arXiv subjects

Alexander Mushtukov

Publications and source records attributed to Alexander Mushtukov.

6 recordsLinked to original sources

arXiv2026

NICER detection of a new candidate cyclotron line in the bursting X-ray pulsar GRO J1744-28

We report the detection of cyclotron resonant scattering features (CRSFs) in the spectrum of the unique bursting pulsar GRO J1744-28, observed during its recent outburst in 2021 with the Neutron Star Interior Composition Explorer (NICER). Clear pulsations at a frequency of 2.141128 Hz as well as Type II X-ray bursts were observed. The pulse profile exhibits a single-peaked shape in all energy bands, with the pulse fraction showing a positive correlation with energy. We find that the persistent X-ray continuum of the accreting pulsar is well described by typical phenomenological models, and we confirm the presence of the cyclotron line at $\sim$5 keV as reported in previous studies. In addition, we detect a candidate absorption feature with a centroid energy of 2 keV. If confirmed, this feature could be interpreted as a CRSF, which would correspond to a magnetic field of $\sim$1.8 $\times 10^{11}$ G. Pulse-phase-resolved analysis also reveals this absorption line around the peak pulse phases. These NICER observations provide tentative evidence for the cyclotron line candidate, establishing GRO J1744-28 as a key laboratory for studying accretion physics in an intermediate-strength magnetic field.

astro-ph.HE↗

arXiv2025

Physics of Strong Magnetism with eXTP

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 on 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.

astro-ph.HE↗

arXiv2024

Cyclotron line evolution revealed with pulse-to-pulse analysis in the 2020 outburst of 1A 0535+262

We present a detailed analysis of the X-ray luminosity (Lx) dependence of the cyclotron absorption line energy (Ecyc) for the X-ray binary pulsar 1A 0535+262 during its 2020 giant outburst based on pulse-to-pulse analysis. By applying this technique to high cadence observations of Insight-HXMT, we reveal the most comprehensive Ecyc-Lx correlation across a broad luminosity range of ~(0.03-1.3)*10^38 erg/s. Apart from the positive and negative correlations between cyclotron line energy and luminosity at Lx~(1-3)*10^37 erg/s and ~(7-13)*10^37 erg/s, which are expected from the typical subcritical and supercritical accretion regimes, respectively, a plateau in the correlation is also detected at ~(3-7)*10^37 erg/s^-1. Moreover, at the lowest luminosity level (Lx<10^37 erg/s), the positive Ecyc-Lx correlation seems to be broken, and the pulse profile also occurs a significant transition. These discoveries provide the first complete view on the correlation between luminosity and the centriod energy of the cyclotron line, and therefore are relevant for understanding how accretion onto magnetized neutron stars depends on luminosity.

astro-ph.HE↗

arXiv2023

X-ray Polarization Reveals the Precessions of the Neutron Star in Hercules X-1

In an accreting X-ray pulsar, a neutron star accretes matter from a stellar companion through an accretion disk. The high magnetic field of the rotating neutron star disrupts the inner edge of the disc, funneling the gas to flow onto the magnetic poles on its surface. Hercules X-1 is in many ways the prototypical X-ray pulsar; it shows persistent X-ray emission and it resides with its companion HZ Her, a two-solar-mass star, at about 7~kpc from Earth. Its emission varies on three distinct timescales: the neutron star rotates every 1.2~seconds, it is eclipsed by its companion each 1.7~days, and the system exhibits a superorbital period of 35~days which has remained remarkably stable since its discovery. Several lines of evidence point to the source of this variation as the precession of the accretion disc, the precession of the neutron star or both. Despite the many hints over the past fifty years, the precession of the neutron star itself has yet not been confirmed or refuted. We here present X-ray polarization measurements with the Imaging X-ray Polarimetry Explorer (IXPE) which probe the spin geometry of the neutron star. These observations provide direct evidence that the 35-day-period is set by the free precession of the neutron star crust, which has the important implication that its crust is somewhat asymmetric fractionally by a few parts per ten million. Furthermore, we find indications that the basic spin geometry of the neutron star is altered by torques on timescale of a few hundred days.

astro-ph.HE↗

arXiv2023

Accreting strongly magnetised neutron stars: X-ray Pulsars

X-ray pulsars (XRPs) are accreting strongly magnetised neutron stars (NSs) in binary systems with, as a rule, massive optical companions. Very reach phenomenology and high observed flux put them into the focus of observational and theoretical studies since the first X-ray instruments were launched into space. The main attracting characteristic of NSs in this kind of system is the magnetic field strength at their surface, about or even higher than $10^{12}\,{\rm G}$, that is about six orders of magnitude stronger than what is attainable in terrestrial laboratories. Although accreting XRPs were discovered about 50 years ago, the details of the physical mechanisms responsible for their properties are still under debate. Here we review recent progress in observational and theoretical investigations of XRPs as a unique laboratory for studies of fundamental physics (plasma physics, QED and radiative processes) under extreme conditions of ultra-strong magnetic field, high temperature, and enormous mass density.

astro-ph.HE↗

arXiv2019

The X-ray Polarization Probe mission concept

The X-ray Polarization Probe (XPP) is a second generation X-ray polarimeter following up on the Imaging X-ray Polarimetry Explorer (IXPE). The XPP will offer true broadband polarimetery over the wide 0.2-60 keV bandpass in addition to imaging polarimetry from 2-8 keV. The extended energy bandpass and improvements in sensitivity will enable the simultaneous measurement of the polarization of several emission components. These measurements will give qualitatively new information about how compact objects work, and will probe fundamental physics, i.e. strong-field quantum electrodynamics and strong gravity.

astro-ph.IM↗