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تسجيل مستخدم جديدA Transient Supergiant X-ray Binary in IC10. An Extragalactic SFXT?
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We report the discovery of a large amplitude (factor of $sim$100) X-ray transient (IC 10 X-2, CXOU J002020.99+591758.6) in the nearby dwarf starburst galaxy IC10 during our Chandra monitoring project. Based on the X-ray timing and spectral properties, and an optical counterpart observed with Gemini, the system is a high mass X-ray binary (HMXB) consisting of a luminous blue supergiant and a neutron star (NS). The highest measured luminosity of the source was 1.8$times$10$^{37}$ erg s$^{-1}$ during an outburst in 2003. Observations before, during and after a second outburst in 2010 constrain the outburst duration to be less than 3 months (with no lower limit). The X-ray spectrum is a hard powerlaw ($Gamma$=0.3) with fitted column density ($N_H$=6.3$times$10$^{21}$ atom cm$^{-2}$) consistent with the established absorption to sources in IC10. The optical spectrum shows hydrogen Balmer lines strongly in emission, at the correct blueshift (-340 km/s) for IC10. The NIII triplet emission feature is seen, accompanied by He II [4686] weakly in emission. Together these features classify the star as a luminous blue supergiant of the OBN subclass, characterized by enhanced nitrogen abundance. Emission lines of HeI are seen, at similar strength to H$beta$. A complex of FeII permitted and forbidden emission lines are seen, as in B[e] stars. The system closely resembles galactic supergiant fast X-ray transients (SFXTs), in terms of its hard spectrum, variability amplitude and blue supergiant primary.
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TAR. We report in this paper the analysis and results obtained from all these X-ray data. Based on the fast variability in the X-ray domain, the spectral energy distribution in the 0.5-80 keV energy range, and the reported association with a highly reddened OB supergiant at ~10 kpc, we conclude that IGR J17503-2636 is most likely a relatively faint new member of the supergiant fast X-ray transients. Spectral analysis of the NuSTAR data revealed a broad feature in addition to the typical power-law with exponential roll-over at high energy. This can be modeled either in emission or as a cyclotron scattering feature in absorption. If confirmed by future observations, this feature would indicate that IGR J17503-2636 hosts a strongly magnetized neutron star with B~2e12 G.
Supergiant fast X-ray transients (SFXTs) are high mass X-ray binaries associated with OB supergiant companions and characterised by an X-ray flaring behaviour whose dynamical range reaches 5 orders of magnitude on timescales of a few hundred to thous
ands of seconds. Current investigations concentrate on finding possible mechanisms to inhibit accretion in SFXTs and explain their unusually low average X-ray luminosity. We present the Swift observations of an exceptionally bright outburst displayed by the SFXT IGR J17544-2619 on 2014 October 10 when the source achieved a peak luminosity of $3times10^{38}$ erg s$^{-1}$. This extends the total source dynamic range to $gtrsim$10$^6$, the largest (by a factor of 10) recorded so far from an SFXT. Tentative evidence for pulsations at a period of 11.6 s is also reported. We show that these observations challenge, for the first time, the maximum theoretical luminosity achievable by an SFXT and propose that this giant outburst was due to the formation of a transient accretion disc around the compact object.
Timing analysis of the INTEGRAL-IBIS and Swift-BAT light curves of the Supergiant Fast X-ray Transient (SFXT) IGR J16465-4507 has identified a period of 30.32+/-0.02 days which we interpret as the orbital period of the binary system. In addition 11 o
utbursts (9 of which are previously unpublished) have been found between MJD 52652 to MJD 54764, all of which occur close to the region of the orbit we regard as periastron. From the reported flux outbursts, we found a dynamical range in the interval ~30-80. Although in this regard IGR J16465-4507 cannot be considered a classical SFXT for which typical dinamical ranges are >100, still our reported values are significantly greater than that of classical persistent variable supergiant HMXBs (<20), supporting the idea that IGRJ16465-4507 is an intermediate SFXT system, much like few other similar cases reported in the literature.
We present NuSTAR spectral and timing studies of the Supergiant Fast X-ray Transient (SFXT) IGR J17544-2619. The spectrum is well-described by a ~1 keV blackbody and a hard continuum component, as expected from an accreting X-ray pulsar. We detect a
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is giving to this field, and how new technology complements and sometimes changes the view of things.
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