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Title: Fermi -LAT Observations of High-energy Behind-the-limb Solar Flares

Abstract

We report on the Fermi -LAT detection of high-energy emission from the behind-the-limb (BTL) solar flares that occurred on 2013 October 11, and 2014 January 6 and September 1. The Fermi -LAT observations are associated with flares from active regions originating behind both the eastern and western limbs, as determined by STEREO . All three flares are associated with very fast coronal mass ejections (CMEs) and strong solar energetic particle events. We present updated localizations of the >100 MeV photon emission, hard X-ray (HXR) and EUV images, and broadband spectra from 10 keV to 10 GeV, as well as microwave spectra. We also provide a comparison of the BTL flares detected by Fermi -LAT with three on-disk flares and present a study of some of the significant quantities of these flares as an attempt to better understand the acceleration mechanisms at work during these occulted flares. We interpret the HXR emission to be due to electron bremsstrahlung from a coronal thin-target loop top with the accelerated electron spectra steepening at semirelativistic energies. The >100 MeV gamma-rays are best described by a pion-decay model resulting from the interaction of protons (and other ions) in a thick-target photospheric source. The protons aremore » believed to have been accelerated (to energies >10 GeV) in the CME environment and precipitate down to the photosphere from the downstream side of the CME shock and landed on the front side of the Sun, away from the original flare site and the HXR emission.« less

Authors:
;  [1]; ; ; ;  [2];  [3];  [4];  [5];  [6]; ; ;  [7];  [8];  [9];  [10];  [11]; ;  [12];  [13] more »; « less
  1. Deutsches Elektronen Synchrotron DESY, D-15738 Zeuthen (Germany)
  2. W. W. Hansen Experimental Physics Laboratory, Kavli Institute for Particle Astrophysics and Cosmology, Department of Physics and SLAC National Accelerator Laboratory, Stanford University, Stanford, CA 94305 (United States)
  3. Università di Pisa and Istituto Nazionale di Fisica Nucleare, Sezione di Pisa I-56127 Pisa (Italy)
  4. Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste (Italy)
  5. Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova (Italy)
  6. Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy)
  7. Istituto Nazionale di Fisica Nucleare, Sezione di Bari, I-70126 Bari (Italy)
  8. Istituto Nazionale di Fisica Nucleare, Sezione di Torino, I-10125 Torino (Italy)
  9. Laboratoire Univers et Particules de Montpellier, Université Montpellier, CNRS/IN2P3, F-34095 Montpellier (France)
  10. Laboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, F-91128 Palaiseau (France)
  11. INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica Milano, via E. Bassini 15, I-20133 Milano (Italy)
  12. Agenzia Spaziale Italiana (ASI) Science Data Center, I-00133 Roma (Italy)
  13. Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia (Italy)
Publication Date:
OSTI Identifier:
22663918
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; BREMSSTRAHLUNG; COMPARATIVE EVALUATIONS; DETECTION; ELECTRON SPECTRA; GAMMA RADIATION; GEV RANGE; HARD X RADIATION; INTERACTIONS; LIMBS; MASS; MEV RANGE; MICROWAVE RADIATION; MICROWAVE SPECTRA; PHOTON EMISSION; PHOTONS; PHOTOSPHERE; PROTONS; SOLAR FLARES; SUN

Citation Formats

Ackermann, M., Buehler, R., Allafort, A., Bottacini, E., Cameron, R. A., Charles, E., Baldini, L., Barbiellini, G., Bastieri, D., Bellazzini, R., Bissaldi, E., Caragiulo, M., Costanza, F., Bonino, R., Bregeon, J., Bruel, P., Caraveo, P. A., Cavazzuti, E., Ciprini, S., Cecchi, C., E-mail: nicola.omodei@stanford.edu, E-mail: vahep@stanford.edu, E-mail: melissa.pesce.rollins@pi.infn.it, and and others. Fermi -LAT Observations of High-energy Behind-the-limb Solar Flares. United States: N. p., 2017. Web. doi:10.3847/1538-4357/835/2/219.
Ackermann, M., Buehler, R., Allafort, A., Bottacini, E., Cameron, R. A., Charles, E., Baldini, L., Barbiellini, G., Bastieri, D., Bellazzini, R., Bissaldi, E., Caragiulo, M., Costanza, F., Bonino, R., Bregeon, J., Bruel, P., Caraveo, P. A., Cavazzuti, E., Ciprini, S., Cecchi, C., E-mail: nicola.omodei@stanford.edu, E-mail: vahep@stanford.edu, E-mail: melissa.pesce.rollins@pi.infn.it, & and others. Fermi -LAT Observations of High-energy Behind-the-limb Solar Flares. United States. doi:10.3847/1538-4357/835/2/219.
Ackermann, M., Buehler, R., Allafort, A., Bottacini, E., Cameron, R. A., Charles, E., Baldini, L., Barbiellini, G., Bastieri, D., Bellazzini, R., Bissaldi, E., Caragiulo, M., Costanza, F., Bonino, R., Bregeon, J., Bruel, P., Caraveo, P. A., Cavazzuti, E., Ciprini, S., Cecchi, C., E-mail: nicola.omodei@stanford.edu, E-mail: vahep@stanford.edu, E-mail: melissa.pesce.rollins@pi.infn.it, and and others. Wed . "Fermi -LAT Observations of High-energy Behind-the-limb Solar Flares". United States. doi:10.3847/1538-4357/835/2/219.
@article{osti_22663918,
title = {Fermi -LAT Observations of High-energy Behind-the-limb Solar Flares},
author = {Ackermann, M. and Buehler, R. and Allafort, A. and Bottacini, E. and Cameron, R. A. and Charles, E. and Baldini, L. and Barbiellini, G. and Bastieri, D. and Bellazzini, R. and Bissaldi, E. and Caragiulo, M. and Costanza, F. and Bonino, R. and Bregeon, J. and Bruel, P. and Caraveo, P. A. and Cavazzuti, E. and Ciprini, S. and Cecchi, C., E-mail: nicola.omodei@stanford.edu, E-mail: vahep@stanford.edu, E-mail: melissa.pesce.rollins@pi.infn.it and and others},
abstractNote = {We report on the Fermi -LAT detection of high-energy emission from the behind-the-limb (BTL) solar flares that occurred on 2013 October 11, and 2014 January 6 and September 1. The Fermi -LAT observations are associated with flares from active regions originating behind both the eastern and western limbs, as determined by STEREO . All three flares are associated with very fast coronal mass ejections (CMEs) and strong solar energetic particle events. We present updated localizations of the >100 MeV photon emission, hard X-ray (HXR) and EUV images, and broadband spectra from 10 keV to 10 GeV, as well as microwave spectra. We also provide a comparison of the BTL flares detected by Fermi -LAT with three on-disk flares and present a study of some of the significant quantities of these flares as an attempt to better understand the acceleration mechanisms at work during these occulted flares. We interpret the HXR emission to be due to electron bremsstrahlung from a coronal thin-target loop top with the accelerated electron spectra steepening at semirelativistic energies. The >100 MeV gamma-rays are best described by a pion-decay model resulting from the interaction of protons (and other ions) in a thick-target photospheric source. The protons are believed to have been accelerated (to energies >10 GeV) in the CME environment and precipitate down to the photosphere from the downstream side of the CME shock and landed on the front side of the Sun, away from the original flare site and the HXR emission.},
doi = {10.3847/1538-4357/835/2/219},
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}
}
  • In this paper, we report on the Fermi-LAT detection of high-energy emission from the behind-the-limb (BTL) solar flares that occurred on 2013 October 11, and 2014 January 6 and September 1. The Fermi-LAT observations are associated with flares from active regions originating behind both the eastern and western limbs, as determined by STEREO. All three flares are associated with very fast coronal mass ejections (CMEs) and strong solar energetic particle events. We present updated localizations of the >100 MeV photon emission, hard X-ray (HXR) and EUV images, and broadband spectra from 10 keV to 10 GeV, as well as microwavemore » spectra. We also provide a comparison of the BTL flares detected by Fermi-LAT with three on-disk flares and present a study of some of the significant quantities of these flares as an attempt to better understand the acceleration mechanisms at work during these occulted flares. We interpret the HXR emission to be due to electron bremsstrahlung from a coronal thin-target loop top with the accelerated electron spectra steepening at semirelativistic energies. The >100 MeV gamma-rays are best described by a pion-decay model resulting from the interaction of protons (and other ions) in a thick-target photospheric source. In conclusion, the protons are believed to have been accelerated (to energies >10 GeV) in the CME environment and precipitate down to the photosphere from the downstream side of the CME shock and landed on the front side of the Sun, away from the original flare site and the HXR emission.« less
  • The reasons for seven considerable increases in proton intensity in March--July 1972 are established. It is shown that four out of the seven increases were produced by solar flares in strong active regions behind the limb.
  • Launched on 2008 June 11, the Large Area Telescope (LAT) instrument on board the Fermi Gamma-ray Space Telescope has provided a rare opportunity to study high-energy photon emission from gamma-ray bursts (GRBs). Although the majority of such events (27) have been identified by the Fermi-LAT Collaboration, four were uncovered by using more sensitive statistical techniques. In this paper, we continue our earlier work by finding three more GRBs associated with high-energy photon emission, GRB 110709A, 111117A, and 120107A. To systematize our matched filter approach, a pipeline has been developed to identify these objects in nearly real time. GRB 120107A ismore » the first product of this analysis procedure. Despite the reduced threshold for identification, the number of GRB events has not increased significantly. This relative dearth of events with low photon number prompted a study of the apparent photon number distribution. We find an extremely good fit to a simple power law with an exponent of -1.8 {+-} 0.3 for the differential distribution. As might be expected, there is a substantial correlation between the number of lower energy photons detected by the Gamma-ray Burst Monitor (GBM) and the number observed by LAT. Thus, high-energy photon emission is associated with some but not all of the brighter GBM events. Deeper studies of the properties of the small population of high-energy emitting bursts may eventually yield a better understanding of these entire phenomena.« less