scholarly journals A Significant Detection of X-ray Polarization in Sco X-1 with PolarLight and Constraints on the Corona Geometry

2022 ◽  
Vol 924 (1) ◽  
pp. L13
Author(s):  
Xiangyun Long ◽  
Hua Feng ◽  
Hong Li ◽  
Jiahuan Zhu ◽  
Qiong Wu ◽  
...  
Keyword(s):  
Polarization Measurement ◽  
Polarization Angle ◽  
X Ray ◽  
Astrophysical Source ◽  
Accretion Rates ◽  
Measured Polarization ◽  
Low Mass ◽  
Marginal Detection ◽  
Energy Dependent ◽  
Polarization Fraction

Abstract We report the detection of X-ray polarization in the neutron-star low-mass X-ray binary Scorpius (Sco) X-1 with PolarLight. The result is energy-dependent, with a nondetection in 3–4 keV but a 4σ detection in 4–8 keV; it is also flux-dependent in the 4–8 keV band, with a nondetection when the source displays low fluxes but a 5σ detection during high fluxes, in which case we obtain a polarization fraction of 0.043 ± 0.008 and a polarization angle of 52.°6 ± 5.°4. This confirms a previous marginal detection with OSO-8 in the 1970s and marks Sco X-1 as the second astrophysical source with a significant polarization measurement in the keV band. The measured polarization angle is in line with the jet orientation of the source on the sky plane (54°), which is supposedly the symmetry axis of the system. Combining previous spectral analysis, our measurements suggest that an optically thin corona is located in the transition layer under the highest accretion rates, and disfavor the extended accretion disk corona model.

scholarly journals Polarization of accreting X-ray pulsars – II. Hercules X-1

2020 ◽  
Vol 501 (1) ◽  
pp. 129-136
Author(s):  
Ilaria Caiazzo ◽  
Jeremy Heyl
Keyword(s):  
Quantum Electrodynamics ◽  
Pulse Shape ◽  
Main Peak ◽  
Polarization Angle ◽  
X Ray ◽  
Structure And Dynamics ◽  
Cyclotron Line ◽  
Magnetic Poles ◽  
Energy Dependent ◽  
Polarization Fraction

ABSTRACT We employ our new model for the polarized emission of accreting X-ray pulsars to describe the emission from the luminous X-ray pulsar Hercules X-1. In contrast with previous works, our model predicts the polarization parameters independently of spectral formation, and considers the structure and dynamics of the accretion column, as well as the additional effects on propagation due to general relativity and quantum electrodynamics. We find that our model can describe the observed pulse fraction and the pulse shape of the main peak, as well as the modulation of the cyclotron line with phase. We pick two geometries, assuming a single accretion column or two columns at the magnetic poles, that can describe current observations of pulse shape and cyclotron modulation with phase. Both models predict a high polarization fraction, between 60 and 80 per cent in the 1–10 keV range, that is phase and energy dependent, and that peaks at the same phase as the intensity. The phase and energy dependence of the polarization fraction and of the polarization angle can help discern between the different geometries.

scholarly journals Hubble Space Telescope Observations of Millisecond Pulsar Companions: Constraints on Evolution

1996 ◽  
Vol 160 ◽  
pp. 497-500 ◽  
Author(s):  
S. C. Lundgren ◽  
R. S. Foster ◽  
F. Camilo
Keyword(s):  
White Dwarfs ◽  
Hubble Space Telescope ◽  
Core Mass ◽  
Space Telescope ◽  
X Ray ◽  
Current Period ◽  
Accretion Rates ◽  
Order Of Magnitude ◽  
Low Mass ◽  
The Masses

AbstractIn observations of six binary millisecond pulsars with the Hubble Space Telescope, we have discovered white dwarf companions to PSRs J0034-0534, J1022+1001, J1713+0747, and J2019+2425 and improved photometry on PSRs J1640+2224 and J2145-0750. Three of the white dwarfs are among the coolest and oldest known. We have determined that the masses for the helium companions are consistent with the expectation based on the core mass of a progenitor that filled its Roche lobe. The cooling times for many of the white dwarfs are much less than the characteristic spin-down times, implying that the spin period at the end of the accretion stage was close to the current period. The initial spin periods calculated are used to place limits on the accretion rate at the end of the low-mass X-ray binary phase. The accretion rates are found to be over an order of magnitude less than the Eddington rate.

scholarly journals A strongly changing accretion morphology during the outburst decay of the neutron star X-ray binary 4U 1608−52

2020 ◽  
Vol 493 (1) ◽  
pp. 1318-1327 ◽  
Author(s):  
J van den Eijnden ◽  
N Degenaar ◽  
R M Ludlam ◽  
A S Parikh ◽  
J M Miller ◽  
...  
Keyword(s):  
Neutron Star ◽  
Dynamic Range ◽  
Signal To Noise Ratio ◽  
X Ray ◽  
Accretion Flow ◽  
Accretion Rates ◽  
Low Mass ◽  
Physical Changes ◽  
X Ray Binaries ◽  
Eddington Limit

ABSTRACT It is commonly assumed that the properties and geometry of the accretion flow in transient low-mass X-ray binaries (LMXBs) significantly change when the X-ray luminosity decays below ∼10−2 of the Eddington limit (LEdd). However, there are few observational cases where the evolution of the accretion flow is tracked in a single X-ray binary over a wide dynamic range. In this work, we use NuSTAR and NICER observations obtained during the 2018 accretion outburst of the neutron star LMXB 4U 1608−52, to study changes in the reflection spectrum. We find that the broad Fe–Kα line and Compton hump, clearly seen during the peak of the outburst when the X-ray luminosity is ∼1037 erg s−1 (∼0.05 LEdd), disappear during the decay of the outburst when the source luminosity drops to ∼4.5 × 1035 erg s−1 (∼0.002 LEdd). We show that this non-detection of the reflection features cannot be explained by the lower signal-to-noise ratio at lower flux, but is instead caused by physical changes in the accretion flow. Simulating synthetic NuSTAR observations on a grid of inner disc radius, disc ionization, and reflection fraction, we find that the disappearance of the reflection features can be explained by either increased disc ionization (log ξ ≳ 4.1) or a much decreased reflection fraction. A changing disc truncation alone, however, cannot account for the lack of reprocessed Fe–Kα emission. The required increase in ionization parameter could occur if the inner accretion flow evaporates from a thin disc into a geometrically thicker flow, such as the commonly assumed formation of a radiatively inefficient accretion flow at lower mass accretion rates.

Suzaku Observations of Low-Mass X-ray Binaries at High Mass-Accretion Rates

2008 ◽  
Author(s):  
Hiromitsu Takahashi ◽  
Ayumi Hirasawa ◽  
Yasushi Fukazawa ◽  
Kazuo Makishima ◽  
Ye-Fei Yuan ◽  
...  
Keyword(s):  
High Mass ◽  
X Ray ◽  
Accretion Rates ◽  
Low Mass ◽  
X Ray Binaries

scholarly journals Asymmetric accretion and thermal ‘mountains’ in magnetized neutron star crusts

2020 ◽  
Vol 493 (3) ◽  
pp. 3866-3878 ◽  
Author(s):  
N Singh ◽  
B Haskell ◽  
D Mukherjee ◽  
T Bulik
Keyword(s):  
Gravitational Wave ◽  
Rotation Frequency ◽  
X Ray ◽  
Accretion Rates ◽  
Low Mass ◽  
Compositional Gradients ◽  
Mass Quadrupole ◽  
Pressure Perturbations ◽  
X Ray Binaries ◽  
The Magnetic Field

ABSTRACT Accreting neutron stars (NSs) are one of the main targets for continuous gravitational wave searches, as asymmetric accretion may lead to quadrupolar deformations, or ‘mountains’, on the crust of the star, which source gravitational wave (GW) emission at twice the rotation frequency. The GW torque may also impact on the spin evolution of the star, possibly dictating the currently observed spin periods of NSs in low-mass X-ray binaries and leading to the increased spin-down rate observed during accretion in PSR J1023+0038. Previous studies have shown that deformed reaction layers in the crust of the NS lead to thermal and compositional gradients that can lead to GW emission. However, there are no realistic constraints on the level of asymmetry that is expected. In this paper, we consider a natural source of asymmetry, namely the magnetic field, and calculate the density and pressure perturbations that are expected in the crust of accreting NSs. In general, we find that only the outermost reaction layers of the NS are strongly perturbed. The mass quadrupole that we estimate is generally small and cannot explain the increase of spin-down rate of PSR J1023+0038. However, if strong shallow heating sources are present at low densities in the crust, as cooling observations suggest, these layers will be strongly perturbed and the resulting quadrupole could explain the observed spin-down of PSR J1023+0038, and lead to observable GW signals from systems with higher accretion rates.

scholarly journals X-ray emission from magnetized neutron star atmospheres at low mass-accretion rates. I. Phase-averaged spectrum

2021 ◽  
Author(s):  
E. Sokolova-Lapa ◽  
M. Gornostaev ◽  
J. Wilms ◽  
R. Ballhausen ◽  
S. Falkner ◽  
...  
Keyword(s):  
Neutron Star ◽  
X Ray ◽  
Accretion Rates ◽  
Low Mass

Iron K-Line Emission from X-Ray Binaries

1988 ◽  
Vol 102 ◽  
pp. 47-50
Author(s):  
K. Masai ◽  
S. Hayakawa ◽  
F. Nagase
Keyword(s):  
Accretion Disk ◽  
Radiative Recombination ◽  
Characteristic Temperature ◽  
Line Emission ◽  
Ionization Front ◽  
Continuum Radiation ◽  
X Ray ◽  
Low Mass ◽  
X Ray Binaries

AbstractEmission mechanisms of the iron Kα-lines in X-ray binaries are discussed in relation with the characteristic temperature Txof continuum radiation thereof. The 6.7 keV line is ascribed to radiative recombination followed by cascades in a corona of ∼ 100 eV formed above the accretion disk. This mechanism is attained for Tx≲ 10 keV as observed for low mass X-ray binaries. The 6.4 keV line observed for binary X-ray pulsars with Tx> 10 keV is likely due to fluorescence outside the He II ionization front.

SIGMAL: A Program for Calculating L-Shell lonization Cross-Sections

1981 ◽  
Vol 39 ◽  
pp. 198-199 ◽  
Author(s):  
R.F. Egerton
Keyword(s):  
Cross Sections ◽  
Fortran Program ◽  
Absorption Data ◽  
X Ray ◽  
Atomic Electrons ◽  
Energy Dependent ◽  
Hydrogenic Model ◽  
Electron Energy Loss ◽  
X Ray Absorption ◽  
Shell Ionization

SIGMAL is a short (∼ 100-line) Fortran program designed to rapidly compute cross-sections for L-shell ionization, particularly the partial crosssections required in quantitative electron energy-loss microanalysis. The program is based on a hydrogenic model, the L1 and L23 subshells being represented by scaled Coulombic wave functions, which allows the generalized oscillator strength (GOS) to be expressed analytically. In this basic form, the model predicts too large a cross-section at energies near to the ionization edge (see Fig. 1), due mainly to the fact that the screening effect of the atomic electrons is assumed constant over the L-shell region. This can be remedied by applying an energy-dependent correction to the GOS or to the effective nuclear charge, resulting in much closer agreement with experimental X-ray absorption data and with more sophisticated calculations (see Fig. 1 ).

scholarly journals Phase lags of quasi-periodic oscillations across source states in the low-mass X-ray binary 4U 1636–53

2016 ◽  
Vol 461 (1) ◽  
pp. 79-92 ◽  
Author(s):  
Marcio G. B. de Avellar ◽  
Mariano Méndez ◽  
Diego Altamirano ◽  
Andrea Sanna ◽  
Guobao Zhang
Keyword(s):  
Periodic Oscillations ◽  
X Ray ◽  
Phase Lags ◽  
Low Mass
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