scholarly journals Pulsed fraction of super-critical column accretion flows on to neutron stars: Modeling of ultraluminous X-ray pulsars

2020 ◽  
Vol 72 (2) ◽  
Author(s):  
Akihiro Inoue ◽  
Ken Ohsuga ◽  
Tomohisa Kawashima
Keyword(s):  
Neutron Stars ◽  
Rotation Axis ◽  
Polar Angle ◽  
Geodesic Equation ◽  
Magnetic Axis ◽  
Viewing Angle ◽  
X Ray ◽  
Accretion Flows ◽  
Bending Effect ◽  
Simulation Results

Abstract We calculate the pulsed fraction (PF) of the super-critical column accretion flows on to magnetized neutron stars (NSs), of which the magnetic axis is misaligned with the rotation axis, based on the simulation results by Kawashima et al. (2016, PASJ, 68, 83). Here, we solve the geodesic equation for light in the Schwarzschild spacetime in order to take into account the light-bending effect. The gravitational redshift and the relativistic Doppler effect from gas motions of the accretion columns are also incorporated. The pulsed emission appears since the observed luminosity, which exceeds the Eddington luminosity for the stellar-mass black holes, periodically changes via precession of the column caused by the rotation of the NS. The PF tends to increase as $\theta _{\rm obs}$ approaches to $\theta _{\rm B}$, where $\theta _{\rm obs}$ and $\theta _{\rm B}$ are the observer’s viewing angle and the polar angle of the magnetic axis measured from the rotation axis, respectively. The maximum PF is around 50%. Also, we find that the PF becomes less than 5% for $\theta _{\rm obs} \lesssim 5^\circ$ or for $\theta _{\rm B} \lesssim 5^\circ$. Our results are consistent with observations of ultraluminous X-ray pulsars (ULXPs) with few exceptions, since the ULXPs mostly exhibit the PF of $\lesssim 50$%. Our present study supports the hypothesis that the ULXPs are powered by the super-critical column accretion on to NSs.

scholarly journals Modeling pulse profiles in X-Ray pulsars with accretion column

2021 ◽  
Author(s):  
I. D. Markozov ◽  
Keyword(s):  
Neutron Star ◽  
Gravitational Lensing ◽  
Rotation Axis ◽  
Magnetic Axis ◽  
Line Of Sight ◽  
Schwarzschild Metric ◽  
X Ray

The pulse profiles of the radiation coming from X-ray pulsars with an accretion column were modeled. Gravitational lensing and redshift in the Schwarzschild metric, as well as the reflection of X-Ray photons from the surface of a neutron star, were taken into account. On the basis of the obtained pulse profiles an analysis of possible errors in the measurements of the luminosities of X-ray pulsars associated with the inability of the observer to correctly take into account the anisotropy in the radiation emerging from the neutron star, as well as the angles between the pulsar’s rotation axis, the magnetic axis and the line of sight, was carried out.

scholarly journals Spin-Down of Neutron Stars and Compositional Transitions in the Cold Crustal Matter

1998 ◽  
Vol 188 ◽  
pp. 345-345 ◽  
Author(s):  
Kei Iida ◽  
Katsuhiko Sato
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Ground State ◽  
Rotation Axis ◽  
Mass Density ◽  
Rotation Period ◽  
Equatorial Region ◽  
Compressible Liquid ◽  
Shell Correction ◽  
X Ray

Transitions of nuclear compositions in the crust of a neutron star induced by stellar spin-down are evaluated at zero temperature. We construct a compressible liquid-drop model for the energy of nuclei immersed in a neutron gas, including pairing and shell correction terms, in reference to the known properties of the ground state of matter above neutron drip density, 4.3 × 1011 g cm−3. Recent experimental values and extrapolations of nuclear masses are used for a description of matter at densities below neutron drip. Changes in the pressure of matter in the crust due to the stellar spin-down are calculated by taking into account the structure of the crust of a slowly and uniformly rotating relativistic neutron star. If the initial rotation period is of the order of milliseconds, these changes cause nuclei, initially being in the ground-state matter above a mass density of about 3 × 1013 g cm−3, to absorb neutrons in the equatorial region where the matter undergoes compression, and to emit them in the vicinity of the rotation axis where the matter undergoes decompression. Heat generation by these processes is found to have significant effects on the thermal evolution of old neutron stars with low magnetic fields; the surface emission predicted from this heating is compared with the ROSAT observations of X-ray emission from millisecond pulsars and is shown to be insufficient to explain the observed X-ray luminosities (Iida and Sato, 1997).

BIRTH RATES OF DIFFERENT TYPES OF NEUTRON STARS AND POSSIBLE EVOLUTIONS OF THESE OBJECTS

2005 ◽  
Vol 14 (03n04) ◽  
pp. 643-656 ◽  
Author(s):  
OKTAY H. GUSEINOV ◽  
AŞKIN ANKAY ◽  
SEVINÇ O. TAGIEVA
Keyword(s):  
Magnetic Field ◽  
Neutron Star ◽  
Neutron Stars ◽  
Rotation Axis ◽  
Solar Mass ◽  
Birth Rates ◽  
X Ray ◽  
Soft Gamma Repeaters ◽  
Different Types ◽  
The Magnetic Field

It is shown that anomalous X-ray pulsars and soft gamma repeaters are neutron stars with mass less than 1 solar mass and with magnetic field about 3×1013–1014 G . Their ages (t≤105 yr ) are considerably larger than their characteristic times. The angle between the rotation axis and the axis of the magnetic field must be large for these objects. From time to time as a result of activities their value of Ṗ considerably increases because of the propeller mechanism. Using such an approach Guseinov et al.1 have predicted the transient characteristic of these sources which has been confirmed recently.2 We estimate the spatial densities and lifetimes of different types of isolated neutron star. Some of these sources must have relations with anomalous X-ray pulsars and soft gamma repeaters. In order to understand the locations of different types of isolated neutron star on the P–Ṗ diagram it is also necessary to take into account the differences in the mass and the magnetic field of neutron stars. We have also estimated the birth rates of different types of isolated neutron stars.

scholarly journals Search for intermittent X-ray pulsations from neutron stars in low-mass X-ray binaries

2021 ◽  
Vol 38 ◽  
Author(s):  
Yunus Emre Bahar ◽  
Manoneeta Chakraborty ◽  
Ersin Göğüş
Keyword(s):  
Neutron Stars ◽  
Orbital Period ◽  
Oscillation Frequency ◽  
Orbital Motion ◽  
X Rays ◽  
X Ray ◽  
Second Stage ◽  
Corrected Data ◽  
Low Mass ◽  
X Ray Binaries

Abstract We present the results of our extensive binary orbital motion corrected pulsation search for 13 low-mass X-ray binaries. These selected sources exhibit burst oscillations in X-rays with frequencies ranging from 45 to 1 122 Hz and have a binary orbital period varying from 2.1 to 18.9 h. We first determined episodes that contain weak pulsations around the burst oscillation frequency by searching all archival Rossi X-ray Timing Explorer data of these sources. Then, we applied Doppler corrections to these pulsation episodes to discard the smearing effect of the binary orbital motion and searched for recovered pulsations at the second stage. Here we report 75 pulsation episodes that contain weak but coherent pulsations around the burst oscillation frequency. Furthermore, we report eight new episodes that show relatively strong pulsations in the binary orbital motion corrected data.

scholarly journals A New View on Young Pulsars in Supernova Remnants: Slow, Radio-quiet & X-ray Bright

2000 ◽  
Vol 177 ◽  
pp. 699-702 ◽  
Author(s):  
E. V. Gotthelf ◽  
G. Vasisht
Keyword(s):  
Magnetic Field ◽  
Neutron Stars ◽  
Supernova Remnants ◽  
Simple Explanation ◽  
Crab Pulsar ◽  
Radio Pulsars ◽  
Substantial Fraction ◽  
Subsequent Evolution ◽  
X Ray ◽  
Field Decay

AbstractWe propose a simple explanation for the apparent dearth of radio pulsars associated with young supernova remnants (SNRs). Recent X-ray observations of young remnants have revealed slowly rotating (P∼ 10s) central pulsars with pulsed emission above 2 keV, lacking in detectable radio emission. Some of these objects apparently have enormous magnetic fields, evolving in a manner distinct from the Crab pulsar. We argue that these X-ray pulsars can account for a substantial fraction of the long sought after neutron stars in SNRs and that Crab-like pulsars are perhaps the rarer, but more highly visible example of these stellar embers. Magnetic field decay likely accounts for their high X-ray luminosity, which cannot be explained as rotational energy loss, as for the Crab-like pulsars. We suggest that the natal magnetic field strength of these objects control their subsequent evolution. There are currently almost a dozen slow X-ray pulsars associated with young SNRs. Remarkably, these objects, taken together, represent at least half of the confirmed pulsars in supernova remnants. This being the case, these pulsars must be the progenitors of a vast population of previously unrecognized neutron stars.

scholarly journals X-ray variability of the HMXB Cen X-3: evidence for inhomogeneous accretion flows.

2020 ◽  
Author(s):  
G Sanjurjo-Ferrín ◽  
J M Torrejón ◽  
K Postnov ◽  
L Oskinova ◽  
J J Rodes-Roca ◽  
...  
Keyword(s):  
Equivalent Width ◽  
Compact Star ◽  
Timing Analysis ◽  
Roche Lobe ◽  
The Other ◽  
Emission Lines ◽  
High Mass ◽  
X Ray ◽  
Accretion Flows ◽  
Inner Radius

Abstract Cen X-3 is a compact high mass X-ray binary likely powered by Roche lobe overflow. We present a phase-resolved X-ray spectral and timing analysis of two pointed XMM-Newton observations. The first one took place during a normal state of the source, when it has a luminosity LX ∼ 1036 erg s−1. This observation covered orbital phases φ = 0.00 − 0.37, i.e. the egress from the eclipse. The egress lightcurve is highly structured, showing distinctive intervals. We argue that different intervals correspond to the emergence of different emitting structures. The lightcurve analysis enables us to estimate the size of such structures around the compact star, the most conspicuous of which has a size ∼0.3R*, of the order of the Roche lobe radius. During the egress, the equivalent width of Fe emission lines, from highly ionized species, decreases as the X-ray continuum grows. On the other hand, the equivalent width of the Fe Kα line, from near neutral Fe, strengthens. This line is likely formed due to the X-ray illumination of the accretion stream. The second observation was taken when the source was 10 times X-ray brighter and covered the orbital phases φ = 0.36 − 0.80. The X-ray lightcurve in the high state shows dips. These dips are not caused by absorption but can be due to instabilities in the accretion stream. The typical dip duration, of about 1000 s, is much longer than the timescale attributed to the accretion of the clumpy stellar wind of the massive donor star, but is similar to the viscous timescale at the inner radius of the accretion disk.

scholarly journals Monte Carlo Modeling and Design of Photon Energy Attenuation Layers for >10× Quantum Yield Enhancement in Si-Based Hard X-ray Detectors

Instruments ◽  
2021 ◽  
Vol 5 (2) ◽  
pp. 17
Author(s):  
Eldred Lee ◽  
Kaitlin M. Anagnost ◽  
Zhehui Wang ◽  
Michael R. James ◽  
Eric R. Fossum ◽  
...  
Keyword(s):  
Monte Carlo Simulation ◽  
Monte Carlo ◽  
Quantum Yield ◽  
Photon Energy ◽  
High Efficiency ◽  
High Energy ◽  
Yield Enhancement ◽  
X Ray ◽  
Simulation Results ◽  
Conversion Efficiencies

High-energy (>20 keV) X-ray photon detection at high quantum yield, high spatial resolution, and short response time has long been an important area of study in physics. Scintillation is a prevalent method but limited in various ways. Directly detecting high-energy X-ray photons has been a challenge to this day, mainly due to low photon-to-photoelectron conversion efficiencies. Commercially available state-of-the-art Si direct detection products such as the Si charge-coupled device (CCD) are inefficient for >10 keV photons. Here, we present Monte Carlo simulation results and analyses to introduce a highly effective yet simple high-energy X-ray detection concept with significantly enhanced photon-to-electron conversion efficiencies composed of two layers: a top high-Z photon energy attenuation layer (PAL) and a bottom Si detector. We use the principle of photon energy down conversion, where high-energy X-ray photon energies are attenuated down to ≤10 keV via inelastic scattering suitable for efficient photoelectric absorption by Si. Our Monte Carlo simulation results demonstrate that a 10–30× increase in quantum yield can be achieved using PbTe PAL on Si, potentially advancing high-resolution, high-efficiency X-ray detection using PAL-enhanced Si CMOS image sensors.

DO YOUNG NEUTRON STARS WHICH SHOW THEMSELVES AS AXPs AND SGRs ACCRETE?

2003 ◽  
Vol 12 (05) ◽  
pp. 825-831 ◽  
Author(s):  
S. O. TAGIEVA ◽  
E. YAZGAN ◽  
A. ANKAY
Keyword(s):  
Neutron Star ◽  
Neutron Stars ◽  
Supernova Explosion ◽  
X Ray ◽  
X Ray Binaries

We examined the fall-back disk models, and in general accretion, proposed to explain the properties of AXPs and SGRs. We checked the possibility of some gas remaining around the neutron star after a supernova explosion. We also compared AXPs and SGRs with the X-ray pulsars in X-ray binaries. We conclude that the existing models of accretion from a fall-back disk are insufficient to explain the nature of AXPs and SGRs.

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