18 research outputs found
Losing a minute every two years: SRG X-ray view of the rapidly accelerating X-ray pulsar SXP 1323
High Energy Astrophysic
First characterization of a new high-mass X-ray binary in LMC eRASSU J050810.4-660653 with SRG/ART-XC, NuSTAR, and Swift
Galaxie
SRG/ART-XC, Swift, NICER, and NuSTAR study of different states of the transient X-ray pulsar MAXI J0903-531
High Energy Astrophysic
Nonquasiparticle states in half-metallic ferromagnets
Anomalous magnetic and electronic properties of the half-metallic
ferromagnets (HMF) have been discussed. The general conception of the HMF
electronic structure which take into account the most important correlation
effects from electron-magnon interactions, in particular, the spin-polaron
effects, is presented. Special attention is paid to the so called
non-quasiparticle (NQP) or incoherent states which are present in the gap near
the Fermi level and can give considerable contributions to thermodynamic and
transport properties. Prospects of experimental observation of the NQP states
in core-level spectroscopy is discussed. Special features of transport
properties of the HMF which are connected with the absence of one-magnon
spin-flip scattering processes are investigated. The temperature and magnetic
field dependences of resistivity in various regimes are calculated. It is shown
that the NQP states can give a dominate contribution to the temperature
dependence of the impurity-induced resistivity and in the tunnel junction
conductivity. First principle calculations of the NQP-states for the prototype
half-metallic material NiMnSb within the local-density approximation plus
dynamical mean field theory (LDA+DMFT) are presented.Comment: 27 pages, 9 figures, Proceedings of Berlin/Wandlitz workshop 2004;
Local-Moment Ferromagnets. Unique Properties for Moder Applications, ed. M.
Donath, W.Nolting, Springer, Berlin, 200
Changes in the nature of the spectral continuum and stability of the cyclotron line in the X-ray pulsar GRO J2058+42
High Energy Astrophysic
Changes in the nature of the spectral continuum and stability of the cyclotron line in the X-ray pulsar GRO J2058+42
The results of the broadband spectral and timing study of the transient X-ray
pulsar GRO J2058+42 in a wide energy range at a low luminosity erg s are reported. The data revealed that the pulse
profile and pulse fraction of the source are significantly changed in
comparison with previous NuSTAR observations, when the source was ten times
brighter. The cyclotron absorption line at keV in the narrow phase
interval is consistent with the high state observations. Spectral analysis
showed that at high luminosities erg
s the spectrum has a shape typical of accreting pulsars, while when the
luminosity drops by about an order of magnitude, to erg
s a two-component model is necessary to its describing. This behavior
fits into a model in which the low-energy part of the spectrum is formed in a
hot spot, and the high-energy part is formed as a result of resonant Compton
scattering by incident matter in an accretion channel above the surface of a
neutron star.Comment: 16 pages, 6 figures, 3 table
Study of the X-ray pulsar IGR J19294+1816 with NuSTAR: Detection of cyclotron line and transition to accretion from the cold disk
High Energy Astrophysic
On the magnetic field of the first Galactic ultraluminous X-ray pulsar Swift J0243.6+6124
We report on the monitoring of the final stage of the outburst from the first Galactic ultraluminous X-ray pulsar Swift J0243.6+6124, which reached ∼40 Eddington luminosities. The main aim of the monitoring program with the Swift/XRT telescope was to measure the magnetic field of the neutron star using the luminosity of transition to the ‘propeller’ state. The visibility constraints, unfortunately, did not permit us to observe the source down to the fluxes low enough to detect such a transition. The tight upper limit on the propeller luminosity Lprop 1013 G. Given the existing uncertainty in the effective magnetosphere size, we conclude that both estimates are marginally compatible with each other
Luminosity dependence of the cyclotron line and evidence for the accretion regime transition in V 0332+53
We report on the analysis of NuSTAR observations of the Be-transient X-ray pulsar V 0332+53 during the giant outburst in 2015 and another minor outburst in 2016. We confirm the cyclotron-line energy–luminosity correlation previously reported in the source and the line energy decrease during the giant outburst. Based on 2016 observations, we find that a year later the line energy has increased again essentially reaching the pre-outburst values. We discuss this behaviour and conclude that it is likely caused by a change of the emission region geometry rather than previously suggested accretion-induced decay of the neutron stars magnetic field. At lower luminosities, we find for the first time a hint of departure from the anticorrelation of line energy with flux, which we interpret as a transition from super- to sub-critical accretion associated with the disappearance of the accretion column. Finally, we confirm and briefly discuss the orbital modulation observed in the outburst light curve of the source