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Abstract:

Radiation of X-ray pulsars is powered by accretion on the neutron star surface from a binary companion under the influence of a strong magnetic field. We study the beaming of this radiation in the case of subcritical X-ray pulsars, where it is formed in the accretion channel close to the neutron star surface. We solve equations of the hydrodynamics and radiative transfer of two coupled polarization modes in the accretion channel numerically, taking into account resonant Compton scattering and vacuum polarization. The beaming patterns are obtained for different accretion rates, photon energies, and polarizations, as well as for different models of the neutron star surface radiation. The calculated beaming patterns are converted into light curves for both the intensity and polarization, taking into account the effects of General Relativity. These beaming patterns and light curves are found to be strongly affected by the resonant Compton scattering for photon energies comparable with the electron cyclotron energy. In particular, the angular redistribution of radiation near the cyclotron resonance may reduce the light-curve modulation amplitude, which is consistent with observational indications of a suppressed pulsed fraction at these energies.

Abstract:

We present a detailed polarimetric analysis of Cen X-3 using IXPE observations during its high state, revealing a complex, energy-dependent polarization behavior. While phase-averaged polarization shows marginal energy dependence, phase-resolved analysis reveals that the energy dependence of the polarization angle is strongly phase-dependent, with dramatic variations visible in a few specific phase intervals. We modeled this behavior using a two-component polarization framework consisting of a pulsed component governed by the rotating vector model (RVM) and an additional phase-dependent component. By allowing the additional component’s polarized flux to vary with pulse phase while fixing its PA, the observed complex behavior can be reconciled with a single set of RVM parameters across all energies. Spectroscopic analysis using IXPE , NICER, and NuSTAR during the high state reveals phase-modulated intrinsic hydrogen column density and covering fraction, suggesting that the wind properties are modulated with pulse phase. Our findings indicate that phase-dependent scattering in the disk wind may significantly alter the observed polarization properties of X-ray pulsars.

Abstract:

Abstract: The paper is devoted to modeling the gravitational waves from the X-ray pulsar Her X-1. The neutron star is considered as a freely precessing ellipsoid. The gravitational wave signal is calculated in the quadrupole approximation. The and polarization profiles are constructed for the precession parameters of the neutron star in Her X-1 measured in up-to-date works. The possibility of signal detection with the DECIGO telescope is assessed. The formulas for the semi-analytical modeling of the gravitational wave signal from precessing neutron stars by the method of perturbations in the small neutron star ellipticity parameter are deduced.

Abstract:

We present the first broadband spectral and timing study of the Be/X-ray pulsar XTE J0111.2−7317 (SXP31.0) during the first major outburst since its discovery in 1998. This giant type II outburst, observed between April and September 2025, marks the source’s return to activity after nearly three decades of quiescence. Using NuSTAR observations together with data from Swift /XRT and SRG /ART-XC, we followed the outburst’s evolution, with the source reaching a bolometric luminosity of L bol = 3.6 × 10 38 erg s −1 . The broadband spectra are well described by an absorbed cutoff power law, two blackbody components (hot and soft), and a narrow Fe K α line. No cyclotron absorption features were detected in either the phase-averaged or phase-resolved spectra in the 5–50 keV band. Most notably, we report the discovery of a previously undetected quasiperiodic oscillation (QPO) at 0.8 ± 0.1 mHz, characterized by a fractional root-mean-square (rms) amplitude of 14% at a super-Eddington bolometric luminosity of L bol = 2.5 × 10 38 erg s −1 . In contrast, the previously reported 1.27 Hz QPO was not detected. While the 0.8 mHz QPO is present, the pulsed fraction (PF) is low in soft X-rays, which is consistent with other super-Eddington pulsars exhibiting mHz QPOs; however, it rises above 20 keV to reach 35%. The QPO vanishes in subsequent observations coinciding with a sharp increase in the PF and a distinct change in pulse profile morphology. It was not observed in any follow-up observations at luminosities above or below its initial detection, suggesting it is a transient phenomenon.

Abstract:

In this paper we present the science potential of the enhanced X-ray Timing and Polarimetry (eXTP) mission, in its new configuration, for studies of strongly magnetized compact objects. We discuss the scientific potential of eXTP for quantum electrodynamic (QED) studies, especially leveraging the recent observations made with the NASA IXPE mission. Given eXTP’s unique combination of timing, spectroscopy, and polarimetry, we focus on the perspectives for physics and astrophysics studies of strongly magnetized compact objects, such as magnetars and accreting X-ray pulsars. Developed by an international Consortium led by the Institute of High Energy Physics of the Chinese Academy of Sciences, the eXTP mission is expected to launch in early 2030.