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Title: A Statistical Study to Determine the Origin of Long-duration Gamma-Ray Flares

Abstract

Two scenarios have been proposed to account for sustained ≥30 MeV gamma-ray emission in solar flares: (1) prolonged particle acceleration/trapping involving large-scale magnetic loops at the flare site, and (2) precipitation of high-energy (>300 MeV) protons accelerated at coronal/interplanetary shock waves. To determine which of these scenarios is more likely, we examine the associated soft X-ray flares, coronal mass ejections (CMEs), and solar energetic proton events for (a) the long-duration gamma-ray flares (LDGRFs) observed by the Large Area Telescope on Fermi, and (b) delayed and/or spatially extended high-energy gamma-ray flares observed by the Gamma-ray Spectrometer on the Solar Maximum Mission, the Gamma-1 telescope on the Gamma satellite, and the Energetic Gamma-Ray Experiment Telescope on the Compton Gamma-Ray Observatory. For the Fermi data set of 11 LDGRFs with >100 MeV emission lasting for ≥~2 hr, we search for associations and reverse associations between LDGRFs, X-ray flares, CMEs, and SEPs, i.e., beginning with the gamma-ray flares and also, in turn, with X-class soft X-ray flares, fast (≥1500 km s -1) and wide CMEs, and intense (peak flux ≥2.67 × 10 -3 protons cm -2 s -1 sr -1, with peak to background ratio >1.38) >300 MeV SEPs at 1 au. While LDGRFsmore » tend to be associated with bright X-class flares, we find that only one-third of the X-class flares during the time of Fermi monitoring coincide with an LDGRF. However, nearly all fast, wide CMEs are associated with an LDGRF. These preliminary association analyses favor the proton precipitation scenario, however there is a prominent counter-example of a potentially magnetically well-connected solar eruption with >100 MeV emission for ~10 hr for which the near-Earth >300 MeV proton intensity did not rise above background.« less

Authors:
ORCiD logo [1];  [2]; ORCiD logo [3]; ORCiD logo [4]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
  2. Univ. of Colorado, Boulder, CO (United States). Ann and H.J. Smead Aerospace Engineering Sciences
  3. SLAC National Accelerator Lab. and Stanford Univ., Menlo Park, CA (United States). W.W. Hansen Experimental Physics Lab., Kavli Inst. for Particle Astrophysics and Cosmology and Dept. of Physics
  4. National Inst. of Nuclear Physics (INFN), Pisa (Italy)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE; National Science Foundation (NSF); Atmospheric and Environmental Research (AER), Lexington, MA (United States)
OSTI Identifier:
1473799
Report Number(s):
LA-UR-17-27146
Journal ID: ISSN 1538-4357
Grant/Contract Number:  
AC52-06NA25396
Resource Type:
Accepted Manuscript
Journal Name:
The Astrophysical Journal (Online)
Additional Journal Information:
Journal Name: The Astrophysical Journal (Online); Journal Volume: 864; Journal Issue: 1; Journal ID: ISSN 1538-4357
Publisher:
Institute of Physics (IOP)
Country of Publication:
United States
Language:
English
Subject:
79 ASTRONOMY AND ASTROPHYSICS; 58 GEOSCIENCES; Heliospheric and Magnetospheric Physics; solar flares

Citation Formats

Winter, Lisa Marie, Bernstein, Valerie, Omodei, Nicola, and Pesce-Rollins, Melissa. A Statistical Study to Determine the Origin of Long-duration Gamma-Ray Flares. United States: N. p., 2018. Web. doi:10.3847/1538-4357/aad3c0.
Winter, Lisa Marie, Bernstein, Valerie, Omodei, Nicola, & Pesce-Rollins, Melissa. A Statistical Study to Determine the Origin of Long-duration Gamma-Ray Flares. United States. doi:10.3847/1538-4357/aad3c0.
Winter, Lisa Marie, Bernstein, Valerie, Omodei, Nicola, and Pesce-Rollins, Melissa. Wed . "A Statistical Study to Determine the Origin of Long-duration Gamma-Ray Flares". United States. doi:10.3847/1538-4357/aad3c0. https://www.osti.gov/servlets/purl/1473799.
@article{osti_1473799,
title = {A Statistical Study to Determine the Origin of Long-duration Gamma-Ray Flares},
author = {Winter, Lisa Marie and Bernstein, Valerie and Omodei, Nicola and Pesce-Rollins, Melissa},
abstractNote = {Two scenarios have been proposed to account for sustained ≥30 MeV gamma-ray emission in solar flares: (1) prolonged particle acceleration/trapping involving large-scale magnetic loops at the flare site, and (2) precipitation of high-energy (>300 MeV) protons accelerated at coronal/interplanetary shock waves. To determine which of these scenarios is more likely, we examine the associated soft X-ray flares, coronal mass ejections (CMEs), and solar energetic proton events for (a) the long-duration gamma-ray flares (LDGRFs) observed by the Large Area Telescope on Fermi, and (b) delayed and/or spatially extended high-energy gamma-ray flares observed by the Gamma-ray Spectrometer on the Solar Maximum Mission, the Gamma-1 telescope on the Gamma satellite, and the Energetic Gamma-Ray Experiment Telescope on the Compton Gamma-Ray Observatory. For the Fermi data set of 11 LDGRFs with >100 MeV emission lasting for ≥~2 hr, we search for associations and reverse associations between LDGRFs, X-ray flares, CMEs, and SEPs, i.e., beginning with the gamma-ray flares and also, in turn, with X-class soft X-ray flares, fast (≥1500 km s-1) and wide CMEs, and intense (peak flux ≥2.67 × 10-3 protons cm-2 s-1 sr-1, with peak to background ratio >1.38) >300 MeV SEPs at 1 au. While LDGRFs tend to be associated with bright X-class flares, we find that only one-third of the X-class flares during the time of Fermi monitoring coincide with an LDGRF. However, nearly all fast, wide CMEs are associated with an LDGRF. These preliminary association analyses favor the proton precipitation scenario, however there is a prominent counter-example of a potentially magnetically well-connected solar eruption with >100 MeV emission for ~10 hr for which the near-Earth >300 MeV proton intensity did not rise above background.},
doi = {10.3847/1538-4357/aad3c0},
journal = {The Astrophysical Journal (Online)},
number = 1,
volume = 864,
place = {United States},
year = {2018},
month = {8}
}

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Figures / Tables:

FIG. 1 FIG. 1: Fermi LAT fluence (see Table 1) compared to the associated X-ray flare class (left) and Rmax (right). Long duration gamma-ray flares (with duration > 2 hours), are indicated with triangles, while shorter duration gamma-ray flares are shown with circles. There is no evidence of a correlation between themore » peak flux or flare temperature diagnostic (Rmax) and the gamma-ray emission.« less

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Figures/Tables have been extracted from DOE-funded journal article accepted manuscripts.