High energy behaviour of Neutron Star Low Mass X-ray binary systems seen by INTEGRAL

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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Hardness Ratio in Evolving Low-Mass X-ray Binary Systems

Symposium - International Astronomical Union ◽

10.1017/s0074180900160723 ◽

1987 ◽

Vol 125 ◽

pp. 199-199

Author(s):

J. Shaham ◽

M. Tavani

Keyword(s):

Neutron Star ◽

Accretion Disk ◽

Binary Systems ◽

Spectral Component ◽

Soft Component ◽

Hard Component ◽

X Ray ◽

Low Mass ◽

Additional Support ◽

X Ray Binaries

Spectral observations of low-mass X-ray binaries (LMXBs) show that the soft component usually dominates over the hard one. These results provide additional support to an interpretation based on models of LMXBs in which the neutron star while, on the average, spinning up, is also experiencing a spinning down torque. Under these conditions, a fraction of the luminosity associated with the gravitational release of energy on the surface of the accreting neutron star may manifest itself as luminosity originating in the inner part of the accretion disk. It is probably possible to separate the two contributions; the stellar luminosity can be associated with the hard component of the spectrum and the disk luminosity, related to the exchange of energy due to the torque between the rapidly spinning neutron star and the accretion disk, can be associated with the soft spectral component.

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The Galactic Pulsar Population and Neutron Star Birth

Symposium - International Astronomical Union ◽

10.1017/s0074180900160516 ◽

1987 ◽

Vol 125 ◽

pp. 67-78

Author(s):

Ramesh Narayan

Keyword(s):

Angular Momentum ◽

Neutron Star ◽

Binary Systems ◽

Magnetic Coupling ◽

Scale Height ◽

High Magnetic Fields ◽

Radio Pulsars ◽

X Ray ◽

The Galaxy ◽

Low Mass

The radio pulsars in the Galaxy are found predominantly in the disk, with a scale height of several hundred parsecs. After allowing for pulsar velocities, the data are consistent with the hypothesis that single pulsars form from massive stellar progenitors. The number of active single pulsars in the Galaxy is ∼ 1.5 × 105, and their birthrate is 1 per ∼ 60 yrs. There is some evidence that many single pulsars, particularly those with high magnetic fields, are born spinning slowly, with initial periods ∼ 0.5–1s. This could imply an origin through binary “recycling” followed by orbit disruption, or might suggest that the pre-supernova stellar core efficiently loses angular momentum to the envelope through magnetic coupling. The birthrate of binary radio pulsars, particularly of the millisecond variety, seems to be much larger than previous estimates, and might suggest that these systems do not originate in low mass X-ray binary systems.

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On the ultra-compact nature of the neutron star system 1RXS J170854.4−321857: insights from X-ray spectroscopy

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz2004 ◽

2019 ◽

Vol 488 (4) ◽

pp. 5014-5019 ◽

Cited By ~ 1

Author(s):

M Armas Padilla ◽

E López-Navas

Keyword(s):

Neutron Star ◽

Spectral Study ◽

Binary Systems ◽

Absorption Model ◽

Star System ◽

X Ray ◽

Emission Component ◽

The Past ◽

Solar Composition ◽

Low Mass

ABSTRACT The relatively small family of ultra-compact X-ray binary systems is of great interest for many areas of astrophysics. We report on a detailed X-ray spectral study of the persistent neutron star low-mass X-ray binary 1RXS J170854.4−321857. We analysed two XMM–Newton observations obtained in late 2004 and early 2005 when, in agreement with previous studies, the system displayed an X-ray luminosity (0.5–10 keV) of ${\sim} 1\times 10^{36}\, \mathrm{erg~s}^{-1}$. The spectrum can be described by a Comptonized emission component with Γ ∼ 1.9 and a distribution of seed photons with a temperature of ∼0.23 keV. A prominent residual feature is present at soft energies, which is reproduced by the absorption model if overabundances of Ne and Fe are allowed. We discuss how similar observables, which might be attributed to the peculiar (non-solar) composition of the plasma donated by the companion star, are a common feature in confirmed and candidate ultra-compact systems. Although this interpretation is still under debate, we conclude that the detection of these features along with the persistent nature of the source at such low luminosity and the intermediate–long burst that it displayed in the past confirms 1RXS J170854.4−321857 as a solid ultra-compact X-ray binary candidate.

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News on the X-ray emission from hot subdwarf stars

Open Astronomy ◽

10.1515/astro-2017-0435 ◽

2017 ◽

Vol 26 (1) ◽

Author(s):

Nicola La Palombara ◽

Sandro Mereghetti

Keyword(s):

Neutron Star ◽

Binary Systems ◽

High Sensitivity ◽

Research Area ◽

X Rays ◽

Low Mass Stars ◽

X Ray ◽

Low Mass ◽

Hot Subdwarfs ◽

Weak Winds

AbstractIn latest years, the high sensitivity of the instruments on-board the XMM-Newton and Chandra satellites allowed us to explore the properties of the X-ray emission from hot subdwarf stars. The small but growing sample of X-ray detected hot subdwarfs includes binary systems, in which the X-ray emission is due to wind accretion onto a compact companion (white dwarf or neutron star), as well as isolated sdO stars, in which X-rays are probably due to shock instabilities in the wind. X-ray observations of these low-mass stars provide information which can be useful for our understanding of the weak winds of this type of stars and can lead to the discovery of particularly interesting binary systems. Here we report the most recent results we have recently obtained in this research area.

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Some Constraints on Neutron Star Properties from Gamma Ray Burster Observations

Symposium - International Astronomical Union ◽

10.1017/s0074180900161261 ◽

1987 ◽

Vol 125 ◽

pp. 489-500

Author(s):

K. Hurley

Keyword(s):

Neutron Star ◽

Low Temperature ◽

Neutron Stars ◽

Binary Systems ◽

Main Sequence ◽

Gamma Ray ◽

Cooling Curves ◽

X Ray ◽

Upper Limits ◽

Low Mass

The results of recent soft X-ray and optical searches for quiescent gamma ray burster counterparts are used to constrain the properties of the neutron stars responsible for bursters. Ages are restricted to the range 2×105 y and above based on temperature upper limits and theoretical cooling curves, or 107 y and above if bursters have evolved from pulsars. Velocities are greater than 20 km/s if the neutron stars are unmagnetized. Practically no main sequence star could have escaped detection in the optical/IR searches, so if the neutron stars are in binary systems, the companion is most likely a degenerate, low mass, low temperature object.

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High energy characteristics of Neutron star low mass X-ray binaries as seen by INTEGRAL: the 4U 1722-30 case

10.22323/1.176.0045 ◽

2013 ◽

Author(s):

Antonella Tarana

Keyword(s):

Neutron Star ◽

High Energy ◽

Energy Characteristics ◽

X Ray ◽

Low Mass ◽

X Ray Binaries

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Binary X-Ray Stars and Supernovae of Type I

Symposium - International Astronomical Union ◽

10.1017/s0074180900011815 ◽

1976 ◽

Vol 73 ◽

pp. 19-25

Author(s):

H. Gursky

Keyword(s):

Black Hole ◽

Neutron Star ◽

White Dwarf ◽

Binary Systems ◽

Close Binary ◽

Type I ◽

Mass Limit ◽

X Ray ◽

Close Binary Systems ◽

Low Mass

Most of the strong galactic X-ray sources must be low mass, close binary systems, such as Her X-1 and Sco X-1. Two evolutionary scenarios are discussed, both involving type I supernovae that occur when mass-accreting white dwarfs are driven over their mass limit. In one, accepting the correctness of the idea that a neutron star or black hole is the seat of the X-ray emission, the SN occurs before the system is an X-ray source. Another possibility is that the white dwarf is the X-ray source, just prior to its collapse and the ensuing SN.

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X-ray Transient Sources (Multifrequency Laboratories) The Case of the Prototype A0535+26/HDE 245770

Acta Polytechnica ◽

10.14311/1310 ◽

2011 ◽

Vol 51 (1) ◽

Author(s):

F. Giovannelli ◽

L. Sabau-Graziati

Keyword(s):

Neutron Star ◽

Coming Out ◽

Stellar Wind ◽

Binary Systems ◽

High Energy ◽

Primary Star ◽

X Ray ◽

Transient Sources ◽

Orbital Phase ◽

Be Star

The goal of this paper is to discuss the behaviour of the X-ray transient source A0535+26 which is considered for historical reasons and for the huge amount of multifrequency data, spread over a period of 35 years, as the prototype of this class of objects. Transient sources are formed by a Be star — the primary — and a neutron star X-ray pulsar — the secondary — and constitute a sub-class of X-ray binary systems. We will emphasize the discovery of low-energy indicators of high-energy processes. They are UBVRI magnitudes and Balmer lines of the optical companion. Particular unusual activity of the primary star — usually at the periastron passage of the neutron star – indicates that an X-ray flare is drawing near. The shape and intensity of X-ray outbursts are dependent on the strength of the activity of the primary. We derive the optical orbital period of the system as 110.856 ± 0.02 days. By using the optical flare of December 5, 1981 (here after 811205-E) that triggered the subsequent X-ray outburst of December 13, 1981, we derive the ephemeris of the system as JD Popt−outb = JD0 (2, 444, 944) ± n(110.856 ± 0.02). Thus the passage of the neutron star at the periastron occurs with a periodicity of 110.856 ± 0.02 days and the different kinds of X-ray outbursts of A0535+26 — following the definitions reported in the review by Giovannelli & Sabau-Graziati (1992) — occur just after ∼ 8 days. The delay between optical and X-ray outbursts is just the transit time of the material coming out from the optical companion to reach the neutron star X-ray pulsar. The occurrence of X-ray “normal outbursts”, “anomalous outbursts” or “casual outbursts” is dependent on the activity of the Be star: “quiet state: steady stellar wind”, “excited state: stellar wind plus puffs of material”, and “expulsion of a shell”, respectively. In the latter case, the primary manifests a strong optical activity and the consequent strong X-ray outburst can occur in any orbital phase, with a preference at the periastron passage of the neutron star, because of its gravitational effects on the Be star.

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