研究対象

Supernovae and Supernova remnants

-- I aim at linking simulation results from dynamics and non-thermal emission from supernova remnants by using multi-D simulation.

Supernova is a phenomenon that some stars explode after their death. Its spectrum within after several months from the explosion can be classified into, type Ia which possess Si absorption line with no H lines, and core-collapse ones. The two types are interpreted as the thermonuclear explosion of carbon+oxygen white dwarfs and gravitational collapse of evolved massive stars respectively. 

In the supernova remnant phase (~100yr after the explosion), bright radio and X-ray emission is observed and the key problem in this phase is whether we can get back to supernova phase, e.g., constraining types, using such emission. The clues for constraining explosion types can be morphology, expansion measurement, or spectrum (non-thermal / thermal emission) etc. For intstance, considering such estimation of progenitor system and its evolutionary path, supernovae with dense wind-like circumstellar materials tend to have been regarded as core-collapse type. noting some exceptions that such supernovae can be re-classified into type Ia based on thermal X-ray e.g., a low ionization state with Fe-K emission centroid energy (RCW86). 

##Diversity in environment, Explosion mechanisms, Non-thermal emission

Particle acceleration at shocks

--  Here I aim at a PeV cosmic ray acceleration by the multi-D simulation calculating microphysics occurred behind the shock, e.g., the enhanced magnetic turbulence and the reflected shock. 

Cosmic ray, which is high-energy charged particles traveling through the interstellar space, have several open questions: "Where and which mechanisms accelerates them?"/"How much and how high-energy do the mechanisms accelerate?". If we focus on Galactic cosmic ray, on the acceleration sites and the mechanism, from the observed power-law of energy spectrum of Galactic cosmic rays, diffusive shock acceleration at shocks on supernova remnants seems and is believed to be a main source. While the number estimate is also enough to explain as the Galactic cosmic ray source, the high-energy-limit (maximum energy) of Galactic cosmic ray, ~3・10^15 eV (3 PeV) cannot be well explained in this theory without enough amplification of interstellar magnetic field. To understand the magnetic field amplification fully, it requires a full consideration of particle acceleration theory including magnetic turbulence generated by the interaction between the shock and interstellar clumps and Bell instability. Although such calculations are taken in  several works, e.g., Marcowith+18, Inoue+21, and successfully reached to PeV energy, the duration  time at PeV is estimated too short to be explained as PeVatron. We are planning to investigate whether including multi-D simulations will overcome this problem. 

##PeV cosmic-ray acceleration, Bell instability, Clumpy ISM

Type Ia supernovae

-- Focusing on the gap between type Ia-CSM supernovae and their (possible) remnants. I am planning to challenge the number of the detected populations and to make a unified model to link these phases.

Ia supernovae have long been considered a kind of unique explosions since they have homogeneity over their light curves so that are also used as a "standard candle" in cosmology. However, recently observation of subtypes among Type Ia is increasing thanks to surveys, and is now intensively investigated. One of the subtypes "Ia-CSM" show a narrow Ha line, and this infers the interaction with dense circumstellar material (CSM). On the other hand, Ia-CSM supernova remnants have not been observed among type Ia although two objects, N103B and Kepler’s SNR, have the amount of estimated CSM near that of type Ia-CSM. This gap of classified numbers between the phase in supernovae and their remnants remains an open question. Now as one clue to this question, I am planning to investigate whether a single CSM model can explain physics during the phases through supernovae to remnants of Ia-CSM. These understanding of subtypes  may in turn lead to more robust distance measurement in cosmology. 

##Explosion mechanisms and progenitors, Pre-supernova environment, Clumpy ISM