Flux State Research Articles

Distribution of flux states in a hysteretic dc SQUID

Abstract This work investigates the distribution of flux states of hysteretic dc superconducting quantum interference devices (SQUIDs) obtained from standard current ramp measurement at 2.50 K and 0.35 K. Each flux state corresponds to a specific number of flux quanta trapped in the superconducting loop, associated with a metastable state in the two-dimensional potential energy of the hysteretic SQUID. The flux states can be distinguished by the multiple switching currents. The observed distribution is different from the distribution caused only by thermal excitation at a specific temperature. It shows good agreement with a quasi-Boltzmann distribution with multiple different inverse temperatures, dependent on the bottom energy of the potential wells and featuring a short equilibrium time. The standard Boltzmann distribution is insufficient to accurately describe the observed results. The finding suggests that the observed distribution of flux states is established during the SQUID’s transition from the dissipative state to the zero-voltage state, and multiple equivalent temperatures may be involved in the process.

Constraining γ-ray dissipation site in gravitationally lensed quasar - PKS 1830−211

Abstract Variable γ-ray flares upto minute timescales reflect extreme particle acceleration sites. However, for high-redshift blazars, the detection of such rapid variations remains limited by current telescope sensitivities. Gravitationally lensed blazars serve as powerful tools to probe γ-ray production zones in distant sources, with time delays between lensed signals providing crucial insights into the spatial distribution of emission regions relative to the lens’s mass-weighted center. We have utilized 15 years of Fermi-LAT γ-ray data from direction of PKS 1830−211 to understand the origin of flaring high-energy production zone at varying flux states. To efficiently estimate the (lensed) time delay, we used a machine learning-based tool - the Gaussian Process regression algorithm, in addition to - Autocorrelation function and Double power spectrum. We found a consistent time delay across all flaring activity states, indicating a similar location for the γ-ray emission zone, possibly within the radio core. The estimated time delay of approximately 20 days for the five flaring epochs was significantly shorter than previously estimated radio delays. This suggests that the γ-ray emission zone is closer to the central engine, in contrast to the radio emission zone, which is expected to be much farther away. A linear relationship between lag and magnification has been observed in the identified source and echo flares. Our results suggest that the γ-ray emission zone originates from similar regions away from the site of radio dissipation.

Gas Dynamics in 3 “Dippers”: EPIC 203850058, EPIC 204638512, and EPIC 205151387 in 2017–2018

Abstract We have examined variability of the three dipper stars—EPIC 203850058, EPIC 204638512, and EPIC 205151387—using the SpeX spectrograph on NASA’s Infrared Telescope facility on two nights in 2018. We combined these data with those previously published from 2017. In EPIC 204638512, the He i line was in absorption, but blueshifted in wavelength on all 4 nights, indicating outflowing gas near the disk surface. In EPIC 203850058, no net emission is seen in 2018, but in 2017 it had an absorption core that was degraded to longer wavelengths, suggesting inflowing gas. In EPIC 205151387 the He i line went from emission in the spectrum with the least extinction by dust (highest flux state), became an inverse P Cygni profile, indicating inflowing gas as the extinction increased, and finally to pure absorption when the extinction was greatest.

Insights into the Long-term Flaring Events of Blazar PKS 0805-07: A Multiwavelength Analysis Over the Period of 2009–2023

We conducted a comprehensive temporal and spectral study of the FSRQ PKS 0805-07 by using broadband observations from the Fermi-LAT and Swift-XRT/UVOT instruments over the period of MJD 54684-60264. The 3 day binned γ-ray light curve during the active state revealed 11 distinct peak structures with the maximum integral flux (E > 100 MeV) reached (1.56 ± 0.16) × 10−6 photons cm−2 s−1 on MJD 59904.5. The shortest observed γ-ray variability was 2.80 ± 0.77 days. A correlation analysis between the γ-ray spectral index and flux indicated the typical trend of hardening when the source is brighter, commonly observed in blazars. We identified a lag of 121 (+27.21, −3.51) days in the spectral index relative to the flux, within the time interval MJD 59582 to 60112. The Anderson–Darling test and histogram fit rejected the normality of the γ-ray flux distribution and instead suggested a log-normal distribution. To gain insight into the underlying physical processes, we extracted broadband spectra from different time periods in the light curve. The spectral energy distribution during various flux states was well-reproduced using synchrotron, synchrotron-self-Compton, and external-Compton emissions from a broken power-law electron distribution. The seed photons required for the external Compton process are from the IR region. A comparison of the best-fit physical parameters indicated that the variations in different flux states were primarily associated with an increase in the bulk Lorentz factor and magnetic field from low to high flux states.

Superconducting memory and trapped magnetic flux in ternary lanthanum polyhydrides

Superconducting memory is a promising technology for data storage because of its speed, high energy efficiency, non-volatility, and compatibility with quantum computing devices. However, the need for cryogenic temperatures renders superconducting memory an extremely expensive and specialized device. Ternary lanthanum polyhydrides, due to their high critical temperatures of 240–250 K, represent a convenient platform for studying effects associated with superconductivity in disordered granular systems. In this work, we investigate trapped magnetic flux and memory effects in recently discovered lanthanum-neodymium (La,Nd)H10 and lanthanum-scandium (La,Sc)H12 superhydrides at a pressure of 175–196 GPa. We use a steady magnetic field of a few Tesla (T) and strong pulsed fields up to 68 T to create the trapped flux state in the compressed superhydrides. We find a clockwise hysteresis of magnetoresistance in cerium CeH9-10 and lanthanum-cerium (La,Ce)H10+x polyhydrides, a characteristic feature of granular superconductors. A study of the current-voltage characteristics and voltage-temperature curves of the samples with trapped magnetic flux indicates a significant memory effect in La-Sc polyhydrides already at 225–230 K.

An X-ray flaring event and a variable soft X-ray excess in the Seyfert LCRS B040659.9–385922 as detected with eROSITA

Context. Extreme continuum variability in extragalactic nuclear sources can indicate extreme changes in accretion flows onto supermassive black holes. Aims. We explore the multiwavelength nature of a continuum flare in the Seyfert LCRS B040659.9−385922. The all-sky X-ray surveys conducted by the Spectrum Roentgen Gamma (SRG)/extended ROentgen Survey with an Imaging Telescope Array (eROSITA) showed that its X-ray flux increased by a factor of roughly five over six months, and concurrent optical photometric monitoring with the Asteroid Terrestrial-impact Last Alert System (ATLAS) showed a simultaneous increase. Methods. We complemented the eROSITA and ATLAS data by triggering a multiwavelength follow-up monitoring program (X-ray Multi-Mirror Mission: XMM-Newton, Neutron star Interior Composition Explorer: NICER; optical spectroscopy) to study the evolution of the accretion disk, broad-line region, and X-ray corona. During the campaign, X-ray and optical continuum flux subsided over roughly six months. Our campaign includes two XMM-Newton observations, one taken near the peak of this flare and the other taken when the flare had subsided. Results. The soft X-ray excess in both XMM-Newton observations was power law-like (distinctly nonthermal). Using a simple power law, we observed that the photon index of the soft excess varies from a steep value of Γ ∼ 2.7 at the flare peak to a relatively flatter value of Γ ∼ 2.2 as the flare subsided. We successfully modeled the broadband optical/UV/X-ray spectral energy distribution at both the flare peak and post-flare times with the AGNSED model, incorporating thermal disk emission into the optical/UV and warm thermal Comptonization in the soft X-rays. The accretion rate falls by roughly 2.5, and the radius of the hot Comptonizing region increases from the flaring state to the post-flare state. Additionally, from the optical spectral observations, we find that the broad He IIλ4686 emission line fades significantly as the optical/UV/X-ray continuum fades, which could indicate a substantial flare of disk emission above 54 eV. We also observed a redshifted broad component in the Hβ emission line that is present during the high flux state of the source and disappears in subsequent observations. Conclusions. A sudden strong increase in the local accretion rate in this source manifested itself via an increase in accretion disk emission and in thermal Comptonized emission in the soft X-rays, which subsequently faded. The redshifted broad Balmer component could be associated with a transient kinematic component distinct from that comprising the rest of the broad-line region.

Probing broadband spectral energy distribution and variability of Mrk 501 in the low flux state

We conducted a multi-wavelength analysis of the blazar Mrk501, utilizing observations from AstroSat (SXT, LAXPC), Swift-UVOT, and Fermi-LAT during the period August 15, 2016 to March 27, 2022. The resulting multi-wavelength light curve revealed relatively low activity of the source across the electromagnetic spectrum. Notably, logparabola and broken power-law models provided a better fit to the joint X-ray spectra from AstroSat-SXT/LAXPC instruments compared to the power-law model. During the low activity state, the source showed the characteristic “harder when brighter” trend at the X-ray energies. To gain insights into underlying physical processes responsible for the broadband emission, we performed a detailed broadband spectral analysis using the convolved one-zone leptonic model with different forms of particle distributions such as logparabola (LP), broken power-law (BPL), power-law model with maximum energy (ξmax), and energy-dependent acceleration (EDA) models. Our analysis revealed similar reduced-χ2 values for the four particle distributions. The LP and EDA models exhibited the lowest jet powers. The correlation analyses conducted for the LP and BPL models revealed that there is a positive correlation between jet power and bulk Lorentz factor. Specifically, in the LP model, jet power proved independent of γmin, whereas in the broken power-law model, jet power decreased with an increase in γmin. The jet power in the LP/EDA particle distribution is nearly 10 percent of the Eddington luminosity of a 107 M⊙ black hole. This result suggests that the jet could potentially be fueled by accretion processes.

A second view on the X-ray polarization of NGC 4151 with IXPE

We report on the second observing program of the active galactic nucleus NGC 4151 with simultaneous Imaging X-ray Polarimetry Explorer (IXPE; 750 ks), NuSTAR (∼60 ks), XMM-Newton (∼75 ks), and NICER (∼65 ks) pointings. NGC 4151 is the first Type-1 radio-quiet Seyfert galaxy with constrained polarization properties for the X-ray corona. Despite the lower flux state in which the source was re-observed and the resulting higher contribution of the constant reflection component in the IXPE energy band, our results are in agreement with the first detection. From polarimetric analysis, a polarization degree Π = 4.7 ± 1.3% and polarization angle Ψ = 77° ± 8° east of north (68% c.l.) were derived in the 2.0–8.0 keV energy range. Combining the two observations leads to polarization properties that are more constrained than those of the individual detections, showing Π = 4.5 ± 0.9% and Ψ = 81° ± 6° (with a detection significance of ∼4.6σ). The observed polarization angle aligns very well with the radio emission in this source, supporting, together with the significant polarization degree, a slab or wedge geometry for the X-ray corona. However, a switch in the polarization angle at low energies (37° ±7° in the 2–3.5 keV bin) suggests the presence of another component. When it is included in the spectro-polarimetric fit, a high polarization degree disfavors an interpretation in terms of a leakage through the absorbers, instead pointing to scattering from some kind of mirror.

Stability limits of flux states in two-band superconductor rings

Stability limits of flux states in two-band superconductor rings

The Remarkable X-Ray Spectra and Variability of the Ultraluminous Weak-line Quasar SDSS J1521+5202

We present a focused X-ray and multiwavelength study of the ultraluminous weak-line quasar (WLQ) SDSS J1521+5202, one of the few X-ray weak WLQs that is amenable to basic X-ray spectral and variability investigations. J1521+5202 shows striking X-ray variability during 2006–2023, by up to a factor of ≈32 in 0.5–2 keV flux, and our new 2023 Chandra observation caught it in its brightest X-ray flux state to date. Concurrent infrared/optical observations show only mild variability. The 2023 Chandra spectrum can be acceptably described by a power law with intrinsic X-ray absorption, and it reveals a nominal intrinsic level of X-ray emission relative to its optical/ultraviolet emission. In contrast, an earlier Chandra spectrum from 2013 shows apparent spectral complexity that is not well fit by a variety of models, including ionized absorption or standard Compton-reflection models. Overall, the observations are consistent with the thick-disk plus outflow model previously advanced for WLQs, where a nominal level of underlying X-ray emission plus variable absorption leads to the remarkable observed X-ray variability. In the case of J1521+5202, it appears likely that the outflow, and not the thick disk itself, lies along our line of sight and causes the X-ray absorption.

Shoreline and land use–land cover changes along the 2004-tsunami-affected South Andaman coast: understanding changing hazard susceptibility

Abstract. The 2004 tsunami affected the South Andaman coast, causing it to experience dynamic changes in the coastal geomorphology and making the region vulnerable. We focus on pre-and post-tsunami shoreline and land use–land cover changes from 2004, 2005, and 2022 to analyze the dynamic change in hazard. We used General Bathymetric Chart of the Ocean (GEBCO) data to calculate run-up [m], arrival times [min], and inundation [m] at a few locations using three tsunamigenic earthquake source parameters, namely the 2004 Sumatra, 1941 North Andaman, and 1881 Car Nicobar earthquakes. The Digital Shoreline Analysis System is used for the shoreline change estimates. Landsat data are used to calculate shoreline and land use–land cover (LULC) change in five classes, namely built-up areas, forests, inundation areas, croplands, and water bodies during the above period. We examine the correlation between the LULC changes and the dynamic change in shoreline due to population flux, infrastructural growth, and gross state domestic product growth. The Indian industry estimates the Andaman and Nicobar Islands losses exceeded INR 10 billion during 2004, which would today see a 5-fold increase in economic loss due to a doubling of built-up area, a 3-fold increase in tourist inflow, and population density growth. The unsustainable decline in the forest cover, mangroves, and cropland would affect sustainability during a disaster despite coastal safety measures.

Broad-Band X-Ray Analysis of NGC 3227

Abstract Previously in Project A we carried out analysis of the data obtained by observations of the 1.5 Seyfert galaxy NGC 3227—the two observations performed by XMM-Newton in 2000 and 2006 and six observations by Suzaku in 2008. In the current paper, Project B, our work was extended to joint XMM-Newton and NuSTAR observations in 2016 as well as a NuSTAR observation in 2017. In Project A a unified model was constructed. The model consists of a hard power law ($\Gamma _{\mathrm{ Hard}}=1.4{\!-\!}1.7$) which is interpreted as the Comptonized emission from the corona above an accretion disk. In the high flux states an additional soft excess component dominates, which is consistent with either a power law ($\Gamma _{\mathrm{ Soft}}=3.3{\!-\!}3.85$) or warm Comptonization. These emissions are absorbed by a partially covering material and warm absorbers. A reflection component and several emission lines are also present. In Project B, the model presented in Project A was applied to more recent observations. It was found that this model remains valid. Our conclusion is that this model is consistent, valid with the long observations from 2000 to 2017 and over the broad frequency band from 0.3 keV to 50 keV.

Dynamic control of divertor heat flux during n = 4 resonant magnetic perturbation edge localized mode suppression by small variation of q 95 in EAST

Experiments at EAST demonstrate effective modulation of the stationary heat flux to the secondary lobes of the magnetic footprint induced by the resonant magnetic perturbations (RMPs) by slightly varying the equilibrium q 95, consistent with prior numerical modeling. During the small q 95 variation, the edge localized mode control is well maintained, and the position of the secondary heat flux peak is effectively shifted, thus avoiding a specific location heat flux accumulation. As the divertor heat load is one of the significant concerns in tokamaks, these results provide a promising choice, varying magnetic equilibrium periodically to shift stationary heat load deposition position during static n = 4 (n is the toroidal mode number) RMP condition, for further fusion devices. In this respect, the use of this technique for n = 4 RMPs is advantageous because the q 95 range that needs to be covered to spread the divertor heat load is reduced due to the smaller toroidal extent of the off-separatrix heat deposition zones compared to lower n’s.

Long Term X-Ray Spectral Variations of the Seyfert-1 Galaxy Mrk 279

We present the results from a long term X-ray analysis of Mrk 279 during the period 2018–2020. We use data from multiple missions – AstroSat, NuSTAR and XMM-Newton, for the purpose. The X-ray spectrum can be modeled as a double Comptonization along with the presence of neutral Fe Kα line emission, at all epochs. We determined the source’s X-ray flux and luminosity at these different epochs. We find significant variations in the source’s flux state. We also investigate the variations in the source’s spectral components during the observation period. We find that the photon index and hence the spectral shape follow the variations only over longer time periods. We probe the correlations between fluxes of different bands and their photon indices, and found no significant correlations between the parameters.

On the Connection between the Repeated X-Ray Quasiperiodic Oscillation and Warm Absorber in the Active Galaxy RE J1034+396

We conduct an in-depth spectral analysis of ∼1 Ms XMM-Newton data of the narrow line Seyfert 1 galaxy RE J1034+396. The long exposure ensures high spectral quality and provides us with a detailed look at the intrinsic absorption and emission features toward this target. Two warm-absorber (WA) components with different ionization states ( log(ξ/ergcms−1)∼4 and log(ξ/ergcms−1)∼2.5–3 ) are required to explain the intrinsic absorption features in the Reflection Grating Spectrometer spectra. The estimated outflow velocities are around −1400 km s−1 and −(100–300) km s−1 for the high- and low-ionization WA components, respectively. Both absorbers are located beyond the broad-line region and cannot significantly affect the host environment. We analyze the warm absorbers in different flux states. We also examine the 2007 May observation in the low and high phases of quasiperiodic oscillation (QPO). In contrast to previous analyses showing a negative correlation between the high-ionization WA and the QPO phase, we have found no such variation in this WA component. We discover a broad emission bump in the spectral range of ∼12–18 Å, covering the primary features of the high-ionization WA. This emission bump shows a dramatic change in different source states, and its intensity may positively correlate with the QPO phase. The absence of this emission bump in previous work may contribute to the suggested WA–QPO connection.

Synthesis of lead-free piezoelectric potassium sodium niobates for the preparation of anti-fouling KNN porous membrane

Potassium sodium niobates (KNNs) have garnered significant attention owing to their lead-free nature and potential for use in self-cleaning membranes. This paper presents the synthesis of (K0.5Na0.5)NbO3 materials for the fabrication of porous membranes, which enable in situ ultrasonic resonance to effectively eliminate contaminants from the membrane surface. KNN powder was synthesized via solid-state reactions, and the membranes were prepared using conventional sintering techniques. The effects of ball-milling time and calcination temperature on the phase structure, pore size, permeance, flexural strength, chemical stability, and piezoelectric properties were comprehensively investigated. The optimal membranes exhibited an average pore size of approximately 300 nm, a porosity of 23 %, and permeance of 220 L m−2 h−1 bar−1 at a sintering temperature of 1050 °C. A polarized electrical field with a strength of 1 kV/mm was applied to the membranes, resulting in an ultrasonic response of 20 mV at an excitation voltage of 20 V with a frequency of 200 kHz. Furthermore, the in situ anti-fouling performance was evaluated by conducting filtration tests on a 500 ppm oil-in-water (O/W) emulsion, demonstrating that the stationary flux increased by 46.7 % when subjected to an excitation voltage of 60 V.

Numerical investigation of jet impingement on flat/concave cooling of CO2 with different phase states under high heat flux

The thermal load and high temperature brought by the increase in power of electronic devices or the increase in speed of supersonic aircraft limit the respective development. In this paper, a numerical model of CO2 jet impingement cooling of a constant heat flux plate/concave surface in different phase states was established. Secondly, the non-equilibrium phase transition and the real-thermophysical properties of CO2 was considered. The effects of different wall heat flux (0.7 MW/m2 ∼ 6.5 MW/m2) and initial phase states on the impact cooling performance of CO2 jet were studied.It is found that for SCO2 jet impingement, when the inlet temperature is lower than the pseudo-critical temperature, the heat transfer coefficient increases with the increase of inlet pressure, and the maximum increase is 24.7 %. For near-critical liquid CO2 (LCO2) jet impingement, low latent heat prevents temperature overshoot in the heat flux range studied. With the increase of the proportion of dry ice in the inlet, the heat transfer coefficient also increases. When q > 3 MW/m2, the heat transfer coefficient of dry ice jet impact is 2.5 ∼ 3 times and 1 ∼ 1.4 times of that of SCO2 and near-critical LCO2 jet impingement for the flat plate model, respectively. For concave surface with high heat flux, near-critical LCO2 jet impingement cooling effect is relatively good. In addition, concave surface will aggravate the uneven cooling surface temperature.The results can provide more references for the CO2 jet impingement technology in the design of stagnation cooling system of supersonic aircraft and thermal management of high-power electronic devices.

Gamma-ray variability and multi-wavelength insights into the unprecedented outburst from 4C 31.03

The blazar 4C31.03 recently underwent a major γ-ray outburst at the beginning of 2023 after a prolonged quiescent phase. Fermi-LAT reported a daily average flux of 5×10−6 phs cm−2 s−1, which is about 60 times its average value. We investigated this extraordinary outbreak through temporal and multi-wavelength analysis. From the statistical analysis of the γ-ray lightcurves using Bayesian blocks, we identified 3 epochs of prominent flares. The fastest flux decay during this major outburst was observed within 5.5±0.7 hours. The highest energy of γ-ray photons found from the source during the active phase is ∼82GeV. Using the transparency of γ-rays against pair production and light crossing time argument, we could obtain the minimum jet Doppler factor as 17 corresponding to the flaring state. The broadband spectral energy distribution study performed using synchrotron, SSC and EC emission processes supports the external Compton scattering of IR photons as the likely mechanism for the γ-ray emission from the source. The results of this study support the scenario of the emission region in 4C31.03, being located beyond the Broad line region from the central blackhole. The long-term γ-ray flux distribution depicts a double log-normal variability, indicating that two distinct flux states are active in this energy band. The index distribution also reveals a two distinct variability pattern and hints that the γ-ray spectrum can be more precisely described by two photon indices.

Effects of non-continuous inverse Compton cooling in blazars

Blazar flares provide a window onto the extreme physical processes occurring in relativistic outflows. Most numerical codes used for modelling blazar emission during flares use a simplified continuous-loss description of particle cooling due to the inverse Compton (IC) process, neglecting non-continuous (discrete) effects that arise in the Klein-Nishina (KN) regime. The significance of such effects has not yet been explored in detail. In this study, we investigate the importance of non-continuous Compton cooling losses and their impact on the electron spectrum and spectral energy distribution (SED) of blazars during high flux states (flares), as well as in the low state. We solve the full transport equation numerically, accounting for large relative jumps in energy by extending our existing blazar flare modelling code EMBLEM. We perform a detailed physical modelling of the brightest gamma -ray flare of the archetypal flat-spectrum radio quasar (FSRQ) 3C\,279 detected in June 2015. We then compare results obtained using the full cooling term and using the continuous-loss approximation. We show that during flaring states of FSRQs characterised by high Compton dominance, the non-continuous cooling can lead to significant modification of the electron spectrum, introducing a range of distinct features, such as low-energy tails, hardening and/or softening, narrow and extended particle excesses, and shifts in the cooling break position . Such distortion translates to differences in the associated SED of up to sim 50<!PCT!>. This highlights the importance of non-continuous effects and the need to consider them in blazar emission models, particularly applied to extreme gamma -ray flares.

Comparison of the Climatic Characteristics of Ozone Valley Over the Tibetan Plateau and the Rocky Mountains

AbstractThis study compares the ozone valleys over the Tibetan Plateau (TP) and the Rocky Mountains (RM) using the ERA5 reanalysis data set. The dynamical transport of the ozone over these two regions is analyzed using the Lorenz circulation decomposition method. The ozone content valley over TP is observed around 200–50 hPa (upper troposphere and lower stratosphere, or UTLS), and that over RM is around 300–100 hPa. It is shown that the TP ozone content is smaller than that over RM. By analyzing the spatiotemporal distribution of the ozone content and the general circulation, the anticyclone over Southern Asian (SAH) plays a significant role in existence of the TP ozone valley, and the ozone content flux reaches its maximum in July. Large‐scale terrain and related general circulation determine the ozone valley appearance. Further analysis suggests that stationary transport has a larger impact on the ozone valley formation than the transient transport. The transport by the zonal circulation nearly cancels out most of that by the meridional circulation, due to the fact that the zonal transport magnitude is nearly equal to the meridional transport. The transport center over the RM is much weaker than that over the TP. Furthermore, the contrasts between transient and stationary transports are less evident over RM than over TP. The eddy‐driven stationary ozone transport flux significantly impacts the development of the two low ozone centers across these large terrains.