Hard State Research Articles

The luminous, hard state can’t be MAD

ABSTRACT We present a straightforward argument for why the luminous, hard state of black hole X-ray binaries (BHXRBs) cannot always be associated with a magnetically arrested accretion disc (MAD). It relies on three core premises: (1) that the type-C quasi-periodic oscillation (QPO) is best explained by Lense–Thirring (LT) precession of a tilted, inner, hot flow; (2) that observed optical and infrared (IR) QPOs with the same or lower frequency as the type-C QPO suggest the jet, too, must precess in these systems; and (3) that numerical simulations of MADs show that their strong magnetic fields promote alignment of the disc with the black hole and, thereby, suppress LT precession. If all three premises hold true, then, at least whenever the optical and IR QPOs are observed alongside the type-C QPO, these systems cannot be in the MAD state. Extending the argument further, if the type-C QPO is always associated with LT precession, then it would rule out MADs anytime this timing feature is seen, which covers nearly all BHXRBs when they are in the luminous, hard and hard-intermediate states.

High-density Reflection Spectroscopy of Black Hole X-Ray Binaries in the Hard State

We present a high-density relativistic reflection analysis of 21 spectra of six black hole X-ray binaries in the hard state with data from NuSTAR and Swift. We find that 76% of the observations in our sample require a disk density higher than the 1015 cm−3 assumed in the previous reflection analysis. Compared with the measurements from active galactic nuclei, stellar mass black holes have higher disk densities. Our fits indicate that the inner disk radius is close to the innermost stable circular orbit in the luminous hard state. The coronal temperatures are significantly lower than the prediction of a purely thermal plasma, which can be explained with a hybrid plasma model. If the disk density is fixed at 1015 cm−3, the disk ionization parameter is overestimated while the inner disk radius is unaffected.

Cyber-enabled tradecraft and contemporary espionage: assessing the implications of the tradecraft paradox on agent recruitment in Russia and China

ABSTRACTThe acquisition of clandestine human sources – or agents – inside Russia and China likely remains the key priority for Western HUMINT agencies, and yet their ability to do this safely is quickly waning. This paper considers the utility of cyberspace for espionage recruitment in these two hard target states, and assesses its value as a potential solution to emerging surveillance threats. With the aid of history, this paper proposes that hard target espionage is fundamentally afflicted by a tradecraft paradox, one that will severely curtail the utility of cyberspace to agent recruitment.

Multi-scale Multi-physics Phase-field coupled Thermo-mechanical approach for modeling of powder bed fusion process

The present study investigates the thermomechanical simulation of powder bed fusion (PBF) process, focusing on the characterization of the melt pool. With the aim of comprehensively understanding the complex multi-physics phenomena inherent to the PBF process, our objective is to establish a robust and refined computational framework that is capable of systematic evaluation of the dynamic evolution of the melt pool geometry and temporal characteristics across the various stages of its formation. For this purpose, the Allen-Cahn phase field formulation is integrated with the elastoplastic material model based on J2 plasticity theory and the model implementation is conducted based on a finite element method (FEM) framework using the Multi-physics Object-Oriented Simulation Environment (MOOSE). As an objective, the model tends to depict the intricate, nonlinear, and non-equilibrium nature of the melt pool, encompassing multi-physics process of the PBF, while assuming powder particles as a homogenized continuum medium and neglecting complex interactions between the particles and their surroundings. This includes the separation of geometry into two domains (i) the powder layer and (ii) the substrate, the melting and solidification of the material, the phase-changing process, and the resulting induced distortion and residual stresses. Additionally, the model incorporates a phase indicator to account for the degree of solidification or consolidation of powder, whose evolution describes diffusion, solidification and shrinkage phenomena. This approach enables the tracking of the movement of the melting front of the metallic material induced by a heat source, effectively dividing the domain into regions of soft and hard solid states with a diffusive interface in between. Furthermore, to enhance the model's fidelity, an adaptive mesh refinement (AMR) strategy is employed to precisely capture important aspects of the phase changing process, such as characteristics of the solidification front and powder melting. To assess the model's performance, it is tested by simulating the processing of a three-dimensional Inconel 625 thin plate, as well as a benchmark example, where the influence of parameters such as temperature and phase change on the mechanical response of the system during the solidification process is elucidated.

NuSTAR View of the R − Γ Correlation in the Hard State of Black Hole Low-mass X-Ray Binaries

The power law and reflection emission have been observed in the X-ray spectra of both black hole X-ray binaries (BHXRBs) and active galactic nuclei (AGNs), indicating a common physical origin of the X-ray emission from these two types of sources. The relevant parameters describing the shape of both components and the potential correlation between these parameters can provide important clues on the geometric and physical properties of the disk and the corona in these sources. In this work, we present a positive correlation between the photon index Γ and the reflection strength R for the low-mass BHXRBs in the hard state by modeling NuSTAR data, which is qualitatively consistent with the previous studies. We compare our results with the predictions from different theoretical disk-corona models. We show that the R − Γ correlation found in this work seems to favor the moving corona model proposed by Beloborodov. Our results indicate that the coronal geometry varies significantly among BHXRBs. We further compare our results with that of AGNs. We find that the reflection strength R is smaller than unity in the hard state of BHXRBs, while it can be as large as ∼5 in AGNs, which implies that the variations of the disk-coronal geometry of AGNs are more vigorous than that of the BHXRBs in the hard state.

Detection of high-frequency quasi-periodic oscillation during the reflare of MAXI J1348−630

ABSTRACT In this work, we report the detection of high-frequency quasi-periodic oscillation (QPO) in the black hole X-ray binary MAXI J1348−630 in its hard spectral state. MAXI J1348−630 went through a reflare during MJD 58634 to MJD 58674 after a 104 d long outburst which began on MJD 58509. During the reflare, the binary system evolved through a series of hard states of varying luminosity. We detected a high-frequency QPO at 98.3 Hz with a significance of 3.7σ in one of the NICER observations during its evolution. It was argued that the QPO frequency might be related to the Keplerian frequency of the accretion flow at the inner radius around a Kerr black hole.

Timing analysis of the new black hole candidate MAXI J1803−298 with Insight–HXMT and NICER

ABSTRACT We present the timing analysis results of MAXI J1803−298, a black hole candidate, during its 2021 outburst using data obtained from the Insight–Hard X-ray Modulation Telescope (Insight–HXMT) and the Neutron star Interior Composition Explorer (NICER). Our analysis reveals that the source undergoes a state transition from the low hard state to the hard intermediate state, followed by the soft intermediate state, ultimately reaching the high soft state. We searched for the quasi-periodic oscillations (QPOs) and studied the characteristics of the outburst. At the beginning of the outburst, the source was in the hard state, many type-C QPOs were seen in the Insight–HXMT data, and the frequency of these QPOs increased from ∼0.16 to 2.6 Hz. Our analysis of the rms–frequency relationship of the type-C QPOs indicates a turning point in the frequency. We also analysed the phase lag versus frequency and energy relationship and deduced that the source likely has a high inclination angle, consistent with previous research. The observed rms and phase-lag features in type-C QPOs could be explained by the Lense–Thirring precession model, although alternatives would be still viable. The lag spectrum of type-B QPOs exhibits a U-shaped pattern similar to that of many other sources, and the type-B QPOs’ rms increases as the energy increases. This phenomenon can be explained by the dual-corona model.

Research on effects of the cement and magnesium oxide contents on some characteristics of stabilized dredging soil in Ca Mau province

Using a mixture of cement combined with additives including (fly ash, blast furnace slag and magnesium oxide) to harden dredged silt as a substitute for sand is necessary in construction areas where sand resources are scarce nature. In the study, the mixtures (cement + fly ash + ground blast furnance slag + magnesium oxide) were used to harden mud in brackish and salt water areas in Ca Mau province of the Mekong Delta. The experimental results show that when hardening dredged sludge with content of 6% Cement combined with a mixture of ground blast furnace slag, fly ash and MgO, the viscosity, internal friction angle, adhesive force and compressive strength of the mixture sludge solidification will improve. The higher the ratio of MgO content, the lower the viscosity; the greater the internal friction angle, adhesive force and compressive strength of the hardened sludge. However, in order to balance the design requirements of the sludge after hardening, it was found that: With the rate of 4% fly ash, 2% ground blast furnace slag and 0.5% MgO, the design requirements were met, the quality of the dredging soil after hardening meets the requirements according to TCVN 8217:2009, equivalent to the hard plastic state (0.25 < IL < 0.5, Ctc = 32÷57 kPa and  = 11 ÷ 18°). With such hardening mud quality, it will meet the requirement of replacing sand for embankment, embankment and other works in Ca Mau in particular, and the whole Mekong Delta in general.

“It’s illegal but it’s not, like, really illegal”: Sri Lanka’s ‘sodomy laws’, the politics of equivocation, and queer men’s sexual citizenship in The One Who Loves You So

ABSTRACT This paper explores the representation of queer men’s unequal sexual citizenship in Sri Lanka in a Sri Lankan Anglophone play, focusing on its problematisation of an ambiguous ‘sodomy’ prohibition. I examine The One Who Loves You So (2019), a text in which the illegality of queer men’s offline and online intimacies is paradoxically depicted as both affirmed and open to interpretation. The textual analysis is contextualised by the Sri Lankan state’s consistent history of equivocating on who or what the country’s ‘sodomy laws’ criminalise, particularly when facing international human rights pressure. The state’s equivocation is surprisingly overlooked or dismissed as strategy in most current scholarship and activism: the trend is to think in terms of a hard state stance and a categorical criminalisation. The play lays the ground to grapple with the work done by equivocation, for instance in insidiously regulating same-sex intimacy and marking the conditional status of queer sexual citizenship in Sri Lanka. I plead for attention to the play’s intersectional approach, in particular how queer privilege/disprivilege mediates gradations of empowerment and disempowerment in an uncertain legal situation. The essay argues for moving beyond the idea of strategic evasiveness to recognising a state politics of equivocation on decriminalisation.

A Detailed View of Low-frequency Quasi-periodic Oscillation in the Broadband 0.2–200 keV with Insight-HXMT and NICER

We report the X-ray timing results of the black hole candidate MAXI J1820+070 during its 2018 outburst using the Hard X-ray Modulation Telescope (Insight-HXMT) and Neutron Star Interior Composition Explorer Mission (NICER) observations. Low-frequency quasi-periodic oscillations (LFQPOs) are detected in the low/hard state and the hard intermediate state, which lasted for ∼90 days. Thanks to the large effective area of Insight-HXMT at high energies and NICER at low energies, we are able to present the energy dependence of the LFQPO characteristics and phase lags from 0.2 to 200 keV, which has never been explored by previous missions. We find that the centroid frequency of the LFQPOs does not change significantly with energy, while the full width at half maximum and fractional rms show a complex evolution with energy. The LFQPO phase lags at high energies and low energies show consistent energy-dependence relations taking the ∼2 keV as reference. Our results suggest that the LFQPOs from high energy come from the LT precession of the relativistic jet, while the low-energy radiation is mainly from the perpendicular innermost regions of the accretion disk.

Polarized X-Rays from Windy Accretion in Cygnus X-1

Recent X-ray polarimetric data on the prototypical black hole X-ray binary Cyg X-1 from the Imaging X-ray Polarimetry Explorer present tight constraints on accretion geometry in the hard spectral state. Contrary to general expectations of a low, ≲1% polarization degree (PD), the observed average PD was found to be a factor of 4 higher. Aligned with the jet position angle on the sky, the observed polarization favors geometry of the X-ray emission region stretched normally to the jet in the accretion disk plane. The high PD is, however, difficult to reconcile with the low orbital inclination of the binary i ≈ 30°. We suggest that this puzzle can be explained if the emitting plasma is outflowing with a mildly relativistic velocity ≳0.4 c. Our radiative transfer simulations show that Comptonization in the outflowing medium elongated in the plane of the disk and radiates X-rays with the degree and direction of polarization consistent with observations at i ≈ 30°.

A journey from the hard to the soft state: How do QPOs evolve in the 2021 outburst of GX 339–4?

ABSTRACT We investigated the snapshots of five NICER observations of the black hole transient GX 339–4 when the source transited from the hard state into the soft state during its outburst in 2021. In this paper, we focused our study on the evolution of quasi-periodic oscillations (QPOs) and noise components using power-density spectra. In addition, we derived hardness ratios by comparing count rates above and below 2 keV. The evolution from the hard to the soft state was a somewhat erratic process, showing several transitions between states that are dominated by top-flat noise and can show type-C QPOs; those that are dominated by red noise and can show type-B QPOs. From the parameters that we studied, we only found a strong correlation between the hardness ratio and the type of QPO observed. This implies that the appearance of type-B QPOs is related to a change in the accretion geometry of the system that also reflects in altered spectral properties. We also observed that the type-B QPO forms from or disintegrates into a broad peaked feature when the source comes out of or goes to the hard intermediate state, respectively. This implies some strong decoherence in the process that creates this feature.

Domain wall state diagram for SrTiO3/BaTiO3 superlattice structures

The domain wall structure of ferroelectric/ paraelectric superlattices can be much more complex due to the influence of the superlattice stacking structure, the in-plane strain induced by the substrate and environmental temperature. In this study, we employed a phase field model to investigate the domain wall state of the SrTi[Formula: see text]/BaTi[Formula: see text] superlattice structure. The domain wall thickness for the SrTi[Formula: see text]/BaTi[Formula: see text] layer was measured using a hyperbolic function. Based on the simulation results, here, we show a domain wall state diagram to distinguish the hard and soft domain states. The polarization profiles across hard/ soft domain walls were illustrated and analyzed. Our simulation results offer a useful concept for the control of the domain wall state in the ferroelectric superlattice.

Hydration, mechanical performance and porosity of Portland cement pastes with functionalized nanosilica with APTES

This study reports on the microstructure of Portland cement pastes with nanosilica (NS) and amino-functionalized nanosilica (NSF). For this, NSF dispersion was prepared in a two-phase reaction system, consisting of an aqueous dispersion with dichloromethane, using 3-aminopropyltriethoxysilane (APTES):NS molar ratio 1:28.62. Cement pastes were analyzed in the fresh state by consistency and in the hardness state by compressive strength, conduction calorimetry, X-ray diffraction (XRD), thermal analysis (TGA), infrared spectroscopy (FTIR) and mercury intrusion porosimetry (MIP). It was verified that the functionalized nanoparticles affected the hydration kinetic properties, indicating the extension of the induction period. Through microstructural analysis, it was observed that NSF increased the amount of the main mineralogical phases generated during Portland cement hydration or the pozzolanic reaction. Therefore, the NSF improves the Portland cement hydration and contributes to the densification of the microstructure of the cement pastes at 28 days.

Tracking the Enigmatic Globular Cluster Ultracompact X-Ray Binary X1850–087: Extreme Radio Variability in the Hard State

The conditions under which accreting neutron stars launch radio-emitting jets and/or outflows are still poorly understood. The ultracompact X-ray binary X1850–087, located in the globular cluster NGC 6712, is a persistent atoll-type X-ray source that has previously shown unusual radio-continuum variability. Here we present the results of a pilot radio-monitoring program of X1850–087 undertaken with the Karl G. Jansky Very Large Array, with simultaneous or quasi-simultaneous Swift/XRT data obtained at each epoch. The binary is clearly detected in the radio in two of the six new epochs. When combined with previous data, these results suggest that X1850–087 shows radio emission at a slightly elevated hard-state X-ray luminosity of L X ≳ 2 × 1036 erg s−1, but no radio emission in its baseline hard state L X ∼ 1036 erg s−1. No clear X-ray spectral changes are associated with this factor of ≳10 radio variability. At all detected epochs, X1850–087 has a flat to inverted radio spectral index, more consistent with the partially absorbed optically thick synchrotron of a compact jet rather than the evolving optically thick to thin emission associated with transient expanding synchrotron-emitting ejecta. If the radio emission in X1850–087 is indeed due to a compact jet, then it is plausibly being launched and quenched in the hard state on timescales as short as a few days. Future radio monitoring of X1850–087 could help elucidate the conditions under which compact jets are produced around hard-state accreting neutron stars.

Influence of the WAAM process and design aspects on residual stresses in high-strength structural steels

Wire arc additive manufacturing (WAAM) enables the efficient production of weight-optimized modern engineering structures. Further increases in efficiency can be achieved by using high-strength structural steels. Commercial welding consumables for WAAM are already available on the market. Lack of knowledge and guidelines regarding welding residual stress and component safety during production and operation leads to severely limited use for industry applications. The sensitive microstructure of high-strength steels carries a high risk of cold cracking; therefore, residual stresses play a crucial role. For this reason, the influences of the material, the WAAM process, and the design on the formation of residual stresses and the risk of cold cracking are being investigated. The material used has a yield strength of over 800 MPa. This strength is adjusted via solid solution strengthening and a martensitic phase transformation. The volume expansion associated with martensite formation has a significant influence on the residual stresses. The focus of the present investigation is on the additive welding parameters and component design on their influence on hardness and residual stresses, which are analyzed by means of X-ray diffraction (XRD). Reference specimens (hollow cuboids) are welded fully automated with a systematic variation of heat control and design. Welding parameters and AM geometry are correlated with the resulting microstructure, hardness, and residual stress state. Increased heat input leads to lower tensile residual stresses which causes unfavorable microstructure and mechanical properties. The component design affects heat dissipation conditions and the intensity of restraint during welding and has a significant influence on the residual stress.

X-Ray Spectral Correlations in a Sample of Low-mass Black Hole X-Ray Binaries in the Hard State

The power-law emission and reflection component provide valuable insights into the accretion process around a black hole. In this work, thanks to the broadband spectra coverage of the Nuclear Spectroscopic Telescope Array, we study the spectral properties for a sample of low-mass black hole X-ray binaries (BHXRBs). We find that there is a positive correlation between the photon index Γ and the reflection fraction R (the ratio of the coronal intensity that illuminates the disk to the coronal intensity that reaches the observer), consistent with previous studies, but except for MAXI J1820+070. It is quite interesting that this source also deviates from the well-known “V”-shaped correlation between the photon index Γ and the X-ray luminosity , when it is in the bright hard state. More specifically, the Λ-shaped correlation between Γ and logL X is observed, as the luminosity decreases by a factor of 3 in a narrow range from ∼1038 to 1037.5 erg s−1. Furthermore, we discover a strong positive correlation between R and the X-ray luminosity for BHXRBs in the hard state, which puts a constraint on the disk-corona coupling and the evolution.

Laser surface hardening: A simulative study of tempering mechanisms on hardness and residual stress

Although laser surface hardening of AISI 4140 has been an established process for years, inaccuracies still exist with regards to process prediction, leading to the use of the trial-and-error method for parameter optimization. The proposed FE-simulation model aims to improve the hardness and residual stress prediction of laser surface hardening simulations by regarding tempering effects occurring during the process. The proposed phase-dependent thermal-mechanical FE-simulation is validated by a comparison to experimental data and used for a parameter study analyzing the effects of different initial tempering states and additional post process tempering methods. The results are evaluated regarding changes to the phase fractions, hardness and residual stress states. The implementation of tempering effects showed a 30HV0.1 decrease in hardness for the hardened zone (HZ) due to self-tempering effects and a significant decrease in hardness for the transition zone (TZ) and heat affected zone (HAZ), leading to a local hardness that can be lower than the base material hardness. Modeling tempering mechanisms during laser surface hardening leads to a significant improvement in prediction of the resulting hardness and residual stress states. This enables a simulation based process optimization regarding the initial tempering state as well as additional post process tempering steps.

On the infrared coincidence: What is the jet contribution to the X‐ray power law in GX 339–4?

AbstractThe hard X‐ray power law, prominent in the hard state in black hole X‐ray binaries, is generally due to thermal Comptonization in the corona. Optically thin synchrotron emission from compact jets is commonly seen at infrared wavelengths in the hard state. The extent of this spectrum to higher energies remains uncertain. Here, a multi‐wavelength study of GX 339–4 is presented. The infrared (IR) to X‐ray spectral index is measured and compared to the X‐ray spectral index fitted separately. On some dates in which the jet dominates the IR emission, the X‐ray power law and the IR to X‐ray power‐law spectral indices are both in the range (where ), that is, photon index, . This suggests they could be the same power law with the same origin, or that this is a coincidence. On other dates in the hard state, , ruling out a common origin. It is likely that Comptonization dominates on most dates, as expected. However, the X‐ray power law never appears to be fainter than the jet power law extrapolated from IR to X‐ray, implying that the jet contribution imposes a lower limit to the X‐ray flux. If confirmed, this would imply the cooling break in the synchrotron spectrum probably resides at X‐ray or higher energies. It is suggested that X‐ray spectral fitting should include an extra power law with a break (ideally fit to IR too).

Broad-band X-ray properties of black holes GRS 1758−258 and 1E 1740.7−2942: AstroSat and NuSTAR results

ABSTRACT We present the results on broad-band X-ray properties of persistent black hole binaries GRS 1758−258 and 1E 1740.7−2942 using AstroSat, NuSTAR, and Swift–XRT observations carried out during 2016–2022. We perform spectral modelling of both sources after eliminating the contamination in their LAXPC spectra from nearby X-ray sources. Preliminary spectral modelling using Comptonization and line emission (∼6.4 keV) models suggest that GRS 1758−258 occupies both dim-soft state (kTbb = 0.37 ± 0.01 keV, Γ ∼ 5.9, $L_{bol}=1{{\ \rm per\ cent}}$ of Eddington luminosity LEdd) and hard state (Γ = 1.64–2.22, kTe = 4–45 keV, Lbol = 1–5 per cent LEdd) that requires a multicolour disc blackbody model (kTin = 0.54 ± 0.01 keV) occasionally. 1E 1740.7−2942 instead is found only in hard state (Γ = 1.67–2.32, kTe = 5–16 keV, Lbol = 1–2 per cent LEdd). Reflection properties of both sources are studied by applying relativistic reflection model RELXILL to the broad-band spectra. Our results from AstroSat and NuSTAR consistently unveiled the presence of a Comptonizing region along with an ionized reflection region (ionization parameter log ξ = 2.7–3.8 and 2.7–4.7 erg cm s−1 in GRS 1758−258 and 1E 1740.7−2942, respectively) in both sources. Reflection modelling revealed GRS 1758−258 to have a high metal abundance ($A_{fe}=3.9^{+0.4}_{-0.3}$ times solar metal abundance) and inclination angle (i) of 61 ± 2°. In case of 1E 1740.7−2942, i is constrained to be 55 ± 1°. Finally, we discuss the implication of our findings in the context of accretion dynamics by comparing our results with the previous studies.