X-Ray Bursts of Nuclear Origin?

The fate of nuclear energy carried by matter accreted onto a neutron star was considered e.g. by Rosenbluth et al. (1973). They examined pycnonuclear reactions on an originally cold star, and found that the whole star is thereby heated up to 106−107 °K. The thermonuclear reactions that can be ignited then, have been studied by Hansen and Van Horn (1975), who computed stationary burning shells, finding, however, that in most cases the shells are thermally unstable.We consider here the possibility that X-ray bursts are due to instabilities of this type. The observational constraints fix the parameters uniquely.

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An approach to constrain models of accreting neutron stars with the use of an equation of state

Progress of Theoretical and Experimental Physics ◽

10.1093/ptep/ptaa010 ◽

2020 ◽

Vol 2020 (3) ◽

Author(s):

Akira Dohi ◽

Masa-aki Hashimoto ◽

Rio Yamada ◽

Yasuhide Matsuo ◽

Masayuki Y Fujimoto

Keyword(s):

Neutron Star ◽

Equation Of State ◽

Light Curve ◽

Nuclear Energy ◽

Evolution Equations ◽

Energy Generation ◽

Reaction Rates ◽

Computational Time ◽

Recurrence Time ◽

X Ray

Abstract We investigate X-ray bursts during the thermal evolution of an accreting neutron star that corresponds to the X-ray burster GS 1826$-$24. Physical quantities of the neutron star are included using an equation of state below and above the nuclear matter density. We adopt an equation of state and construct an approximate network that saves computational time and calculates nuclear energy generation rates accompanying the abundance evolutions. The mass and radius of the neutron star are found by solving the stellar evolution equations from the center to the surface; this involves necessary information such as the nuclear energy generation in accreting layers, heating from the crust, and neutrino emissions inside the stellar core. We reproduce the light curve and recurrence time of the X-ray burst from GS 1826$-$24 within the standard deviation of 1$\sigma$ for the assumed accretion rate, metallicity, and equation of state. It is concluded that the observed recurrence time is consistent with the theoretical model with metallicity of the initial CNO elements $Z_{\rm CNO} = 0.01$. We suggest that the nuclear reaction rates responsible for the $rp$-process should be examined in detail, because the rates may change the shape of the light curve and our conclusion.

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Aperiodic Flux Variability in A 0535+262

Symposium - International Astronomical Union ◽

10.1017/s0074180900055777 ◽

1996 ◽

Vol 165 ◽

pp. 313-319

Author(s):

Mark H. Finger ◽

Robert B. Wilson ◽

B. Alan Harmon ◽

William S. Paciesas

Keyword(s):

Neutron Star ◽

Gamma Ray ◽

Beat Frequency ◽

Power Spectra ◽

Center Frequency ◽

X Ray ◽

Binary Pulsar ◽

Transient Source ◽

Flux Variability ◽

Burst And Transient Source

A “giant” outburst of A 0535+262, a transient X-ray binary pulsar, was observed in 1994 February and March with the Burst and Transient Source Experiment (BATSE) onboard the Compton Gamma-Ray Observatory. During the outburst power spectra of the hard X-ray flux contained a QPO-like component with a FWHM of approximately 50% of its center frequency. Over the course of the outburst the center frequency rose smoothly from 35 mHz to 70 mHz and then fell to below 40 mHz. We compare this QPO frequency with the neutron star spin-up rate, and discuss the observed correlation in terms of the beat frequency and Keplerian frequency QPO models in conjunction with the Ghosh-Lamb accretion torque model.

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Quasi-periodic oscillations and noise in neutron star and black-hole X-ray binaries

Advances in Space Research ◽

10.1016/s0273-1177(01)00417-3 ◽

2001 ◽

Vol 28 (2-3) ◽

pp. 469-479 ◽

Cited By ~ 17

Author(s):

Rudy Wijnands

Keyword(s):

Black Hole ◽

Neutron Star ◽

Periodic Oscillations ◽

X Ray ◽

X Ray Binaries

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A minimal timescale for the continuum in 4U 1608-52 and Aql X-1

Monthly Notices of the Royal Astronomical Society Letters ◽

10.1093/mnrasl/slab004 ◽

2021 ◽

Vol 502 (1) ◽

pp. L72-L78

Author(s):

K Mohamed ◽

E Sonbas ◽

K S Dhuga ◽

E Göğüş ◽

A Tuncer ◽

...

Keyword(s):

Black Hole ◽

Neutron Star ◽

Power Spectra ◽

Light Curves ◽

State Transitions ◽

Strong Positive Correlation ◽

Present Evidence ◽

X Ray ◽

X Ray Binaries ◽

The Continuum

ABSTRACT Similar to black hole X-ray binary transients, hysteresis-like state transitions are also seen in some neutron-star X-ray binaries. Using a method based on wavelets and light curves constructed from archival Rossi X-ray Timing Explorer observations, we extract a minimal timescale over the complete range of transitions for 4U 1608-52 during the 2002 and 2007 outbursts and the 1999 and 2000 outbursts for Aql X-1. We present evidence for a strong positive correlation between this minimal timescale and a similar timescale extracted from the corresponding power spectra of these sources.

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The study of multipeaked type-I X-ray bursts in the neutron star low-mass X-ray binary 4U 1636 − 536 with RXTE

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3539 ◽

2020 ◽

Vol 501 (1) ◽

pp. 168-178

Author(s):

Chen Li ◽

Guobao Zhang ◽

Mariano Méndez ◽

Jiancheng Wang ◽

Ming Lyu

Keyword(s):

Neutron Star ◽

Flux Ratio ◽

Light Curves ◽

Type I ◽

X Ray ◽

Soft State ◽

Peak Flux ◽

Low Mass ◽

Two Peaks ◽

Second Peak

ABSTRACT We have found and analysed 16 multipeaked type-I bursts from the neutron-star low-mass X-ray binary 4U 1636 − 53 with the Rossi X-ray Timing Explorer (RXTE). One of the bursts is a rare quadruple-peaked burst that was not previously reported. All 16 bursts show a multipeaked structure not only in the X-ray light curves but also in the bolometric light curves. Most of the multipeaked bursts appear in observations during the transition from the hard to the soft state in the colour–colour diagram. We find an anticorrelation between the second peak flux and the separation time between two peaks. We also find that in the double-peaked bursts the peak-flux ratio and the temperature of the thermal component in the pre-burst spectra are correlated. This indicates that the double-peaked structure in the light curve of the bursts may be affected by enhanced accretion rate in the disc, or increased temperature of the neutron star.

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A Machine Learning Approach For Classifying Low-mass X-ray Binaries Based On Their Compact Object Nature

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3899 ◽

2020 ◽

Author(s):

R Pattnaik ◽

K Sharma ◽

K Alabarta ◽

D Altamirano ◽

M Chakraborty ◽

...

Keyword(s):

Machine Learning ◽

Black Hole ◽

Neutron Star ◽

Binary Systems ◽

Compact Object ◽

X Ray ◽

Average Accuracy ◽

Machine Learning Approach ◽

Low Mass ◽

X Ray Binaries

Abstract Low Mass X-ray binaries (LMXBs) are binary systems where one of the components is either a black hole or a neutron star and the other is a less massive star. It is challenging to unambiguously determine whether a LMXB hosts a black hole or a neutron star. In the last few decades, multiple observational works have tried, with different levels of success, to address this problem. In this paper, we explore the use of machine learning to tackle this observational challenge. We train a random forest classifier to identify the type of compact object using the energy spectrum in the energy range 5-25 keV obtained from the Rossi X-ray Timing Explorer archive. We report an average accuracy of 87±13% in classifying the spectra of LMXB sources. We further use the trained model for predicting the classes for LMXB systems with unknown or ambiguous classification. With the ever-increasing volume of astronomical data in the X-ray domain from present and upcoming missions (e.g., SWIFT, XMM-Newton, XARM, ATHENA, NICER), such methods can be extremely useful for faster and robust classification of X-ray sources and can also be deployed as part of the data reduction pipeline.

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