arXiv subjects

Masamune Matsuda

Publications and source records attributed to Masamune Matsuda.

6 recordsLinked to original sources

arXiv2024

SUIM project: measuring the upper atmosphere from the ISS by observations of the CXB transmitted through the Earth rim

The upper atmosphere at the altitude of 60-110 km, the mesosphere and lower thermosphere (MLT), has the least observational data of all atmospheres due to the difficulties of in-situ observations. Previous studies demonstrated that atmospheric occultation of cosmic X-ray sources is an effective technique to investigate the MLT. Aiming to measure the atmospheric density of the MLT continuously, we are developing an X-ray camera, "Soipix for observing Upper atmosphere as Iss experiment Mission (SUIM)", dedicated to atmospheric observations. SUIM will be installed on the exposed area of the International Space Station (ISS) and face the ram direction of the ISS to point toward the Earth rim. Observing the cosmic X-ray background (CXB) transmitted through the atmosphere, we will measure the absorption column density via spectroscopy and thus obtain the density of the upper atmosphere. The X-ray camera is composed of a slit collimator and two X-ray SOI-CMOS pixel sensors (SOIPIX), and will stand on its own and make observations, controlled by a CPU-embedded FPGA "Zynq". We plan to install the SUIM payload on the ISS in 2025 during the solar maximum. In this paper, we report the overview and the development status of this project.

astro-ph.IM↗

arXiv2024

Evaluation of the X-ray SOI pixel detector with the on-chip ADC

XRPIX is the monolithic X-ray SOI (silicon-on-insulator) pixel detector, which has a time resolution better than 10 $\rmμ$s as well as a high detection efficiency for X-rays above 10 keV. XRPIX is planned to be installed on future X-ray satellites. To mount on satellites, it is essential that the ADC (analog-to-digital converter) be implemented on the detector because such peripheral circuits must be as compact as possible to achieve a large imaging area in the limited space in satellites. Thus, we developed a new XRPIX device with the on-chip ADC, and evaluated its performances. As the results, the integral non-linearity was evaluated to be 6 LSB (least significant bit), equivalent to 36 eV. The differential non-linearity was less than 0.7 LSB, and input noise from the on-chip ADC was 5~$\rm{e^{-}}$. Also, we evaluated end-to-end performance including the sensor part as well as the on-chip ADC. As the results, energy resolution at 5.9 keV was 294 $\rm{\pm}$ 4 eV in full-width at half maximum for the best pixel.

astro-ph.IM↗

arXiv2022

ISAI: Investigating Solar Axion by Iron-57

The existence of the axion is a unique solution for the strong CP problem, and the axion is one of the most promising candidates of the dark matter. Investigating Solar Axion by Iron-57 (ISAI) is being prepared as a complemented table-top experiment to confirm the solar axion scenario. Probing an X-ray emission from the nuclear transitions associated with the axion-nucleon coupling is a leading approach. ISAI searches for the monochromatic 14.4 keV X-ray from the first excited state of 57Fe using a state-of-the-art pixelized silicon detector, dubbed XRPIX, under an extremely low-background environment. We highlight scientific objectives, experimental design and the latest status of ISAI.

astro-ph.IM↗

arXiv2022

Discovery of Year-Scale Time Variability from Thermal X-ray Emission in Tycho's Supernova Remnant

Mechanisms of particle heating are crucial to understanding the shock physics in supernova remnants (SNRs). However, there has been little information on time variabilities of thermalized particles so far. Here, we present a discovery of a gradually-brightening thermal X-ray emission found in Chandra data of Tycho's SNR obtained during 2000--2015. The emission exhibits a knot-like feature (Knot1) with a diameter of $\simeq0.04$~pc located in the northwestern limb, where we also find localized H$α$ filaments in an optical image taken with the Hubble Space Telescope in 2008. The model with the solar abundance reproduces the spectra of Knot1, suggesting that Knot1 originates from interstellar medium; this is the first detection of thermal X-ray emission from swept-up gas found in Tycho's SNR. Our spectral analysis indicates that the electron temperature of Knot1 has increased from $\sim0.30$ keV to $\sim0.69$ keV within the period between 2000 and 2015. These results lead us to ascribe the time-variable emission to a small dense clump recently heated by the forward shock at the location of Knot1. The electron-to-proton temperature ratio immediately downstream the shock ($β_{0}\equiv T_e/T_p$) is constrained to be $m_e/m_p\leqβ_{0}\leq0.15$ to reproduce the data, indicating the collisionless electron heating with efficiency consistent with previous H$α$ observations of Tycho and other SNRs with high shock velocities.

astro-ph.HE↗

arXiv2020

Temporal and Spatial Variation of Synchrotron X-ray Stripes in Tycho's Supernova Remnant

The synchrotron X-ray "stripes" discovered in Tycho's supernova remnant (SNR) have been attracting attention since they may be evidence for proton acceleration up to PeV. We analyzed Chandra data taken in 2003, 2007, 2009, and 2015 for imaging and spectroscopy of the stripes in the southwestern region of the SNR. Comparing images obtained at different epochs, we find that time variability of synchrotron X-rays is not limited to two structures previously reported but is more common in the region. Spectral analysis of nine bright stripes reveals not only their time variabilities but also a strong anti-correlation between the surface brightness and photon indices. The spectra of the nine stripes have photon indices of Γ= 2.1--2.6 and are significantly harder than those of the outer rim of the SNR in the same region with Γ= 2.7--2.9. Based on these findings, we indicate that the magnetic field is substantially amplified, and suggest that particle acceleration through a stochastic process may be at work in the stripes.

astro-ph.HE↗

arXiv2020

Time Variability of Nonthermal X-ray Stripes in Tycho's Supernova Remnant with Chandra

Analyzing Chandra data of Tycho's supernova remnant (SNR) taken in 2000, 2003, 2007, 2009, and 2015, we search for time variable features of synchrotron X-rays in the southwestern part of the SNR, where stripe structures of hard X-ray emission were previous found. By comparing X-ray images obtained at each epoch, we discover a knot-like structure in the northernmost part of the stripe region became brighter particularly in 2015. We also find a bright filamentary structure gradually became fainter and narrower as it moved outward. Our spectral analysis reveal that not only the nonthermal X-ray flux but also the photon indices of the knot-like structure change from year to year. During the period from 2000 to 2015, the small knot shows brightening of $\sim 70\%$ and hardening of $ΔΓ\sim 0.45$. The time variability can be explained if the magnetic field is amplified to $\sim 100~\mathrm{μG}$ and/or if magnetic turbulence significantly changes with time.

astro-ph.HE↗