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Register a new userThe Ephemeris and Dipping Spectral Behavior of X1624-490
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We present striking results from Rossi X-ray Timing Explorer (RXTE) observations of the 21-hr low mass X-ray binary X1624-490, showing five complex dips in unprecedented detail. For the first time, dipping is detected up to 15 keV. Prominent flares are also observed in the light curves, limited to energies above 8 keV. Spectra selected by intensity during dip episodes can be well fit with a two-component model consisting of a point-like blackbody from the neutron star and progressive covering of an extended Comptonized region, presumably an accretion disk corona (ADC), corrected for photons scattered into and out of the X-ray beam by a interstellar dust halo. We find that the outer regions of the absorber are highly ionized and that electron scattering is totally responsible for the X-ray attenuation during shallow dipping. The timescales of dip ingress and egress indicate that the envelope of material absorbing the ADC has smaller angular size than the ADC itself, and that the ADC is likely limited to a height-to-radius ratio of 10%, rather than being spherical in extent. In addition, we have analyzed 4.5 yrs of RXTE All Sky Monitor (ASM) coverage to derive the first accurate orbital ephemeris for X1624-490, with phase zero (the time of dip centers) well-described by the relation 2450088.63918(69) + N*0.869907(12) (JD).
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We report on the precise localization of the low mass X-ray binaries X1624-490 and X1702-429 with the Chandra HRC-I. We determine the best positions to be 16:28:02.825 -49:11:54.61 (J2000) and 17:06:15.314 -43:02:08.69 (J2000) for X1624-490 and X1702-429, respectively, with the nominal Chandra positional uncertainty of 0.6. We also obtained deep IR observations of the fields of these sources in an effort to identify the IR counterparts. A single, faint (Ks=18.3 +/- 0.1) source is visible inside the Chandra error circle of X1624-490, and we propose this source as its IR counterpart. For X1702-429, a Ks=16.5 +/- 0.07 source is visible at the edge of the Chandra error circle. The brightness of both counterpart candidates is comparable to that of other low mass X-ray binary IR counterparts when corrected for extinction and distance.
Context: XB 1916-053 is a low mass X-ray binary system (LMXB) hosting a neutron star (NS) and showing periodic dips. The spectrum of the persistent emission was modeled with a blackbody component having a temperature between 1.31 and 1.67 keV and with a Comptonization component with an electron temperature of 9.4 keV and a photon index $Gamma$ between 2.5 and 2.9. The presence of absorption features associated with highly ionized elements suggested the presence of partially ionized plasma in the system. Aims: In this work we performed a study of the spectrum of XB 1916-053, which aims to shed light on the nature of the seed photons that contribute to the Comptonization component. Methods: We analyzed three Suzaku observations of XB 1916-053: the first was performed in November 2006 and the others were carried out in October 2014. We extracted the persistent spectra from each observation and combined the spectra of the most recent observations, obtaining a single spectrum with a higher statistic. We also extracted and combined the spectra of the dips observed during the same observations. Results: On the basis of the available data statistics, we infer that the scenario in which the corona Comptonizes photons emitted both by the innermost region of the accretion disk and the NS surface is not statistically relevant with respect to the case in which only photons emitted by the NS surface are Comptonized. We find that the source is in a soft spectral state in all the analyzed observations. We detect the K$alpha$ absorption lines of ion{Fe}{xxv} and ion{Fe}{xxvi}, which have already been reported in literature, and for the first time the K$beta$ absorption lines of the same ions. We also detect an edge at 0.876 keV, which is consistent with a ion{O}{viii} K absorption edge. (Abridged)
We report the discovery of unusually strong optical and X-ray emission associated with a knot in the radio jet of PKS B1421-490. The knot is the brightest feature observed beyond the radio band, with knot/core flux ratios ~300 and 3.7 at optical and X-ray frequencies. We interpret the extreme optical output of the knot as synchrotron emission. The nature of the X-ray emission is unclear. We consider a second synchrotron component, inverse Compton emission from a relativistic, decelerating jet, and the possibility that this feature is a chance superposition of an unusual BL Lac object.
We present the results of a 73 ks long Chandra observation of the dipping source X 1624-490. During the observation a complex dip lasting 4 hours is observed. We analyse the persistent emission detecting, for the first time in the 1st-order spectra of X 1624-490, an absorption line associated to ion{Ca}{xx}. We confirm the presence of the ion{Fe}{xxv} K$_alpha$ and ion{Fe}{xxvi} K$_alpha$ absorption lines with a larger accuracy with respect to a previous XMM observation. Assuming that the line widths are due to a bulk motion or a turbulence associated to the coronal activity, we estimate that the lines have been produced in a photoionized absorber between the coronal radius and the outer edge of the accretion disk.
The aim of this work is to study the spectral statistics of the asymmetric rotor model (triaxial rigid rotator). The asymmetric top is classically integrable and, according to the Berry-Tabor theory, its spectral statistics should be Poissonian. Surprisingly, our numerical results show that the nearest neighbor spacing distribution $P(s)$ and the spectral rigidity $Delta_3(L)$ do not follow Poisson statistics. In particular, $P(s)$ shows a sharp peak at $s=1$ while $Delta_3(L)$ for small values of $L$ follows the Poissonian predictions and asymptotically it shows large fluctuations around its mean value. Finally, we analyze the information entropy, which shows a dissolution of quantum numbers by breaking the axial symmetry of the rigid rotator.
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