Soft X-ray Flux Research Articles

Two Successive Type II Radio Bursts Associated With B-Class Flares and Slow CMEs

From 2018 Oct 12 to 13, three successive solar eruptions (E1--E3) with B-class flares and poor white light coronal mass ejections (CMEs) occurred from the same active region NOAA AR 12724. Interestingly, the first two eruptions are associated with Type II radio bursts but the third is not. Using the soft X-ray flux data, radio dynamic spectra and dual perspective EUV intensity images, we comparatively investigate the three events. Our results show that their relevant flares are weak (B2.1, B7.9 and B2.3) and short-lived (13, 9 and 14 minutes). The main eruption directions of E1 and E2 are along $\sim$45$^\circ$ north of their radial directions, while E3 primarily propagated along the radial direction. In the EUV channels, the early speeds of the first two CMEs have apparent speeds of $\sim$320 km s$^{-1}$ and $\sim$380 km s$^{-1}$, which could exceed their respective local Alfv$\acute{e}$n speeds of $\sim$300 km s$^{-1}$ and $\sim$350 km s$^{-1}$. However, the CME in the third eruption possesses a much lower speed of $\sim$160 km s$^{-1}$. These results suggest that the observed Type II radio bursts in the eruptions E1 and E2 are likely triggered by their associated CMEs and the direction of eruption and the ambient plasma and magnetic environments may take an important place in producing Type II radio burst or shock as well.

The unusual behavior of the young X-ray pulsar SXP 1062 during the 2019 outburst

We present the results of the first dedicated observation of the young X-ray pulsar SXP 1062 in the broad X-ray energy band obtained during its 2019 outburst with the NuSTAR and XMM-Newton observatories. The analysis of the pulse-phase averaged and phase-resolved spectra in the energy band from 0.5 to 70 keV did not reveal any evidence for the presence of a cyclotron line. The spin period of the pulsar was found to have decreased to 979.48 ± 0.06 s implying a ∼10% reduction compared to the last measured period during the monitoring campaign conducted about five years ago, and is puzzling considering that the system apparently has not shown major outbursts ever since. The switch of the pulsar to the spin-up regime supports the common assumption that torques acting on the accreting neutron star are nearly balanced and thus SXP 1062 likely also spins with a period close to the equilibrium value for this system. The current monitoring of the source also revealed a sharp drop in its soft X-ray flux right after the outburst, which is in drastic contrast to the behavior during the previous outburst when the pulsar remained observable for years with only a minor flux decrease after the end of the outburst. This unexpected off state of the source lasted for at most 20 days after which SXP 1062 returned to the level observed during previous campaigns. We discuss this and other findings in context of the modern models of accretion onto strongly magnetized neutron stars.

Sunquakes of Solar Cycle 24

Abstract The paper presents results of a search for helioseismic events (sunquakes) produced by M-X class solar flares during Solar Cycle 24. The search is performed by analyzing photospheric Dopplergrams from the Helioseismic Magnetic Imager. Among the total number of 500 M-X class flares, 94 helioseismic events were detected. Our analysis has shown that many strong sunquakes were produced by solar flares of low M class (M1–M5), while in some powerful X-class flares helioseismic waves were not observed or were weak. Our study has also revealed that only several active regions were characterized by the most efficient generation of helioseismic waves during flares. We found that the sunquake power correlates with the maximum value of the soft X-ray flux time derivative better than with the X-ray class, indicating that the sunquake mechanism is associated with high-energy particles. We also show that the seismically active flares are more impulsive than the flares without helioseismic perturbations. We present a new catalog of helioseismic solar flares, which opens opportunities for performing statistical studies to better understand the physics of sunquakes as well as the flare-energy release and transport.

Characterisation of flare Soft X-ray distribution with solar magnetic activity

We analyse the 0.1 — 0.8 nm solar soft X-ray flux catalogue from Geostationary Operational Environmental Satellites (GOES), managed by NASA/NOAA, between September 1978 and September 2017, in order to investigate the possible role of solar activity and solar cycle epoch on the distribution of soft X-ray peak fluxes. We concentrate our attention on the last three solar cycles because solar activity proxies seem to indicate a decrease in the magnetic activity of our star. We know that flare soft X-ray peak fluxes are characterised by a power-law distribution with an index α ≃ 2 that shows a minor dependence on solar cycle. More in detail, we study the dependence of the power-law parameters during each single solar cycle (cycles 21-24) and during different regimes of solar activity defined using three different proxies: i) Sunspot Number (SSN), ii) Mg II core-to-wing ratio (Mg II Index), and iii) solar radio flux at 10.7 cm or 2800 MHz (F10.7). The power-law estimation analysis is performed in maximum likelihood estimation (MLE) fitting method with goodness-of-fit based on Kolmogorv- Smirnov test. Preliminary results indicate that the power-law index shows a slight decrease as solar activity decreases. This except for the F10.7 proxy. More in-depth statistical analysis is necessary to confirm our findings. A post-publication change was made to this article on 22 Jun 2020 to correct the webpage title to match the pdf.

The Composite X-Ray Spectrum of 3CRR Quasars

Abstract The reason for the difference between the composite X-ray spectrum for radio-loud quasars (RLQs) versus radio-quiet quasars (RQQs) is still unclear. To study this difference, we built a new composite X-ray spectrum of RLQs using Chandra X-ray data and Sloan Digital Sky Survey optical data for the sample of 3CRR quasars. We find the X-ray spectra of all 3CRR quasars, except for 3C 351, have no soft X-ray excess and can be fitted well with an absorbed power-law model. Our composite X-ray spectrum is similar to that of Shang et al. for RLQs, showing higher hard X-ray and lower soft X-ray flux than the composite X-ray spectrum of RQQs. Most blazar-like 3CRR quasars have higher X-ray flux than the median composite X-ray spectrum, which could be related to the contribution of beamed jet emission at X-ray band. From the literature, we find that nineteen 3CRR quasars have extended X-ray emission related to radio jets, indicating the inevitable contribution of jets at X-ray band. In contrast to RQQs, the X-ray photon index of 3CRR quasars does not correlate with the Eddington ratio. Our results suggest that the jet emission at X-ray band in RLQs could be related to the difference in composite X-ray spectrum between RLQs and RQQs.

Fast degradation of the circular flare ribbon on 2014 August 24

Context. The separation and elongation motions of solar flare ribbons have extensively been investigated. The degradation and disappearance of ribbons have rarely been explored. Aims. We report our multiwavelength observations of a C5.5 circular-ribbon flare associated with two jets (jet1 and jet2) on 2014 August 24, focusing on the fast degradation of the outer circular ribbon (CR). Methods. The flare was observed in ultraviolet (UV) and extreme-ultraviolet (EUV) wavelengths by the Atmospheric Imaging Assembly (AIA) on board the Solar Dynamics Observatory spacecraft. Soft X-ray fluxes of the flare in 0.5−4 and 1−8 Å were recorded by the GOES spacecraft. Results. The flare, consisting of a short inner ribbon (IR) and outer CR, was triggered by the eruption of a minifilament. The brightness of IR and outer CR reached their maxima simultaneously at ∼04:58 UT in all AIA wavelengths. Subsequently, the short eastern part of the CR faded out quickly in 1600 Å but only gradually in EUV wavelengths. The long western part of the CR degraded in the counterclockwise direction and decelerated. The degradation was distinctly divided into two phases: phase I with faster apparent speeds (58−69 km s−1), and phase II with slower apparent speeds (29−35 km s−1). The second phase stopped at ∼05:10 UT when the western CR disappeared entirely. In addition to the outward propagation of jet1, the jet spire experienced untwisting motion in the counterclockwise direction during 04:55−05:00 UT. Conclusions. We conclude that the event can be explained by the breakout jet model. The coherent brightenings of the IR and CR at ∼04:58 UT may result from the impulsive interchange reconnection near the null point, whereas sub-Alfvénic slipping motion of the western CR in the counterclockwise direction indicates the occurrence of slipping magnetic reconnection. Another possible explanation of the quick disappearance of the hot loops that are connected to the western CR is that they are simply reconnected sequentially without the need for significant slippage after the null-point reconnection.

Regulation of accretion by its outflow in a symbiotic star: the 2016 outflow fast state of MWC 560

ABSTRACT How are accretion discs affected by their outflows? To address this question for white dwarfs accreting from cool giants, we performed optical, radio, X-ray, and ultraviolet observations of the outflow-driving symbiotic star MWC 560 (≡V694 Mon) during its 2016 optical high state. We tracked multi-wavelength changes that signalled an abrupt increase in outflow power at the initiation of a months-long outflow fast state, just as the optical flux peaked: (1) an abrupt doubling of Balmer absorption velocities; (2) the onset of a 20 μJy per month increase in radio flux; and (3) an order-of-magnitude increase in soft X-ray flux. Juxtaposing to prior X-ray observations and their coeval optical spectra, we infer that both high-velocity and low-velocity optical outflow components must be simultaneously present to yield a large soft X-ray flux, which may originate in shocks where these fast and slow absorbers collide. Our optical and ultraviolet spectra indicate that the broad absorption-line gas was fast, stable, and dense (≳106.5 cm−3) throughout the 2016 outflow fast state, steadily feeding a lower density (≲105.5 cm−3) region of radio-emitting gas. Persistent optical and ultraviolet flickering indicate that the accretion disc remained intact. The stability of these properties in 2016 contrasts to their instability during MWC 560’s 1990 outburst, even though the disc reached a similar accretion rate. We propose that the self-regulatory effect of a steady fast outflow from the disc in 2016 prevented a catastrophic ejection of the inner disc. This behaviour in a symbiotic binary resembles disc/outflow relationships governing accretion state changes in X-ray binaries.

The long-term enhanced brightness of the magnetar 1E 1547.0–5408

We present the evolution of the X-ray emission properties of the magnetar 1E 1547.0–5408 since February 2004 over a time period covering three outbursts. We analyzed new and archival observations taken with the Swift, NuSTAR, Chandra, and XMM–Newton X-ray satellites. The source has been observed at a relatively steady soft X-ray flux of ≈10−11 erg cm−2 s−1 (0.3–10 keV) over the last 9 years, which is about an order of magnitude fainter than the flux at the peak of the last outburst in 2009, but a factor of ∼30 larger than the level in 2006. The broad-band spectrum extracted from two recent NuSTAR observations in April 2016 and February 2019 showed a faint hard X-ray emission up to ∼70 keV. Its spectrum is adequately described by a flat power law component, and its flux is ∼7 × 10−12 erg cm−2 s−1 (10–70 keV), that is a factor of ∼20 smaller than at the peak of the 2009 outburst. The hard X-ray spectral shape has flattened significantly in time, which is at variance with the overall cooling trend of the soft X-ray component. The pulse profile extracted from these NuSTAR pointings displays variability in shape and amplitude with energy (up to ≈25 keV). Our analysis shows that the flux of 1E 1547.0–5408 is not yet decaying to the 2006 level and that the source has been lingering in a stable, high-intensity state for several years. This might suggest that magnetars can hop among distinct persistent states that are probably connected to outburst episodes and that their persistent thermal emission can be almost entirely powered by the dissipation of currents in the corona.

X-ray emission characteristics in magnetically driven plasma jet experiments on PTS facility

Jets are commonly observed astrophysical phenomena. To study the x-ray emission characteristics of jets, a series of radial foil Z-pinch experiments are carried out on the Primary Test Stand at the Institute of Fluid Physics, China Academy of Engineering Physics. In these experiments, x-ray emission ranging from the soft region (0.1–10 keV) to the hard region (10 keV–500 keV) is observed when the magnetic cavity breaks. The radiation flux of soft x-rays is measured by an x-ray diode and the dose rate of the hard x-rays by an Si-PIN detector. The experimental results indicate that the energy of the soft x-rays is several tens of kilojoules and that of the hard x-rays is ∼200 J. The radiation mechanism of the x-ray emission is briefly analyzed. This analysis indicates that the x-ray energy and the plasma kinetic energy come from the magnetic energy when the magnetic cavity breaks. The soft x-rays are thought to be produced by bremsstrahlung of thermal electrons (∼100 eV), and the hard x-rays by bremsstrahlung of super-hot electrons (∼mega-electron-volt). These results may be helpful to explain the x-ray emission by the jets from young stellar objects.

Neutron star radius measurement from the ultraviolet and soft X-ray thermal emission of PSR J0437−4715

ABSTRACT We analysed the thermal emission from the entire surface of the millisecond pulsar PSR J0437−4715 observed in the ultraviolet and soft X-ray bands. For this, we calculated non-magnetized, partially ionized atmosphere models of hydrogen, helium, and iron compositions and included plasma frequency effects that may affect the emergent spectrum. This is particularly true for the coldest atmospheres composed of iron (up to a few per cent changes in the soft X-ray flux). Employing a Markov chain Monte Carlo method, we found that the spectral fits favour a hydrogen atmosphere, disfavour a helium composition, and rule out iron atmosphere and blackbody models. By using a Gaussian prior on the dust extinction, based on the latest 3D map of Galactic dust, and accounting for the presence of hot polar caps found in the previous work, we found that the hydrogen atmosphere model results in a well-constrained neutron star radius ${R_{\rm NS}}= 13.6^{+0.9}_{-0.8}{\, {\rm km}}$ and bulk surface temperature ${T_{\rm eff}^{\infty }}=\left(2.3\pm 0.1\right){\times 10^{5}}{\, {\rm K}}$. This relatively large radius favours a stiff equation of state and disfavours a strange quark composition inside neutron stars.

A Correlation in the Waiting-time Distributions of Solar Flares

Abstract In a limited sample of isolated solar active regions, we find that the waiting times between flares may correlate well with flare magnitudes as determined by the GOES soft X-ray fluxes. A “build-up and release” scenario (BUR) for magnetic energy storage in the solar corona suggests the existence of such a relationship, relating the slowly varying subphotospheric energy sources to the sudden coronal energy releases of flares and CMEs. Substantial amounts of research effort had not previously found any obvious observational evidence for such a BUR process. This has posed a puzzle since coronal magnetic energy storage represents the consensus view of the basic flare mechanism. We have revisited the GOES soft X-ray flare statistics for any evidence of correlations, using two isolated active regions, and have found significant evidence for a “saturation” correlation. Rather than a “reset” form of this relaxation, in which the time before a flare correlates with its magnitude, the “saturation” relationship results in the time after the flare showing the correlation. The observed correlation competes with the “obscuration” effect of reduced GOES sensitivity following a strong event, by which weaker events can be under-reported systematically. This complicates the observed correlation, and we discuss several approaches to remedy this.

Preflare Processes, Flux Rope Activation, Large-scale Eruption, and Associated X-class Flare from the Active Region NOAA 11875

Abstract We present a multiwavelength analysis of the eruption of a hot coronal channel associated with an X1.0 flare (SOL2013-10-28T02:03) from the active region NOAA 11875 by combining observations from Atmospheric Imaging Assembly/Solar Dynamics Observatory (SDO), Helioseismic and Magnetic Imager/SDO, Reuven Ramaty High Energy Solar Spectroscopic Imager, and Hiraiso Radio Spectrograph. EUV images at high coronal temperatures indicated the presence of a hot channel at the core of the active region from the early preflare phase evidencing the preexistence of a quasi-stable magnetic flux rope. The hot channel underwent an activation phase after a localized and prolonged preflare event occurring adjacent to one of its footpoints. Subsequently, the flux rope continued to rise slowly for ≈16 minutes during which soft X-ray flux gradually built-up characterizing a distinct precursor phase. The flux rope transitioned from the state of slow rise to the eruptive motion with the onset of the impulsive phase of the X1.0 flare. The eruptive expansion of the hot channel is accompanied by a series of type III radio bursts in association with the impulsive rise of strong hard X-ray nonthermal emissions that included explicit hard X-ray sources of energies up to ≈50 keV from the coronal loops and ≈100 keV from their footpoint locations. Our study contains evidence that preflare activity occurring within the spatial extent of a stable flux rope can destabilize it toward eruption. Moreover, sudden transition of the flux rope from the state of slow rise to fast acceleration precisely bifurcated the precursor and the impulsive phases of the flare, which points toward a feedback relationship between early coronal mass ejection dynamics and the strength of the large-scale magnetic reconnection.

Constraining the Coronal Heights and Readjustment Velocities Based on the Detection of a Few Hundred Seconds Delays in the Z Source GX 17+2

Abstract Neutron star Z-type sources provide a unique platform in order to understand the structure of accretion disk–corona geometry emitting close to the Eddington luminosity. Using RXTE and Nuclear Spectroscopic Telescope Array Mission (NuSTAR) satellite data, we performed crosscorrelation function (CCF) studies in GX 17+2 in order to constrain the size of the corona responsible for hard X-rays. From the RXTE data, we found that during horizontal and normal branches, the CCFs show anticorrelated hard (16–30 keV) and soft (2–5 keV) X-ray delays of the order of a few tens to hundred seconds with a mean correlation coefficient of 0.42 ± 0.11. Few observations shows correlated lags and, on one occasion, coincident with radio emission. We also report an anticorrelated hard X-ray delay of 113 ± 51 s using the NuSTAR data of GX 17+2. Based on RXTE data, we find that soft and hard X-ray fluxes are varying, indicating the changes in the disk–corona structure during delays. We bridle the size of the corona using relativistic precession, transition layer models, and boundary layer models. Assuming the delays to be a readjustment timescale of the disk–corona structure, the height of the corona was estimated to be ∼17–100 km. Assuming that the inner region of the truncated disk is occupied by the corona, we constrain the coronal readjustment velocities (v corona = βv disk, where v disk is the radial velocity component of the disk) of the order of β = 0.06–0.12. This study indicates that the observed delays are primarily dependent on the varying coronal readjustment velocities.

Extreme-ultraviolet and X-Ray Emission of Turbulent Solar Flare Loops

Abstract Turbulence has been observed in flare loops and is believed to be crucial for the acceleration of particles and in the emission of X-ray photons in flares, but how the turbulence is produced is still an open question. A scenario proposed by Fang et al. suggests that fast evaporation flows from flare loop footpoints can produce turbulence in the looptop via the Kelvin–Helmholtz instability (KHI). We revisit and improve on this scenario and study how the KHI turbulence influences extreme-ultraviolet (EUV) and X-ray emission. A 2.5D numerical simulation is performed in which we incorporate the penetration of high-energy electrons as a spatio-temporal dependent trigger for chromospheric evaporation flows. EUV, soft X-ray (SXR), and hard X-ray (HXR) emission are synthesized based on the evolving plasma parameters and given energetic electron spectra. KHI turbulence leads to clear brightness fluctuations in the EUV, SXR, and HXR emission, with the SXR light curve demonstrating a clear quasi-periodic pulsation (QPP) with period of 26 s. This QPP derives from a locally trapped, fast standing wave that resonates in between KHI vortices. The spectral profile of the Fe xxi 1354 line is also synthesized and found to be broadened due to the turbulent motion of plasma. HXR tends to mimic the variation of SXR flux and the footpoint HXR spectrum is flatter than the looptop HXR spectrum.

Condition of Surface of Titanium after Pulsed X-ray Exposure

The effect of the pulsed soft X-ray flux on the topography of surface the VТ 1-0 titanium alloy has been studied. The radiation energy density on the surface of the sample is ~10 J/cm2 for one pulse. It is found that a corrugated topography is formed on the surface of titanium as a result of melting followed by freezing: a cellular- or mesh-type topography is formed after one X-ray pulse, the mesh-type topography becomes more sharply defined after two pulses, and the surface of titanium is melted and the mesh structure is almost invisible after three pulses. Crater-like defects are not found, but small cracks are formed on the surface of titanium after melting caused by pulsed X-ray exposure followed by fast cooling of the molten metal.

Investigations of the Ohmic Decay and the Soft X-Ray Emission of the High-braking-index Pulsar PSR J1640−4631

The young pulsar PSR J1640−4631 is the first pulsar reported with a high braking index, n = 3.15 ± 0.03, and has attracted extensive attention. In this work, by inputting the equation of state, we obtain two typical and feasible ranges of the electrical conductivity in the crust of PSR J1640−4631. Then, by considering the effects of general relativity, we formulate the induction equation and use it to investigate the decay of crustal magnetic fields within two scenarios: pure Ohmic decay, and the combination of Ohmic decay and Hall drift. In the former scenario, we calculate the current magnetic field decay rates as dBp/dt ∼ (0.78–1.00) × 107 G yr−1 and dBt/dt ∼ (0.82–1.05) × 108 G yr−1 for the poloidal and toroidal parts, respectively, and estimate the current magnetic energy decay rate as LB ∼ (0.95–1.22) × 1032 erg s−1. In the latter scenario, the combination of Ohmic decay and Hall drift accelerates the decay of magnetic fields, and we calculate the current magnetic field decay rates as dBp/dt ∼ (1.26–1.47) × 107 G yr−1, and dBt/dt ∼ (1.32–1.54) × 108 G yr−1 for the poloidal and toroidal parts, respectively, and estimate the current magnetic energy decay rate as LB ∼ (1.86–2.18) × 1032 erg s−1. It is found that the recalculated value of the braking index n of the star is lower than its observed value, which implies that other factors influence the spin-down evolution. The current magnetic energy decay rates calculated in both scenarios are far less than the isotropic soft X-ray luminosity obtained from Chandra+NuStar telescopes. The observed soft X-ray flux in the (2–10) keV band is FX ∼ 1.8(4) × 10−13 erg cm−2 s−1, which corresponds to a high surface temperature, T ∼ 1.54(6) × 106 K. The observed X-ray flux of the star could be caused by the decay of a multipolar magnetic field near the pole, which is strong enough to activate the slot-gap mechanism. The high surface temperature of the star is attributed either to magnetic spot formation or thermoplastic wave heating due to the decay of the toroidal field near the pole. Our results could be useful in interpreting the high soft X-ray flux from high magnetic field pulsars.

Statistical Properties of Soft X-Ray Emission of Solar Flares

Abstract We present a statistical analysis of properties of Soft X-Ray (SXR) emission, plasma temperature (T), and emission measure (EM), derived from Geostationary Operational Environmental Satellite observations of flares in 2002–2017. The temperature and EMs are obtained using the Temperature and EM-based Background Subtraction algorithm, which delivers reliable results together with uncertainties even for weak B-class flare events. More than 96% of flares demonstrate a sequential appearance of T, SXR, and EM maxima, in agreement with the expected behavior of the chromospheric evaporation process. The relative number of such flares increases with increasing the SXR flux maximum. The SXR maximum is closer in time to the T maximum for B-class flares than for ≥C-class flares, while it is very close to the EM maximum for M- and X-class flares. We define flares as “T-controlled” if the time interval between the SXR and T maxima is at least two times shorter than the interval between the EM and SXR maxima, and as “EM-controlled” if the time interval between the EM and SXR maxima is at least two times shorter than the interval between the SXR and T maxima. For any considered flare class range, the T-controlled events compared to EM-controlled events have: (a) higher EM but lower T; (b) longer durations and shorter relative growth times; and (c) longer FWHM and characteristic decay times. Interpretation of these statistical results based on analysis of a single loop dynamics suggests that for flares of the same class range, the T-controlled events can be developed in longer loops than the EM-controlled events.

Long-term X-ray variation of the colliding-wind Wolf–Rayet binary WR 125

WR 125 is considered as a Colliding Wind Wolf-rayet Binary (CWWB), from which the most recent infrared flux increase was reported between 1990 and 1993. We observed the object four times from November 2016 to May 2017 with Swift and XMM-Newton, and carried out a precise X-ray spectral study for the first time. There were hardly any changes of the fluxes and spectral shapes for half a year, and the absorption-corrected luminosity was 3.0e+33 erg/s in the 0.5 - 10.0 keV range at a distance of 4.1 kpc. The hydrogen column density was higher than that expected from the interstellar absorption, thus the X-ray spectra were probably absorbed by the WR wind. The energy spectrum was successfully modeled by a collisional equilibrium plasma emission, where both the plasma and the absorbing wind have unusual elemental abundances particular to the WR stars. In 1981, the Einstein satellite clearly detected X-rays from WR 125, whereas the ROSAT satellite hardly detected X-rays in 1991, when the binary was probably around the periastron passage. We discuss possible causes for the unexpectedly low soft X-ray flux near the periastron.

On the relative roles of dynamics and chemistry governing the abundance and diurnal variation of low-latitude thermospheric nitric oxide

Abstract. We use data from two NASA satellites, the Thermosphere Ionosphere Energetics and Dynamics (TIMED) and the Aeronomy of Ice in the Mesosphere (AIM) satellites, in conjunction with model simulations from the thermosphere-ionosphere-mesosphere-electrodynamics general circulation model (TIME-GCM) to elucidate the key dynamical and chemical factors governing the abundance and diurnal variation of lower thermospheric nitric oxide (NO) at near-solar minimum conditions and low latitudes. This analysis was enabled by the recent orbital precession of the AIM satellite which caused the solar occultation pattern measured by the Solar Occultation for Ice Experiment (SOFIE) to migrate down to low and mid-latitudes for specific periods of time. We use a month of NO data collected in January 2017 to compare with two versions of the TIME-GCM; one is driven solely by climatological tides and analysis-derived planetary waves at the lower boundary and is free running at all other altitudes, and the other is constrained by a high-altitude analysis from the Navy Global Environmental Model (NAVGEM) up to the mesopause. We also compare SOFIE data with a NO climatology from the nitric oxide empirical model (NOEM). Both SOFIE and NOEM yield peak NO abundances of around 4×107 cm−3; however, the SOFIE profile peaks about 6–8 km lower than NOEM. We show that this difference is likely a local time effect, with SOFIE being a dawn measurement and NOEM representing late morning and/or near noon. The constrained version of TIME-GCM exhibits a low-altitude dawn peak, while the model that is forced solely at the lower boundary and free running above does not. We attribute this difference to a phase change in the semi-diurnal tide in the NAVGEM-constrained model, causing the descent of high NO mixing ratio air near dawn. This phase difference between the two models arises due to differences in the mesospheric zonal mean zonal winds. Regarding the absolute NO abundance, all versions of the TIME-GCM overestimate this. Tuning the model to yield calculated atomic oxygen in agreement with TIMED data helps but is insufficient. Furthermore, the TIME-GCM underestimates the electron density (Ne) as compared with the International Reference Ionosphere (IRI) empirical model. This suggests a potential conflict with the requirements of NO modeling and Ne modeling, since one solution typically used to increase model Ne is to increase the solar soft X-ray flux, which would, in this case, worsen the NO model–data discrepancy.

Conductivity of neutron star crust under superhigh magnetic fields and Ohmic decay of toroidal magnetic field of magnetar

<sec>Magnetar is a kind of pulsar powered by magnetic field energy. Part of the X-ray luminosities of magnetars in quiescence have a thermal origin and can be fitted by a blackbody spectrum with temperature <i>kT</i> ～ 0.2－0.6 keV, much higher than the typical values for rotation-powered pulsars. The observation and theoretical study of magnetar are one of hot topics in the field of pulsar research. The activity and emission characteristics of magnetar can be attributed to internal superhigh magnetic field. According to the work of WGW19 and combining with the equation of state, we first calculate the electric conductivity of the crust under a strong magnetic field, and then calculate the toroidal magnetic field decay rate and magnetic energy decay rate by using an eigenvalue equation of toroidal magnetic field decay and considering the effect of general relativity. We reinvestigate the <i>L</i><sub>X</sub>-<i>L</i><sub>rot</sub> relationship of 22 magnetars with persistent soft X-ray luminosities and obtain two new fitting formulas on <i>L</i><sub>X</sub>-<i>L</i><sub>rot</sub>. We find that for the magnetars with <i>L</i><sub>X</sub> < <i>L</i><sub>rot</sub>, the soft X-ray radiations may originate from their rotational energy loss rate, or from magneto-sphere flow and particle wind heating. For the magnetars with <i>L</i><sub>X</sub> > <i>L</i><sub>rot</sub>, the Ohmic decay of crustal toroidal magnetic fields can provide their observed isotropic soft X-ray radiation and maintain higher thermal temperature.</sec><sec>As for the initial dipole magnetic fields of magnetars, we mainly refer to the rersearch by Viganò et al. (Viganò D, Rea N, Pons J A, Perna R, Aguilera D N, Miralles J A 2013 <i>Mon. Not. R. Astron. Soc.</i> <b>434</b> 123), because they first proposed the up-dated neutron star magneto-thermal evolution model, which can successfully explain the X-ray radiation and cooling mechanism of young pulsars including magnetars and high-magnetic field pulsars. Objectively speaking, as to the decay of toroidal magnetic fields, there are some differences between our theoretical calculations of magnetic energy release rates and the actual situation of magnetic field decay in magnetars, this is because the estimate of initial dipolar magnetic field, true age and the thickness of inner crust of a magnetar are somewhat uncertain. In addition, due to the interstellar-medium’s absorptions to soft X-ray and the uncertainties of distance estimations, the observed soft X-ray luminosities of magnetars have certain deviations. With the continuous improvement of observation, equipment and methods, as well as the in-depth development of theoretical research, our model will be further improved, and the theoretical results are better accordant with the high-energy observation of magnetars.</sec><sec>We also discuss other possible anisotropy origins of soft X-ray fluxes of magnetars, such as the formation of magnetic spots and thermoplastic flow wave heating in the polar cap. Although anisotropic heating mechanisms are different from Ohmic decay, all of them require that there exist strong toroidal magnetic fields inside a magnetar. However, the anisotropic heating mechanisms require higher toroidal multipole fields inside a magnetar (such as magnetic octupole field) and are related to complex Hall drift: these may be our research subjects in the future.</sec>