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تسجيل مستخدم جديدThe Hard State of the Highly Absorbed High Inclination Black Hole Binary Candidate Swift J1658.2-4242 Observed by NuSTAR and Swift
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We present a spectral and timing analysis of the newly reported Galactic X-ray transient Swift J1658.2-4242 observed by NuSTAR and Swift. The broad-band X-ray continuum is typical of a black hole binary in the bright hard state, with a photon index of $Gamma=1.63pm0.02$ and a low coronal temperature of $kT_{rm e}=22pm1$ keV, corresponding to a low spectral cutoff well constrained by NuSTAR. Spectral modeling of the relativistic disk reflection features, consisting of a broad Fe K$alpha$ line and the Compton reflection hump, reveals that the black hole is rapidly spinning with the spin parameter of $a^{*}>0.96$, and the inner accretion disk is viewed at a high inclination angle of $i=64^{+2}_{-3}{^circ}$ (statistical errors, 90% confidence). The high inclination is independently confirmed by dips in the light curves, which can be explained by absorbing material located near the disk plane temporarily obscuring the central region. In addition, we detect an absorption line in the NuSTAR spectra centered at $7.03^{+0.04}_{-0.03}$ keV. If associated with ionized Fe K absorption lines, this provides evidence for the presence of outflowing material in the low/hard state of a black hole binary candidate. A timing analysis shows the presence of a type-C QPO in the power spectrum, with the frequency increasing from $sim0.14$ Hz to $sim0.21$ Hz during the single NuSTAR exposure. Our analysis reveals that Swift J1658.2-4242 displays characteristics typical for a black hole binary that is viewed at a high inclination angle, making it a good system for studying the accretion geometry in black hole binaries.
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hard state. We observe clear disk reflection features, including a broad Fe K$alpha$ line and a Compton hump peaking around 30 keV. Detailed spectral modeling reveals narrow Fe K$alpha$ line complex centered around 6.5 keV on top of the strong relativistically broadened Fe K$alpha$ line. The narrow component is consistent with distant reflection from moderately ionized material. The spectral continuum is well described by a combination of cool thermal disk photons and a Comptonized plasma with the electron temperature $kT_{rm e}=19.7pm{0.4}$ keV. An adequate fit can be achieved for the disk reflection features with a self-consistent relativistic reflection model that assumes a lamp-post geometry for the coronal illuminating source. The spectral fitting measures a black hole spin $a>0.84$, inner disk radius $R_{rm in}<2.01~r_{rm ISCO}$, and a lamp-post height $h=7.2^{+0.8}_{-2.0} r_{rm g}$ (statistical errors, 90% confidence), indicating no significant disk truncation and a compact corona. Although the distance and mass of this source are not currently known, this suggests the source was likely in the brighter phases of the hard state during this NuSTAR observation.
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