High-energy Phenomena in the Universe Revealed with Ground-based Plasma Experiments and High-resolution X-ray Spectroscopy

Jan. 25, 2024 | Aerospace Project Research Associate, ISAS people

AMANO Yuki / Department of Space Astronomy and Astrophysics, ISAS

Research Summary

High-energy astronomical objects such as stellar flares, black hole accretion disks, supernova remnants, and galaxy clusters are accompanied by high-temperature plasma with temperatures exceeding several million Kelvin. I study X-ray*1 astronomy which focuses on the research of X-rays emitted by these objects. In particular, I am working on observational research on supernova remnants, and on ground-based plasma experiments as a project research of JAXA/ISAS.

High-resolution X-ray Spectroscopy of Supernova Remnants using XRISM and a Grating Spectrometer

Figure 1
Figure 1:(left) X-ray image of supernova remnant N49 in the Large Magellanic Cloud (taken with the American X-ray astronomical satellite Chandra). (Right) X-ray spectrum of N49 (modified from Amano et al. 2020). The gray data points are spectra from CCD, the main detector for current X-ray astronomy, and the black data points are from X-ray diffraction gratings. Emission lines that cannot be separated with a CCD can be separated with a diffraction grating.

A supernova is an explosion at the end of a star’s life. After a supernova explosion, the material ejected by the progenitor expands at supersonic speed through interstellar space, colliding with surrounding gas and turning into high-temperature plasma. X-ray spectra of supernova remnants contain X-ray emission lines from various elements (see Figure 1, right), which allows us to learn which elements and how much were produced by the progenitor during its evolution and explosion process.

In such research, it is important to accurately measure the energy of the photons. An ability of a detector to determine the energy of photons is called energy resolution. I have been conducting high resolution X-ray spectroscopy of various supernova remnants using an X-ray diffraction grating, which has the highest energy resolution among current X-ray detectors (see Figure 1, right). As a result, we have found a lot of evidence for physical processes that have been overlooked in supernova remnants are important for accurately measuring elements such as abundance. In addition to observational research, I have also developed X-ray CCD detectors aboard XRISM, scheduled to be launched in 2023. XRISM is a satellite equipped with a micro calorimeter, a new high resolution X-ray spectrometer.In the future, we plan to use XRISM to conduct observational research on not only supernova remnants but also galaxy clusters.

X-ray Spectroscopy Experiment of Highly-charged Ion Spectroscopy using the Electron Beam Ion Trap

In order to extract physical information about supernova remnants from their X-ray spectral analysis, it is essential to understand the atomic processes underlying X-ray emission. However, since the highly-charged ions*2 involved in supernova remnants are multi-electron systems, it is difficult to theoretically calculate their physical behavior. Therefore, we are conducting an experiment to reproduce high-temperature plasma equivalent to a high-energy astronomical object in the laboratory and perform spectroscopic measurements as a project research of JAXA/ISAS.

図2
Figure 2:(Upper row) EBIT that we developed. Operated at JAXA/ISAS. (Bottom row) Enlarged view of the main parts of EBIT (modified from Kuehn et al. 2019). The valence of ions is controlled using an electron beam, and photons are introduced from a synchrotron radiation facility to excite the ions.

We develop a device called the Electron Beam Ion Trap (EBIT) in collaboration with Max-Planck-Institut für Kernphysik (MPIK) in Germany. EBIT is a device that generates ions of arbitrary valence using an electron beam focused by a magnetic field and detects characteristic X-rays due to its electron transitions (Figure 2). Because our EBIT has introduced MPIK's unique technology, it is possible to conduct experiments at synchrotron radiation facilities such as SPring-8. This allows us to reproduce various physical processes that occur in high-energy astronomical objects. As of August 2023, I am working to upgrade the equipment in preparation for the experiment at SPring-8 scheduled for the end of this year.

This experiment is a joint research project with domestic and international nuclear physics and synchrotron radiation facilities such as MPIK, the National Institute for Fusion Science, the University of Electro-Communications, and the RIKEN Synchrotron Radiation Center (SPring-8). Working closely with astronomy researchers at the JAXA Institute of Space and Astronautical Science, which is the central organization for operational development of XRISM, and promoting cross-disciplinary research with researchers from other fields is very stimulating.

Terminologies

  • *1 X-ray : Electromagnetic waves with short wavelengths. The wavelengths is from 1 pm to 10 nm.
  • *2 highly-charged ions : An ion stripped of multiple electrons.

Links