scholarly journals An underlying clock in the extreme flip-flop state transitions of the black hole transient Swift J1658.2-4242

2020 ◽  
Vol 641 ◽  
pp. A101 ◽  
Author(s):  
D. Bogensberger ◽  
G. Ponti ◽  
C. Jin ◽  
T. M. Belloni ◽  
H. Pan ◽  
...  
Keyword(s):  
Black Hole ◽  
Binary Systems ◽  
Periodic Oscillation ◽  
Accretion Disc ◽  
Power Density Spectrum ◽  
State Transitions ◽  
Coronal Emission ◽  
Flip Flop ◽  
Density Spectrum ◽  
X Ray

Aims. Flip-flops are top-hat-like X-ray flux variations, which have been observed in some transient accreting black hole binary systems, and feature simultaneous changes in the spectral hardness and the power density spectrum (PDS). They occur at a crucial time in the evolution of these systems, when the accretion disc emission starts to dominate over coronal emission. Flip-flops remain a poorly understood phenomenon, so we aim to thoroughly investigate them in a system featuring several such transitions. Methods. Within the multitude of observations of Swift J1658.2-4242 during its outburst in early 2018, we detected 15 flip-flops, enabling a detailed analysis of their individual properties and the differences between them. We present observations by XMM-Newton, NuSTAR, Astrosat, Swift, Insight-HXMT, INTEGRAL, and ATCA. We analysed their light curves, searched for periodicities, computed their PDSs, and fitted their X-ray spectra, to investigate the source behaviour during flip-flop transitions and how the interval featuring flip-flops differs from the rest of the outburst. Results. The flip-flops of Swift J1658.2-4242 are of an extreme variety, exhibiting flux differences of up to 77% within ∼100 s, which is much larger than what has been seen previously. We observed radical changes in the PDS simultaneous with the sharp flux variations, featuring transitions between the quasi-periodic oscillation types C and A, which have never been observed before. Changes in the PDS are delayed, but more rapid than changes in the light curve. Flip-flops occur in two intervals within the outburst, separated by about two weeks in which these phenomena were not seen. Transitions between the two flip-flop states occurred at random integer multiples of a fundamental period of 2.761 ks in the first interval and 2.61 ks in the second. Spectral analysis reveals the high and low flux flip-flop states to be very similar, but distinct from intervals lacking flip-flops. A change of the inner temperature of the accretion disc is responsible for most of the flux difference in the flip-flops. We also highlight the importance of correcting for the influence of the dust scattering halo on the X-ray spectra.

scholarly journals Properties of Faint X-ray Activity of XTE J1908+094 in 2019

Galaxies ◽  
2021 ◽  
Vol 9 (2) ◽  
pp. 25
Author(s):  
Debjit Chatterjee ◽  
Arghajit Jana ◽  
Kaushik Chatterjee ◽  
Riya Bhowmick ◽  
Sujoy Kumar Nath ◽  
...  
Keyword(s):  
Black Hole ◽  
Temporal Analysis ◽  
Power Density Spectrum ◽  
Periodic Oscillations ◽  
Telescope Array ◽  
Density Spectrum ◽  
X Ray ◽  
Black Hole Candidate ◽  
Short Period ◽  
Spectral State

We study the properties of the faint X-ray activity of Galactic transient black hole candidate XTE J1908+094 during its 2019 outburst. Here, we report the results of detailed spectral and temporal analysis during this outburst using observations from Nuclear Spectroscopic Telescope Array (NuSTAR). We have not observed any quasi-periodic-oscillations (QPOs) in the power density spectrum (PDS). The spectral study suggests that the source remained in the softer (more precisely, in the soft–intermediate) spectral state during this short period of X-ray activity. We notice a faint but broad Fe Kα emission line at around 6.5 keV. We also estimate the probable mass of the black hole to be 6.5−0.7+0.5M⊙, with 90% confidence.

scholarly journals Inertial oscillation modes of an inclined dipolar magnetosphere as a source of band-limited noise in X-ray pulsars

2020 ◽  
Vol 496 (1) ◽  
pp. 13-18
Author(s):  
Pavel Abolmasov ◽  
Anton Biryukov
Keyword(s):  
Equilibrium Points ◽  
Broad Band ◽  
Periodic Oscillation ◽  
Power Density Spectrum ◽  
Inertial Oscillation ◽  
Noise Component ◽  
Density Spectrum ◽  
X Ray ◽  
Field Lines ◽  
Band Limited

ABSTRACT Magnetic fields of strongly magnetized stars can trap conducting matter due to frozen-in condition. In the force-free regime, the motion of the matter along the field lines may be considered in the ‘bead on a wire’ approximation. Such a motion, if gravity and centrifugal forces are taken into account, has equilibrium points, some of which are stable. In most cases, stability is possible in about several per cent of the possible locations. Corresponding oscillation frequencies span the range from zero to $\sqrt{3}$ of the spin frequency. We suggest that this variability mode may be excited in some X-ray pulsars during the outbursts and create the peaked broad-band noise component near the break frequency in the power density spectrum, as well as produce some of the quasi-periodic oscillation features in this frequency range. Existence of this variability does not require any changes in mass accretion rate and involves only a small amount of matter infiltrating from the disc and magnetic flow due to interchange instabilities.

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 Long-term variability of Swift J1753.5−0127: X-ray spectral–temporal correlations during state transitions

2019 ◽  
Vol 487 (1) ◽  
pp. 1439-1446
Author(s):  
Qingcui Bu ◽  
Lian Tao ◽  
Yu Lu ◽  
Shuangnan Zhang ◽  
Liang Zhang ◽  
...  
Keyword(s):  
Black Hole ◽  
Intermediate State ◽  
State Transition ◽  
Time Lag ◽  
Periodic Oscillation ◽  
State Transitions ◽  
Time Lags ◽  
X Ray ◽  
Hard State

ABSTRACT We studied the long-term evolution of the spectral–temporal correlated properties of the black hole candidate Swift J1753.5−0127 from the onset of its outburst until 2011 with the Rossi X-ray Timing Explorer (RXTE). The source stayed most of its lifetime during hard state, with occasionally transitioned to the hard intermediate state. Similar to typical black hole transients, Swift J1753.5−0127 traces a clear hard line in absolute rms–intensity diagram during the low hard state, with expected highest absolute rms, while shows a clear turn during the hard intermediate state, accompanied by lower absolute rms. Different from Cyg X-1, we found that frequency-dependent time lag increased significantly in the 0.02–3.2 Hz band during state transition in this source. The X-ray time lags in 0.02–3.2 Hz can therefore be used as indicators of state transition in this source. Type-C quasi-periodic oscillation frequency is positively related with its fractional rms and X-ray photon index, suggesting a moving inwards disc/corona scenario. We discussed the physical interpretation of our results in this paper.

scholarly journals ALMA observations of A0620–00: fresh clues on the nature of quiescent black hole X-ray binary jets

2019 ◽  
Vol 488 (1) ◽  
pp. 191-197 ◽  
Author(s):  
Elena Gallo ◽  
Richard Teague ◽  
Richard M Plotkin ◽  
James C A Miller-Jones ◽  
David M Russell ◽  
...  
Keyword(s):  
Black Hole ◽  
Power Systems ◽  
Wide Spectrum ◽  
Lorentz Factor ◽  
Spectral Shape ◽  
Power Density Spectrum ◽  
Shock Model ◽  
Density Spectrum ◽  
X Ray ◽  
Internal Shock

ABSTRACT We report on Atacama Large Millimeter Array (ALMA) continuum observations of the black hole X-ray binary A0620–00 at an X-ray luminosity nine orders of magnitude sub-Eddington. The system was significantly detected at 98 GHz (at 44 ± 7 $\mu$Jy) and only marginally at 233 GHz (20 ± 8 $\mu$Jy), about 40 d later. These results suggest either an optically thin sub-mm synchrotron spectrum, or highly variable sub-mm jet emission on month time-scales. Although the latter appears more likely, we note that, at the time of the ALMA observations, A0620–00 was in a somewhat less active optical-IR state than during all published multiwavelength campaigns when a flat-spectrum, partially self-absorbed jet has been suggested to extend from the radio to the mid-IR regime. Either interpretation is viable in the context of an internal shock model, where the jet’s spectral shape and variability are set by the power density spectrum of the shells’ Lorentz factor fluctuations. While strictly simultaneous radio–mm-IR observations are necessary to draw definitive conclusions for A0620–00, the data presented here, in combination with recent radio and sub-mm results from higher luminosity systems, demonstrate that jets from black hole X-ray binaries exhibit a high level of variability – either in flux density or intrinsic spectral shape, or both – across a wide spectrum of Eddington ratios. This is not in contrast with expectations from an internal shock model, where lower jet power systems can be expected to exhibit larger fractional variability owing to an overall decrease in synchrotron absorption.

scholarly journals Big Game Hunting in the Andromeda Galaxy: Identifying and Weighing Black Holes in Low Mass X-Ray Binaries

2004 ◽  
Vol 194 ◽  
pp. 71-72
Author(s):  
R. Barnard
Keyword(s):  
Black Holes ◽  
Black Hole ◽  
Neutron Star ◽  
Power Density ◽  
Accretion Rate ◽  
Power Density Spectrum ◽  
Density Spectrum ◽  
X Ray ◽  
Low Mass ◽  
X Ray Binaries

AbstractWe have devised a new technique for identifying stellar mass black holes in low mass X-ray binaries, and have applied it to XMM-Newton observations of two X-ray sources in M31. In particular we search for low accretion rate power density spectra; these are very similar for all LMXB, whether the primary is a black hole or a neutron star. Galactic neutron star LMXB exhibit these distinctive PDS at very low luminosities (~ 1036 erg s–1) while black hole LMXB can exhibit them at luminosities > 1038 erg s–1! Following the work of van der Klis (1994), we assume a maximum accretion rate (as a fraction of the Eddington limit) for low accretion rate PDS that is constant for all LMXB, and obtain an empirical value of ~10% Eddington. We have so far discovered two candidate black hole binaries in M31, exhibiting low accretion rate PDS at up to 3 x 1038 and 5 x 1037 erg s–1. If we assume that they are at <10% Eddington, they have minimum masses of 20 and 4 M⊙ respectively. Furthermore, any LMXB exhibiting a low accretion rate power density spectrum at a luminosity > 5 x 1037 erg s–1 is likely to have a black hole primary.

scholarly journals A minimal timescale for the continuum in 4U 1608-52 and Aql X-1

2021 ◽  
Vol 502 (1) ◽  
pp. L72-L78
Author(s):  
K Mohamed ◽  
E Sonbas ◽  
K S Dhuga ◽  
E Göğüş ◽  
A Tuncer ◽  
...  
Keyword(s):  
Black Hole ◽  
Neutron Star ◽  
Power Spectra ◽  
Light Curves ◽  
State Transitions ◽  
Strong Positive Correlation ◽  
Present Evidence ◽  
X Ray ◽  
X Ray Binaries ◽  
The Continuum

ABSTRACT Similar to black hole X-ray binary transients, hysteresis-like state transitions are also seen in some neutron-star X-ray binaries. Using a method based on wavelets and light curves constructed from archival Rossi X-ray Timing Explorer observations, we extract a minimal timescale over the complete range of transitions for 4U 1608-52 during the 2002 and 2007 outbursts and the 1999 and 2000 outbursts for Aql X-1. We present evidence for a strong positive correlation between this minimal timescale and a similar timescale extracted from the corresponding power spectra of these sources.

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.

Sign in / Sign up

Export Citation Format

Share Document