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Figure 1. Schematic images of gamma ray production from cosmic ray protons and electrons. Protons from cosmic rays interact with interstellar protons such as molecular and atomic hydrogen. The interaction creates a neutral pion which quickly decays into two gamma photons (hadronic process). Electrons from cosmic rays energize interstellar photons (mainly the cosmic diffuse background; CMB) into gamma ray energy via reverse Compton scattering (lepton process). Credit: Laboratory of Astrophysics, Nagoya University
Astronomers have succeeded for the first time in quantifying the proton and electronic components of cosmic rays in a supernova remnant. At least 70% of the very high-energy gamma rays emitted by cosmic rays are due to relativistic protons, according to new imaging analysis of radio, X and gamma rays. The acceleration site of protons, the main components of cosmic rays, has been a mystery for 100 years in modern astrophysics, it is the first time that the amount of cosmic rays produced in a supernova remnant has been quantitatively demonstrated. and is an epoch-stage in the elucidation of the origin of cosmic rays.
The origin of cosmic rays, the highest energy particles in the universe, has been a great mystery since their discovery in 1912. Because cosmic rays promote the chemical evolution of interstellar matter, understanding their origin is essential for understand the evolution of our Galaxy. . Cosmic rays are believed to be accelerated by supernova remnants (the aftermath of supernova explosions) in our Galaxy and have traveled to Earth at almost the speed of light. Recent advances in gamma ray observations have revealed that many supernova remnants emit gamma rays at energies of teraelectronvolts (TeV). If gamma rays are produced by protons, which are the main component of cosmic rays, then the origin of cosmic ray supernova remnants can be verified. However, since gamma rays are also produced by electrons, it is necessary to determine whether the origin of the proton or the electron is dominant, and to measure the ratio of the two contributions (see also Figure 1). The results of this study provide compelling evidence for gamma rays originating from the proton component, which is the main component of cosmic rays, and state that galactic cosmic rays are produced by supernova remnants.
The originality of this research is that gamma radiation is represented by a linear combination of proton and electron components. Astronomers knew of a relationship that the intensity of gamma rays from protons is proportional to the density of interstellar gas obtained from radio imaging observations. On the other hand, the gamma rays of the electrons should also be proportional to the intensity of the x-rays of the electrons. Therefore, they expressed the total intensity of gamma rays as the sum of two components of gamma rays, one from the origin of protons and the other from the origin of electrons. This led to a unified understanding of three independent observables (Figure 2). This method was first proposed in this study. As a result, it has been shown that gamma rays from protons and electrons account for 70% and 30% of total gamma rays, respectively. This is the first time that the two origins have been quantified. The results also demonstrate that proton gamma rays are dominated in the gas-rich interstellar regions, while electron gamma rays are enhanced in the gas-poor region. This confirms that the two mechanisms work together and support the predictions of previous theoretical studies.
Figure 2. Maps of gamma ray intensity Ng, interstellar gas density Np and X-ray intensity Nx. Credit: Astrophysics Laboratory, Nagoya University
“This new method could not have been achieved without international collaborations,” said Professor Emeritus Yasuo Fukui at Nagoya University. He led this project and accurately quantified the density distribution of interstellar gas using the NANTEN radio telescope and the Australian Telescope’s compact array since 2003. Although the gamma ray resolution was insufficient to perform a full scan at At the time, Professor Gavin Rowell and Dr Sabrina Einecke of the University of Adelaide and the HESS team dramatically improved the spatial resolution and sensitivity of gamma rays over the years, making it possible to compare them precisely with gas. interstellar. Dr Hidetoshi Sano of the National Astronomical Observatory of Japan led the x-ray imaging analysis of archival data sets from the European X-ray satellite XMM-Newton. Dr Einecke and Prof Rowell worked closely with Prof Fukui and Dr Sano to perform the detailed studies that examined the correlations between gamma rays, x-rays and radio emissions. “This new method will be applied to more supernova remnants using the next-generation CTA (Cherenkov Telescope Array) gamma-ray telescope in addition to existing observatories, which will significantly advance the study of the origin of cosmic rays. “
Figure 3. Three-dimensional fit of a flat plane expressed by an equation of Ng = a Np + b Nx, where a and b are constants. The data points are colored by the code in the figure as a function of Ng and are represented by filled and open symbols for those above and below the plane. Blue, green, yellow and red represent Ng is less than 1.2 arcmin-2 counts, 1.2 to 1.7 arcmin-2 counts, 1.7 to 2.2 arcmin-2 counts and greater than 2.2 arcmin-2 accounts, respectively. The blue, green, orange, red, and purple dashed lines on the best-fit plane indicate 1.0, 1.5, 2.0, 2.5, and 3.0 arcmin-2, respectively. Credit: Astrophysics Laboratory, Nagoya University
Most accurate measurements of proton and helium spectra of cosmic rays above TeV
Yasuo Fukui et al, Pursue the origin of gamma rays in RX J1713.7-3946 Quantify hadronic and leptonic components, The Journal of Astrophysics (2021). DOI: 10.3847 / 1538-4357 / abff4a
Provided by Nagoya University
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