Asymmetric Expansion of the Fe ejecta in Kepler’s Supernova Remnant

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Our paper titled “Asymmetric Expansion of the Fe ejecta in Kepler’s Supernova Remnant” has been accepted for publication in PASJ.
arXiv: https://arxiv.org/abs/1807.04029

The ejecta kinematics of supernova remnants (SNRs) is one of crucial clues to understand the explosion mechanism of type Ia supernovae (SNe). In particular, the kinematic asymmetry of iron-peak elements provides the key to understanding physical processes taking place in the core of the exploding white dwarfs (WDs) although it has been poorly understood by observations. Kasuga et al. shows for the first time the asymmetric expansion structure in the line-of-sight direction of Fe ejecta in Kepler’s SNR revealed by spectral and imaging analysis using the Chandra archival data. We found that the K alpha line centroid energy and line width is relatively lower and narrower around the center of the remnant, which implies that the majority of the Fe ejecta in the central region is red-shifted. At the outer regions, we identify bright blue-shifted structures as it might have been ejected as high velocity dense clumps. As the origin of the asymmetric motion of the Fe ejecta, we suggest three scenarios, (1) the asymmetric distribution of the CSM, (2) the “shadow” in Fe cast by the companion star, and (3) the asymmetric explosion.

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Radioactivation background in satellites’ orbits

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Our paper titled “Modeling of proton-induced radioactivation background in hard X-ray telescopes: Geant4-based simulation and its demonstration by Hitomi’s measurement in a low Earth orbit” has been published in Nuclear Instruments and Methods A.
arXiv: https://arxiv.org/abs/1804.00827
ADS: http://adsabs.harvard.edu/abs/2018NIMPA.891…92O

Hard X-ray observation must be conducted in a satellite’s orbit due to atmospheric absorption, and therefore suffers from significant backgrounds induced by cosmic rays and/or geomagnetically trapped charged particles. Hirokazu Odaka et al. have developed a new, effective, general-purpose framework of full Monte Carlo simulation of radioactivation background. We applied this framework to data measured with the Hard X-ray Imager onboard the Hitomi satellite, and obtained excellent agreement between the in-orbit background data and the simulation. The simulation technique newly developed in this work will be indispensable for designing future hard X-ray missions and for making their scientific plans. (This work was mainly done when H. Odaka was working at Stanford University.)

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Discovery of a recombining plasma from the SNR HB 21

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Our paper titled “Discovery of recombining plasma from the faintest GeV SNR HB 21 and a possible scenario of the cosmic ray escaping from SNR shocks” has been accepted for publication in PASJ.
arXiv: https://arxiv.org/abs/1805.02882
ADS: http://adsabs.harvard.edu/abs/2018PASJ…70…75S

Hiromasa Suzuki et al. revealed for the first time that a thermal plasma in the soft GeV gamma-ray SNR HB 21 had been suffered from rapid cooling very long time ago (~170 kyr), and is still on the way of recombination to the collisional ionization equilibrium. Furthermore, by comparing published data of 9 similar SNRs, the authors discovered a clue of a positive correlation between the elapsed time from the rapid cooling and the degree of escape of accelerated particles from SNRs. This result can be crucial for understanding escaping processes of Galactic cosmic rays from SNRs.

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