arXiv subjects

Misaki Mizumoto

Publications and source records attributed to Misaki Mizumoto.

At least 55 records · Page 3Linked to original sources

arXiv2025

XRISM forecast for the Coma cluster: stormy, with a steep power spectrum

The XRISM Resolve microcalorimeter array measured the velocities of hot intracluster gas at two positions in the Coma galaxy cluster: 3'x3' squares at the center and at 6' (170 kpc) to the south. We find the line-of-sight velocity dispersions in those regions to be sigma_z=208+-12 km/s and 202+-24 km/s, respectively. The central value corresponds to a 3D Mach number of M=0.24+-0.015 and the ratio of the kinetic pressure of small-scale motions to thermal pressure in the intracluster plasma of only 3.1+-0.4%, at the lower end of predictions from cosmological simulations for merging clusters like Coma, and similar to that observed in the cool core of the relaxed cluster A2029. Meanwhile, the gas in both regions exhibits high line-of-sight velocity differences from the mean velocity of the cluster galaxies, Delta v_z=450+-15 km/s and 730+-30 km/s, respectively. A small contribution from an additional gas velocity component, consistent with the cluster optical mean, is detected along a sightline near the cluster center. The combination of the observed velocity dispersions and bulk velocities is not described by a Kolmogorov velocity power spectrum of steady-state turbulence; instead, the data imply a much steeper effective slope (i.e., relatively more power at larger linear scales). This may indicate either a very large dissipation scale resulting in the suppression of small-scale motions, or a transient dynamic state of the cluster, where large-scale gas flows generated by an ongoing merger have not yet cascaded down to small scales.

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arXiv2025

Optimization of x-ray event screening using ground and in-orbit data for the Resolve instrument onboard the XRISM satellite

The XRISM (X-Ray Imaging and Spectroscopy Mission) satellite was successfully launched and put into a low-Earth orbit on September 6, 2023 (UT). The Resolve instrument onboard XRISM hosts an x-ray microcalorimeter detector, which was designed to achieve a high-resolution ($\leq$7 eV FWHM at 6 keV), high-throughput, and non-dispersive spectroscopy over a wide energy range. It also excels in a low background with a requirement of $< 2 \times 10^{-3}$ s$^{-1}$ keV$^{-1}$ (0.3--12.0 keV), which is equivalent to only one background event per spectral bin per 100 ks exposure. Event screening to discriminate x-ray events from background is a key to meeting the requirement. We present the result of the Resolve event screening using data sets recorded on the ground and in orbit based on the heritage of the preceding x-ray microcalorimeter missions, in particular, the Soft X-ray Spectrometer (SXS) onboard ASTRO-H. We optimize and evaluate 19 screening items of three types based on (1) the event pulse shape, (2) relative arrival times among multiple events, and (3) good time intervals. We show that the initial screening, which is applied for science data products in the performance verification phase, reduces the background rate to $1.8 \times 10^{-3}$ s$^{-1}$ keV$^{-1}$ meeting the requirement. We further evaluate the additional screening utilizing the correlation among some pulse shape properties of x-ray events and show that it further reduces the background rate particularly in the $<$2 keV band. Over 0.3--12 keV, the background rate becomes $1.0 \times 10^{-3}$ s$^{-1}$ keV$^{-1}$.

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arXiv2025

High count rate effects in event processing for XRISM/Resolve x-ray microcalorimeter

The spectroscopic performance of x-ray instruments can be affected at high count rates. The effects and mitigation in the optical chain, such as x-ray attenuation filters or de-focusing mirrors, are widely discussed, but those in the signal chain are not. Using the Resolve x-ray microcalorimeter onboard the XRISM satellite, we discuss the effects observed during high count rate measurements and how these can be modeled. We focus on three instrumental effects that impact performance at high count rate: CPU limit, pile up, and electrical cross talk. High count rate data were obtained during ground testing using the flight model instrument and a calibration x-ray source. A simulated observation of GX 13+1 is presented to illustrate how to estimate these effects based on these models for observation planning. The impact of these effects on high count rate observations is discussed.

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arXiv2025

High count rate effects in event processing for XRISM/Resolve x-ray microcalorimeter: I. Ground test

The spectroscopic performance of an X-ray microcalorimeter is compromised at high count rates. In this study, we utilize the Resolve X-ray microcalorimeter onboard the XRISM satellite to examine the effects observed during high count rate measurements and propose modeling approaches to mitigate them. We specifically address the following instrumental effects that impact performance: CPU limit, pile-up, and untriggered electrical cross talk. Experimental data at high count rates were acquired during ground testing using the flight model instrument and a calibration X-ray source. In the experiment, data processing not limited by the performance of the onboard CPU was run in parallel, which cannot be done in orbit. This makes it possible to access the data degradation caused by limited CPU performance. We use these data to develop models that allow for a more accurate estimation of the aforementioned effects. To illustrate the application of these models in observation planning, we present a simulated observation of GX 13+1. Understanding and addressing these issues is crucial to enhancing the reliability and precision of X-ray spectroscopy in situations characterized by elevated count rates.

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arXiv2024

X-ray Winds In Nearby-to-distant Galaxies (X-WING) - I: Legacy Surveys of Galaxies with Ultrafast Outflows and Warm Absorbers in $z \sim 0$-$4$

As an inaugural investigation under the X-ray Winds In Nearby-to-distant Galaxies (X-WING) program, we assembled a dataset comprising 132 active galactic nuclei (AGNs) spanning redshifts $z \sim 0$-$4$ characterized by blueshifted absorption lines indicative of X-ray winds. Through an exhaustive review of previous research, we compiled the outflow parameters for 573 X-ray winds, encompassing key attributes such as outflow velocities ($V_{\rm out}$), ionization parameters ($ξ$), and hydrogen column densities. By leveraging the parameters $V_{\rm out}$ and $ξ$, we systematically categorized the winds into three distinct groups: ultrafast outflows (UFOs), low-ionization parameter (low-IP) UFOs, and warm absorbers. Strikingly, a discernible absence of linear correlations in the outflow parameters, coupled with distributions approaching instrumental detection limits, was observed. Another notable finding was the identification of a velocity gap around $V_{\rm out} \sim 10,000~{\rm km~s^{-1}}$. This gap was particularly evident in the winds detected via absorption lines within the $\lesssim$2 keV band, indicating disparate origins for low-IP UFOs and warm absorbers. In cases involving Fe XXV/Fe XXVI lines, where the gap might be attributed to potential confusion between emission/absorption lines and the Fe K-edge, the possibility of UFOs and galactic-scale warm absorbers being disconnected is considered. An examination of the outflow and dust sublimation radii revealed a distinction: UFOs appear to consist of dust-free material, whereas warm absorbers likely comprise dusty gas. From 2024, the X-Ray Imaging and Spectroscopy Mission (XRISM) is poised to alleviate observational biases, providing insights into the authenticity of the identified gap, a pivotal question in comprehending AGN feedback from UFOs.

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arXiv2024

[N I] 10400/10410 Å Lines as Possible Disk Wind Tracers in a Young Intermediate-Mass Star

In this study, we performed high-resolution near-infrared (NIR) spectroscopy (R = 28,000; $λ = 0.90$-1.35 $μ$m) with a high signal-to-noise ratio on HD 200775, a very young (${\sim}$0.1 Myr old) and massive intermediate-mass star (a binary star with a mass of about 10 $M_{\odot}$ each) with a protoplanetary disk. The obtained spectra show eight forbidden lines of three elements: two of [S II] (10289 and 10323 Å), two of [N I] (10400 and 10410 Å), and four of [Fe II] (12570, 12946, 12981, and 13209 Å). This is the first time that the [N I] lines are detected in a young stellar object with a doublet deblended. Gaussian fitting of the spectra indicates that all line profiles have low-velocity components and exhibit blueshifted features, suggesting that all lines originate from the disk winds (magnetohydrodynamic disk wind and/or photoevaporative wind). Based on the fit, the [N I] and [Fe II] lines are categorized into narrow components, while the [S II] lines are at the boundary between broad and narrow components. These forbidden lines are suggested to be very promising disk wind tracers among the existing ones because they are in the NIR-wavelength range, which can be observed from early stages with high sensitivities. Among these lines, [N I] lines would be a rather powerful probe for deriving the basic physical parameters of disk wind gases. However, the study of these lines herein is limited to one object; thus, further studies are needed to examine their properties.

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arXiv2023

Shock Excitation in Narrow Line Regions Powered by AGN Outflows

Outflows in the Active Galactic Nucleus (AGN) are considered to play a key role in the host galaxy evolution through transfer of a large amount of energy. A Narrow Line Region (NLR) in the AGN is composed of ionized gas extending from pc-scales to kpc-scales. It has been suggested that shocks are required for ionization of the NLR gas. If AGN outflows generate such shocks, they will sweep through the NLR and the outflow energy will be transferred into a galaxy-scale region. In order to study contribution of the AGN outflow to the NLR-scale shock, we measure the [\ion{Fe}{2}]$\lambda12570$/[\ion{P}{2}]$\lambda11886$ line ratio, which is a good tracer of shocks, using near-infrared spectroscopic observations with WINERED (Warm INfrared Echelle spectrograph to Realize Extreme Dispersion and sensitivity) mounted on the New Technology Telescope. Among 13 Seyfert galaxies we observed, the [\ion{Fe}{2}] and [\ion{P}{2}] lines were detected in 12 and 6 targets, respectively. The [\ion{Fe}{2}]/[\ion{P}{2}] ratios in 4 targets were found to be higher than 10, which implies the existence of shocks. We also found that the shock is likely to exist where an ionized outflow, i.e., a blue wing in [\ion{S}{3}]$\lambda9533$, is present. Our result implies that the ionized outflow present over a NLR-scale region sweeps through the interstellar medium and generates a shock.

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arXiv2023

Spectral Modeling of the Supersoft X-ray Source CAL87 based on Radiative Transfer Codes

Super Soft X-ray Sources (SSS) are white dwarf (WD) binaries that radiate almost entirely below $\sim$1~keV. Their X-ray spectra are often complex when viewed with the X-ray grating spectrometers, where numerous emission and absorption features are intermingled and hard to separate. The absorption features are mostly from the WD atmosphere, for which radiative transfer models have been constructed. The emission features are from the corona surrounding the WD atmosphere, in which incident emission from the WD surface is reprocessed. Modeling the corona requires different solvers and assumptions for the radiative transfer, which is yet to be achieved. We chose CAL87, a SSS in the Large Magellanic Cloud, which exhibits emission-dominated spectra from the corona as the WD atmosphere emission is assumed to be completely blocked by the accretion disk. We constructed a radiative transfer model for the corona using the two radiative transfer codes; xstar for a one-dimensional two-stream solver and MONACO for a three-dimensional Monte Carlo solver. We identified their differences and limitations in comparison to the spectra taken with the Reflection Grating Spectrometer onboard the XMM-Newton satellite. We finally obtained a sufficiently good spectral model of CAL87 based on the radiative transfer of the corona plus an additional collisionally ionized plasma. In the coming X-ray microcalorimeter era, it will be required to interpret spectra based on radiative transfer in a wider range of sources than what is presented here.

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arXiv2023

Origin of the complex iron line structure and spectral variation in Mrk 766

Complex Fe-K emission/absorption line features are commonly observed in the 6--11 keV band from Active Galactic Nuclei (AGN). These features are formed in various physical components surrounding the black holes. The Narrow-Line Seyfert 1 (NLS1) galaxy Mrk 766, in particular, exhibits characteristic blue-shifted Fe-K absorption lines caused by the ultra-fast outflow (UFO), and a broad Fe-K emission line, as well as variable absorbers partially covering the X-ray emitting region. We re-analyze the Mrk 766 archival data of XMM-Newton, NuSTAR, and Swift to investigate the origin of the Fe-K line feature and the 0.3--79 keV energy spectral variation. We have found that the spectral variation in $\lesssim$10 keV is primarily explained by the variable partial covering of the central X-ray source by multi-layer absorbing clouds. The Fe-K line feature consists of the blue-shifted absorption lines due to the UFO, a narrow emission line from the distant material, a broad emission line from the inner-disk reflection, and a slightly broadened weak emission line at around 6.4--6.7 keV whose equivalent width is $\sim$0.05 keV. The last one is presumably due to the resonance scattering in the UFO out of the line-of-sight, as predicted by a Monte Carlo simulation based on the hydrodynamical UFO modeling. We suggest that the seemingly complex Fe-K line features and the X-ray energy spectra of Mrk 766 are explained by a moderately extended central X-ray source around a Schwarzschild black hole, an optically thick accretion disk with a truncated inner-radius, the UFO, multi-layer partial covering clouds, and a torus.

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arXiv2023

Radiatively-driven clumpy X-ray absorbers in the NLS1 galaxy IRAS 13224-3809

Recent radiation-magnetohydrodynamic simulations of active galactic nuclei predict the presence of the disk winds, which may get unstable and turn into fragmented clumps far from the central black hole. These inner winds and the outer clumps may be observed as the ultrafast outflows (UFOs) and the partial absorbers, respectively. However, it is challenging to observationally constrain their origins because of the complicated spectral features and variations. To resolve such degeneracies of the clumpy absorbers and other components, we developed a novel ``spectral-ratio model fitting'' technique that estimates the variable absorbing parameters from the ratios of the partially absorbed spectra to the non-absorbed one, canceling the complex non-variable spectral features. We applied this method to the narrow-line Seyfert 1 galaxy \iras observed by \xmm in 2016 for $\sim$1.5 Ms. As a result, we found that the soft spectral variation is mostly caused by changes in the partial covering fraction of the mildly-ionized clumpy absorbers, whose outflow velocities are similar to those of the UFO ($\sim$0.2--0.3 $c$). Furthermore, the velocities of the clumpy absorbers and UFOs increase similarly with the X-ray fluxes, consistent with the change in the UV-dominant continuum flux. We also discovered a striking correlation between the clump covering fraction and the equivalent width of the UFO absorption lines, which indicates that increasing the outflow in the line-of-sight lead to more prominent UFOs and more partial absorption. These findings strongly suggest that the clumpy absorbers and the UFO share the same origin, driven by the same UV-dominant continuum radiation.

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arXiv2023

A broadband X-ray imaging spectroscopy in the 2030s: the FORCE mission

In this multi-messenger astronomy era, all the observational probes are improving their sensitivities and overall performance. The Focusing on Relativistic universe and Cosmic Evolution (FORCE) mission, the product of a JAXA/NASA collaboration, will reach a 10 times higher sensitivity in the hard X-ray band ($E >$ 10~keV) in comparison with any previous hard X-ray missions, and provide simultaneous soft X-ray coverage. FORCE aims to be launched in the early 2030s, providing a perfect hard X-ray complement to the ESA flagship mission Athena. FORCE will be the most powerful X-ray probe for discovering obscured/hidden black holes and studying high energy particle acceleration in our Universe and will address how relativistic processes in the universe are realized and how these affect cosmic evolution. FORCE, which will operate over 1--79 keV, is equipped with two identical pairs of supermirrors and wideband X-ray imagers. The mirror and imager are connected by a high mechanical stiffness extensible optical bench with alignment monitor systems with a focal length of 12~m. A light-weight silicon mirror with multi-layer coating realizes a high angular resolution of $<15''$ in half-power diameter in the broad bandpass. The imager is a hybrid of a brand-new SOI-CMOS silicon-pixel detector and a CdTe detector responsible for the softer and harder energy bands, respectively. FORCE will play an essential role in the multi-messenger astronomy in the 2030s with its broadband X-ray sensitivity.

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arXiv2023

X-ray time lag evaluation of MAXI J1820+070 with a differential cross-correlation analysis

MAXI J1820$+$070 is a transient black hole binary (BHB) discovered on 2018 March 11. The unprecedented rich statistics brought by the NICER X-ray telescope allows detailed timing analysis up to $\sim$1~kHz uncompromised by the photon shot noise. To estimate the time lags, the Fourier analysis was applied, which led to two different conclusions for the system configuration; one supporting the lamp-post configuration with a stable accretion disk extending close to the innermost stable circular orbit and the other supporting the truncated accretion disk contracting with time. Using the same data set, we present the results based on the cross-correlation function (CCF). The CCF is calculated between two different X-ray bands and one side is subtracted from the other side, which we call the differential CCF (dCCF). The soft and hard lags respectively of $\sim$0.03 and 3~s are clearly identified without being diluted by the spectral mixture, demonstrating the effectiveness of the dCCF analysis. The evolution of these lags is tracked, along with spectral changes for the first 120~days since the discovery. Both the dCCF and spectral fitting results are interpreted that the soft lag is a reverberation lag between the Comptonized emission and the soft excess emission and that the hard lag is between the disk black body emission and the Comptonized emission. The evolution of these lags is in line with the picture of the truncated disk contracting with time.

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arXiv2022

A novel "spectral-ratio model fitting" to resolve complicated AGN X-ray spectral variations

Contemporary radiation-magnetohydrodynamic simulation of the AGNs predicts presence of the hot and strong accretion disk wind, which gets unstable far from the central region and turns into gas clumps. These inner-wind and outer clumps may be actually observed as the ultrafast outflows (UFOs) and the clumpy absorbers, respectively. We may call this picture as the "hot inner and clumpy outer wind model". Observationally, it is challenging to place constraints on the origin of the UFOs and clumpy absorbers due to complicated spectral variations. We developed a novel method, "spectral-ratio model fitting", to resolve parameter degeneracy of the clumpy absorbers and other spectral components. In this method, the parameters of the absorber in the line of sight are estimated from the ratio of the partially absorbed spectrum to the non-absorbed one. We applied this method to the narrow-line Seyfert 1 galaxy IRAS 13224-3809 observed by XMM-Newton in 2016 for 1.5 Ms, where the source showed extreme spectral variability and complex absorption features. As a result, we found that the soft spectral variation is mostly explained by a change of the covering fraction of the mildly-ionized clumpy absorbers, and that these absorbers are outflowing with such a high velocity that is comparable to that of the UFO (~ 0.2-0.3 c). This result implies that the formation of the clumpy absorbers and the UFO shares the same origin, supporting the "hot inner and clumpy outer wind model".

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arXiv2022

Simple interpretation of the seemingly complicated X-ray spectral variation of NGC 5548

NGC 5548 is a very well-studied Seyfert 1 galaxy in broad wavelengths. Previous multiwavelength observation campaigns have indicated that its multiple absorbers are highly variable and complex. A previous study applied a two-zone partial covering model with different covering fractions to explain the complex X-ray spectral variation and reported a correlation between one of the covering fractions and the photon index of the power-law continuum. However, it is not straightforward to physically understand such a correlation. In this paper, we propose a model to avoid this unphysical situation; the central X-ray emission region is partially covered by clumpy absorbers composed of double layers. These "double partial coverings" have precisely the same covering fraction. Based on our model, we have conducted an extensive spectral study using the data taken by XMM-Newton, Suzaku, and NuSTAR in the range of 0.3-78 keV for 16 years. Consequently, we have found that the X-ray spectral variations are mainly explained by independent changes of the following three components; (1) the soft excess spectral component below ~1 keV, (2) the cut-off power-law normalization, and (3) the partial covering fraction of the clumpy absorbers. In particular, spectral variations above ~1 keV are mostly explained only by the changes of the partial covering fraction and the power-law normalization. In contrast, the photon index and all the other spectral parameters are not significantly variable.

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arXiv2021

Warm Absorbers in the Radiation-driven Fountain Model of Low-mass Active Galactic Nuclei

To investigate the origins of the warm absorbers in active galactic nuclei (AGNs), we study the ionization-state structure of the radiation-driven fountain model in a low-mass AGN (Wada et al. 2016) and calculate the predicted X-ray spectra, utilizing the spectral synthesis code Cloudy (Ferland et al. 2017). The spectra show many absorption and emission line features originated in the outflowing ionized gas. The O VIII 0.654 keV lines are produced mainly in the polar region much closer to the SMBH than the optical narrow line regions. The absorption measure distribution of the ionization parameter ($ξ$) at a low inclination spreads over 4 orders of magnitude in $ξ$, indicating multi-phase ionization structure of the outflow, as actually observed in many type-1 AGNs. We compare our simulated spectra with the high energy-resolution spectrum of the narrow line Seyfert 1 galaxy, NGC 4051. The model reproduces slowly outflowing (a few hundreds km s$^{-1}$) warm absorbers. However, the faster components with a few thousands km s$^{-1}$ observed in NGC 4051 are not reproduced. The simulation also underproduces the intensity and width of the O VIII 0.654 keV line. These results suggest that the ionized gas launched from sub-parsec or smaller regions inside the torus, which are not included in the current fountain model, must be important ingredients of the warm absorbers with a few thousands km s$^{-1}$. The model also consistently explains the Chandra/HETG spectrum of the Seyfert 2 galaxy, the Circinus galaxy.

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arXiv2020

Mg II and Fe II fluxes of luminous quasars at z ~ 2.7 and evaluation of the Baldwin effect in the flux-to-abundance conversion method for quasars

To investigate the chemical abundance of broad-line region clouds in quasars at high redshifts, we performed near-infrared spectroscopy of six luminous quasars at z ~ 2.7 with the WINERED spectrograph mounted on the New Technology Telescope (NTT) at the La Silla Observatory, Chile. The measured Fe II/Mg II flux ratios nearly matched with the published data for 0.7 < z < 1.6, suggesting that there is no evolution over a long period of cosmic time, which is consistent with previous studies. To derive the chemical abundances from the measured equivalent widths (EWs), their dependence on nonabundance factors must be corrected. In our previous paper, we proposed a method to derive the [Mg/Fe] abundance ratio and the [Fe/H] abundance by correcting the dependence of EW(Mg II) and EW(Fe II) on the Eddington ratio. To the best of our knowledge, that was the first report to discuss the star-formation history through a direct comparison with chemical evolution models. In the present study, we further investigated the dependence of EWs on luminosity, which is known as the Baldwin effect (BEff). Additional correction for the BEff significantly affects the derived chemical abundances for the six luminous quasars at z ~ 2.7, and the resultant abundances agree well with the prediction of chemical evolution models. Given that most distant quasars found thus far are biased toward luminous ones, the correction of the measured EWs for the BEff is crucial for extending the chemical evolution study to higher redshifts.

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arXiv2020

UV line driven disc wind as the origin of ultrafast outflows in AGN

UltraFast Outflows (UFO) are observed in some active galactic nuclei (AGN), with blueshifted and highly ionised Fe-K absorption features. AGN typically have a UV bright accretion flow, so UV line driving is an obvious candidate for launching these winds. However this mechanism requires material with UV opacity, in apparent conflict with the observed high ionisation state of the wind. In this paper we synthesise the X-ray energy spectra resulting from different lines of sight through a state of the art radiation hydrodynamics UV line driven disc wind simulation. We demonstrate that there are some lines of sight which only intercept highly ionised and fast outflowing material. The cooler material required for the UV line driving acceleration is out of the line of sight, close to the disc, shielded from the X-rays by a failed wind. We fit these simulated wind spectra to data from the archetypal UFO source PG 1211+143 and show that they broadly reproduce the depth and velocity of the iron absorption lines seen. This directly demonstrates that UV line driving is a viable mechanism to launch even the fastest UFOs. We simulate microcalorimeter observations of this wind and show that their high energy resolution can resolve the detailed structure in the wind and recover the wind energetics when combined with models which correctly estimate the line formation radius of the wind. New data from microcalorimeters will pave the way for physical predictions of AGN wind feedback in cosmological simulations.

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arXiv2020

Geometry of the X-ray source 1H 0707-495

We investigate constraints for the size and location of the X-ray source in 1H 0707-495 determined from the shape of the relativistically smeared reflection from the accretion disc. We develop a new code to model an extended X-ray source and we apply it to all archival XMM observations of 1H 0707-495. Contrary to Wilkins et al. we find that the relativistic reflection in this source is not consistent with an extended uniform corona. Instead, we find that the X-ray source must be very compact, with the size of at most a gravitational radius, and located at most at a few gravitational radii from the black hole horizon. A uniform extended corona does indeed produce an emissivity which is like a twice broken power law, but the inner emissivity is fixed by the source geometry rather than being a free parameter. In 1H0707-495, reflection from the inner disc is much stronger than expected for a uniformly extended source. Including the effect of ionised absorption from a wind does not change this conclusion, but including scattered emission (and more complex absorption) from the wind can dramatically change the reflection parameters.

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