Comparison of the X-Ray Sources CIR X-1. GX301-2 and 2S0535-668

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).

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Evidence for periodic accretion–ejection in LS I +61°303

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2623 ◽

2020 ◽

Vol 498 (3) ◽

pp. 3592-3600 ◽

Cited By ~ 1

Author(s):

M Massi ◽

M Chernyakova ◽

A Kraus ◽

D Malyshev ◽

F Jaron ◽

...

Keyword(s):

Binary System ◽

Compact Object ◽

Eccentric Orbit ◽

Physical Processes ◽

X Ray ◽

Accretion Flow ◽

Single Orbit ◽

Orbital Modulation ◽

Γ Ray ◽

Two Peaks

ABSTRACT The stellar binary system LS I +61°303, composed of a compact object in an eccentric orbit around a B0 Ve star, emits from radio up to γ-ray energies. The orbital modulation of radio spectral index, X-ray, and GeV γ-ray data suggests the presence of two peaks. This two-peaked profile is in line with the accretion theory predicting two accretion–ejection events for LS I +61°303 along the 26.5 d orbit. However, the existing multiwavelength data are not simultaneous. In this paper, we report the results of a campaign covering radio, X-ray, and γ-ray observations of the system along one single orbit. Our results confirm the two predicted events along the orbit and in addition show that the positions of radio and γ-ray peaks are coincident with X-ray dips as expected for radio and γ-ray emitting ejections depleting the X-ray emitting accretion flow. We discuss future observing strategies for a systematic study of the accretion–ejection physical processes in LS I +61°303.

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Swift J011511.0-725611: discovery of a rare Be star/white dwarf binary system in the SMC

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab2632 ◽

2021 ◽

Vol 508 (1) ◽

pp. 781-788

Author(s):

J A Kennea ◽

M J Coe ◽

P A Evans ◽

L J Townsend ◽

Z A Campbell ◽

...

Keyword(s):

Neutron Star ◽

Binary System ◽

South African ◽

White Dwarf ◽

Compact Object ◽

Type Ii ◽

Large Telescope ◽

X Ray ◽

Be Star

ABSTRACT We report on the discovery of Swift J011511.0-725611, a rare Be X-ray binary system (BeXRB) with a white dwarf (WD) compact object, in the Small Magellanic Cloud (SMC) by S-CUBED, a weekly X-ray/UV survey of the SMC by the Neil Gehrels Swift Observatory. Observations show an approximately 3 month outburst from Swift J011511.0-725611, the first detected by S-CUBED since it began in 2016 June. Swift J011511.0-725611 shows supersoft X-ray emission, indicative of a WD compact object, which is further strengthened by the presence of an 0.871 keV edge, commonly attributed to O viii K-edge in the WD atmosphere. Spectroscopy by South African Large Telescope confirms the Be nature of the companion star, and long term light curve by OGLE finds both the signature of a circumstellar disc in the system at outburst time, and the presence of a 17.4 day periodicity, likely the orbital period of the system. Swift J011511.0-725611 is suggested to be undergoing a Type-II outburst, similar to the previously reported SMC Be white dwarf binary (BeWD), Swift J004427.3-734801. It is likely that the rarity of known BeWD is in part due to the difficulty in detecting such outbursts due to both their rarity, and their relative faintness compared to outbursts in Neutron Star BeXRBs.

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Discovery of thermonuclear Type-I X-ray bursts from the X-ray binary MAXI J1807+132

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa3657 ◽

2020 ◽

Vol 501 (1) ◽

pp. 261-268

Author(s):

A C Albayati ◽

D Altamirano ◽

G K Jaisawal ◽

P Bult ◽

S Rapisarda ◽

...

Keyword(s):

Neutron Star ◽

Strong Evidence ◽

Compact Object ◽

Type I ◽

Time Resolved ◽

X Ray ◽

Upper Limit ◽

Low Mass ◽

Photospheric Radius ◽

Peak Luminosity

ABSTRACT MAXI J1807+132 is a low-mass X-ray binary (LMXB) first detected in outburst in 2017. Observations during the 2017 outburst did not allow for an unambiguous identification of the nature of the compact object. MAXI J1807+132 that was detected in outburst again in 2019 and was monitored regularly with Neutron Star Interior Composition Explorer(NICER). In this paper, we report on 5 days of observations during which we detected three thermonuclear (Type-I) X-ray bursts, identifying the system as a neutron star LMXB. Time-resolved spectroscopy of the three Type-I bursts revealed typical characteristics expected for these phenomena. All three Type-I bursts show slow rises and long decays, indicative of mixed H/He fuel. We find no strong evidence that any of the Type-I bursts reached the Eddington Luminosity; however, under the assumption that the brightest X-ray burst underwent photospheric radius expansion, we estimate a <12.4 kpc upper limit for the distance. We searched for burst oscillations during the Type-I bursts from MAXI J1807+132 and found none (<10 per cent amplitude upper limit at 95 per cent confidence level). Finally, we found that the brightest Type-I burst shows a ∼1.6 s pause during the rise. This pause is similar to one recently found with NICER in a bright Type-I burst from the accreting millisecond X-ray pulsar SAX J1808.4–3658. The fact that Type-I bursts from both sources can show this type of pause suggests that the origin of the pauses is independent of the composition of the burning fuel, the peak luminosity of the Type-I bursts, or whether the NS is an X-ray pulsar.

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SS433 and the nature of ultra-luminous X-ray sources

Proceedings of the International Astronomical Union ◽

10.1017/s1743921307005005 ◽

2006 ◽

Vol 2 (S238) ◽

pp. 219-224

Author(s):

P. A. Charles ◽

A. D. Barnes ◽

J. Casares ◽

J. S. Clark ◽

R. Cornelisse ◽

...

Keyword(s):

Black Hole ◽

Neutron Star ◽

High Resolution ◽

Binary System ◽

Compact Object ◽

High Mass ◽

X Ray ◽

New Class ◽

The Galaxy ◽

X Ray Binaries

AbstractThe prototypical micro-quasar, SS433, one of the most bizarre objects in the Galaxy, is a weak X-ray source, yet the kinetic energy of its relativistic, precessing jets is vastly greater. In spite of its importance as the nearest example of directly observable relativistic phenomena, we know remarkably little about the nature of this binary system. There are ongoing arguments not only about the mass of the compact object, but even as to whether it is a black hole or a neutron star, an argument that recent high resolution optical spectroscopy has contributed to.Combined with the INTEGRAL discovery of a new class of highly obscured galactic high-mass X-ray binaries, one of which has been found to precess on a similar timescale to SS433, we suggest that these would indeed be seen by external observers as ULXs, once additional effects such as beaming (either relativistic or geometrical) are included.

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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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Swift/XRT, Chandra, and XMM–Newton observations of IGR J17091–3624 as it returns into quiescence

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa2009 ◽

2020 ◽

Vol 497 (1) ◽

pp. 1115-1126

Author(s):

M Pereyra ◽

D Altamirano ◽

J M C Court ◽

N Degenaar ◽

R Wijnands ◽

...

Keyword(s):

Black Hole ◽

Neutron Star ◽

Time Scales ◽

Strong Evidence ◽

Spectral Properties ◽

X Ray ◽

Term Evolution ◽

Wide Range ◽

Low Mass

ABSTRACT IGR J17091–3624 is a low-mass X-ray binary (LMXB), which received wide attention from the community thanks to its similarities with the bright black hole system GRS 1915+105. Both systems exhibit a wide range of highly structured X-ray variability during outburst, with time-scales from few seconds to tens of minutes, which make them unique in the study of mass accretion in LMXBs. In this work, we present a general overview into the long-term evolution of IGR J17091–3624, using Swift/XRT observations from the onset of the 2011–2013 outburst in 2011 February till the end of the last bright outburst in 2016 November. We found four re-flares during the decay of the 2011 outburst, but no similar re-flares appear to be present in the latter one. We studied, in detail, the period with the lowest flux observed in the last 10 yr, just at the tail end of the 2011–2013 outburst, using Chandra and XMM-Newton observations. We observed changes in flux as high as a factor of 10 during this period of relative quiescence, without strong evidence of softening in the spectra. This result suggests that the source has not been observed at its true quiescence so far. By comparing the spectral properties at low luminosities of IGR J17091–3624 and those observed for a well-studied population of LMXBs, we concluded that IGR J17091–3624 is most likely to host a black hole as a compact companion rather than a neutron star.

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The Nature of the Compact Object in the Hard X-Ray Source 4U2206+54

International Astronomical Union Colloquium ◽

10.1017/s0252921100152546 ◽

2004 ◽

Vol 194 ◽

pp. 208-208

Author(s):

J. M. Torrejón ◽

I. Kreykenbohni ◽

A. Orr ◽

L. Titarchuk ◽

I. Negueruela

Keyword(s):

Neutron Star ◽

Accretion Disk ◽

Compact Object ◽

High Energy ◽

Energy Data ◽

X Ray ◽

Hot Plasma ◽

Cyclotron Line ◽

First Time

We present an analysis of archival RXTE and BeppoSAX data of the X-ray source 4U2206+54. For the first time, high energy data (≥ 30 keV) is analyzed. The data is well described by comptonization models in which seed photons with temperatures between 1.1 keV arid 1.5 keV are comptonized by a hot plasma at 50 keV thereby producing a hard tail which extends up to 100 keV. From luminosity arguments it is shown that the area of the soft photons source must be small (r ≈ 1 km) and that the presence of an accretion disk in this system is unlikely. Here we report on the possible existence of a cyclotron line around 30 keV . The presence of a neutron star in the system is strongly favored by the available data.

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Torque Reversals in Disk Accreting Pulsars

Publications of the Astronomical Society of Australia ◽

10.1071/as98250 ◽

1998 ◽

Vol 15 (2) ◽

pp. 250-253

Author(s):

Jianke Li ◽

Dayal T. Wickramasinghe

Keyword(s):

Neutron Star ◽

Binary System ◽

Recent Work ◽

Time Scale ◽

Accretion Rate ◽

Future Studies ◽

X Ray ◽

The Past ◽

X Ray Binaries ◽

Coherent Picture

AbstractX-ray binaries in which the accreting component is a neutron star commonly exhibit significant changes in their spin. In the system Cen X-3, a disk accreting binary system, the pulsar was observed to spin up at a rate ḟ = 8 × 10−13 Hz s−1 when averaged over the past twenty years, but significant fluctuations were observed above this mean. Recent BASTE observations have disclosed that these fluctuations are much larger than previously noted, and appeared to be a system characteristic. The change in the spin state from spin-up to spin-down or vice-versa occurs on a time scale that is much shorter than the instrument can resolve (≤1 d), but appears always to be a similar amplitude, and to occur stochastically. These observations have posed a problem for the conventional torque–mass accretion relation for accreting pulsars, because in this model the spin rate is closely related to the accretion rate, and the latter needs to be finely tuned and to change abruptly to explain the observations. Here we review recent work in this direction and present a coherent picture that explains these observations. We also draw attention to some outstanding problems for future studies.

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