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Title: Hard X-Ray Emission from Partially Occulted Solar Flares: RHESSI Observations in Two Solar Cycles

Abstract

Flares close to the solar limb, where the footpoints are occulted, can reveal the spectrum and structure of the coronal looptop source in X-rays. We aim at studying the properties of the corresponding energetic electrons near their acceleration site, without footpoint contamination. To this end, a statistical study of partially occulted flares observed with Reuven Ramaty High-Energy Solar Spectroscopic Imager is presented here, covering a large part of solar cycles 23 and 24. We perform detailed spectra, imaging, and light curve analyses for 116 flares and include contextual observations from SDO and STEREO when available, providing further insights into flare emission that were previously not accessible. We find that most spectra are fitted well with a thermal component plus a broken power-law, non-thermal component. A thin-target kappa distribution model gives satisfactory fits after the addition of a thermal component. X-ray imaging reveals small spatial separation between the thermal and non-thermal components, except for a few flares with a richer coronal source structure. A comprehensive light curve analysis shows a very good correlation between the derivative of the soft X-ray flux (from GOES ) and the hard X-rays for a substantial number of flares, indicative of the Neupert effect. The resultsmore » confirm that non-thermal particles are accelerated in the corona and estimated timescales support the validity of a thin-target scenario with similar magnitudes of thermal and non-thermal energy fluxes.« less

Authors:
; ;  [1]; ; ;  [2];  [3];  [4]
  1. Department of Physics and KIPAC, Stanford University, Stanford, CA 94305 (United States)
  2. Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450 (United States)
  3. Bay Area Environmental Research Institute, 625 2nd Street, Suite 209, Petaluma, CA 94952 (United States)
  4. School of Physics and Astronomy, University of Minnesota, Minneapolis, MN 55455 (United States)
Publication Date:
OSTI Identifier:
22663855
Resource Type:
Journal Article
Resource Relation:
Journal Name: Astrophysical Journal; Journal Volume: 835; Journal Issue: 2; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ACCELERATION; CORRELATIONS; DISTRIBUTION; EMISSION; GAMMA RADIATION; HARD X RADIATION; LIMBS; PARTICLES; SOFT X RADIATION; SOLAR CYCLE; SOLAR FLARES; SPECTRA; SUN; TAIL ELECTRONS; ULTRAVIOLET RADIATION; VISIBLE RADIATION

Citation Formats

Effenberger, Frederic, Costa, Fatima Rubio da, Petrosian, Vahé, Oka, Mitsuo, Saint-Hilaire, Pascal, Krucker, Säm, Liu, Wei, and Glesener, Lindsay, E-mail: feffen@stanford.edu, E-mail: frubio@stanford.edu. Hard X-Ray Emission from Partially Occulted Solar Flares: RHESSI Observations in Two Solar Cycles. United States: N. p., 2017. Web. doi:10.3847/1538-4357/835/2/124.
Effenberger, Frederic, Costa, Fatima Rubio da, Petrosian, Vahé, Oka, Mitsuo, Saint-Hilaire, Pascal, Krucker, Säm, Liu, Wei, & Glesener, Lindsay, E-mail: feffen@stanford.edu, E-mail: frubio@stanford.edu. Hard X-Ray Emission from Partially Occulted Solar Flares: RHESSI Observations in Two Solar Cycles. United States. doi:10.3847/1538-4357/835/2/124.
Effenberger, Frederic, Costa, Fatima Rubio da, Petrosian, Vahé, Oka, Mitsuo, Saint-Hilaire, Pascal, Krucker, Säm, Liu, Wei, and Glesener, Lindsay, E-mail: feffen@stanford.edu, E-mail: frubio@stanford.edu. Wed . "Hard X-Ray Emission from Partially Occulted Solar Flares: RHESSI Observations in Two Solar Cycles". United States. doi:10.3847/1538-4357/835/2/124.
@article{osti_22663855,
title = {Hard X-Ray Emission from Partially Occulted Solar Flares: RHESSI Observations in Two Solar Cycles},
author = {Effenberger, Frederic and Costa, Fatima Rubio da and Petrosian, Vahé and Oka, Mitsuo and Saint-Hilaire, Pascal and Krucker, Säm and Liu, Wei and Glesener, Lindsay, E-mail: feffen@stanford.edu, E-mail: frubio@stanford.edu},
abstractNote = {Flares close to the solar limb, where the footpoints are occulted, can reveal the spectrum and structure of the coronal looptop source in X-rays. We aim at studying the properties of the corresponding energetic electrons near their acceleration site, without footpoint contamination. To this end, a statistical study of partially occulted flares observed with Reuven Ramaty High-Energy Solar Spectroscopic Imager is presented here, covering a large part of solar cycles 23 and 24. We perform detailed spectra, imaging, and light curve analyses for 116 flares and include contextual observations from SDO and STEREO when available, providing further insights into flare emission that were previously not accessible. We find that most spectra are fitted well with a thermal component plus a broken power-law, non-thermal component. A thin-target kappa distribution model gives satisfactory fits after the addition of a thermal component. X-ray imaging reveals small spatial separation between the thermal and non-thermal components, except for a few flares with a richer coronal source structure. A comprehensive light curve analysis shows a very good correlation between the derivative of the soft X-ray flux (from GOES ) and the hard X-rays for a substantial number of flares, indicative of the Neupert effect. The results confirm that non-thermal particles are accelerated in the corona and estimated timescales support the validity of a thin-target scenario with similar magnitudes of thermal and non-thermal energy fluxes.},
doi = {10.3847/1538-4357/835/2/124},
journal = {Astrophysical Journal},
number = 2,
volume = 835,
place = {United States},
year = {Wed Feb 01 00:00:00 EST 2017},
month = {Wed Feb 01 00:00:00 EST 2017}
}