宇宙物理セミナーのご案内


題 名:Chandra X-Ray Kinematics Study of Young Supernova Remnants
講師: Sangwook Park(University of Texas at Arlington)
日 時:2018年4月16日(月) 16時20分〜
会 場:理学部1号館物理会議室

Abstract
Supernova remnants are an excellent laboratory to study fundamental subjects of modern astronomy and astrophysics such as stellar evolution and explosion. Realizing the 3-dimensional structure of supernova explosions is critical to understand the explosion physics and the nature of the exploded star. Based on the high resolution grating spectroscopy of Chandra X-ray Observatory, we can perform X-ray kinematic studies of metal-rich stellar debris of supernova explosions to address their 3-D nature. We briefly discuss such kinematic studies of supernova remnants, including our on-going studies of historical events: stellar explosions eye-witnessed in 1987, 1604, and 1572.
Poster: PDF


過去の宇宙物理セミナー


題 名:天文画像データの解析手法
講師: 森井幹雄(統計数理研究所)
日 時:2018年2月23日(金) 16時00分〜
会 場:理学部1号館物理会議室

Abstract
近年、すばる望遠鏡/Hyper Suprime-CamやTomo-e Gozenなど可視光望遠鏡を用いた大規模サーベイにより、大量の観測データが得られるようになってきた。そのため膨大なデータを効率的に解析する必要がある。我々は、機械学習を用 いることで効率的に超新星など突発天体を選出する手法を開発した。天体形状の特徴量を用いた方法と、動画からスパース性を用いて抽出する方法を紹介する。また、X線画像データを 効率的に分離したり、移動量を求める方法についても紹介する。
Poster: PDF


題 名:Evidence for GeV Cosmic Rays from White Dwarfs in the Local Cosmic Ray Spectra and in the Gamma-ray Emissivity of the Inner Galaxy
講師:釜江常好 (東京大学・名誉教授)
日 時:2018年2月16日(金) 17時30分〜
会 場:理学部1号館物理会議室

Abstract
Recent observations found that electrons are accelerated to 10 GeV and emit synchrotron hard X-rays in two magnetic white dwarfs (WDs), also known as cataclysmic variables (CVs). In nova outbursts of WDs, multi-GeV gamma-rays were detected inferring that protons are accelerated to 100 GeV or higher. In recent optical surveys, the WD density is found to be higher near the Sun than in the Galactic disk by a factor 2.5. The cosmic rays (CR) produced by local CVs and novae will accumulate in the local bubble for 10^6 -- 10^7 yrs. On these findings, we search for CRs from historic CVs and novae in the observed CR spectra. We model the CR spectra at the heliopause as sums of Galactic and local components based on observational data as much as possible. The initial Galactic CR electron and proton spectra are deduced from the gamma-ray emissivity, the local electron spectrum from the hard X-ray spectra at the CVs, and the local proton spectrum inferred by gamma-ray spectrum at novae. These spectral shapes are then expressed in a simple set of polynomial functions of CR energy and regressively fitted until the high-energy (>100 GeV) CR spectra near Earth and the Voyager-1 spectra at the heliopause are reproduced. We then extend the modeling to nuclear CR spectra and find that one spectral shape fits all local nuclear CRs and the apparent hardening of the nuclear CR spectra is caused by the roll-down of local nuclear spectra around 100 -- 200 GeV. All local CR spectra populate in a limited energy band below 100 -- 200 GeV and enhance gamma-ray emissivity below 10 GeV. Such an enhancement is observed in the inner Galaxy, suggesting the CR fluxes from CVs and novae are substantially higher there.
Poster: PDF


題 名:Cyclotron resonance scattering features and Magnetic field of pulsars
講師:Dr. Gaurava K. Jaisawal (インド Astronomy and Astrophysics Division Physical Research Laboratory)
日 時:2016年12月9日(金) 15時00分〜
会 場:理学部1号館物理会議室

Abstract
Cyclotron resonance scattering features or cyclotron absorption lines are unique features observed in hard Xray spectra of accretion powered X-ray pulsars with magnetic field of the order of 1012 G. Detection of these features is a powerful tool and the only direct method to estimate the magnetic field strength close to the surface of neutron stars. Corresponding to magnetic field of ~1012 G, the fundamental lines are expected in 10-100 keV energy range with harmonics expected at multiples of fundamental line energy. However, we detected first harmonics of cyclotron line at less than twice of the fundamental line energy (~ 1.7 times the fundamental line energy) in Be/X-ray binary pulsar Cep X-4. With the broadband spectral capability of Suzaku and NuSTAR observatories, we have investigated several X-ray pulsars to understand line shape, width, magnetic field mapping, anharmonicity in the line energies and luminosity-dependent properties of cyclotron lines. The results obtained from these works and new detection of cyclotron line in unknown/ poorly studied sources will be discussed in detail.

Poster: PDF


題 名:SFXTs vs sgHMXBs: does the difference lie in the companion wind?
講師:Dr. Pragati Pradhan (インド St. Joseph's College)
日 時:2016年12月9日(金) 16時00分〜
会 場:理学部1号館物理会議室

Abstract
We present a comparative study of classical supergiant HMXB and SFXT systems by using the absorption column density and equivalent width of iron Kα line in their X-ray emission. The work has been carried out using out-of-eclipse observations sgHMXBs(SFXTs) with Suzaku and XMM-Newton and we have taken care to separately analyse parts of any observation with significant variation in the spectrum. Analysis of all archival Suzaku and XMM-Newton observations of these systems show that sgHMXBs have a wide range of equivalent width of iron emission line and equivalent column density of absorption, both over three orders of magnitude. In comparison, the SFXTs show a smaller range for both the parameters, less than one and a half order of magnitude. These findings indicate a crucial difference in the wind characteristics of the companions of sgHMXBs and SFXTs, which could be an important factor for the intriguing difference in average X-ray luminosity and transient behavior between these two classes of sources.

Poster: PDF