A5059168304- Gamma-ray bursts and supernovae
- Nuclear Materials and Properties
- Nuclear Engineering Thermal-Hydraulics
- Astrophysical Phenomena and Observations
- Pulsars and Gravitational Waves Research
- Nuclear reactor physics and engineering
- Astrophysics and Cosmic Phenomena
- Particle Dynamics in Fluid Flows
- Nuclear and radioactivity studies
- Synthetic Organic Chemistry Methods
- Stellar, planetary, and galactic studies
- Astro and Planetary Science
- Fluid Dynamics and Mixing
- Metallurgical Processes and Thermodynamics
- Astronomy and Astrophysical Research
- Nanoplatforms for cancer theranostics
- Ionosphere and magnetosphere dynamics
- Astronomical Observations and Instrumentation
- Asymmetric Synthesis and Catalysis
- Photodynamic Therapy Research Studies
- Granular flow and fluidized beds
- Colorectal Cancer Surgical Treatments
- Lattice Boltzmann Simulation Studies
- Optical Coatings and Gratings
- Metastasis and carcinoma case studies
Columbia University
2022-2024
Kyoto University
2015-2024
Tohoku University
2024
Japan Steel Works (Japan)
2023
Takasaki University of Health and Welfare
2023
The University of Tokyo
2019-2022
Hebrew University of Jerusalem
2018-2022
Kyushu University
2010-2021
Tokyo University of Science
2006-2021
Kyoto Prefectural University of Medicine
2017-2021
Abstract We present the discovery of Type II supernova SN 2023ixf in M101 and follow-up photometric spectroscopic observations, respectively, first month week its evolution. Our was made within a day estimated light, following light curve is characterized by rapid rise (≈5 days) to luminous peak ( M V ≈ − 18.2 mag) plateau 17.6 extending 30 days with fast decline rate ≈0.03 mag −1 . During rising phase, U color shows blueward evolution, followed redward evolution phase. Prominent flash...
Abstract We present optical photometry and spectroscopy of the Type IIn supernova (SN) 2021qqp. Its unusual light curve is marked by a long precursor for ≈300 days, rapid increase in brightness ≈60 then sharp ≈1.6 mag only few days to first peak M r ≈ −19.5 mag. The declines rapidly until it rebrightens second distinct −17.3 centered at ≈335 after peak. spectra are dominated Balmer lines with complex morphology, including narrow component width ≈1300 km s −1 (first peak) ≈2500 (second that...
The process of unstable mass transfer in a stellar binary can result either complete merger the stars or successful removal donor envelope leaving surviving more compact binary. "Luminous red nova" (LRN) are class optical transients believed to accompany such merger/common events. Past works typically model LRNe using analytic formulae for supernova light curves which make assumptions (e.g., radiation dominated ejecta, neglect hydrogen recombination energy) not justified mergers due lower...
The equipartition analysis yields estimates of the radius and energy synchrotron self-absorbed radio sources. Here we generalize this method to relativistic off-axis viewed emitters. We find that Lorentz factor $\Gamma$ viewing angle $\theta$ cannot be determined independently but become degenerate along a trajectory minimal solutions. solutions are divided into on-axis branches with former reproducing classical analysis. A source can disguised as an apparent Newtonian one. Applying...
Abstract A fraction of core-collapse supernovae (SNe) with signs interaction a dense circumstellar matter are preceded by bright precursor emission. While the precursors likely caused mass ejection before core collapse, their mechanism to power energetic bursts—sometimes reaching 10 48 –10 49 erg, which is larger than binding energies red supergiant envelopes—is still under debate. Remarkably, such huge energy deposition should result in an almost complete envelope and hence strong sign...
Abstract Radio monitoring unveiled late (hundreds to a thousand days) radio flares in significant fraction of tidal disruption events. We propose that these late-time are natural outcome if the surrounding density profile flattens outside Bondi radius. At radius, outflow is optically thin (above few GHz) synchrotron self-absorption. As more and material swept up, emission rises asymptotically as ∝ t 3 until begins decelerate. A detection such rise maximum constrains black hole mass energy...
The gravitational waves from the neutron star merger event GW170817 were accompanied by an unusually weak short GRB 170817A, optical/IR macronova/kilonova and a long lasting radio to X-rays counterpart. While association of GRBs with mergers was predicted time ago, luminosity this prompt {\gamma}-ray emission weaker few orders magnitude than all known previous sGRBs it softer typical sGRBs. This raise question whether {\gamma}-rays that we have seen regular sGRB viewed off-axis. We revisit...
During a winter thunderstorm on 24 November 2017, strong burst of gamma rays with energies up to $\ensuremath{\sim}10\text{ }\text{ }\mathrm{MeV}$ was detected coincident lightning discharge, by scintillation detectors installed at the Kashiwazaki-Kariwa Nuclear Power Station sea level in Japan. The had subsecond duration, which is suggestive photoneutron production. leading part resolved into four intense gamma-ray bunches, each low-frequency radio pulse. These bunches were separated...
To understand the nature of brightest γ-ray binary system LS 5039, hard x-ray data object, taken with Suzaku and NuSTAR observatories in 2007 2016, respectively, were analyzed. The two sets jointly gave tentative evidence for a periodicity, period ∼9 s increase rate by ∼3×10^{-10} s^{-1}. Therefore, compact object 5039 is inferred to be rotating neutron star, rather than black hole. Furthermore, several lines arguments suggest that this has magnetic field times ∼10^{10} T, orders magnitude...
Abstract A growing number of core-collapse supernovae (SNe) that show evidence for interaction with dense circumstellar medium (CSM) are accompanied by “precursor” optical emission rising weeks to months prior the explosion. The precursor luminosities greatly exceed Eddington limit progenitor star, implying they substantial mass loss. Here, we present a semi-analytic model SN light curves, which apply constrain properties and mechanisms pre-explosion We explore two limiting mass-loss...
We present the optical discovery and multiwavelength follow-up observations of AT2024kmq, a likely tidal disruption event (TDE) associated with supermassive ($M_{\rm BH}\sim 10^{8} M_\odot$) black hole in massive galaxy at $z=0.192$. The light curve AT2024kmq exhibits two distinct peaks: an early fast (timescale 1 d) luminous ($M\approx-20$ mag) red peak, then slower month) blue peak higher luminosity ($M\approx-22$ featureless spectra. second component is similar to spectroscopic class...
A $\gamma$-ray source must have a limited optical depth to pair production. This simple condition, called compactness, implies that gamma-ray bursts (GRBs) involve highly relativistic motion ($\Gamma \gtrsim 100$) giving the first and most important clue on their nature. So far, this condition has been discussed under assumption sources are viewed on-axis, is, by an observer within beaming cone of source. Recently, following detection weak short GRB 170817A, extensive interest arose in...
In 2015, the Gamma-Ray Observation of Winter Thunderstorms (GROWTH) collaboration launched a mapping observation campaign for high-energy atmospheric phenomena related to thunderstorms and lightning discharges. This has developed detection network gamma rays with up 10 radiation monitors installed in cities Kanazawa Komatsu, Ishikawa Prefecture, Japan, where low-charge-center winter frequently occur. During four seasons from October 2016 April 2020, total 70 gamma-ray glows, i.e.,...
ABSTRACT The tidal disruption event AT2019dsg was observed from radio to X-rays and possibly accompanied by a high-energy neutrino. Previous interpretations have focused on continued injection central engine as the source of energy for emission. We show that continuous is unnecessary; data can be explained single ejection plasma supplies all needed. To support this assertion, we analyse synchrotron self-absorbed spectra in terms equipartition model. Similar previous analyses, find...
ABSTRACT One of the intriguing puzzles concerning Swift J1644+57, first jetted tidal disruption event (TDE) discovered, is constant increase in its jet energy, as implied by radio observations. During two hundred days, energy has increased an order magnitude. We suggest that was viewed slightly off-axis. In this case, apparent arises due to slowing down and corresponding broadening beaming cone. Using equipartition analysis, we infer increasing a larger region observed. A simple off-axis...
During a hypothetical core-disruptive accident (CDA) in sodium-cooled fast reactor (SFR), degraded core materials can form roughly conically-shaped debris beds over the core-support structure and/or lower inlet plenum of vessel from rapid quenching and fragmentation material pool. However, coolant boiling may ultimately lead to leveling bed, which is crucial relocation molten heat-removal capability bed. To clarify mechanisms underlying this self-leveling behavior, large number experiments...
The existence of black holes (BHs) mass ~ 10^{9} M_sun at z > 6 is a big puzzle in astrophysics because even optimistic estimates the accretion time are insufficient for stellar BHs 10 to grow into such supermassive BHs. A resolution this might be direct collapse stars with M 10^{5} massive seed We find that if jet launched from disk around central BH, can break out star structure radiation pressure-dominated envelope. Such ultra-long gamma-ray bursts duration 10^{4} - 10^{6} s and flux...
The aim of this study was to evaluate the temporal impact 2011 Japan earthquake and tsunami on incidence sudden cardiac unexpected death (SCUD).We surveyed disaster clinical characteristics SCUD in Iwate. To perform complete identification for 8 weeks before 40 after disaster, medical records certificates relevant were area. Compared with previous year's rate, (per 10 000 person-year) initial 4 (acute phase) double (33.5 vs 18.9), thereafter rate returned level. Significant relationships...
Neutron star mergers produce a substantial amount of fast-moving ejecta, expanding outwardly for years after the merger. The interaction these ejecta with surrounding medium may weak isotropic radio remnant, detectable in relatively nearby events. We use late-time observations short duration gamma-ray bursts (sGRBs) to constrain this model. Two samples events were studied: four sGRBs that are possibly local (<200 Mpc) universe selected remnant non-thermal emission from sub-relativistic...
The Gravity Collaboration detected a near-infrared hotspot moving around Sgr A* during the 2018 July 22 flare. They fitted partial loop made on sky with circular Keplerian orbit of radius $\simeq7.5\,r_{\rm g}$ supermassive black hole (BH), where $r_{\rm is gravitational radius. However, because traversed in short time, models which tracks motion some fluid element tend to produce best-fit trajectory smaller than observed loop. This true for orbit, even when BH spin accounted for, and along...
Radio flares from tidal disruption events (TDEs) are generally interpreted as synchrotron emission arising the interaction of an outflow with surrounding circumnuclear medium (CNM). We generalize common equipartition analysis to be applicable in cases lacking a clear spectral peak or even just upper limit. show that, for detected events, there is lower limit on combination outflow's velocity $v$ and solid angle $\Omega$, $\simeq v\Omega^{a}$ (with $a \simeq 0.5$) that constrains properties....
ABSTRACT AT 2022cmc is a luminous optical transient (νLν ≳ 1045 erg s−1) accompanied by decaying non-thermal X-rays (peak duration tX ≲ days and isotropic energy EX,iso 1053 erg) long-lived radio/mm synchrotron afterglow, which has been interpreted as jetted tidal disruption event (TDE). Both an equipartition analysis detailed afterglow model reveal the emitting plasma to be expanding mildly relativistically (Lorentz factor $\Gamma \gtrsim \, \mathrm{ few}$ ) with opening angle θj ≃ 0.1...
Abstract SN 2023ixf is one of the most well-observed core-collapse supernovae in recent decades, yet there inconsistency inferred zero-age main-sequence (ZAMS) mass M ZAMS its progenitor. Direct observations pre-supernova (SN) red supergiant (RSG) estimate spanning widely from 11 to 18 ⊙ . Additional constraints, including host environment and pulsation progenitor RSG, suggest a massive with > 17 However, analysis properties, light-curve modeling late-phase spectroscopy, favors relatively...
In a core-disruptive accident of sodium-cooled fast breeder reactor, core debris may settle on the coresupport structure and/or in lower inlet plenum reactor vessel because rapid quenching and fragmentation molten materials subcooled sodium plenum. Coolant boiling is mechanism driving self-leveling bed that causes significant changes heat-removal capability beds. present study, we develop criteria establishing onset this behavior base force balance model assuming with single-sized spherical...