47 research outputs found
年単位でのX線時間変動から探る超新星残骸のエネルギー輸送と膨張過程
京都大学新制・課程博士博士(理学)甲第25113号理博第5020号京都大学大学院理学研究科物理学・宇宙物理学専攻(主査)教授 鶴 剛, 准教授 榎戸 輝揚, 教授 田島 治学位規則第4条第1項該当Doctor of ScienceKyoto UniversityDFA
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 and
hardening of . The time variability can be explained
if the magnetic field is amplified to and/or if
magnetic turbulence significantly changes with time.Comment: 8 pages, 3 figures, 2 tables, accepted for publication in Ap
Discovery of Year-scale Time Variability from Thermal X-Ray Emission in Tycho’s Supernova Remnant
ティコの超新星残骸で増光する構造を発見 --加熱過程をリアルタイムで捉える--. 京都大学プレスリリース. 2022-11-29.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 the Chandra data of Tycho's SNR obtained during 2000–2015. The emission exhibits a knot-like feature (Knot1) with a diameter of ≃0.04 pc located in the northwestern limb, where we also find localized Hα 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 the 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 ∼0.30 to ∼0.69 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 of the shock (β₀ ≡ Te/Tp) is constrained to be me/mp ≤ β₀ ≤ 0.15 to reproduce the data, indicating the collisionless electron heating with efficiency is consistent with previous Hα observations of Tycho and other SNRs with high shock velocities
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
Dual supermassive black holes at close separation revealed by the Hyper Suprime-Cam Subaru Strategic Program
The unique combination of superb spatial resolution, wide-area coverage, and
deep depth of the optical imaging from the Hyper Suprime-Cam (HSC) Subaru
Strategic Program is utilized to search for dual quasar candidates. Using an
automated image analysis routine on 34,476 known SDSS quasars, we identify
those with two (or more) distinct optical point sources in HSC images covering
796 deg^2. We find 421 candidates out to a redshift of 4.5 of which one hundred
or so are more likely after filtering out contaminating stars. Angular
separations of 0.6 - 4.0" correspond to projected separations of 3 - 30 kpc, a
range relatively unexplored for population studies of luminous dual quasars.
Using Keck-I/LRIS and Gemini-N/NIFS, we spectroscopically confirm three dual
quasar systems at z < 1, two of which are previously unknown out of eight
observed, based on the presence of characteristic broad emission lines in each
component, while highlighting that the continuum of one object in one of the
pairs is reddened. In all cases, the [OIII]5007 emission lines have mild
velocity offsets, thus the joint [OIII] line profile is not double-peaked. We
find a dual quasar fraction of 0.26+/-0.18% and no evidence for evolution. A
comparison with the Horizon-AGN simulation seems to support the case of no
evolution in the dual quasar fraction when broadly matching the quasar
selection. These results may indicate a scenario in which the frequency of the
simultaneous triggering of luminous quasars is not as sensitive as expected to
the cosmic evolution of the merger rate or gas content of galaxies.Comment: 11 pages; 12 figures; Accepted for publication in The Astrophysical
Journa
Fibroblast heterogeneity in the cancer wound
Fibroblasts regulate the structure and function of healthy tissues, participate transiently in tissue repair after acute inflammation, and assume an aberrant stimulatory role during chronic inflammatory states including cancer. Such cancer-associated fibroblasts (CAFs) modulate the tumor microenvironment and influence the behavior of neoplastic cells in either a tumor-promoting or tumor-inhibiting manner. These pleiotropic functions highlight the inherent plasticity of fibroblasts and may provide new avenues to understand and therapeutically intervene in malignancies. We discuss the emerging themes of CAF biology in the context of tumorigenesis and therapy