Puzzling blue dips in the black hole candidate Swift J1357.2 − 0933, from ULTRACAM, SALT, ATCA, Swift, and NuSTAR

Abstract We present rapid, multiwavelength photometry of the low-mass X-ray binary Swift J1357.2-0933 during its 2017 outburst. Using several sets of quasi-simultaneous ULTRACAM/NTT (optical), NuSTAR (X-ray), XRT/Swift (X-ray), SALT (optical), and ATCA (radio) observations taken during outburst decline, we confirm the frequent optical dipping that has previously been noted both in outburst and in quiescence. We also find: (1) that the dip frequency decreases as the outburst decays, similar to what was seen in the previous outburst, (2) that the dips produce a shape similar to that in binary systems with partial disc occultations, (3) that the source becomes significantly bluer during these dips, indicating an unusual geometry compared to other LMXB dippers, and (4) that dip superposition analysis confirms the lack of an X-ray response to the optical dips. These very unusual properties appear to be unique to Swift J1357.2−0933, and are likely the result of a high binary inclination, as inferred from features such as its very low outburst X-ray luminosity. From this analysis as well as X-ray/optical timing correlations, we suggest a model with multicomponent emission/absorption features with differing colours. This could include the possible presence of a sporadically occulted jet base and a recessed disc. This source still hosts many puzzling features, with consequences for the very faint X-ray transients population.

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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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Discovery of a New X-ray Transient in Scorpius GRO J1655-40 ≡ X-ray Nova Scorpii 1994

Symposium - International Astronomical Union ◽

10.1017/s0074180900055820 ◽

1996 ◽

Vol 165 ◽

pp. 363-367

Author(s):

W.S. Paciesas ◽

S.N. Zhang ◽

B.C. Rubin ◽

B.A. Harmon ◽

C.A. Wilson ◽

...

Keyword(s):

Black Hole ◽

High Resolution ◽

Power Law ◽

Radio Observations ◽

X Ray ◽

Black Hole Candidate ◽

Radio Jets ◽

Transient Source ◽

Galactic Source ◽

Photon Index

A bright transient X-ray source, GRO J1655-40 (X-ray Nova Scorpii 1994) was discovered with BATSE (the Burst and Transient Source Experiment) in late July 1994. More recently, the source also became a strong radio emitter, its rise in the radio being approximately anti-correlated with a decline in the hard X-ray intensity. High-resolution radio observations subsequent to this symposium showed evidence for superluminally expanding jets. Since the hard X-ray emission extends to at least 200 keV and we find no evidence of pulsations, we tentatively classify the source as a black-hole candidate. However, its hard X-ray spectrum is unusually steep (power-law photon index α ≃ −3) relative to most other black-hole candidates. In this regard, it resembles GRS 1915+105, the first galactic source to show superluminal radio jets.

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The MAVERIC survey: a hidden pulsar and a black hole candidate in ATCA radio imaging of the globular cluster NGC 6397

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/staa631 ◽

2020 ◽

Vol 493 (4) ◽

pp. 6033-6049 ◽

Cited By ~ 4

Author(s):

Yue Zhao ◽

Craig O Heinke ◽

Vlad Tudor ◽

Arash Bahramian ◽

James C A Miller-Jones ◽

...

Keyword(s):

Black Hole ◽

Globular Cluster ◽

Radio Observation ◽

Millisecond Pulsar ◽

Radio Flux ◽

X Ray ◽

Black Hole Candidate ◽

Radio Imaging ◽

Low Mass ◽

Compact Array

ABSTRACT Using a 16.2-h radio observation by the Australia Telescope Compact Array and archival Chandra data, we found >5σ radio counterparts to four known and three new X-ray sources within the half-light radius (rh) of the Galactic globular cluster NGC 6397. The previously suggested millisecond pulsar (MSP) candidate, U18, is a steep-spectrum (Sν ∝ να; $\alpha =-2.0^{+0.4}_{-0.5}$) radio source with a 5.5-GHz flux density of 54.7 ± 4.3 $\mu \mathrm{ Jy}$. We argue that U18 is most likely a ‘hidden’ MSP that is continuously hidden by plasma shocked at the collision between the winds from the pulsar and companion star. The non-detection of radio pulsations so far is probably the result of enhanced scattering in this shocked wind. On the other hand, we observed the 5.5-GHz flux of the known MSP PSR J1740−5340 (U12) to decrease by a factor of >2.8 during epochs of 1.4-GHz eclipse, indicating that the radio flux is absorbed in its shocked wind. If U18 is indeed a pulsar whose pulsations are scattered, we note the contrast with U12’s flux decreases in eclipse, which argues for two different eclipse mechanisms at the same radio frequency. In addition to U12 and U18, we also found radio associations for five other Chandra X-ray sources, four of which are likely background galaxies. The last, U97, which shows strong H α variability, is mysterious; it may be either a quiescent black hole low-mass X-ray binary or something more unusual.

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Wind accretion in Cygnus X-1

Astronomy and Astrophysics ◽

10.1051/0004-6361/202037561 ◽

2020 ◽

Vol 637 ◽

pp. A66 ◽

Cited By ~ 1

Author(s):

E. Meyer-Hofmeister ◽

B. F. Liu ◽

E. Qiao ◽

R. E. Taam

Keyword(s):

Black Hole ◽

Stellar Wind ◽

Binary Systems ◽

Three Dimensional ◽

Stable States ◽

X Ray ◽

Hard State ◽

Hard Spectrum ◽

Low Mass ◽

Hydrodynamical Simulations

Context. Cygnus X-1 is a black hole X-ray binary system in which the black hole captures and accretes gas from the strong stellar wind emitted by its supergiant O9.7 companion star. The irradiation of the supergiant star essentially determines the flow properties of the stellar wind and the X-ray luminosity from the system. The results of three-dimensional hydrodynamical simulations of wind-fed X-ray binary systems reported in recent work reveal that the ionizing feedback of the X-ray irradiation leads to the existence of two stable states with either a soft or a hard spectrum. Aims. We discuss the observed radiation of Cygnus X-1 in the soft and hard state in the context of mass flow in the corona and disk, as predicted by the recent application of a condensation model. Methods. The rates of gas condensation from the corona to the disk for Cygnus X-1 are determined, and the spectra of the hard and soft radiation are computed. The theoretical results are compared with the MAXI observations of Cygnus X-1 from 2009 to 2018. In particular, we evaluate the hardness-intensity diagrams (HIDs) for its ten episodes of soft and hard states which show that Cygnus X-1 is distinct in its spectral changes as compared to those found in the HIDs of low-mass X-ray binaries. Results. The theoretically derived values of photon counts and hardness are in approximate agreement with the observed data in the HID. However, the scatter in the diagram is not reproduced. Improved agreement could result from variations in the viscosity associated with clumping in the stellar wind and corresponding changes of the magnetic fields in the disk. The observed dipping events in the hard state may also contribute to the scatter and to a harder spectrum than predicted by the model.

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Low-Mass X-ray Binaries—Recent Developments

Symposium - International Astronomical Union ◽

10.1017/s0074180900055765 ◽

1996 ◽

Vol 165 ◽

pp. 301-312

Author(s):

M. Van Der Klis

Keyword(s):

Magnetic Field ◽

Black Hole ◽

Neutron Stars ◽

X Ray ◽

Black Hole Candidate ◽

Recent Developments ◽

Low Mass ◽

Low Magnetic Field ◽

X Ray Binaries ◽

Black Hole Candidates

Recent developments in the field of low-mass X-ray binaries are briefly reviewed, with particular emphasis on a comparison between the systems that contain accreting low magnetic-field neutron stars and those that contain black-hole candidates. The possibility that inclination effects play a role in black-hole candidate phenomenology is explored.

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Low-Mass X-Ray Binaries in the LMC

International Astronomical Union Colloquium ◽

10.1017/s0252921100105548 ◽

1987 ◽

Vol 93 ◽

pp. 689-689

Author(s):

M.W. Pakull ◽

K. Beuermann ◽

L.P. Angebault ◽

L. Bianchi

Keyword(s):

Black Holes ◽

Black Hole ◽

Interstellar Medium ◽

Compact Objects ◽

X Rays ◽

X Ray ◽

Black Hole Candidate ◽

Low Mass ◽

X Ray Binaries

AbstractWe report results on three low-mass X-ray binaries (LMXB) in the LMC, obtained with EXOSAT, IUE and ground-based (ESO) telescopes: LMC X-2 which appears to be “Sco X-l”-like, LHG 83 and LHG 87. The latter are two weaker sources first detected in the course of the HEAO-B LMC survey. They have faint optical counterparts of which LHG 87 was only recently identified by us. In X-rays, they are characterized by ultrasoft X-ray spectra possibly characteristic of black-hole primaries. LHG 83 furthermore shows evidence for X-ray ionization of the surrounding interstellar medium, similar to the He III region around the black-hole candidate LMC X-l. X-ray binaries with masses of compact objects in excess of 3 M⊙ and ultrasoft X-ray spectra are comparatively frequent in the LMC. We suggest that subcritical accretion onto black holes takes place in LHG 83 and LHG 87.

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Simultaneous detection of an intrinsic absorber and a compact jet emission in the X-ray binary IGR J17091−3624 during a hard accretion state

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stz3385 ◽

2019 ◽

Vol 491 (4) ◽

pp. 4857-4868 ◽

Cited By ~ 2

Author(s):

E Gatuzz ◽

M Díaz Trigo ◽

J C A Miller-Jones ◽

S Migliari

Keyword(s):

Black Hole ◽

Detailed Analysis ◽

Simultaneous Detection ◽

The Other ◽

Radio Observations ◽

X Ray ◽

Other Hand ◽

Low Mass ◽

Ionization Parameter ◽

Compact Array

ABSTRACT We present a detailed analysis of three XMM–Newton observations of the black hole low-mass X-ray binary IGR J17091−3624 taken during its 2016 outburst. Radio observations obtained with the Australia Telescope Compact Array indicate the presence of a compact jet during all observations. From the best X-ray data fit results, we concluded that the observations were taken during a transition from a hard accretion state to a hard-intermediate accretion state. For Observations 1 and 2, a local absorber can be identified in the EPIC-pn spectra but not in the RGS spectra, preventing us from distinguishing between absorption local to the source and that from the hot ISM component. For Observation 3, on the other hand, we have identified an intrinsic ionized static absorber in both EPIC-pn and RGS spectra. The absorber, observed simultaneously with a compact jet emission, is characterized by an ionization parameter of 1.96 < log ξ < 2.05 and traced mainly by Ne x, Mg xii, Si xiii, and Fe xviii.

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A black hole X-ray binary at ∼100 Hz: multiwavelength timing of MAXI J1820+070 with HiPERCAM and NICER

Monthly Notices of the Royal Astronomical Society Letters ◽

10.1093/mnrasl/slz148 ◽

2019 ◽

Vol 490 (1) ◽

pp. L62-L66 ◽

Cited By ~ 4

Author(s):

J A Paice ◽

P Gandhi ◽

T Shahbaz ◽

P Uttley ◽

Z Arzoumanian ◽

...

Keyword(s):

Black Hole ◽

Time Scales ◽

X Rays ◽

X Ray ◽

Black Hole Candidate ◽

Optical Wavelength ◽

The Third ◽

Binary Black Hole ◽

Internal Shock ◽

Low Mass

ABSTRACT We report on simultaneous sub-second optical and X-ray timing observations of the low-mass X-ray binary black hole candidate MAXI J1820+070. The bright 2018 outburst rise allowed simultaneous photometry in five optical bands (ugrizs) with HiPERCAM/GTC (Optical) at frame rates over 100 Hz, together with NICER/ISS observations (X-rays). Intense (factor of 2) red flaring activity in the optical is seen over a broad range of time-scales down to ∼10 ms. Cross-correlating the bands reveals a prominent anticorrelation on time-scales of ∼seconds, and a narrow sub-second correlation at a lag of ≈ +165 ms (optical lagging X-rays). This lag increases with optical wavelength, and is approximately constant over Fourier frequencies of ∼0.3–10 Hz. These features are consistent with an origin in the inner accretion flow and jet base within ∼5000 Gravitational radii. An additional ∼+5 s lag feature may be ascribable to disc reprocessing. MAXI J1820+070 is the third black hole transient to display a clear ∼0.1 s optical lag, which may be common feature in such objects. The sub-second lag variation with wavelength is novel, and may allow constraints on internal shock jet stratification models.

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A self-lensing binary massive black hole interpretation of quasi-periodic eruptions

Monthly Notices of the Royal Astronomical Society ◽

10.1093/mnras/stab609 ◽

2021 ◽

Vol 503 (2) ◽

pp. 1703-1716

Author(s):

Adam Ingram ◽

Sara E Motta ◽

Suzanne Aigrain ◽

Aris Karastergiou

Keyword(s):

Black Hole ◽

Active Galactic Nuclei ◽

Binary Systems ◽

Galactic Nuclei ◽

Galaxy Mergers ◽

Massive Black Hole ◽

X Ray ◽

Binary Separation ◽

Low Mass ◽

Optical Time

ABSTRACT Binary supermassive black hole (SMBH) systems result from galaxy mergers, and will eventually coalesce due to gravitational wave (GW) emission if the binary separation can be reduced to ≲0.1 pc by other mechanisms. Here, we explore a gravitational self-lensing binary SMBH model for the sharp (duration ∼1 h), quasi-regular X-ray flares – dubbed quasi-periodic eruptions – recently observed from two low-mass active galactic nuclei: GSN 069 and RX J1301.9+2747. In our model, the binary is observed ∼edge-on, such that each SMBH gravitationally lenses light from the accretion disc surrounding the other SMBH twice per orbital period. The model can reproduce the flare spacings if the current eccentricity of RX J1301.9+2747 is ϵ0 ≳ 0.16, implying a merger within ∼1000 yr. However, we cannot reproduce the observed flare profiles with our current calculations. Model flares with the correct amplitude are ∼2/5 the observed duration, and model flares with the correct duration are ∼2/5 the observed amplitude. Our modelling yields three distinct behaviours of self-lensing binary systems that can be searched for in current and future X-ray and optical time-domain surveys: (i) periodic lensing flares, (ii) partial eclipses (caused by occultation of the background mini-disc by the foreground mini-disc), and (iii) partial eclipses with a very sharp in-eclipse lensing flare. Discovery of such features would constitute very strong evidence for the presence of a supermassive binary, and monitoring of the flare spacings will provide a measurement of periastron precession.

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