Title & Abstract
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Keiichi Maeda
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[Title]
Radio Emission from Infant Supernovae: A key to Massive Star Evolution in The Final Moment
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[Abstract]
The final evolution of massive stars is one of the main unresolved problems in stellar evolution theory. Supernovae (SNe) serve as a unique laboratory to tackle to this problem; the nature of the circumstellar matter (CSM) in the immediate visibility of the progenitor (e.g., < 10**15 cm) reflects the mass-loss activity in the final months to decades before the SN. Especially interesting is a class of stripped-envelope SNe (SESNe), for which one can probe the mass-loss rate in the final months by looking for signatures of CSM by rapid radio observations within a week of the explosion. In this talk, we present results of our ALMA rapid follow-up observations of two nearby SESNe and the theoretical analysis based on the synchrotron emission model.
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Kenta Taguchi
Slides used in the talk are uploaded to here.
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[Title]
Brief Introduction to the Scheme utilized in CMFGEN
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[Abstract]
Spectroscopic observation is a powerful tool in understanding many astrophysical objects.
Especially in understanding nova spectra, solving non-LTE (or non-equilibrium?) radiative transfer in spherical geometry with winds is thought necessary.
In the talk, I will review the techniques utilized in the grid-based code CMFGEN, which uses the difference method (i.e., not the Monte-Carlo method).
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Tomoki Matsuoka
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[Title]
Long-term evolution of a supernova remnant hosting a binary neutron star
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[Abstract]
An ultra-stripped supernova (USSN) is a type of core-collapse SN explosion proposed to be a candidate formation site of a double neutron star (DNS) binary. We investigate the dynamical evolution of an ultra-stripped supernova remnant (USSNR), which should host a DNS at its center. By accounting for the mass-loss history of the progenitor binary using a model developed by a previous study, we construct the large-scale structure of the CSM up to a radius $\sim 100\,{\rm pc}$, and simulate the explosion and subsequent evolution of a USSN surrounded by such a CSM environment. We find that the CSM encompasses an extended region characterized by a hot plasma with a temperature $\sim 10^8\,$K located around the termination shock of the wind from the progenitor binary ($\sim 10\,$pc), and the USSNR blastwave is drastically weakened while penetrating through this hot plasma. Radio continuum emission from a young USSNR is sufficiently bright to be detectable if it inhabits our Galaxy but faint compared to the observed Galactic SNRs, and thereafter declines in luminosity through adiabatic cooling. Within our parameter space, USSNRs typically exhibit a low radio luminosity and surface brightness compared to the Galactic SNRs.
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Qiliang Fang
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[Title]
Revealing the ejecta dynamics of stripped-envelope supernova through nebular spectra
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[Abstract]
When the nuclear fuel of a massive star is exhasted, the central core will collapse and explode as a core collapse supernova (CCSN). The explosion mechanism, along with its relation with the progenitor, are important open questions in modern astronomy. One of the key toward the solution is the properties of the stellar core, which is mainly determined by the progenitor main-sequence mass but severely affected by the explosion process. Stripped envelope supernova (SESN) is a subtype of CCSN. SESN loss most of the hydrogen envelope before the explosion. and its ejecta becomes transparent several months after the explosion. At this so-called nebular phase, the innermost layer is fully exposed to the observer, therefore is an ideal tool to study the properties of the stellar core.
In previous works, we have developed several tools to measure the abundance, velocity scale and geometry of the innermost ejecta from nebular features. These tools are applied to a large sample of 103 SESNe nebular spectra and further compared with the early phase observations. We find the helium deficient SNe tend to have more massive progenitor. The expansion velocity of the ejecta is also correlated with the progenitor CO core mass, and this relation is further applied to constrain the relation between progenitor mass and the kinetic energy of the ejecta. A correlation between the ejecta geometry and the progenitor CO core mass is also discerned, which can be an important probe of the mechanism that drives the development of the asphericity of the explosion.
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Kohki Uno
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[Title]
Analytical Modeling for The Initial Light Curve of Fast Blue Optical Transients
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[Abstract]
Thanks to new-generation transient surveys, some enigmatic transients have been discovered. Among them, FBOTs (Fast Blue Optical Transients), which show high peak luminosity and rapid rising/decay of light curve, are particularly interesting. To explain the observational properties of FBOTs, we propose new analytical model: Wind-Driven Model, which assumes a continuous outflow like a stellar wind instead of an explosion like SNe (KU & maeda 2020a, b). However, the model assumes steady-state solutions, and thus it is difficult to apply to the initial rapid rising phase, which is one of the notable features of FBOTs. We have tried to overcome this problem by extending the WD model to a time-dependent model.
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Mao Ogawa
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[Title]
The Explosion models of Type Ia Supernovae
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[Abstract]
It is widely accepted that Type Ia supernovae (SNe Ia) are thermonuclear explosions of a CO white dwarf in a binary system, but it is still unknown how the explosive nucleosynthesis proceeds during the explosion. Theoretical calculations of various explosion models are being conducted, varying the initial conditions and how the burning front spread. In this talk, I will review some kinds of explosion models of Type Ia Supernovae and introduce my ongoing study for my next presentation.
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Shin Mineshige
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[Title]
A simple model for the soft excess of AGN
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[Abstract]
We present a basic idea and simple calculation of a model for the soft excess of AGN spectra. The soft excess is commonly observed in the soft X-ray ranges (0.1 - 0.2 keV) of AGN spectra, however, its origin remains to be a long-standing puzzle. We construct a simple model along the line of the warm corona model and discuss to what extent such a simple model can account for the observations.
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Norita Kawanaka
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[Title]
Detectability of Black Hole Binaries with Gaia: Dependence on Binary Evolution Models
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[Abstract]
Astrometric satellite Gaia is expected to observe non-interacting black hole (BH) binaries with luminous companions (LCs), a different population from BH X-ray binaries. The detectability of such BH binaries with Gaia might be dependent on binary evolution models. We investigated the Gaia’s detectability of BH binaries formed through isolated binary evolution by means of binary population synthesis technique, and examined its dependence on single and binary star models: supernova (SN) models, BH natal kick models, and common envelope (CE) ejection efficiency. We estimated that 1.1–46 BH binaries can be detected within five-year observation, and we found three important implications; (1) if the lower BH mass gap is not intrinsic (i.e.3–5 solar mass BHs exist),Gaia will observe BHs in that mass range, (2) we may observe short orbital period binaries with light LCs if CE efficiency is significantly high, and (3) we may be able to identify the existence of natal kick from eccentricity distribution.
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Ignacio Botella Lasaga
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[Title]
Study on the outflow impact of SMBH seed at high-z through radiation hydrodynamic (RHD) simulations
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[Abstract]
We study the structure and impact of the outflow generated by supermassive black holes (SMBH) seeds. Our objective is to simulate the evolution of the gas outflow ejected from the vicinity of a SMBH seed (with mass of 10^3 Msun) to the edge of cosmological simulations (r = 0.1 pc) with a new method. In this new method, we perform consecutive RHD simulations that allow us to cover a larger range.
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Yuh Tsunetoe
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[Title]
Linear and Circular Polarization Images around the Black Hole: the Plasma and Observational Properties in M87
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[Abstract]
So far, we have suggested the peak separation among the total, linear and circular polarization intensity distribution because of the Faraday rotation and conversion, through the radiative transfer calculations based on the theoretical model of the M87 jet. Here, we survey the LP-CP separation feature for different model parameters, including the electron temperature in the disk region, observer's inclination angle, and mass accretion rate onto the black hole. From these survey, we newly suggest that the separation should reflect both of the plasma and observational properties such as the proton-electron coupling in the jet-disk structure.
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Masayuki Furuno
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[Title]
The spectrum calculation of low luminosity accretion flow for detecting isolated Black Holes
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[Abstract]
It is expected that there will be many black holes in the galaxy. To know how many black holes exist in galaxies and how they are distributed is important in discussing the theory of black hole formation and stellar evolution. However, only X-ray binaries are currently observed, and the number is at most dozens. On the other hand, theoretical predictions indicate that there are as many as 10^8 (e.g., Caputo+2017), and most of the undiscovered ones are isolated black holes (Fender+2013). In this seminar, I will explain the outline of IBH researches and the calculation result of the spectrum when IBH rushes into the gas cloud existing in the galaxy, causes gas accretion.
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Shogo Yoshioka
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[Title]
Large-scale outflow structure and radiation properties of super-Eddington flow: Dependence on the accretion rates
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[Abstract]
It is widely believed that super-Eddington accretion flow can produce powerful outflow and give impact through the mass flux and the energy flux onto surrounding environment. In order to clarify the dependence of outflow structure and radiation properties on the accretion rate, we perform large-scale RHD simulations with different mass accretion rates. As a result, we found that the outflow launching region expanded with the increase of accretion rate, and had the following structures in common: the inner edge area where the outflow is negligible, the middle area where the pure outflow blows, and the outer area where the failed outflow blows. We also found the mechanical luminosity is more sensitive to the accretion rate dependence than the radiation luminosity. In addition to the above results, I introduce the fitting formula of physical quantities we revealed.
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Mutsuko Inoguchi
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Takanori Sasaki
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[Title]
Moons of Moons?
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[Abstract]
The planets in our solar system have many satellites, but none of the satellites have their own satellites (which we call “submoons”). Investigating the tidal-dynamical stability of submoons, it has been shown that submoons can only survive around large (1000 km-scale) satellites on wide- separation orbits. I will introduce how to study the stability of submoons and discuss the orbital evolution of the Moon-subMoon system.
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Yodai Kihara
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Naho Fujita
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[Title]
Atmospheric escape of two ultra-short period super-Earths around M dwarfs
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[Abstract]
Two ultra-short period (USP) super-Earths (TOI-1685b and TOI-1634b) around two different M dwarfs have been discovered; the number of such planets detected so far is still small. According to the mass-radius(MR) relations of these planets, both planets are estimated to have Earth-like compositions. We investigated whether these two planets can retain their initial atmospheres or not in the context of the photoevaporation theory. As a result, both planets are expected to completely lose their initial atmospheres by photoevaporation within 1 Gyr, which are also consistent with the expectation by MR relations. The two USP planets may provide clues to help understand how such unusual planets are formed.
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Keiya Murashima
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[Title]
Modification of SPH for the simulation of an icy moon with internal ocean
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[Abstract]
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Yuri Fujii
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[Title]
Formation of satellite systems around Jupiter and Saturn
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[Abstract]
Satellite systems around Jupiter and Saturn have different characteristics. The Saturnian system is dominated by a giant moon, Titan, which holds over 95% of the total mass of Saturnian moons. On the other hand, the Jovian system has four large moons in a compact orbital area, and inner three, Io, Europa and Ganymede, are known to be in resonant orbits. Previous studies have shown that the specific resonance can be obtained if there is some structure, such as inner cavity, in the satellite forming circum-Jovian disk. However, the mechanism making such a structure is poorly understood. We estimated the strengths of planetary magnetic fields for Jupiter and Saturn that are generated by dynamo process by calculating the thermal evolution of them. Saturn’s magnetic field is too weak to open a gap between Saturn and the circum-Saturnian disk, thus the moons in the inner orbits fall onto Saturn due to inward orbital migration. Our models show there are cases where a moon in an outer orbit evacuated into “safety zone” and survived till the disk dispersal. In the case of Jupiter, its strong enough magnetic fields generate magnetosphere around it, and moons migrating toward Jupiter stop at the outer edge of the magnetosphere during a certain period of the disk evolution. Our results suggest that Io, Europa and Ganymede should be captured into resonance while there exists a cavity around Jupiter and evolve as a system after the magnetosphere has vanished. We believe our scenario can explain the difference of Jovian and Saturnian moon systems.
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Shiu-Hang Lee
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[Title]
On the origin of over-ionized/recombining plasma in supernova remnants
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[Abstract]
An "unnatural" over-ionization state has been discovered in recent years from spectroscopic X-ray observations of a number of supernova remnants (SNRs). Despite the existence of a few proposed theories, there is no consensus on the general formation mechanism underlying the emergence of over-ionized/recombining plasma that dominates the X-ray spectra in those objects. Using hydro simulation with microphysics, we performed an extensive parametric survey on the evolution of SNRs in various surrounding environments up to a few ten thousand years to search for the parameter space(s) in which a recombining plasma can exist for a prolonged period. Without invoking any contrived mechanism, our results suggest that there are three situations in which an over-ionization state can prevail in a SNR, especially if the progenitor exploded in a non-uniform circumstellar environment. This implies that over-ionization can be a pretty common phenomenon in contrast to the "standard picture" of SNR evolution.
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Haruo Yasuda
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[Title]
Dark Age of Type II Supernova Remnants
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[Abstract]
Supernova remnants (SNRs) are important objects in terms of their connections with supernova (SN) explosion mechanism(s), progenitor stars, and cosmic-ray acceleration. Non-thermal emission from SNRs is an effective probe of the structure of their surrounding circumstellar media (CSM), which can in turn shed lights on the mechanism and history of the elusive mass loss of massive stars. In this work, we calculate the time evolution of broadband non-thermal emission from SNRs originating from Type II SNe embedded in a CSM environment linked to the mass-loss history of the progenitor. Our results predict that Type II SNRs experience a prolonged period of weak radio and γ-ray emission if they run into a spatially extended bubble of low density and high temperature created by the stellar wind during main sequence. For a typical red supergiant progenitor evolved within an average interstellar medium, this “dark age” corresponds to a range of SNR ages spanning from ∼1000 to 5000 yr old. This result suggests that a majority of Type II SNRs are too faint to be detected, which may help explain why the number of known Galactic SNRs is significantly less than what we expect from the SN rate in our Galaxy.
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Ryosuke Kobashi
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[Title]
Long-term evolution of non-thermal emission from Type Ia and core-collapse supernova remnants in diversified circumstellar media
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[Abstract]
Supernova remnants (SNRs) have been thought to be the origin of galactic cosmic rays (CRs). Because CRs generated in SNRs will interact with dense circumstellar material (CSM) or molecular clouds and then utter non-thermal emission, non-thermal emission from SNRs can bring us some information of CSM (and CRs accelerated in SNRs). In this work we calculate long-term time evolution of non-thermal emission from different types of SNRs in different environments until the age becomes 50,000 yr by using CR-hydro code (Yasuda & Lee 2019; Yasuda et al. 2021). We assume uniform density media for the ambient environment of Type Ia SNRs and constant mass loss rate with outer uniform density for CC (core-collapse) SNRs, which is associated with the structure of pre-SN mass loss of progenitors in ISM. In our results, light curves for Type Ia remain almost the same with the age, and their values depend on density of environments. For CC SNR, when the shock wave of SNR sweeeps the wind purely made by constant mass loss rate, which is roughly less than 1,000 yr, the luminosity is determined by the density of the wind only as pi0-decay dominates. After that, when the shock will enter uniform medium, the light curves have no longed the information on mass loss history in all models.