximately MJD 53050), since when we find that it too displays a quasi-periodic modulation (~181d) in its light-curve. This must be a superorbital modulation, as the orbital period of EXO0748-676 is well established (3.8hrs), and hence we interpret both objects long periods as representing some intrinsic properties of the accretion disc (such as coupled precessional and warping effects). By analogy, we therefore suggest that IGR J17098-3628 is another member of this class of pseudo-transient LMXBs and is likely to have a <1d orbital period.
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IGR J17091-3624 and IGR J17098-3628 are two X-ray transients discovered by INTEGRAL and classified as possible black hole candidates (BHCs). We present here the results obtained from the analysis of multi-wavelength data sets collected by different i
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We report the discovery with INTEGRAL on March 24, 2005, and follow-up observations of the distant Galactic X-ray nova IGR J17098-3628.
Orbital period changes are an important diagnostic for understanding low mass X-ray binary (LMXB) accretion-induced angular momentum exchange and overall system evolution. We present our most recent results for the eclipse timing of the LMXB EXO0748-
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We report the detection of pulsations at 552 Hz in the rising phase of two type-I (thermonuclear) X-ray bursts observed from the accreting neutron star EXO 0748-676 in 2007 January and December, by the Rossi X-ray Timing Explorer. The fractional ampl
itude was 15% (rms). The dynamic power density spectrum for each burst revealed an increase in frequency of approx. 1-2 Hz while the oscillation was present. The frequency drift, the high significance of the detections and the almost identical signal frequencies measured in two bursts separated by 11 months, confirms this signal as a burst oscillation similar to those found in 13 other sources to date. We thus conclude that the spin frequency in EXO 0748-676 is within a few Hz of 552 Hz, rather than 45 Hz as was suggested from an earlier signal detection by Villarreal & Strohmayer (2004). Consequently, Doppler broadening must significantly affect spectral features arising from the neutron star surface, so that the narrow absorption features previously reported from an XMM-Newton spectrum could not have arisen there. The origin of both the previously reported 45 Hz oscillation and the X-ray absorption lines is now uncertain.
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