A. Okumura
A5075493545- Astrophysics and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Dark Matter and Cosmic Phenomena
- Particle Detector Development and Performance
- Radio Astronomy Observations and Technology
- Radiation Detection and Scintillator Technologies
- Astrophysical Phenomena and Observations
- Neutrino Physics Research
- Pulsars and Gravitational Waves Research
- Particle Accelerators and Free-Electron Lasers
- Astronomical Observations and Instrumentation
- Particle physics theoretical and experimental studies
- Adaptive optics and wavefront sensing
- Astronomy and Astrophysical Research
- Nuclear Physics and Applications
- Astrophysics and Star Formation Studies
- Solar and Space Plasma Dynamics
- Medical Imaging Techniques and Applications
- Gallbladder and Bile Duct Disorders
- Scientific Computing and Data Management
- Planetary Science and Exploration
- Cosmology and Gravitation Theories
- MRI in cancer diagnosis
- Atomic and Subatomic Physics Research
- Distributed and Parallel Computing Systems
Nagoya University
2015-2024
Obayashi (Japan)
2019-2024
Universitat de Barcelona
2024
Institut d'Estudis Espacials de Catalunya
2024
RWTH Aachen University
2022-2024
Durham University
2023
Universidad Complutense de Madrid
2023
Universitat Politècnica de Catalunya
2023
University of Geneva
2023
The University of Tokyo
1990-2023
The gamma-ray sky >100 MeV is dominated by the diffuse emissions from interactions of cosmic rays with interstellar gas and radiation fields Milky Way. Observations these provide a tool to study cosmic-ray origin propagation, medium. We present measurements first 21 months Fermi-LAT mission compare models emission generated using GALPROP code. are fitted data incorporate astrophysical input for distribution sources, fields. To assess uncertainties associated input, grid created varying...
We measured separate cosmic-ray electron and positron spectra with the Fermi Large Area Telescope. Because instrument does not have an onboard magnet, we distinguish two species by exploiting Earth's shadow, which is offset in opposite directions for charges due to magnetic field. estimate subtract proton background using different methods that produce consistent results. report electron-only spectrum, positron-only fraction between 20 GeV 200 GeV. confirm rises energy 20-100 range. The...
Satellite galaxies of the Milky Way are among most promising targets for dark matter searches in gamma rays. We present a search consisting weakly interacting massive particles, applying joint likelihood analysis to 10 satellite with 24 months data Fermi Large Area Telescope. No signal is detected. Including uncertainty distribution, robust upper limits placed on annihilation cross sections. The 95% confidence level range from about 10(-26) cm3 s(-1) at 5 GeV 5×10(-23) 1 TeV, depending final...
Recent detections of the starburst galaxies M82 and NGC 253 by gamma-ray telescopes suggest that rapidly forming massive stars are more luminous at energies compared to their quiescent relatives. Building upon those results, we examine a sample 69 dwarf, spiral, ultraluminous infrared photon 0.1–100 GeV using 3 years data collected Large Area Telescope (LAT) on Fermi Gamma-ray Space (Fermi). Measured fluxes from significantly detected sources flux upper limits for remaining used explore...
The origin of Galactic cosmic rays is a century-long puzzle. Indirect evidence points to their acceleration by supernova shockwaves, but we know little escape from the shock and evolution through turbulent medium surrounding massive stars. Gamma can probe spreading ambient gas radiation fields. Fermi Large Area Telescope (LAT) has observed star-forming region Cygnus X. 1- 100-gigaelectronvolt images reveal 50-parsec-wide cocoon freshly accelerated that flood cavities carved stellar winds...
Dark matter particle annihilation or decay can produce monochromatic gamma-ray lines and contribute to the diffuse background. Flux upper limits are presented for spectral from 7 200 GeV background 4.8 264 obtained two years of Fermi Large Area Telescope data integrated over most sky. We give cross-section lifetime lower dark models that spectrum, including proposed as explanations PAMELA cosmic-ray data.
Weakly interacting massive particles (WIMPs) are a theoretical class of that excellent dark matter candidates. WIMP annihilation or decay may produce essentially monochromatic γ rays detectable by the Fermi Large Area Telescope (LAT) against astrophysical γ-ray emission Galaxy. We have searched for spectral lines in energy range 5–300 GeV using 3.7 years data, reprocessed with updated instrument calibrations and an improved dispersion model compared to previous Fermi-LAT Collaboration line...
We present a detailed statistical analysis of the correlation between radio and gamma-ray emission Active Galactic Nuclei (AGN) detected by Fermi during its first year operation, with largest datasets ever used for this purpose. use both archival interferometric 8.4 GHz data (from VLA ATCA, full sample 599 sources) concurrent single-dish 15 measurements from Owens Valley Radio Observatory (OVRO, sub 199 objects). Our unprecedentedly large permits us to assess high accuracy significance...
The contribution of unresolved sources to the diffuse gamma-ray background could induce anisotropies in this emission on small angular scales. We analyze power spectrum measured by Fermi LAT at Galactic latitudes |b| > 30 deg four energy bins spanning 1 50 GeV. At multipoles \ell \ge 155, corresponding scales \lesssim 2 deg, above photon noise level is detected >99.99% CL 1-2 GeV, 2-5 and 5-10 GeV bins, >99% 10-50 Within each bin takes approximately same value all suggesting that it...
We report the detection of high-energy γ-rays from quiescent Sun with Large Area Telescope on board Fermi Gamma-Ray Space (Fermi) during first 18 months mission. These observations correspond to recent period low solar activity when emission induced by cosmic rays (CRs) is brightest. For time, high statistical significance allows clear separation two components: point-like disk due CR cascades in atmosphere and extended inverse Compton (IC) scattering electrons photons heliosphere. The...
Numerical simulations based on the Lambda-CDM model of cosmology predict a large number as yet unobserved Galactic dark matter satellites. We report results Large Area Telescope (LAT) search for these satellites via gamma-ray emission expected from annihilation weakly interacting massive particle (WIMP) matter. Some are to have hard spectra, finite angular extents, and lack counterparts at other wavelengths. sought identify LAT sources with characteristics, focusing spectra consistent WIMP...
SUMMARY We previously reported that the number of TNF-α-producing cells was increased in liver patients with type C chronic disease. To understand further pathophysiology this change, we examined serum levels two soluble TNF receptors, TNF-αRI (p55) and -αRII (p75), IL-10, all which act as TNF-α buffer, IL-15, a novel cytokine sharing many immunological activities IL-2, using ELISA methods. studied control individuals disease, including asymptomatic hepatitis virus (HCV) carriers...
We report an analysis of the interstellar $\gamma$-ray emission in third Galactic quadrant measured by {Fermi} Large Area Telescope. The window encompassing plane from longitude $210\arcdeg$ to $250\arcdeg$ has kinematically well-defined segments Local and Perseus arms, suitable study cosmic-ray densities across outer Galaxy. measure no large gradient with Galactocentric distance emissivities per H atom over regions sampled this study. depends, however, on optical depth correction applied...
We present an analysis of the gamma-ray data obtained with Large Area Telescope (LAT) on board Fermi Gamma-ray Space in direction SNR W49B (G43.3−0.2). A bright unresolved source detected at a significance 38σ is found to coincide W49B. The energy spectrum 0.2–200 GeV range gradually steepens toward high energies. luminosity estimated be 1.5 × 1036 (D/8 kpc)2 erg s−1 this range. There no indication that emission comes from pulsar. Assuming supernova remnant (SNR) shell site production,...
Abstract Purpose To investigate whether the vessel wall MRI of carotid arteries would differentiate at‐risk soft plaque from solid fibrous by identifying liquid components more accurately than color Doppler ultrasonography (US). Materials and Methods This study included 54 in consecutive patients who underwent endarterectomy. was performed using black‐blood fat‐suppressed (FS) T1‐and FS T2‐weighted TSE sequences. A total 68 major segments plaques were grouped into four MR categories based on...
We present a detailed analysis of the GeV gamma-ray emission toward supernova remnant (SNR) G8.7−0.1 with Large Area Telescope (LAT) on board Fermi Gamma-ray Space Telescope. An investigation relationship between and TeV unidentified source HESS J1804−216 provides us an important clue diffusion process cosmic rays if particle acceleration operates in SNR. The is extended most positional coincidence SNR lesser part located outside western boundary G8.7−0.1. region overlaps spatially connected...
The GOES M2-class solar flare, SOL2010-06-12T00:57, was modest in many respects yet exhibited remarkable acceleration of energetic particles. flare produced an ~50 s impulsive burst hard X- and \gamma-ray emission up to at least 400 MeV observed by the Fermi GBM LAT experiments. remarkably similar X-ray high-energy time profiles suggest that most particles were accelerated energies >300 with a delay ~10 from mildly relativistic electrons, but some reached these as little ~3 s. line fluence...
The blazar AO 0235+164 (z = 0.94) has been one of the most active objects observed by Fermi Large Area Telescope (LAT) since its launch in Summer 2008. In addition to continuous coverage Fermi, contemporaneous observations were carried out from radio {\gamma} -ray bands between 2008 September and 2009 February. this paper, we summarize rich multi-wavelength data collected during campaign (including F-GAMMA, GASP- WEBT, Kanata, OVRO, RXTE, SMARTS, Swift, other instruments), examine...
Photomultiplier tubes (PMTs) have been widely used in imaging atmospheric Cherenkov telescopes (IACTs). The Large-Sized Telescopes (LSTs) of the Telescope Array Observatory (CTAO), latest-generation IACTs, are optimized for challenging observations low-energy gamma rays, specifically 20 to 150 GeV range. To this end, PMTs with an exceptionally low afterpulsing probability developed and installed. However, rate increases over time due infiltration molecules, particularly helium, into tube....
To determine whether emergency subtraction dynamic contrast-enhanced MR imaging (DCE-MRI) in combination with T2- and T2*-weighted of the testis is useful evaluation patients testicular torsion.Fourteen surgically proven torsion were examined using preoperative MRI, including T2-weighted, T2*-weighted, DCE-MRI. The affected was histologically eight who underwent orchiectomy, by postoperative follow-up MRI six orchiopexy. diagnostic criteria for detection hemorrhagic necrosis decreased or no...