A5024560873- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- Stellar, planetary, and galactic studies
- Solar and Space Plasma Dynamics
- Astronomical Observations and Instrumentation
- Astrophysics and Cosmic Phenomena
- Chemical Synthesis and Analysis
- Chemical Synthesis and Reactions
- Organophosphorus compounds synthesis
- Galaxies: Formation, Evolution, Phenomena
- Astrophysics and Star Formation Studies
- Astro and Planetary Science
- Adaptive optics and wavefront sensing
- Atmospheric Ozone and Climate
- Synthesis and biological activity
- Geophysics and Gravity Measurements
- Paleopathology and ancient diseases
- Organic and Inorganic Chemical Reactions
- Synthesis and Reactions of Organic Compounds
- Astronomy and Astrophysical Research
- Image Retrieval and Classification Techniques
- Phosphorus compounds and reactions
- Advanced X-ray and CT Imaging
- Radio Astronomy Observations and Technology
Tokyo Institute of Technology
1974-2024
Gamma-ray bursts (GRBs) are flashes of high-energy radiation arising from energetic cosmic explosions. Bursts long (>2 s) duration produced by the core-collapse massive stars, those short (< 2 merger two neutron stars (NSs). A third class events with hybrid properties was identified, but never conclusively linked to a stellar progenitor. The lack bright supernovae rules out typical explosions, their distance scales prevent sensitive searches for direct signatures progenitor system. Only...
Solar flares are often accompanied by filament/prominence eruptions ($\sim10^{4}$ K and $\sim 10^{10-11}$ cm$^{-3}$), sometimes leading to coronal mass ejections (CMEs) that directly affect the Earth's environment. `Superflares' found on some active solar-type (G-type main-sequence) stars, but association of filament eruptions/CMEs has not been established. Here we show our optical spectroscopic observation young star EK Draconis reveals evidence for a stellar eruption associated with...
We report multi-wavelength monitoring observations of an M-dwarf flare star AD Leonis with Seimei Telescope (6150--7930 {\AA}), SCAT (Spectroscopic Chuo-university Astronomical Telescope; 3700--7500 NICER (Neutron Star Interior Composition Explorer; 0.2--12.0 keV), and collaborations OISTER (Optical Infrared Synergetic Telescopes for Education Research) program. Twelve flares are detected in total which include ten H$\alpha$, four X-ray, optical-continuum flares; one them is a superflare the...
Young solar-type stars are known to show frequent "superflares", which may severely influence the habitable worlds on young planets via intense radiations and coronal mass ejections. Here we report an optical spectroscopic photometric observation of a long-duration superflare star EK Draconis (50-120 Myr age) with Seimei telescope $Transiting$ $Exoplanet$ $Survey$ $Satellite$ ($TESS$). The flare energy 2.6$\times$10$^{34}$ erg white-light duration 2.2 hr much larger than those largest solar...
Abstract We present optical observations of the Type Ia supernova (SN) 2019ein, starting two days after estimated explosion date. The spectra and light curves show that SN 2019ein belongs to a high-velocity (HV) broad-line group with relatively rapid decline in (Δ m 15 ( B ) = 1.36 ± 0.02 mag) short rise time (15.37 0.55 days). Si ii λ 6355 velocity, associated photospheric component but not detached feature, reached ∼20,000 km s −1 12 before -band maximum. line however, decreased very...
PETREL (Platform for Extra & Terrestrial Remote Examination with LCTF) is a 50kg class satellite 80mm-diameter Ultraviolet Telescope (UVT). The science missions of the UVT system are discovery high-energy transients, such as supernovae and gravitational-wave electromagnetic sources. To achieve them, optical optimized to detect near-UV photons between 250 300 nm. Within 30-minutes exposure time per every revolution, it surveys remarkably wide field 50 deg^2 high sensitivity 20~ AB magnitude....
A micro-satellite for wide-field near-UV transient exploration PETREL is presented. The scientific goal to detect sources, such as GW sources accompanied by EM emission, supernovae, and other unknown phenomena in the UV sky, reveal nature of explosive universe through multimessenger observations. equipped with an 80 mm refractor coupled BI-CMOS detector. powerful OBC automatically processes received data searches orbital transients. If a detected, alert immediately sent over Globalstar...
Abstract The Laser Interferometer Gravitational-wave Observatory Scientific Collaboration and Virgo (LVC) sent out 56 gravitational-wave (GW) notices during the third observing run (O3). Japanese for Gravitational wave ElectroMagnetic follow-up (J-GEM) performed optical near-infrared observations to identify observe an electromagnetic (EM) counterpart. We constructed a web-based system that enabled us obtain share information on candidate host galaxies counterpart, status of our...
ABSTRACT We analysed optical/X-ray quasi-simultaneous light curves of Aql X-1, obtained by Monitor All-sky X-ray Image, Zwicky Transient Facility, and Las Cumbres Observatory Global Telescope network in about 3.6 yr from 2016, for understanding electromagnetic radiation mechanisms during its outbursts. As a result, we confirmed that five outbursts had detected the epoch, three underwent state transition across Low-Hard, In-Transition, High-Soft while remaining two stayed Low-Hard state....
We report the results of quasi-simultaneous multiwavelength (near-infrared, optical, UV, and X-ray) observations Galactic X-ray black hole binary MAXI J1820+070 performed in 2019 May 10-13, $\sim 60$ days after onset first rebrightening phase. It showed a much larger optical-to-X-ray luminosity ratio ($\sim 8$) than initial outburst epoch. The primary components spectral energy distribution (SED) can be best interpreted by radiatively inefficient accretion flow (RIAF) spectrum showing peak...
To understand the evolution of global accretion disk structure in ``rebrightening'' phase MAXI J1820$+$070, we perform a comprehensive analysis its near infrared/optical/UV to X-ray spectral energy distribution (SED) utilizing data obtained by OISTER, Las Cumbres Observatory (LCO), Swift, NICER, and NuSTAR 2019. Optical spectra observed with Seimei telescope 2019 2020 are also analyzed. On basis optical light curves their flux ratios, divide whole into 3 periods, Periods I (flux rise), II...
Abstract The mechanism of X-ray outbursts in Be binaries remains a mystery, and understanding their circumstellar disks is crucial for solution the mass-transfer problem. In particular, it important to identify star activities (e.g., pulsations) that cause mass ejection and, hence, disk formation. Therefore, we investigated relationship between optical flux oscillations infrared (IR) excess sample five binaries. Applying Lomb-Scargle technique high-cadence light curves from Transiting...
We present a detailed study of the MASTER OT J030227.28+191754.5 outburst in 2021-2022, reaching an amplitude 10.2 mag and duration 60 d. The detections (1) double-peaked optical emission lines, (2) early ordinary superhumps, established that is extremely energetic WZ Sge-type dwarf nova (DN). Based on superhump observations, we obtained its orbital period mass ratio as 0.05986(1) d 0.063(1), respectively. These are within typical range low-mass-ratio DNe. According to binary parameters...
Abstract We present a detailed study of the MASTER OT J030227.28$+$191754.5 outburst in 2021–2022, which reached an amplitude $10.2\:$mag and duration $60\:$d. The detections (1) double-peaked optical emission lines, (2) early ordinary superhumps, established that is extremely energetic WZ Sge-type dwarf nova (DN). Based on superhump observations, we obtained its orbital period mass ratio as $0.05986(1)\:$d 0.063(1), respectively. These values are within typical range for low-mass-ratio DNe....
The mechanism of X-ray outbursts in Be binaries remains a mystery, and understanding their circumstellar disks is crucial for solution the mass-transfer problem. In particular, it important to identify star activities (e.g., pulsations) that cause mass ejection and, hence, disk formation. Therefore, we investigated relationship between optical flux oscillations infrared (IR) excess sample five binaries. Applying Lomb-Scargle technique high-cadence light curves from Transiting Exoplanet...
Abstract The extremely luminous infrared galaxy (ELIRG), WISE J090924.01$+$000211.1 (hereafter J0909$+$0002, $z=1.87$) is an extraordinary object with a quasar aspect. This study performed monitoring observations of J0909$+$0002 the 105$\:$cm Murikabushi telescope, Okayama and Akeno 50$\:$cm telescopes/MITSuME ($g^{\,\prime}$, $R_{\rm c}$, $I_{\rm c}$ bands), SaCRA 55$\:$cm telescope/MuSaSHI (r, i, z bands) for three years. We obtain following results by combining UV/optical light curves...
Abstract This study provides the results of simultaneous multicolor observations for first Visorsat (STARLINK-1436) and ordinary Starlink satellite (STARLINK-1113) in U, B, V, g′, r, i, RC, IC, $z$, J, H, Ks bands to quantitatively investigate extent which reduces its reflected light. Our are as follows: (1) most cases, is fainter than STARLINK-1113, sunshade on therefore contributes reduction sunlight; (2) magnitude at 550 km altitude (normalized magnitude) both satellites often reaches...
Gamma-ray bursts (GRBs) are flashes of high-energy radiation arising from energetic cosmic explosions. Bursts long (>2 s) duration produced by the core-collapse massive stars, those short (< 2 merger two neutron stars (NSs). A third class events with hybrid properties was identified, but never conclusively linked to a stellar progenitor. The lack bright supernovae rules out typical explosions, their distance scales prevent sensitive searches for direct signatures progenitor system....
Abstract We developed a high-speed image reduction pipeline using Graphics Processing Units (GPUs) as hardware accelerators. Astronomers desire to detect the emission measure counterpart of gravitational-wave sources soon possible and share in systematic follow-up observation. Therefore, processing is important. new image-reduction for our robotic telescope system, which uses GPU via Python package CuPy processing. As result, has increased speed by more than 40 times compared with current...
We analyzed optical/X-ray quasi-simultaneous light curves of Aql X-1, obtained by MAXI (Monitor All-sky X-ray Image), ZTF (Zwicky Transient Facility) and LCO (Las Cumbres Observatory) in about 3.6 years from 2016, for understanding electromagnetic radiation mechanisms during its outbursts. As a result, we confirmed that 5 outbursts had detected the epoch, 3 underwent state transition across Low-Hard, In-Transition, High-Soft while remaining 2 stayed Low-Hard state. found optical spectral...
Identification of optical counterparts gravitational waves (GWs) is one the most exciting topics in astronomy. Since a typical sky map error region LIGO/Virgo much larger than field-of-view telescopes, it important to search and rapidly identify through follow-up observation by telescopes. The method rapid accurate transient detection huge set observed images important. Motivated this, we are developing with convolutional neural network (CNN). We constructed CNN-based classifier designed...