arXiv subjects

K. Matsumoto

Publications and source records attributed to K. Matsumoto.

At least 19 recordsLinked to original sources

arXiv2026

Energetics and Emission in a Simulated Solar Flare Initialised by a Non-Force Free Magnetic Field

Solar flare simulations are commonly initialised using non-linear force free field (NLFF) extrapolations derived from photospheric vector magnetograms. However, the force free assumption neglects plasma forces and may limit the available free magnetic energy. In this work, we perform a controlled comparison of two three-dimensional resistive magnetohydrodynamic simulations of the X2.1-class flare that occurred on 2011 September 06 in NOAA Active Region 11283. The simulations differ only in their initial magnetic configuration: one is based on a conventional NLFF extrapolation, while the other employs a non-force free extrapolation. Both models are evolved in an identical stratified atmosphere using the same numerical framework, enabling direct assessment of how the initial magnetic assumptions influence flare dynamics and energetics. We find that the non-force free model undergoes more extensive magnetic restructuring and releases approximately twice as much magnetic energy ($\approx4.4 \times 10^{31}$ erg) as the NLFF case ($\approx2.3 \times 10^{31}$ erg), bringing the energy budget into closer agreement with expectations for X-class flares. Synthetic extreme ultraviolet emission in the 94A channel is computed for both simulations and compared with observations from the Solar Dynamics Observatory. The non-force free model produces a brighter and more spatially extended emission structure that more closely resembles the observed flare morphology and light curve. These results demonstrate that assumptions made in constructing the pre-flare coronal magnetic field can significantly affect flare energetics and observable signatures, and suggest that non-force free extrapolations provide a promising pathway toward more realistic data-constrained flare modelling.

astro-ph.SR↗

arXiv2025

TESS and ground-based observations of WZ Sge-type dwarf novae in outburst

Dwarf nova (DN) superoutbursts are accompanied by superhumps, which change their periods and profiles over a superoutburst. We present the TESS and ground-based observations of nine WZ Sge-type DNe and candidates in superoutburst. In TCP J23580961$+$5502508, ASASSN-23ba, PNV J19030433$-$3102187, V748 Hya, and ASASSN-25ci, we confirmed double-peaked oscillations called early superhumps, which are regarded as the unambiguous feature of WZ Sge-type DNe. On the other hand, the superhump and outburst properties of MO Psc and V1676 Her suggest that they may not be a member of WZ Sge-type DNe. The 2022 superoutburst of a confirmed WZ Sge-type DN TCP J05515391$+$6504346, however, lacked an early superhump phase. We find superhumps in a WZ Sge-type DN ASASSN-20mq during its rebrightening outburst. Thanks to the continuous coverage of TESS, we find the broken-powerlaw rise of the outburst light curve in V748 Hya and PNV J19030433$-$3102187, previously found in only one WZ Sge-type DN observed by Kepler. Early superhumps appeared when the system reached $\simeq40$% of the outburst peak flux. No orbital modulation from a hot spot is detected before and after this. This non-detection of orbital humps on the early rise of V748 Hya constrains that the corresponding mass transfer rate should be below $\simeq1\times10^{16}$ g s$^{-1}$, disfavouring an enhancement of a mass transfer rate by an order of magnitude or larger, even if it occurs. The contentious TESS observations also confirm the coexistence of early and ordinary superhumps during their transition and $\leq$2-cycle duration of stage A--B superhump transition in V748 Hya.

astro-ph.SR↗

arXiv2024

Magnetic Nonlinear Response of UPt$_3$: An augmented Landau approach

Several heavy fermion materials, including UPt$_3$, exhibit a rapid but gradual rise in the magnetization at a critical field, without an apparent phase transition at any temperature $T>0$, with the possibility of a first order transition at $T \equiv0$. To model such a quantum phase transition it is most appropriate to develop approaches considering the quantum nature of the spins. Within a fully classical framework, we show that it is sufficient to start from a Landau-type free energy with an added Bragg-Williams entropy term to arrive at a number of key experimental features as seen in UPt$_3$. In particular, we show that correctly arriving at the measured (low-field) higher order susceptibilities necessarily invokes an isobestic (crossing) point at a high field in the magnetization isotherms. We also present a full analysis of the angular dependence of the (low-field) linear and nonlinear susceptibilities which when extended also capture the anisotropic high field response of the magnetization. Key to this success is the proper conversion of the evaluated magnetization from constant volume to a constant pressure situation relevant at high fields in heavy fermion materials.

cond-mat.str-el↗

arXiv2024

Radial properties of dust in galaxies: Comparison between observations and isolated galaxy simulations

We study the importance of several processes that influence the evolution of dust and its grain size distribution on spatially resolved scales in nearby galaxies. Here, we compiled several multi-wavelength observations for the nearby galaxies NGC628(M74), NGC5457(M101), NGC598(M33), and NGC300. We applied spatially resolved spectral energy distribution fitting to the latest iteration of infrared data to get constraints on the galaxy dust masses and the small-to-large grain abundance ratio. For comparison, we took the radial profiles of the stellar mass and gas mass surface density for NGC628 combined with its metallicity gradient in the literature to calibrate a single-galaxy simulation using the GADGET4-OSAKA code. The simulations include a parametrization to separate the dense and diffuse phases of the ISM where different dust-evolution mechanisms are in action. We find that our simulation can reproduce the radial profile of dust mass surface density but overestimates the SLR in NGC628. Changing the dust-accretion timescale has little impact on the dust mass or SLR, as most of the available metals are accreted onto dust grains at early times (< 3Gyr), except in the outer regions of the galaxy. This suggests we can only constrain the accretion timescale of galaxies at extremely low metallicities where accretion still competes with other mechanisms controlling the dust budget. The overestimation of the SLR likely results from (i) overly efficient shattering processes in the diffuse interstellar medium, which were calibrated to reproduce Milky Way-type galaxies and/or (ii) our use of a diffuse and dense gas density subgrid model that does not entirely capture the intricacies of the small-scale structure present in NGC628.

astro-ph.GA↗

arXiv2024

A wiggling filamentary jet at the origin of the blazar multi-wavelength behaviour

Blazars are beamed active galactic nuclei known for their strong multi-wavelength variability on timescales from years down to minutes. We aim to investigate the suitability of the twisting jet model presented in previous works to explain the multi-wavelength behaviour of BL Lacertae, the prototype of one of the blazar classes. According to this model, the jet is inhomogeneous, curved, and twisting, and the long-term variability is due to changes in the Doppler factor due to variations in the orientation of the jet-emitting regions. We analysed optical data of the source obtained during monitoring campaigns organised by the Whole Earth Blazar Telescope (WEBT) in 2019-2022, together with radio data from the WEBT and other teams, and gamma-ray data from the Fermi satellite. In this period, BL Lacertae underwent an extraordinary activity phase, reaching its historical optical and gamma-ray brightness maxima. The application of the twisting jet model to the source light curves allows us to infer the wiggling motion of the optical, radio, and gamma-ray jet-emitting regions. The optical-radio correlation shows that the changes in the radio viewing angle follow those in the optical viewing angle by about 120 days, and it suggests that the jet is composed of plasma filaments, which is in agreement with some radio high-resolution observations of other sources. The gamma-ray emitting region is found to be co-spatial with the optical one, and the analysis of the gamma-optical correlation is consistent with both the geometric interpretation and a synchrotron self-Compton (SSC) origin of the high-energy photons. We propose a geometric scenario where the jet is made up of a pair of emitting plasma filaments in a sort of double-helix curved rotating structure, whose wiggling motion produces changes in the Doppler beaming and can thus explain the observed multi-wavelength long-term variability.

astro-ph.HE↗

arXiv2024

Unravelling the asphericities in the explosion and multi-faceted circumstellar matter of SN 2023ixf

We present a detailed investigation of photometric, spectroscopic, and polarimetric observations of the Type II SN 2023ixf. Earlier studies have provided compelling evidence for a delayed shock breakout from a confined dense circumstellar matter (CSM) enveloping the progenitor star. The temporal evolution of polarization in SN~2023ixf revealed three distinct peaks in polarization evolution at 1.4 d, 6.4 d, and 79.2 d, indicating an asymmetric dense CSM, an aspherical shock front and clumpiness in the low-density extended CSM, and an aspherical inner ejecta/He-core. SN 2023ixf displayed two dominant axes, one along the CSM-outer ejecta and the other along the inner ejecta/He-core, showcasing the independent origin of asymmetry in the early and late evolution. The argument for an aspherical shock front is further strengthened by the presence of a high-velocity broad absorption feature in the blue wing of the Balmer features in addition to the P-Cygni absorption post 16 d. Hydrodynamical light curve modeling indicated a progenitor of 10 solar mass with a radius of 470 solar radii and explosion energy of 2e51 erg, along with 0.06 solar mass of 56-Ni, though these properties are not unique due to modeling degeneracies. The modeling also indicated a two-zone CSM: a confined dense CSM extending up to 5e14 cm, with a mass-loss rate of 1e-2 solar mass per year, and an extended CSM spanning from 5e14 cm to at least 1e16cm with a mass-loss rate of 1e-4 solar mass per year, both assuming a wind-velocity of 10 km/s. The early nebular phase observations display an axisymmetric line profile of [OI], red-ward attenuation of the emission of Halpha post 125 days, and flattening in the Ks-band, marking the onset of dust formation.

astro-ph.HE↗

arXiv2024

Derivation of CPT resonance signals from density-matrix equations with all relevant sublevels of Cs atoms and confirmation of experimental results

Coherent-population-trapping resonance is a quantum interference effect that appears in the two-photon transitions between the ground-state hyperfine levels of alkali atoms and is often utilized in miniature clock devices. To quantitatively understand and predict the performance of this phenomenon, it is necessary to consider the transitions and relaxations between all hyperfine Zeeman sublevels involved in the different excitation processes of the atom. In this study, we constructed a computational multi-level atomic model of the Liouville density-matrix equation for 32 Zeeman sublevels involved in the $D_1$ line of $^{133}$Cs irradiated by two frequencies with circularly polarized components and then simulated the amplitude and shape of the transmitted light through a Cs vapor cell. We show that the numerical solutions of the equation and analytical investigations adequately explain a variety of the characteristics observed in the experiment.

quant-ph↗

arXiv2023

Extreme photometric and polarimetric variability of blazar S4 0954+65 at its maximum optical and $γ$-ray brightness levels

In 2022 the BL Lac object S4 0954+65 underwent a major variability phase, reaching its historical maximum brightness in the optical and $γ$-ray bands. We present optical photometric and polarimetric data acquired by the Whole Earth Blazar Telescope (WEBT) Collaboration from 2022 April 6 to July 6. Many episodes of unprecedented fast variability were detected, implying an upper limit to the size of the emitting region as low as $10^{-4}$ parsec. The WEBT data show rapid variability in both the degree and angle of polarization. We analyse different models to explain the polarization behaviour in the framework of a twisting jet model, which assumes that the long-term trend of the flux is produced by variations in the emitting region viewing angle. All the models can reproduce the average trend of the polarization degree, and can account for its general anticorrelation with the flux, but the dispersion of the data requires the presence of intrinsic mechanisms, such as turbulence, shocks, or magnetic reconnection. The WEBT optical data are compared to $γ$-ray data from the Fermi satellite. These are analysed with both fixed and adaptive binning procedures. We show that the strong correlation between optical and $γ$-ray data without measurable delay assumes different slopes in faint and high brightness states, and this is compatible with a scenario where in faint states we mainly see the imprint of the geometrical effects, while in bright states the synchrotron self-Compton process dominates.

astro-ph.HE↗

arXiv2023

The optical behaviour of BL Lacertae at its maximum brightness levels: a blend of geometry and energetics

In 2021 BL Lacertae underwent an extraordinary activity phase, which was intensively followed by the Whole Earth Blazar Telescope (WEBT) Collaboration. We present the WEBT optical data in the BVRI bands acquired at 36 observatories around the world. In mid 2021 the source showed its historical maximum, with R = 11.14. The light curves display many episodes of intraday variability, whose amplitude increases with source brightness, in agreement with a geometrical interpretation of the long-term flux behaviour. This is also supported by the long-term spectral variability, with an almost achromatic trend with brightness. In contrast, short-term variations are found to be strongly chromatic and are ascribed to energetic processes in the jet. We also analyse the optical polarimetric behaviour, finding evidence of a strong correlation between the intrinsic fast variations in flux density and those in polarisation degree, with a time delay of about 13 h. This suggests a common physical origin. The overall behaviour of the source can be interpreted as the result of two mechanisms: variability on time scales greater than several days is likely produced by orientation effects, while either shock waves propagating in the jet, or magnetic reconnection, possibly induced by kink instabilities in the jet, can explain variability on shorter time scales. The latter scenario could also account for the appearance of quasi-periodic oscillations, with periods from a few days to a few hours, during outbursts, when the jet is more closely aligned with our line of sight and the time scales are shortened by relativistic effects.

astro-ph.HE↗

arXiv2022

Host galaxy magnitude of OJ 287 from its colours at minimum light

OJ 287 is a BL Lacertae type quasar in which the active galactic nucleus (AGN) outshines the host galaxy by an order of magnitude. The only exception to this may be at minimum light when the AGN activity is so low that the host galaxy may make quite a considerable contribution to the photometric intensity of the source. Such a dip or a fade in the intensity of OJ 287 occurred in November 2017, when its brightness was about 1.75 magnitudes lower than the recent mean level. We compare the observations of this fade with similar fades in OJ 287 observed earlier in 1989, 1999, and 2010. It appears that there is a relatively strong reddening of the B$-$V colours of OJ 287 when its V-band brightness drops below magnitude 17. Similar changes are also seen V$-$R, V$-$I, and R$-$I colours during these deep fades. These data support the conclusion that the total magnitude of the host galaxy is $V=18.0 \pm 0.3$, corresponding to $M_{K}=-26.5 \pm 0.3$ in the K-band. This is in agreement with the results, obtained using the integrated surface brightness method, from recent surface photometry of the host. These results should encourage us to use the colour separation method also in other host galaxies with strongly variable AGN nuclei. In the case of OJ 287, both the host galaxy and its central black hole are among the biggest known, and its position in the black hole mass-galaxy mass diagram lies close to the mean correlation.

astro-ph.GA↗

arXiv2021

Magnetic-field-insensitive coherent-population-trapping resonances excited by bichromatic linearly polarized fields on the $D_1$ line of $^{133}$Cs

We have experimentally demonstrated that magnetic-field-insensitive coherent-population-trapping (CPT) resonances are generated between the ground hyperfine levels on the $D_1$ line of $^{133}$Cs using a two-photon $Λ$ scheme excited by lin || lin polarizations. The frequency shift of the CPT resonance is 0.04 Hz for the deviation of 1 $μ$T at a "magic" magnetic field of 139 $μ$T and is 50 times smaller than that of the conventional clock transition at a typical bias magnetic field for the clock operation. The amplitude of the CPT spectrum excited by lin || lin polarizations is enhanced as the excitation intensity increases and is well explained by the three-level model without trap levels. Thus, the CPT resonance on the $D_1$ line of $^{133}$Cs atom excited by a simple lin || lin scheme will be one of the best candidates for frequency reference of miniature atomic clocks.

quant-ph↗

arXiv2021

Hayabusa2 Extended Mission: New Voyage to Rendezvous with a Small Asteroid Rotating with a Short Period

Hayabusa2 is the Japanese Asteroid Return Mission and targeted the carbonaceous asteroid Ryugu, conducted by the Japan Aerospace Exploration Agency (JAXA). The goal of this mission was to conduct proximity operations including remote sensing observations, material sampling, and a Small Carry-On Impact experiment, as well as sample analyses. As of September 2020, the spacecraft is on the way back to Earth with samples from Ryugu with no critical issues after the successful departure in November 2019. Here, we propose an extended mission in which the spacecraft will rendezvous with a small asteroid with ~30 m - ~40 m in diameter that is rotating at a spin period of ~10 min after an additional ~10-year cruise phase. We introduce that two scenarios are suitable for the extended mission. In the first scenario, the spacecraft will perform swing-by maneuvers at Venus once and Earth twice to arrive at asteroid 2001 AV43. In the second scenario, it will perform swing-by maneuvers at Earth twice to reach asteroid 1998 KY26. In both scenarios, the mission will continue until the early 2030s. JAXA recently released the decision that the spacecraft will rendezvous with 1998 KY26. This paper focuses on our scientific assessments of the two scenarios but leaves the decision process to go to 1998 KY26 for future reports. Rendezvous operations will be planned to detail the physical properties and surrounding environments of the target, one of the smallest elements of small planetary bodies. By achieving the planned operations, the mission will provide critical hints on the violent histories of collisions and accumulations of small bodies in the solar system. Furthermore, the established scientific knowledge and techniques will advance key technologies for planetary defense.

astro-ph.IM↗

arXiv2020

The dual nature of blazar fast variability. Space and ground observations of S5 0716+714

Blazar S5 0716+714 is well-known for its short-term variability, down to intra-day time-scales. We here present the 2-min cadence optical light curve obtained by the TESS space telescope in 2019 December - 2020 January and analyse the object fast variability with unprecedented sampling. Supporting observations by the Whole Earth Blazar Telescope Collaboration in B, V , R, and I bands allow us to investigate the spectral variability during the TESS pointing. The spectral analysis is further extended in frequency to the UV and X-ray bands with data from the Neil Gehrels Swift Observatory. We develop a new method to unveil the shortest optical variability time-scales. This is based on progressive de-trending of the TESS light curve by means of cubic spline interpolations through the binned fluxes, with decreasing time bins. The de-trended light curves are then analysed with classical tools for time-series analysis (periodogram, auto-correlation and structure functions). The results show that below 3 d there are significant characteristic variability time-scales of about 1.7, 0.5, and 0.2 d. Variability on time-scales < 0.2 d is strongly chromatic and must be ascribed to intrinsic energetic processes involving emitting regions, likely jet sub-structures, with dimension less than about milliparsec. In contrast, flux changes on time-scales > 0.5 d are quasi-achromatic and are probably due to Doppler factor changes of geometric origin.

astro-ph.HE↗

arXiv2020

Multi-Wavelength Variability of BL Lacertae Measured with High Time Resolution

In an effort to locate the sites of emission at different frequencies and physical processes causing variability in blazar jets, we have obtained high time-resolution observations of BL Lacertae over a wide wavelength range: with the \emph{Transiting Exoplanet Survey Satellite} (TESS) at 6,000-10,000 Å with 2-minute cadence; with the Neil Gehrels \emph{Swift} satellite at optical, UV, and X-ray bands; with the Nuclear Spectroscopic Telescope Array at hard X-ray bands; with the \emph{Fermi} Large Area Telescope at $γ$-ray energies; and with the Whole Earth Blazar Telescope for measurement of the optical flux density and polarization. All light curves are correlated, with similar structure on timescales from hours to days. The shortest timescale of variability at optical frequencies observed with TESS is $\sim 0.5$ hr. The most common timescale is $13\pm1$~hr, comparable with the minimum timescale of X-ray variability, 14.5 hr. The multi-wavelength variability properties cannot be explained by a change solely in the Doppler factor of the emitting plasma. The polarization behavior implies that there are both ordered and turbulent components to the magnetic field in the jet. Correlation analysis indicates that the X-ray variations lag behind the $γ$-ray and optical light curves by up to $\sim 0.4$ days. The timescales of variability, cross-frequency lags, and polarization properties can be explained by turbulent plasma that is energized by a shock in the jet and subsequently loses energy to synchrotron and inverse Compton radiation in a magnetic field of strength $\sim3$ G

astro-ph.GA↗

arXiv2020

Towards a More Complete and Accurate Experimental Nuclear Reaction Data Library (EXFOR): International Collaboration Between Nuclear Reaction Data Centres (NRDC)

The International Network of Nuclear Reaction Data Centres (NRDC) coordinated by the IAEA Nuclear Data Section (NDS) is successfully collaborating in the maintenance and development of the EXFOR library. As the scope of published data expands (e.g., to higher energy, to heavier projectile) to meet the needs from the frontier of sciences and applications, it becomes nowadays a hard and challenging task to maintain both completeness and accuracy of the whole EXFOR library. The paper describes evolution of the library with highlights on recent developments.

nucl-ex↗

arXiv2020

Multiwavelength behaviour of the blazar 3C279: decade-long study from $γ$-ray to radio

We report the results of decade-long (2008-2018) $γ$-ray to 1 GHz radio monitoring of the blazar 3C 279, including GASP/WEBT, $\it{Fermi}$ and $\it{Swift}$ data, as well as polarimetric and spectroscopic data. The X-ray and $γ$-ray light curves correlate well, with no delay > 3 hours, implying general co-spatiality of the emission regions. The $γ$-ray-optical flux-flux relation changes with activity state, ranging from a linear to a more complex dependence. The behaviour of the Stokes parameters at optical and radio wavelengths, including 43 GHz VLBA images, supports either a predominantly helical magnetic field or motion of the radiating plasma along a spiral path. Apparent speeds of emission knots range from 10 to 37c, with the highest values requiring bulk Lorentz factors close to those needed to explain $γ$-ray variability on very short time scales. The Mg II emission line flux in the `blue' and `red' wings correlates with the optical synchrotron continuum flux density, possibly providing a variable source of seed photons for inverse Compton scattering. In the radio bands we find progressive delays of the most prominent light curve maxima with decreasing frequency, as expected from the frequency dependence of the $τ=1$ surface of synchrotron self-absorption. The global maximum in the 86 GHz light curve becomes less prominent at lower frequencies, while a local maximum, appearing in 2014, strengthens toward decreasing frequencies, becoming pronounced at $\sim5$ GHz. These tendencies suggest different Doppler boosting of stratified radio-emitting zones in the jet.

astro-ph.HE↗

arXiv2020

Phase Boundary Exchange Coupling in the Mixed Magnetic Phase Regime of a Pd-doped FeRh Epilayer

Spin-wave resonance measurements were performed in the mixed magnetic phase regime of a Pd-doped FeRh epilayer that appears as the first-order ferromagnetic-antiferromagnetic phase transition takes place. It is seen that the measured value of the exchange stiffness is suppressed throughout the measurement range when compared to the expected value of the fully ferromagnetic regime, extracted via the independent means of a measurement of the Curie point, for only slight changes in the ferromagnetic volume fraction. This behavior is attributed to the influence of the antiferromagnetic phase: inspired by previous experiments that show ferromagnetism to be most persistent at the surfaces and interfaces of FeRh thin films, we modelled the antiferromagnetic phase as forming a thin layer in the middle of the epilayer through which the two ferromagnetic layers are coupled up to a certain critical thickness. The development of this exchange stiffness is then consistent with that expected from the development of an exchange coupling across the magnetic phase boundary, as a consequence of a thickness dependent phase transition taking place in the antiferromagnetic regions and is supported by complimentary computer simulations of atomistic spin-dynamics. The development of the Gilbert damping parameter extracted from the ferromagnetic resonance investigations is consistent with this picture.

cond-mat.mtrl-sci↗

arXiv2019

Investigating the multiwavelength behaviour of the flat spectrum radio quasar CTA 102 during 2013-2017

We present a multiwavelength study of the flat-spectrum radio quasar CTA 102 during 2013-2017. We use radio-to-optical data obtained by the Whole Earth Blazar Telescope, 15 GHz data from the Owens Valley Radio Observatory, 91 and 103 GHz data from the Atacama Large Millimeter Array, near-infrared data from the Rapid Eye Monitor telescope, as well as data from the Swift (optical-UV and X-rays) and Fermi ($γ$ rays) satellites to study flux and spectral variability and the correlation between flux changes at different wavelengths. Unprecedented $γ$-ray flaring activity was observed during 2016 November-2017 February, with four major outbursts. A peak flux of (2158 $\pm$ 63)$\times$10$^{-8}$ ph cm$^{-2}$ s$^{-1}$, corresponding to a luminosity of (2.2 $\pm$ 0.1)$\times$10$^{50}$ erg s$^{-1}$, was reached on 2016 December 28. These four $γ$-ray outbursts have corresponding events in the near-infrared, optical, and UV bands, with the peaks observed at the same time. A general agreement between X-ray and $γ$-ray activity is found. The $γ$-ray flux variations show a general, strong correlation with the optical ones with no time lag between the two bands and a comparable variability amplitude. This $γ$-ray/optical relationship is in agreement with the geometrical model that has successfully explained the low-energy flux and spectral behaviour, suggesting that the long-term flux variations are mainly due to changes in the Doppler factor produced by variations of the viewing angle of the emitting regions. The difference in behaviour between radio and higher energy emission would be ascribed to different viewing angles of the jet regions producing their emission.

astro-ph.HE↗