scholarly journals X-Ray Bursts

1977 ◽  
Vol 4 (1) ◽  
pp. 101-110 ◽  
Author(s):  
George W. Clark
Keyword(s):  
Neutron Star ◽  
Compact Star ◽  
Compact Object ◽  
Gravitational Potential Energy ◽  
X Rays ◽  
High Luminosity ◽  
Emission Pattern ◽  
X Ray ◽  
Accretion Rates ◽  
Nuclear Burning

Most of the variable phenomena of high-luminosity (≳1036erg s−1) stellar X-ray sources can be explained, at least qualitatively, within the general framework of binary accretion models in which thermal X-rays are emitted in the vicinity of a neutron star or blackhole by plasma that has flowed downhill from the surface of a nuclear burning companion and been heated by conversion of its gravitational potential energy. The yield of X-ray energy in this process is so high, exceeding in some cases 0.1c2per unit mass, that X-ray luminosities in excess of 104L⊙can be generated with accretion rates of only ˜10−BM⊙per year. Since the transfer process depends strongly on many parameters that specify the relevant properties of two stars and their interaction, one finds a remarkable variety and range of X-ray phenomena. If the compact object is a magnetized neutron star, rotation will cause its X-ray emission pattern to sweep over a distant observer and thereby produce regular pulsations like those observed with periods in the range from 1 to 103seconds. Orbital motions can cause regular eclipses and absorption dips like those observed with periods in the range from hours to days. Changes in the rate of mass loss by the nuclear burning star or in the transfer efficiency can account for the variations in intrinsic X-ray luminosities that appear as flares, novae and on-off transitions. Irregularities in the flow of plasma near the compact star can also affect the intrinsic luminosity and appear as erratic fluctuations, spikes and shot-noise in the observed intensity.

scholarly journals Effect of Compact Objects Near Be Stars

1987 ◽  
Vol 92 ◽  
pp. 516-518
Author(s):  
Krishna M.V. Apparao ◽  
S.P. Tarafdar
Keyword(s):  
Black Holes ◽  
Neutron Star ◽  
Rotation Period ◽  
Compact Object ◽  
Compact Objects ◽  
X Rays ◽  
Be Stars ◽  
Eccentric Orbit ◽  
X Ray ◽  
Be Star

Several Be stars are identified with bright X-ray sources. (Rappaport and Van den Heuvel, 1982). The bright X-ray emission and observed periodicities indicate the existence of compact objects (white dwarfs, neutron stars or black holes) near the Be stars. A prime example is the brightest X-ray source A0538-66 in LMC, which contains a neutron star with a rotation period of 59 ms. Apparao (1985) explained the X-ray emission, which occurs in periodic flares, by considering an inclined eccentric orbit for the neutron star around the assumed Be-star. The neutron star when it enters a gas ring (around the Be-star) accreting matter giving out X-rays.The X-ray emission from the compact objects, when the gas ring from the Be-star envelopes the objects, has interesting consequences. The X-ray emission produces an ionized region (compact object Stromgren sphere or COSS) in the gas surrounding the compact object (CO).

scholarly journals The Lense–Thirring timing-accretion plane for ULXs

2019 ◽  
Vol 489 (1) ◽  
pp. 282-296 ◽  
Author(s):  
M J Middleton ◽  
P C Fragile ◽  
A Ingram ◽  
T P Roberts
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Effective Means ◽  
Compact Object ◽  
Resonance Scattering ◽  
Phase Lag ◽  
Black Hole Mass ◽  
X Ray ◽  
Surface Magnetic Field ◽  
Accretion Rates

ABSTRACT Identifying the compact object in ultraluminous X-ray sources (ULXs) has to date required detection of pulsations or a cyclotron resonance scattering feature (CRSF), indicating a magnetized neutron star. However, pulsations are observed to be transient and it is plausible that accretion on to the neutron star may have suppressed the surface magnetic field such that pulsations and CRSFs will be entirely absent. We may therefore lack direct means to identify neutron star systems whilst we presently lack an effective means by which to identify black hole ULXs. Here we present a possible method for separating the ULX population by assuming the X-ray, mHz quasi-periodic oscillations (QPOs), and day time-scale periods/QPOs are associated with Lense–Thirring precession of the inflow and outflowing wind, respectively. The precession time-scales combined with the temperature of the soft X-ray component produce planes where the accretor mass enters as a free parameter. Depending on the properties of the wind, use of these planes may be robust to a range in the angular momentum (spin) and, for high accretion rates, essentially independent of the neutron star’s surface dipole field strength. Our model also predicts the mHz QPO frequency and magnitude of the phase lag imprinted due to propagation through the optically thick wind; in the case of NGC 5408 X-1 we subsequently infer a black hole mass and moderate-to-high spin. Finally, we note that observing secular QPO evolution over sufficient baselines may indicate a neutron star, as the precession responds to spin-up which is not readily observable for black hole primaries.

scholarly journals Black hole magnetosphere with small-scale flux tubes – II. Stability and dynamics

2019 ◽  
Vol 487 (3) ◽  
pp. 4114-4127 ◽  
Author(s):  
Yajie Yuan ◽  
Anatoly Spitkovsky ◽  
Roger D Blandford ◽  
Dan R Wilkins
Keyword(s):  
Black Hole ◽  
Compact Star ◽  
Dynamical Evolution ◽  
Compact Object ◽  
Accretion Disc ◽  
Small Scale ◽  
X Rays ◽  
Flux Tubes ◽  
X Ray ◽  
Central Object

ABSTRACT In some Seyfert galaxies, the hard X-rays that produce fluorescent emission lines are thought to be generated in a hot corona that is compact and located at only a few gravitational radii above the supermassive black hole. We consider the possibility that this X-ray source may be powered by small-scale magnetic flux tubes attached to the accretion disc near the black hole. We use three-dimensional, time-dependent, special relativistic, force-free simulations in a simplified setting to study the dynamics of such flux tubes as they get continuously twisted by the central compact star/black hole. We find that the dynamical evolution of the flux tubes connecting the central compact object and the accretion disc is strongly influenced by the confinement of the surrounding field. Although differential rotation between the central object and the disc tends to inflate the flux tubes, strong confinement from surrounding field quenches the formation of a jet-like outflow, as the inflated flux tube becomes kink unstable and dissipates most of the extracted rotational energy relatively close to the central object. Such a process may be able to heat up the plasma and produce strong X-ray emission. We estimate the energy dissipation rate and discuss its astrophysical implications.

Galactic X- ray observations - Observations of compact X-ray sources

1979 ◽  
Vol 366 (1726) ◽  
pp. 281-293 ◽  
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
White Dwarf ◽  
Compact Object ◽  
Bright Star ◽  
High Luminosity ◽  
Multiple Star ◽  
X Ray ◽  
Normal Star ◽  
Radio Outburst

The high luminosity galactic X-ray sources, apart from the supernovae remnants, probably all exist in multiple star systems in which matter from a normal star is being transferred to a compact object such as a white dwarf, neutron star or black hole. Recent results, obtained with the Ariel 5 and Copernicus satellites, are presented. A number of sources have been studied over extended periods in order to measure the regular periodicities in their X-ray emission. Observations also included are of the Cygnus X-1 source, which is probably the first black hole discovered in our galaxy. X-ray emission, coincident with a radio outburst, from a nearby bright star HR1099 is also reported.

scholarly journals The Origin of Flaring Activity in AE Aquarii

1995 ◽  
Vol 151 ◽  
pp. 272-275
Author(s):  
Nazar Ikhsanov
Keyword(s):  
Main Sequence ◽  
Compact Star ◽  
Compact Object ◽  
Electromagnetic Spectrum ◽  
Thermal Source ◽  
X Rays ◽  
Mass Ratio ◽  
X Ray ◽  
Γ Rays ◽  
Gas Accretion

AE Aqr is a close non-eclipsing binary system with an orbital period Porb ≈ 9.88 hr, eccentricity of the orbit e = 0.02 (Chincarini & Walker 1981) and a mass ratio q = 1.14 (Reinsch & Beuermann 1994), situated at the distance of ∼ 84 pc (Van Paradijs et al. 1989). The secondary is K3 red dwarf on or close to the main sequence (Bruch 1991). The primary cannot be observed directly. However, the stable photometric oscillations at a period of 33 s (and at half this period) in the optical (Patterson 1979), UV (Eracleous et al. 1994), X-rays (Patterson et al. 1980) and, probably, VHE γ-rays (Meintjes et al. 1992, Bowden et al. 1992) leave no doubt that the primary is a rapidly rotating magnetized compact object. The observed rate of deceleration of the primary rotation is Ṗ = 5.64 × 10−14 ss−1 (De Jager et al. 1994), and its mass is m1sin3i (0.56 ± 0.03) M⊙ (Reinsch & Beuermann 1994). The lack of eclipses allows to put a lower limit to the mass of the primary m1 ≥ 0.62M⊙.AE Aqr emits detectable radiation in all parts of the electromagnetic spectrum. In radio and γ-rays it is a powerful non-thermal source. However, in the optical, UV and X-rays the radiation is likely to be thermal and can be well explained by gas accretion onto a compact star (Patterson 1979, Patterson et al. 1980). The observed impulse profile of the pulsating component (Eracleous et al. 1994) looks similar to that of the accreting X-ray pulsars.

scholarly journals GRB 130603B: No Compelling Evidence for Neutron Star Merger

2015 ◽  
Vol 2015 ◽  
pp. 1-5
Author(s):  
Shlomo Dado ◽  
Arnon Dar
Keyword(s):  
Neutron Star ◽  
Near Infrared ◽  
Gamma Ray ◽  
Hubble Space Telescope ◽  
Compact Star ◽  
Compact Object ◽  
Late Time ◽  
Quark Star ◽  
X Ray ◽  
Relativistic Jet

The near infrared (NIR) flare/rebrightening in the afterglow of the short hard gamma ray burst (SHB) 130603B measured with the Hubble Space Telescope (HST) and an alleged late-time X-ray excess were interpreted as possible evidence of a neutron star merger origin of SHBs. However, the X-ray afterglow that was measured with the Swift XRT and Newton XMM has the canonical behaviour of a synchrotron afterglow produced by a highly relativistic jet. The H-band flux observed with HST 9.41 days after burst is that expected from the measured late-time X-ray afterglow. The late-time flare/rebrightening of the NIR-optical afterglow of SHB 130603B could have been produced also by jet collision with an interstellar density bump. Moreover, SHB plus a kilonova can be produced also by the collapse of a compact star (neutron star, strange star, or quark star) to a more compact object due to cooling, loss of angular momentum, or mass accretion.

scholarly journals Evidence for a Compact Object in the Aftermath of the Extra-Galactic Transient AT2018cow

2021 ◽  
Author(s):  
Dheeraj Pasham ◽  
Wynn Ho ◽  
William Alston ◽  
Ronald Remillard ◽  
Mason Ng ◽  
...  
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Compact Object ◽  
Compact Objects ◽  
Power Density Spectrum ◽  
High Time Resolution ◽  
X Rays ◽  
Density Spectrum ◽  
X Ray ◽  
Circumstellar Medium

Abstract Fast Blue Optical Transients (FBOTs) are mysterious extragalactic explosions that may represent a new class of astrophysical phenomena. Their fast time to maximum brightness of less than 10 days and decline over less than 2 months and unusual optical spectra and evolution are difficult to explain within the context of core-collapse of massive stars which are powered by radioactive decay of Nickel-56 and evolve slowly on months timescales. AT2018cow (at a redshift of 0.014) is an extreme FBOT both in terms of rapid evolution and high X-ray and bolometric luminosities. Several alternative hypotheses have been proposed to explain its unusual properties. These include shock interactions with dense circumstellar medium, tidal disruption of a star by a 10,000−million solar mass black hole, failed supernova with fallback accretion onto a newborn black hole, neutron star formed in a supernova or from merging compact objects, etc. Here, we present evidence for a high-amplitude (fractional root-mean-squared amplitude of>30%) quasi-periodic oscillation (QPO) of AT2018cow’s soft X-rays with a centroid frequency of roughly 225 Hz (statistically significant at the 3.7-sigma level, or a false alarm probability of 0.02%). This signal is found in the average power density spectrum of data taken over the entire outburst lasting roughly 60 days and thus suggests that the signal is highly persistent over several hundreds of millions of cycles (60 daysx225 Hz). This high frequency (rapid timescale) of 225 Hz (4.4 ms) argues for the presence of a compact object in AT2018cow which can either be a neutron star or a black hole, and disfavors circumstellar medium interactions for the origin of X-ray emission. Also, the QPO’s timescale sets an upper limit on the compact object's mass to be 850 solar masses, and thus disfavors models with a heavier black hole. If the QPO represents the spin period of a neutron star we can set upper limits on its magnetic field under different scenarios. This work highlights a new way of using high time-resolution X-ray observations to study FBOTs.

scholarly journals The efficiency of nuclear burning during thermonuclear (Type I) bursts as a function of accretion rate

2020 ◽  
Vol 499 (2) ◽  
pp. 2148-2156
Author(s):  
Y Cavecchi ◽  
D K Galloway ◽  
A J Goodwin ◽  
Z Johnston ◽  
A Heger
Keyword(s):  
Neutron Star ◽  
Binary Systems ◽  
Accretion Rate ◽  
Numerical Models ◽  
Type I ◽  
X Ray ◽  
Accretion Rates ◽  
Key Factor ◽  
Nuclear Burning ◽  
Stable Burning

ABSTRACT We measured the thermonuclear burning efficiency as a function of accretion rate for the Type I X-ray bursts of five low-mass X-ray binary systems. We chose sources with measured neutron star spins and a substantial population of bursts from a large observational sample. The general trend for the burst rate is qualitatively the same for all sources; the burst rate first increases with the accretion rate up to a maximum, above which the burst rate declines, despite the increasing accretion rate. At higher accretion rates, when the burst rate decreases, the α-value (the ratio of accretion energy and burst energy) increases by up to a factor of 10 above that in the rising burst rate regime. These observations are contrary to the predictions of 1D numerical models, but can be explained as the consequence of a zone of stable burning on the neutron star surface, which expands with increasing accretion rate. The stable burning also ‘pollutes’ the unstable burning layer with ashes, contributing to the change in burst properties measured in the falling burst rate regime. We find that the mass accretion rate at which the burst rate begins to decrease is anticorrelated with the spin of the neutron star. We conclude that the neutron star spin is a key factor, moderating the nuclear burning stability, via the local accretion rate and fuel composition over the star.

scholarly journals IGR J17329-2731: The birth of a symbiotic X-ray binary

2018 ◽  
Vol 613 ◽  
pp. A22 ◽  
Author(s):  
E. Bozzo ◽  
A. Bahramian ◽  
C. Ferrigno ◽  
A. Sanna ◽  
J. Strader ◽  
...  
Keyword(s):  
Neutron Star ◽  
Compact Object ◽  
Light Curves ◽  
Strong Absorption ◽  
Emission Lines ◽  
Optical Data ◽  
X Rays ◽  
X Ray ◽  
The Past ◽  
X Ray Binaries

We report on the results of the multiwavelength campaign carried out after the discovery of the INTEGRAL transient IGR J17329-2731. The optical data collected with the SOAR telescope allowed us to identify the donor star in this system as a late M giant at a distance of 2.7-1.2+3.4 kpc. The data collected quasi-simultaneously with XMM–Newton and NuSTAR showed the presence of a modulation with a period of 6680 ± 3 s in the X-ray light curves of the source. This unveils that the compact object hosted in this system is a slowly rotating neutron star. The broadband X-ray spectrum showed the presence of a strong absorption (≫1023 cm−2) and prominent emission lines at 6.4 keV, and 7.1 keV. These features are usually found in wind-fed systems, in which the emission lines result from the fluorescence of the X-rays from the accreting compact object on the surrounding stellar wind. The presence of a strong absorption line around ~21 keV in the spectrum suggests a cyclotron origin, thus allowing us to estimate the neutron star magnetic field as ~2.4 × 1012 G. All evidencethus suggests IGR J17329-2731 is a symbiotic X-ray binary. As no X-ray emission was ever observed from the location of IGR J17329-2731 by INTEGRAL (or other X-ray facilities) during the past 15 yr in orbit and considering that symbiotic X-ray binaries are known to be variable but persistent X-ray sources, we concluded that INTEGRAL caught the first detectable X-ray emission from IGR J17329-2731 when the source shined as a symbiotic X-ray binary. The Swift XRT monitoring performed up to ~3 months after the discovery of the source, showed that it maintained a relatively stable X-ray flux and spectral properties.

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

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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