51ÁÔÆæÈë¿Ú

Abstract:

The source SXP 1323 is a peculiar high-mass X-ray binary located in the Small Magellanic Cloud. It is renowned for its rapid spin-up. We investigate for the first time broadband X-ray properties of SXP 1323 as observed by the Mikhail Pavlinsky ART-XC and eROSITA telescopes on board the Spectrum-Roentgen-Gamma observatory. Using ART-XC and eROSITA data, we produced a first broadband 1 20 keV X-ray spectrum and estimated the pulsed fraction box 8 keV. With the addition of archival XMM-Newton observations, we traced the evolution of the spin period of SXP 1323 over the last five years and found that after 2016, the source switched to a linear spin-up with a rate of 29.9 s yr 1. The broadband X-ray spectrum is typical for accreting X-ray pulsars. It has a steep power-law index (A= 0.15) and an exponential cutoff energy of 5.1 keV. No significant difference between spectra obtained in states with and without pulsations were found.

Abstract:

Abstract: We present the results of our study of the transient X-ray pulsar GRO J2058+42 in a wide energy range in a state with a luminosity (Formula presented.). We have found that the pulse profile of the source, along with the pulse fraction, changed significantly in comparison with the previous NuSTAR observations performed when the pulsar was brighter approximately by a factor of 10. The position of the cyclotron line at (Formula presented.) keV in a narrow phase interval is consistent with the observations in the high state. Spectral analysis has shown that at high luminosities (Formula presented.) erg s-1 the spectrum has a shape typical of accreting pulsars, whereas a two-component model should be used to describe the spectrum when the luminosity drops approximately by an order of magnitude, to (Formula presented.) erg s-1. This behavior fits into the model in which the low-energy part of the spectrum is formed in a hot spot, while the high-energy one is formed as a result of resonant Compton scattering by the infalling matter in the accretion channel above the neutron star surface.

Abstract:

Cyclotron line scattering features are detected in a few tens of X-ray pulsars (XRPs) and used as direct indicators of a strong magnetic field at the surface of accreting neutron stars (NSs). In a few cases, cyclotron lines are known to be variable with the accretion luminosity of XRPs. It is accepted that the observed variations of cyclotron line scattering features are related to variations of geometry and dynamics of accretion flow above the magnetic poles of an NS. A positive correlation between the line centroid energy and luminosity is typical for subcritical XRPs, where the accretion results in hot spots at the magnetic poles. The negative correlation was proposed to be a specific feature of bright supercritical XRPs, where radiation pressure supports accretion columns above the stellar surface. The cyclotron line in the spectra of the Be-transient XRP GRO J1008-57 is detected at energies from ~75 to 90 keV, the highest observed energy of a cyclotron line feature in XRPs. We report the peculiar relation of cyclotron line centroid energies with luminosity in GRO J1008-57 during the Type II outburst in 2017 August observed by Insight-HXMT. The cyclotron line energy was detected to be negatively correlated with the luminosity at 3.2 x 1037 erg s-1 < L < 4.2 × 1037 erg s-1 and positively correlated at L 5 x 1037 erg s-1. We speculate that the observed peculiar behavior of a cyclotron line would be due to variations of accretion channel geometry.