arXiv subjects

Hiroki Akamatsu

Publications and source records attributed to Hiroki Akamatsu.

At least 37 records · Page 2Linked to original sources

arXiv2022

The NuSTAR, XMM-Newton, and Suzaku view of A3395 at the intercluster filament interface

Galaxy clusters are the largest virialized objects in the universe. Their merger dynamics and their interactions with the cosmic filaments that connect them are important for our understanding of the formation of large-scale structure. In addition, cosmic filaments are thought to possess the missing baryons in the universe. Studying the interaction of galaxy clusters and filaments therefore has the potential to unveil the the origin of the baryons and the physical processes that occur during merger stages of galaxy clusters. In this paper, we study the connection between A3395 and the intercluster filament with NuSTAR, XMM-Newton, and Suzaku data. Since the NuSTAR observation is moderately contaminated by scattered light, we present a novel technique developed for disentangling this background from the emission from the intracluster medium. We find that the interface of the cluster and the intercluster filament connecting A3395 and A3391 does not show any signs of heated plasma, as was previously thought. This interface has low temperature, high density, and low entropy, thus we suggest that the gas is cooling, being enhanced by the turbulent or tidal 'weather' driven during the early stage of the merger. Furthermore, our temperature results from the NuSTAR data are in agreement with those from XMM-Newton, and from joint NuSTAR and XMM-Newton analysis for a region with ~25% scattered light contamination within 1 sigma. We show that the temperature constraint of the intracluster medium is valid even when the data are contaminated up to ~25% for ~5 keV cluster emission.

astro-ph.HE↗

arXiv2022

Spectral study of the diffuse synchrotron source in the galaxy cluster Abell 523

The galaxy cluster Abell 523 (A523) hosts an extended diffuse synchrotron source historically classified as a radio halo. Its radio power at 1.4 GHz makes it one of the most significant outliers in the scaling relations between observables derived from multi-wavelength observations of galaxy clusters: it has a morphology that is different and offset from the thermal gas, and it has polarized emission at 1.4 GHz typically difficult to observe for this class of sources. A magnetic field fluctuating on large spatial scales (~ 1 Mpc) can explain these peculiarities but the formation mechanism for this source is not yet completely clear. To investigate its formation mechanism, we present new observations obtained with the LOw Frequency ARray at 120-168 MHz and the Jansky Very Large Array at 1-2 GHz, which allow us to study the spectral index distribution of this source. According to our data the source is observed to be more extended at 144 MHz than previously inferred at 1.4 GHz, with a total size of about 1.8 Mpc and a flux density S_144MHz = (1.52 +- 0.31) Jy. The spectral index distribution of the source is patchy with an average spectral index alpha ~ 1.2 between 144 MHz and 1.410 GHz, while an integrated spectral index alpha ~ 2.1 has been obtained between 1.410 GHz and 1.782 GHz. A previously unseen patch of steep spectrum emission is clearly detected at 144 MHz in the south of the cluster. Overall, our findings suggest that we are observing an overlapping of different structures, powered by the turbulence associated with the primary and a possible secondary merger.

astro-ph.CO↗

arXiv2021

Thermal crosstalk of X-ray transition-edge sensor micro-calorimeters under frequency domain multiplexing readout

We have measured and characterized the thermal crosstalk in two different arrays of transition-edge sensor (TES) X-ray micro-calorimeters with frequency-domain multiplexing (FDM) readout. The TES arrays are fabricated at SRON and are a 8$\times$8 and a 32$\times$32 "kilo-pixel" uniform array. The amount of crosstalk is evaluated as the ratio between the averaged crosstalk signal and the X-ray pulse amplitudes. The crosstalk ratios (CR) for our detectors are compliant with the requirements for future X-ray space missions, such as Athena X-IFU (CR$< 10^{-3}$ for first-neighbour pixels): we measured a nearest-neighbour thermal crosstalk ratio at a level of $10^{-4}$, with a highest crosstalk ratio of $4\times 10^{-4}$ for the kilo-pixel array (worst case, center of array) and $1\times 10^{-4}$ for the 8$\times$8 array, with a margin of improvement achievable by optimizing the Cu metallization and the width of the Si supporting structures (muntins) in the backside of the TES array chip. Based on the measured crosstalk ratios, we have estimated the impact on the spectral resolution by means of noise equivalent power (NEP) considerations and a Monte Carlo simulation, finding an average degradation in quadrature of less than 40~meV, compliant with the < 0.2~eV requirement for Athena X-IFU.

astro-ph.IM↗

arXiv2021

Elemental Abundances of the Hot Atmosphere of Luminous Infrared Galaxy Arp 299

Hot atmospheres of massive galaxies are enriched with metals. Elemental abundances measured in the X-ray band have been used to study the chemical enrichment of supernova remnants, elliptical galaxies, groups and clusters of galaxies. Here we measure the elemental abundances of the hot atmosphere of luminous infrared galaxy Arp 299 observed with XMM-Newton. To measure the abundances in the hot atmosphere, we use a multi-temperature thermal plasma model, which provides a better fit to the Reflection Grating Spectrometer data. The observed Fe/O abundance ratio is subsolar, while those of Ne/O and Mg/O are slightly above solar. Core-collapse supernovae (SNcc) are the dominant metal factory of elements like O, Ne, and Mg. We find some deviations between the observed abundance patterns and theoretical ones from a simple chemical enrichment model. One possible explanation is that massive stars with $M_{\star}\gtrsim23-27~M_{\odot}$ might not explode as SNcc and enrich the hot atmosphere. This is in accordance with the missing massive SNcc progenitors problem, where very massive progenitors $M_{\star}\gtrsim18~M_{\odot}$ of SNcc have not been clearly detected. It is also possible that theoretical SNcc nucleosynthesis yields of Mg/O yields are underestimated.

astro-ph.HE↗

arXiv2021

A test platform for the detection and readout chain for the Athena X-IFU

We present a test platform for the Athena X-IFU detection chain, which will serve as the first demonstration of the representative end-to-end detection and readout chain for the X-IFU, using prototypes of the future flight electronics and currently available subsystems. This test bench, housed in a commercial two-stage ADR cryostat, includes a focal plane array placed at the 50 mK cold stage of the ADR with a kilopixel array of transition-edge sensor microcalorimeter spectrometers and associated cold readout electronics. Prototype room temperature electronics for the X-IFU provide the readout, and will evolve over time to become more representative of the X-IFU mission baseline. The test bench yields critical feedback on subsystem designs and interfaces, in particular the warm readout electronics, and will provide an in-house detection system for continued testing and development of the warm readout electronics and for the validation of X-ray calibration sources. In this paper, we describe the test bench subsystems and design, characterization of the cryostat, and current status of the project.

astro-ph.IM↗

arXiv2021

A shock near the virial radius of the Perseus Cluster

Previous X-ray studies of the Perseus Cluster, consisting of 85 Suzaku pointings along eight azimuthal directions, revealed a particularly steep decrease in the projected temperature profile near the virial radius (~r200) towards the northwest (NW). To further explore this shock candidate, another 4 Suzaku observations on the NW edge of the Perseus Cluster have been obtained. These deeper data were designed to provide the best possible control of systematic uncertainties in the spectral analysis. Using the combined Suzaku observations, we have carefully investigated this interesting region by analyzing the spectra of various annuli and extracting projected thermodynamic profiles. We find that the projected temperature profile shows a break near r200, indicating a shock with M = 1.9+-0.3. Corresponding discontinuities are also found in the projected emission measure and the density profiles at the same location. This evidence of a shock front so far away from the cluster center is unprecedented, and may provide a first insight into the properties of large-scale virial shocks which shape the process of galaxy cluster growth.

astro-ph.HE↗

arXiv2021

Frequency Shift Algorithm: Design of a Baseband Phase Locked Loop for Frequency-Domain Multiplexing Readout of X-ray Transition-Edge Sensor Microcalorimeters

The Transition-Edge Sensor (TES) is an extremely sensitive device which is used to measure the energy of individual X-ray photons. For astronomical spectrometry applications, SRON develops a Frequency Domain Multiplexing (FDM) read-out system for kilopixel arrays of such TESs. Each TES is voltage biased at a specific frequency in the range 1 to 5 MHz. Isolation between the individual pixels is obtained through very narrow-band (high-Q) lithographic LC resonators. To prevent energy resolution degradation due to intermodulation line noise, the bias frequencies are distributed on a regular grid. The requirements on the accuracy of the LC resonance frequency are very high. The deviation of the resonance frequencies due to production tolerances is significant with respect to the bandwidth, and a controller is necessary to compensate for the LC series impedance. We present two such controllers: a simple orthogonal proportional-integrating (PI) controller and a more complex impedance estimator. Both controllers operate in baseband and try to make the TES current in-phase with the bias voltage, effectively operating as phase-locked loops (PLL). They allow off-LC-resonance operation of the TES pixels, while preserving TES thermal response and energy resolution. Extensive experimental results -- published in a companion paper recently -- with the proposed methods, show that these controllers allow the preservation of single pixel energy resolution in multiplexed operation.

physics.ins-det↗

arXiv2021

Jets from MRC 0600-399 bent by magnetic fields in the cluster Abell 3376

Galaxy clusters are known to harbour magnetic fields. The nature of the intra-cluster magnetic fields remains an unresolved question. Intra-cluster magnetic field can be observed at the density contact discontinuity formed by cool and dense plasma running into hot ambient plasma, and the discontinuity exists near the 2nd BCG MRC 0600-399 of a merging galaxy cluster Abell 3376 (z=0.0461, hereafter as A3376). Elongated X-ray image in the east-west direction with a comet-like structure reaches a Mpc-scale (Fig1.(a)). Previous radio observations detected the bent jets from MRC 0600-399, moving in same direction as the sub-cluster's motion against ram pressure.Here we report a new radio observation of a radio galaxy MRC 0600-399 which is 3.4 times and 11 times higher resolution and sensitivity than the previous results. Contrary to typical jets, the MRC 0600-399 shows a 90deg bend at the contact discontinuity and the collimated jets further extend over 100 kpc from the bend point. Diffuse, elongated emission named "double-scythe" structures were detected for the first time. The spectral index flattens downstream of the bend point, indicating cosmic-ray re-acceleration. High-resolution numerical simulations reveal that the ordered magnetic field along the discontinuity plays a significant role in the change in the jet direction. The morphology of the "double-scythe" bear remarkable similarities with the simulations, which strengthens our understanding of the interaction between relativistic electrons and intra-cluster magnetic field.

astro-ph.GA↗

arXiv2021

Signatures of large-scale cold fronts in the optically-selected merging cluster HSC J085024+001536

We represent a joint X-ray, weak-lensing, and optical analysis of the optically-selected merging cluster, HSC J085024+001536, from the Subaru HSC-SSP survey. Both the member galaxy density and the weak-lensing mass map show that the cluster is composed of southeast and northwest components. The two-dimensional weak-lensing analysis shows that the southeast component is the main cluster, and the sub- and main-cluster mass ratio is $0.32^{+0.75}_{-0.23}$. The northwest subcluster is offset by $\sim700$ kpc from the main cluster center, and their relative line-of-sight velocity is $\sim1300\,{\rm km s^{-1}}$ from spectroscopic redshifts of member galaxies. The X-ray emission is concentrated around the main cluster, while the gas mass fraction within a sphere of $1'$ radius of the subcluster is only $f_{\mathrm{gas}}=4.0^{+2.3}_{-3.3}\%$, indicating that the subcluster gas was stripped by ram pressure. X-ray residual image shows three arc-like excess patterns, of which two are symmetrically located at $\sim550$ kpc from the X-ray morphological center, and the other is close to the X-ray core. The excess close to the subcluster has a cold-front feature where dense-cold gas and thin-hot gas contact. The two outer excesses are tangentially elongated about $\sim 450-650$ kpc, suggesting that the cluster is merged with a non-zero impact parameter. Overall features revealed by the multi-wavelength datasets indicate that the cluster is at the second impact or later. Since the optically-defined merger catalog is unbiased for merger boost of the intracluster medium, X-ray follow-up observations will pave the way to understand merger physics at various phases.

astro-ph.GA↗

arXiv2021

Single pixel performance of a 32$\times$32 Ti/Au TES array with broadband X-ray spectra

We are developing a kilo-pixels Ti/Au TES array as a backup option for Athena X-IFU. Here we report on single-pixel performance of a 32$\times$32 array operated in a Frequency Division Multiplexing (FDM) readout system, with bias frequencies in the range 1-5 MHz. We have tested the pixels response at several photon energies, by means of a $^{55}$Fe radioactive source (emitting Mn-K$α$ at 5.9 keV) and a Modulated X-ray Source (MXS, providing Cr-K$α$ at 5.4 keV and Cu-K$α$ at 8.0 keV). First, we report the procedure used to perform the detector energy scale calibration, usually achieving a calibration accuracy better than $\sim$ 0.5 eV in the 5.4 - 8.9 keV energy range. Then, we present the measured energy resolution at the different energies (best single pixel performance: $Δ$E$_{FWHM}$ = 2.40 $\pm$ 0.09 eV @ 5.4 keV; 2.53 $\pm$ 0.10 eV @ 5.9 keV; 2.78 $\pm$ 0.16 eV @ 8.0 keV), investigating also the performance dependency from the pixel bias frequency and the count rate. Thanks to long background measurements ($\sim$ 1 day), we finally detected also the Al-K$α$ line at 1.5 keV, generated by fluorescence inside the experimental setup. We analyzed this line to obtain a first assessment of the single-pixel performance also at low energy ($Δ$E$_{FWHM}$ = 1.91 eV $\pm$ 0.21 eV @ 1.5 keV), and to evaluate the linearity of the detector response in a large energy band (1.5 - 8.9 keV).

astro-ph.IM↗

arXiv2020

Active gas features in three HSC-SSP CAMIRA clusters revealed by high angular resolution analysis of MUSTANG-2 SZE and XXL X-ray observations

We present results from simultaneous modeling of high angular resolution GBT/MUSTANG-2 90 GHz Sunyaev-Zel'dovich effect (SZE) measurements and XMM-XXL X-ray images of three rich galaxy clusters selected from the HSC-SSP Survey. The combination of high angular resolution SZE and X-ray imaging enables a spatially resolved multi-component analysis, which is crucial to understand complex distributions of cluster gas properties. The targeted clusters have similar optical richnesses and redshifts, but exhibit different dynamical states in their member galaxy distributions: a single-peaked cluster, a double-peaked cluster, and a cluster belonging to a supercluster. A large-scale residual pattern in both regular Compton-parameter $y$ and X-ray surface brightness distributions is found in the single-peaked cluster, indicating a sloshing mode. The double-peaked cluster shows an X-ray remnant cool core between two SZE peaks associated with galaxy concentrations. The temperatures of the two peaks reach $\sim20-30$ keV in contrast to the cool core component of $\sim2$ keV, indicating a violent merger. The main SZE signal for the supercluster is elongated along a direction perpendicular to the major axis of the X-ray core, suggesting a minor merger before core passage. The $S_X$ and $y$ distributions are thus perturbed at some level, regardless of the optical properties. We find that the integrated Compton $y$ parameter and the temperature for the major merger are boosted from those expected by the weak-lensing mass and those for the other two clusters show no significant deviations, which is consistent with predictions of numerical simulations.

astro-ph.CO↗

arXiv2020

X-ray spectra of the Fe-L complex II: atomic data constraints from EBIT experiment and X-ray grating observations of Capella

The Hitomi results for the Perseus cluster have shown that accurate atomic models are essential to the success of X-ray spectroscopic missions, and just as important as knowledge on instrumental calibration and astrophysical modeling. Preparing the models requires a multifaceted approach, including theoretical calculations, laboratory measurements, and calibration using real observations. In a previous paper, we presented a calculation of the electron impact cross sections on the transitions forming the Fe-L complex. In the present work, we systematically test the calculation against cross sections of ions measured in an electron beam ion trap experiment. A two-dimensional analysis in the electron beam energies and X-ray photon energies is utilized to disentangle radiative channels following dielectronic recombination, direct electron-impact excitation, and resonant excitation processes in the experimental data. The data calibrated through laboratory measurements are further fed into global modeling of the Chandra grating spectrum of Capella. We investigate and compare the fit quality, as well as sensitivity of the derived physical parameters to the underlying atomic data and the astrophysical plasma modeling. We further list the potential areas of disagreement between the observation and the present calculations, which in turn calls for renewed efforts in theoretical calculations and targeted laboratory measurements.

astro-ph.HE↗

arXiv2020

ASKAP reveals giant radio halos in two merging SPT galaxy clusters -- Making the case for a direction-dependent pipeline --

Early science observations from the Australian Square Kilometre Array Pathfinder (ASKAP) have revealed clear signals of diffuse radio emission associated with two clusters detected by the South Pole Telescope via their Sunyaev Zel'dovich signal. SPT CLJ0553-3342 (MACSJ0553.4-3342) and SPT CLJ0638-5358 (Abell S0592) are both high-mass lensing clusters that have undergone major mergers. To improve the data products of these ASKAP early science observations and create science-fidelity images of the galaxy clusters, we performed direction-dependent (DD) calibration and imaging using state-of-the-art software {\sc killMS} and {\sc DDFacet}. We find that artefacts in the ASKAP images are greatly reduced after directional calibration. Here we present our DD calibrated ASKAP radio images of both clusters showing unambiguous giant radio halos with largest linear scales of $\sim1$~Mpc. The halo in MACSJ0553.4-3342 was previously detected with GMRT observations at 323 MHz, but appears more extended in our ASKAP image. Although there is a shock detected in the thermal X-ray emission of this cluster, we find that the particle number density in the shocked region is too low to allow for the generation of a radio shock. The radio halo in Abell S0592 is a new discovery, and the Southwest border of the halo coincides with a shock detected in X-rays. We discuss the origins of these halos considering both the hadronic and turbulent re-acceleration models as well as sources of \textit{seed} electrons. This work gives a positive indication of the potential of ASKAP's Evolutionary Map of the Universe (EMU) survey in detecting intracluster medium radio sources, and showcases the improvement in data products after utilising third-generation calibration techniques.

astro-ph.GA↗

arXiv2019

X-ray study of the double source plane gravitational lens system Eye of Horus observed with XMM-Newton

A double source plane (DSP) system is a precious probe for the density profile of distant galaxies and cosmological parameters. However, these measurements could be affected by the surrounding environment of the lens galaxy. Thus, it is important to evaluate the cluster-scale mass for detailed mass modeling. We observed the {\it Eye of Horus}, a DSP system discovered by the Subaru HSC--SSP, with XMM--Newton. We detected two X-ray extended emissions, originating from two clusters, one centered at the {\it Eye of Horus}, and the other located $\sim100$ arcsec northeast to the {\it Eye of Horus}. We determined the dynamical mass assuming hydrostatic equilibrium, and evaluated their contributions to the lens mass interior of the Einstein radius. The contribution of the former cluster is $1.1^{+1.2}_{-0.5}\times10^{12}~M_{\odot}$, which is $21-76\%$ of the total mass within the Einstein radius. The discrepancy is likely due to the complex gravitational structure along the line of sight. On the other hand, the contribution of the latter cluster is only $\sim2\%$ on the {\it Eye of Horus}. Therefore, the influence associated with this cluster can be ignored.

astro-ph.GA↗

arXiv2019

X-ray properties of high-richness CAMIRA clusters in the Hyper Suprime-Cam Subaru Strategic Program field

We present the first results of a pilot X-ray study of 37 rich galaxy clusters at $0.1<z<1.1$ in the Hyper Suprime-Cam Subaru Strategic Program (HSC-SSP) field. Diffuse X-ray emissions from these clusters were serendipitously detected in the XMM-Newton fields of view. We systematically analyze X-ray images of 37 clusters and emission spectra of a subsample of 17 clusters with high photon statistics by using the XMM-Newton archive data. The frequency distribution of the offset between the X-ray centroid or peak and the position of the brightest cluster galaxy was derived for the optical cluster sample. The fraction of relaxed clusters estimated from the X-ray peak offsets in 17 clusters is $29\pm11(\pm13)$\%, which is smaller than that of the X-ray cluster samples such as HIFLUGCS. Since the optical cluster search is immune to the physical state of X-ray-emitting gas, it is likely to cover a larger range of the cluster morphology. We also derived the luminosity-temperature relation and found that the slope is marginally shallower than those of X-ray-selected samples and consistent with the self-similar model prediction of 2. Accordingly, our results show that the X-ray properties of the optical clusters are marginally different from those observed in the X-ray samples. The implication of the results and future prospects are briefly discussed.

astro-ph.CO↗

arXiv2019

Characterization of diffuse X-ray emission from IGR~J17448-3232: an implication of a line of sight merging activity

Results of the spectral analysis for the galaxy cluster IGR J17448-3232 are presented. The intracluster medium (ICM) in the central region (r<300", 320 kpc) has a high electron temperature plasma of kTe~13-15 keV and an ionization temperature estimated from an intensity ratio of Fe XXVI Ly alpha/Fe XXV He alpha lines is lower than the electron temperature, which suggests that the ICM is in the non-ionization equilibrium (NEI) state. The spectrum in the central region can be also fitted with a two-component model: a two-temperature plasma model in a collisional ionization equilibrium (CIE) with temperatures of 7.9 keV and >34 keV or a CIE+power law model with a temperature of 9.4 keV and a photon index of 1.1. The two component models can represent the intensity ratio of Fe XXVI Ly alpha/Fe XXV He alpha lines. On the other hand, the spectrum in the outer region (r>300'') can be explained by a single CIE plasma model with a temperature of 5-8 keV. Based on the spectral feature and its circular structure, we propose that the NEI plasma was produced by merging along the line-of-sight direction.

astro-ph.HE↗

arXiv2019

Observations of a Pre-Merger Shock in Colliding Clusters of Galaxies

Clusters of galaxies are the largest known gravitationally-bound structures in the Universe. When clusters collide, they create merger shocks on cosmological scales, which transform most of the kinetic energy carried by the cluster gaseous halos into heat. Observations of merger shocks provide key information of the merger dynamics, and enable insights into the formation and thermal history of the large-scale structures. Nearly all of the merger shocks are found in systems where the clusters have already collided, knowledge of shocks in the pre-merger phase is a crucial missing ingredient. Here we report on the discovery of a unique shock in a cluster pair 1E 2216 and 1E 2215. The two clusters are observed at an early phase of major merger. Contrary to all the known merger shocks observed ubiquitously on merger axes, the new shock propagates outward along the equatorial plane of the merger. This discovery uncovers an important epoch in the formation of massive clusters, when the rapid approach of the cluster pair leads to strong compression of gas along the merger axis. Current theoretical models predict that the bulk of the shock energy might be dissipated outside the clusters, and eventually turn into heat of the pristine gas in the circum-cluster space.

astro-ph.HE↗

arXiv2019

Halo Concentration, Galaxy Red Fraction, and Gas Properties of Optically-defined Merging Clusters

We present multi-wavelength studies of optically-defined merging clusters, based on the Hyper Suprime-Cam Subaru Strategic Program. Luminous red galaxies, tracing cluster mass distributions, enable to identify cluster subhalos at various merging stages, and thus make a homogeneous sample of cluster mergers, which is unbiased with respect to the merger boost of the intracluster medium (ICM). We define, using a peak-finding method, merging clusters with multiple-peaks and single clusters with single-peaks from the CAMIRA cluster catalog. Stacked weak-lensing analysis indicates that our sample of the merging clusters is categorized into major mergers. The average halo concentration for the merging clusters is $\sim70\%$ smaller than that of the single-peak clusters, which agrees well with predictions of numerical simulations. The spatial distribution of subhalos is less centrally concentrated than the mass distribution of the main halo. The fractions of red galaxies in the merging clusters are not higher than those of the single-peak clusters. We find a signature of the merger boost of the ICM from stacked Planck Sunyaev-Zeldovich effect and ROSAT X-ray luminosity, but not in optical richness. The stacked X-ray surface brightness distribution, aligned with the main-subhalo pairs of low redshift and massive clusters, shows that the central gas core is elongated along the merger axis and overall gas distribution is misaligned by $\sim60$ deg. The homogeneous, unbiased sample of cluster mergers and multi-wavelength follow-up studies provide a unique opportunity to make a complete picture of merger physics over the whole process.

astro-ph.CO↗