skip to main content

DOE PAGESDOE PAGES

Title: Evidence for GeV cosmic rays from white dwarfs in the local cosmic ray spectra and in the gamma-ray emissivity of the inner Galaxy

Here, recent observations found that electrons are accelerated to ~10 GeV and emit synchrotron hard X-rays in two magnetic white dwarfs (WDs), also known as cataclysmic variables (CVs). In nova outbursts of WDs, multi-GeV gamma-rays were detected, implying that protons are accelerated to 100 GeV or higher. In recent optical surveys, the WD density is found to be higher near the Sun than in the Galactic disk by a factor ~2.5. The cosmic rays (CRs) produced by local CVs and novae will accumulate in the local bubble for 10 6–10 7 yr. On these findings, we search for CRs from historic CVs and novae in the observed CR spectra. We model the CR spectra at the heliopause as sums of Galactic and local components based on observational data as much as possible. The initial Galactic CR electron and proton spectra are deduced from the gamma-ray emissivity, the local electron spectrum from the hard X-ray spectra at the CVs, and the local proton spectrum from gamma-ray spectra at novae. These spectral shapes are then expressed in a simple set of polynomial functions of CR energy and regressively fitted until the high-energy (>100 GeV) CR spectra near Earth and the Voyager-1 spectramore » at the heliopause are reproduced. We then extend the modeling to nuclear CR spectra and find that one spectral shape fits all local nuclear CRs, and that the apparent hardening of the nuclear CR spectra is caused by the roll-down of local nuclear spectra around 100–200 GeV. All local CR spectra populate a limited energy band below 100–200 GeV and enhance gamma-ray emissivity below ~10 GeV. Such an enhancement is observed in the inner Galaxy, suggesting the CR fluxes from CVs and novae are substantially higher there.« less
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [5]
  1. The Univ. of Tokyo, Tokyo (Japan); Stanford Univ., Menlo Park, CA (United States)
  2. Kyoto Univ., Kyoto (Japan)
  3. RIKEN, Saitama (Japan)
  4. Yamagata Univ., Yamagata (Japan)
  5. The Univ. of Tokyo, Tokyo (Japan)
Publication Date:
Grant/Contract Number:
AC02-76SF00515; 15K05098
Type:
Accepted Manuscript
Journal Name:
Publications of the Astronomical Society of Japan
Additional Journal Information:
Journal Volume: 70; Journal Issue: 2; Journal ID: ISSN 0004-6264
Publisher:
Astronomical Society of Japan
Research Org:
SLAC National Accelerator Lab., Menlo Park, CA (United States)
Sponsoring Org:
USDOE
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS
OSTI Identifier:
1458419

Kamae, Tuneyoshi, Lee, Shiu -Hang, Makishima, Kazuo, Shibata, Shinpei, and Shigeyama, Toshikazu. Evidence for GeV cosmic rays from white dwarfs in the local cosmic ray spectra and in the gamma-ray emissivity of the inner Galaxy. United States: N. p., Web. doi:10.1093/pasj/psy010.
Kamae, Tuneyoshi, Lee, Shiu -Hang, Makishima, Kazuo, Shibata, Shinpei, & Shigeyama, Toshikazu. Evidence for GeV cosmic rays from white dwarfs in the local cosmic ray spectra and in the gamma-ray emissivity of the inner Galaxy. United States. doi:10.1093/pasj/psy010.
Kamae, Tuneyoshi, Lee, Shiu -Hang, Makishima, Kazuo, Shibata, Shinpei, and Shigeyama, Toshikazu. 2018. "Evidence for GeV cosmic rays from white dwarfs in the local cosmic ray spectra and in the gamma-ray emissivity of the inner Galaxy". United States. doi:10.1093/pasj/psy010. https://www.osti.gov/servlets/purl/1458419.
@article{osti_1458419,
title = {Evidence for GeV cosmic rays from white dwarfs in the local cosmic ray spectra and in the gamma-ray emissivity of the inner Galaxy},
author = {Kamae, Tuneyoshi and Lee, Shiu -Hang and Makishima, Kazuo and Shibata, Shinpei and Shigeyama, Toshikazu},
abstractNote = {Here, recent observations found that electrons are accelerated to ~10 GeV and emit synchrotron hard X-rays in two magnetic white dwarfs (WDs), also known as cataclysmic variables (CVs). In nova outbursts of WDs, multi-GeV gamma-rays were detected, implying that protons are accelerated to 100 GeV or higher. In recent optical surveys, the WD density is found to be higher near the Sun than in the Galactic disk by a factor ~2.5. The cosmic rays (CRs) produced by local CVs and novae will accumulate in the local bubble for 106–107 yr. On these findings, we search for CRs from historic CVs and novae in the observed CR spectra. We model the CR spectra at the heliopause as sums of Galactic and local components based on observational data as much as possible. The initial Galactic CR electron and proton spectra are deduced from the gamma-ray emissivity, the local electron spectrum from the hard X-ray spectra at the CVs, and the local proton spectrum from gamma-ray spectra at novae. These spectral shapes are then expressed in a simple set of polynomial functions of CR energy and regressively fitted until the high-energy (>100 GeV) CR spectra near Earth and the Voyager-1 spectra at the heliopause are reproduced. We then extend the modeling to nuclear CR spectra and find that one spectral shape fits all local nuclear CRs, and that the apparent hardening of the nuclear CR spectra is caused by the roll-down of local nuclear spectra around 100–200 GeV. All local CR spectra populate a limited energy band below 100–200 GeV and enhance gamma-ray emissivity below ~10 GeV. Such an enhancement is observed in the inner Galaxy, suggesting the CR fluxes from CVs and novae are substantially higher there.},
doi = {10.1093/pasj/psy010},
journal = {Publications of the Astronomical Society of Japan},
number = 2,
volume = 70,
place = {United States},
year = {2018},
month = {2}
}