High-energy gamma-ray emission from solar flares: Summary of Fermi large area telescope detections and analysis of two M-class flares
- Deutsches Elektronen Synchrotron DESY, D-15738 Zeuthen (Germany)
- Space Sciences Laboratory, 7 Gauss Way, University of California, Berkeley, CA 94720-7450 (United States)
- Department of Physics, Center for Cosmology and Astro-Particle Physics, The Ohio State University, Columbus, OH 43210 (United States)
- 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)
- Università di Pisa and Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy)
- Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, I-34127 Trieste (Italy)
- Istituto Nazionale di Fisica Nucleare, Sezione di Padova, I-35131 Padova (Italy)
- Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, I-56127 Pisa (Italy)
- Institut für Astro- und Teilchenphysik and Institut für Theoretische Physik, Leopold-Franzens-Universität Innsbruck, A-6020 Innsbruck (Austria)
- Istituto Nazionale di Fisica Nucleare, Sezione di Perugia, I-06123 Perugia (Italy)
- Santa Cruz Institute for Particle Physics, Department of Physics and Department of Astronomy and Astrophysics, University of California at Santa Cruz, Santa Cruz, CA 95064 (United States)
- NASA Goddard Space Flight Center, Greenbelt, MD 20771 (United States)
- Dipartimento di Fisica "M. Merlin" dell'Università e del Politecnico di Bari, I-70126 Bari (Italy)
- Laboratoire Leprince-Ringuet, École polytechnique, CNRS/IN2P3, F-91128 Palaiseau (France)
We present the detections of 18 solar flares detected in high-energy γ-rays (above 100 MeV) with the Fermi Large Area Telescope (LAT) during its first 4 yr of operation. This work suggests that particle acceleration up to very high energies in solar flares is more common than previously thought, occurring even in modest flares, and for longer durations. Interestingly, all these flares are associated with fairly fast coronal mass ejections (CMEs). We then describe the detailed temporal, spatial, and spectral characteristics of the first two long-lasting events: the 2011 March 7 flare, a moderate (M3.7) impulsive flare followed by slowly varying γ-ray emission over 13 hr, and the 2011 June 7 M2.5 flare, which was followed by γ-ray emission lasting for 2 hr. We compare the Fermi LAT data with X-ray and proton data measurements from GOES and RHESSI. We argue that the γ-rays are more likely produced through pion decay than electron bremsstrahlung, and we find that the energy spectrum of the proton distribution softens during the extended emission of the 2011 March 7 flare. This would disfavor a trapping scenario for particles accelerated during the impulsive phase of the flare and point to a continuous acceleration process at play for the duration of the flares. CME shocks are known for accelerating the solar energetic particles (SEPs) observed in situ on similar timescales, but it might be challenging to explain the production of γ-rays at the surface of the Sun while the CME is halfway to the Earth. A stochastic turbulence acceleration process occurring in the solar corona is another likely scenario. Detailed comparison of characteristics of SEPs and γ-ray-emitting particles for several flares will be helpful to distinguish between these two possibilities.
- OSTI ID:
- 22356884
- Journal Information:
- Astrophysical Journal, Vol. 787, Issue 1; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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