Figure 1: An example of a cosmic-ray extensive air shower captured by HSC on the Subaru Telescope. The highlighted tracks, which are mostly aligned in similar directions, show the shower particles induced from a high-energy cosmic ray. A high resolution image is here (2.0 MB). Credit: NAOJ/HSC Collaboration
A research team including scientists at the National Astronomical
Observatory of Japan (NAOJ) and Osaka Metropolitan University has
captured extensive cosmic-ray air showers with unprecedented precision
using the ultra-wide-field prime focus camera mounted on the Subaru
Telescope. Advancing this new detection method will unlock deeper
understanding of the Universe’s most energetic particles.
When a high energy cosmic ray collides with the Earth's atmosphere, it
generates an enormous number of particles in what is known as an
extensive air shower. In images taken by the Subaru Telescope's prime
focus camera, Hyper Suprime-Cam (HSC), there are about 20,000 tracks
produced by cosmic rays penetrating the CCDs per single shot (Figures 1
and 2). These tracks of cosmic rays act as noise in astronomical
observations and are removed by the usual data processing.
Figure 2: (left) A conceptual diagram of a track left when a cosmic ray passes through a CCD. (right) The camera section of HSC is lined with 116 large CCDs, each measuring 6 cm by 3 cm. (Credit: NAOJ/ HSC Project)
A research team including Dr. Satoshi Kawanomoto, Dr. Michitaro
Koike, and Dr. Satoshi Miyazaki of Subaru Telescope, NAOJ; Dr. Toshihiro
Fujii and graduate student Fraser Bradfield of Osaka Metropolitan
University; Dr. Tomoki Morokuma of Chiba Institute of Technology; and
Dr. Hiroshi Komiyama of Hosei University, focuses on that very "noise."
By analyzing approximately 17,000 images captured between 2014 and 2020,
the team pinpointed 13 images that contain extensive air showers, with a
number of particle tracks far exceeding the usual count.
"To date, there had been no systematic analysis of such events published in academic journals. An extensive air shower needs to be observed in high altitudes before it spreads out. Also, the detector should be thick enough to record long tracks. The data was obtained for the first time precisely because HSC, which adopted CCDs with a thick depletion layer, was operated for long-term observations at an altitude of 4,200 meters. This demonstrates the uniqueness of HSC and its survey (HSC-SSP) from an entirely new perspective," explains Dr. Miyazaki, the Director of Subaru Telescope.
Traditional cosmic ray detectors (Note 1) record the total number of particles and the time information of the incoming rays, without distinguishing the types of particles (like electrons, positrons, of muons). On the other hand, the new method using HSC has the potential to determine the nature of individual particles from the shapes of their tracks.
"By integrating our method with conventional approaches, we hope to advance our understanding of extensive air showers," says Dr. Fujii.
The air showers captured with HSC suggest the possibility of signals derived from dark matter, pointing to potential applications in dark matter exploration. Furthermore, detailed analysis of the precisely captured tracks will open the door to new insights to the transition of the Universe into a matter-dominated era (Note 2).
The lead author, Dr. Kawanomoto, says, "In astronomical images, cosmic rays are subjects for correction. However, by analyzing the long-term, consistent observation data from HSC-SSP, we were able to demonstrate the potential to extract valuable information in scientific areas not intended for the original purpose. I believe this not only provides insights into the observation methods for high-energy particles but also emphasizes the importance of data archives with guaranteed uniform quality."
These results were published in Scientific Reports on October 12, 2023 as Kawanomoto, et al. "Observing Cosmic-Ray Extensive Air Showers with a Silicon Imaging Detector."
This work was supported by JSPS KAKENHI Grant Numbers 20H00181, 20H05856, 22K21349, and JP20H05852. This work was supported by JST, the establishment of university fellowships towards the creation of science technology innovation, Grant Number JPMJFS2138.
"To date, there had been no systematic analysis of such events published in academic journals. An extensive air shower needs to be observed in high altitudes before it spreads out. Also, the detector should be thick enough to record long tracks. The data was obtained for the first time precisely because HSC, which adopted CCDs with a thick depletion layer, was operated for long-term observations at an altitude of 4,200 meters. This demonstrates the uniqueness of HSC and its survey (HSC-SSP) from an entirely new perspective," explains Dr. Miyazaki, the Director of Subaru Telescope.
Traditional cosmic ray detectors (Note 1) record the total number of particles and the time information of the incoming rays, without distinguishing the types of particles (like electrons, positrons, of muons). On the other hand, the new method using HSC has the potential to determine the nature of individual particles from the shapes of their tracks.
"By integrating our method with conventional approaches, we hope to advance our understanding of extensive air showers," says Dr. Fujii.
The air showers captured with HSC suggest the possibility of signals derived from dark matter, pointing to potential applications in dark matter exploration. Furthermore, detailed analysis of the precisely captured tracks will open the door to new insights to the transition of the Universe into a matter-dominated era (Note 2).
The lead author, Dr. Kawanomoto, says, "In astronomical images, cosmic rays are subjects for correction. However, by analyzing the long-term, consistent observation data from HSC-SSP, we were able to demonstrate the potential to extract valuable information in scientific areas not intended for the original purpose. I believe this not only provides insights into the observation methods for high-energy particles but also emphasizes the importance of data archives with guaranteed uniform quality."
These results were published in Scientific Reports on October 12, 2023 as Kawanomoto, et al. "Observing Cosmic-Ray Extensive Air Showers with a Silicon Imaging Detector."
This work was supported by JSPS KAKENHI Grant Numbers 20H00181, 20H05856, 22K21349, and JP20H05852. This work was supported by JST, the establishment of university fellowships towards the creation of science technology innovation, Grant Number JPMJFS2138.
Notes
(Note 1) Traditional cosmic ray detectors include scintillators, which detect
faint fluorescent light emitted when cosmic rays pass through materials
like plastic, and water Cherenkov detectors that detect Cherenkov
radiation from charged particles in water.
(Note 2) At the beginning of the Universe, it is believed that matter and antimatter existed in equal amounts. However, in the current Universe, antimatter has vanished, and matter dominates. This state is referred to as a "matter-dominated era." The reason why antimatter disappeared is not clear, and it is believed that unknown physical laws may be involved..
(Note 2) At the beginning of the Universe, it is believed that matter and antimatter existed in equal amounts. However, in the current Universe, antimatter has vanished, and matter dominates. This state is referred to as a "matter-dominated era." The reason why antimatter disappeared is not clear, and it is believed that unknown physical laws may be involved..
Relevant Links
Osaka Metropolitan University October 12, 2023 Press Release
Source: Subaru Telescope
