Neutron star atmosphere composition: the quiescent, low-mass X-ray binary in the globular cluster M28

We present here the first detailed spectral observations of the low-mass X-ray binary source X0512–401 located in the globular cluster NGC1851 obtained by Ginga. We have found that the Ginga LAC data of X0512–401 are best fitted by a “two-component” spectral model: power-law with exponential cut-off and a blackbody. The inclusion of a 6.7 KeV Fe emission line did not improve our best fit. In the light of the present observations and the previous studies concerning the importance of Comptonization, our model requires a scattering cloud surrounding the neutron star, with a Thomson optical depth of ~5. The detection of ~30–40 hr periodicity is hard to interpret in terms of the possible binary period of the system, since most of these systems have binary periods of a few hours or even less. It may either suggest that the accretion disk around the neutron star is precessing or there is a third body in the system.

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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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Daily multiwavelength Swift monitoring of the neutron star low-mass X-ray binary Cen X-4: evidence for accretion and reprocessing during quiescence

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stt1741 ◽

2013 ◽

Vol 436 (3) ◽

pp. 2465-2483 ◽

Cited By ~ 35

Author(s):

F. Bernardini ◽

E. M. Cackett ◽

E. F. Brown ◽

C. D'Angelo ◽

N. Degenaar ◽

...

Keyword(s):

Neutron Star ◽

X Ray ◽

Low Mass

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UV and X-ray observations of the neutron star LMXB EXO 0748–676 in its quiescent state

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3734 ◽

2020 ◽

Vol 501 (1) ◽

pp. 1453-1462

Author(s):

A S Parikh ◽

N Degenaar ◽

J V Hernández Santisteban ◽

R Wijnands ◽

I Psaradaki ◽

...

Keyword(s):

Neutron Star ◽

Thermal Emission ◽

Hubble Space Telescope ◽

Dense Matter ◽

Continuum Emission ◽

Quiescent State ◽

X Ray ◽

Low Level ◽

Low Mass ◽

Different Origins

ABSTRACT The accretion behaviour in low-mass X-ray binaries (LMXBs) at low luminosities, especially at <1034 erg s−1, is not well known. This is an important regime to study to obtain a complete understanding of the accretion process in LMXBs, and to determine if systems that host neutron stars with accretion-heated crusts can be used probe the physics of dense matter (which requires their quiescent thermal emission to be uncontaminated by residual accretion). Here, we examine ultraviolet (UV) and X-ray data obtained when EXO 0748–676, a crust-cooling source, was in quiescence. Our Hubble Space Telescope spectroscopy observations do not detect the far-UV continuum emission, but do reveal one strong emission line, C iv. The line is relatively broad (≳3500 km s−1), which could indicate that it results from an outflow such as a pulsar wind. By studying several epochs of X-ray and near-UV data obtained with XMM–Newton, we find no clear indication that the emission in the two wavebands is connected. Moreover, the luminosity ratio of LX/LUV ≳ 100 is much higher than that observed from neutron star LMXBs that exhibit low-level accretion in quiescence. Taken together, this suggests that the UV and X-ray emission of EXO 0748–676 may have different origins, and that thermal emission from crust-cooling of the neutron star, rather than ongoing low-level accretion, may be dominating the observed quiescent X-ray flux evolution of this LMXB.

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The Low-Mass X-Ray Binary Globular Cluster Connection in the ACS Virgo Cluster Survey

Globular Clusters - Guides to Galaxies - Eso Astrophysics Symposia ◽

10.1007/978-3-540-76961-3_72 ◽

2008 ◽

pp. 305-306

Author(s):

A. Jordán ◽

G.R. Sivakoff ◽

C.L. Sarazin ◽

J.P. Blakeslee ◽

E.L. Blanton ◽

...

Keyword(s):

Globular Cluster ◽

Virgo Cluster ◽

X Ray ◽

Cluster Survey ◽

Low Mass

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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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