High-Energy Gamma-Ray Emission From Solar Flares: Summary of Fermi LAT Detections and Analysis of Two M-Class Flares

Markus Ackermann , Marco Ajello , A. Albert , A. Allafort , Luca Baldini , Guido Barbiellini , D. Bastieri , K. Bechtol , R. Bellazzini , E. Bissaldi , E. Bonamente , E. Bottacini , A. Bouvier , T. J. Brandt (1) , J. Bregeon , M. Brigida , Pascal Bruel (2) , R. Buehler , S. Buson , G. A. Caliandro , R. A. Cameron , P. A. Caraveo , C. Cecchi , E. Charles , A. Chekhtman , J. Chiang , G. Chiaro , S. Ciprini , R. Claus , J. Cohen-Tanugi (3) , J. Conrad , F. d'Ammando , A. de Angelis , F. de Palma , C. D. Dermer , S. W. Digel , L. Di Venere , E. Do Couto E Silva , P. S. Drell , A. Drlica-Wagner , C. Favuzzi , S. J. Fegan (2) , W. B. Focke , A. Franckowiak , Y. Fukazawa , F. Gargano (4) , D. Gasparrini , S. Germani , N. Giglietto , F. Giordano , M. Giroletti , T. Glanzman , G. Godfrey , J. E. Grove , S. Guiriec , D. Hadasch (5) , M. Hayashida , E. Hays , D. Horan (2) , Y. Inoue , M. S. Jackson , T. Jogler , T. Kamae , T. Kawano , M. Kuss , J. Lande , S. Larsson , L. Latronico , M. Lemoine-Goumard (6) , F. Longo , F. Loparco (4) , M. N. Lovellette , P. Lubrano , M. Mayer , M. N. Mazziotta , P. F. Michelson , T. Mizuno , A. A. Moiseev , C. Monte , M. E. Monzani , E. Moretti , A. Morselli , I. V. Moskalenko , S. Murgia , R. Murphy , R. Nemmen , M. Ohno , A. Okumura , N. Omodei , M. Orienti , E. Orlando , J. F. Ormes , D. Paneque , J. H. Panetta , J. S. Perkins , M. Pesce-Rollins , V. Petrosian , F. Piron (3) , G. Pivato , T.A. Porter , M. Razzano , C. Sgro , G. Spandre , P. Spinelli , H. Takahashi , Y. Takeuchi , Y. Tanaka , J. G. Thayer , J. B. Thayer , D. J. Thompson , L. Tibaldo , M. Tinivella , G. Tosti , E. Troja , V. Tronconi , J. Vandenbroucke , V. Vasileiou (3) , G. Vianello , V. Vitale , M. Werner , K. S. Wood , M. Wood , Z. Yang

1 IRAP - Institut de recherche en astrophysique et planétologie
2 LLR - Laboratoire Leprince-Ringuet
3 LUPM - Laboratoire Univers et Particules de Montpellier
4 INFN, sezione di Bari - Istituto Nazionale di Fisica Nucleare, sezione di Bari
5 IEEC-CSIC
6 CENBG - Centre d'Etudes Nucléaires de Bordeaux Gradignan

We present the detections of 19 solar flares detected in high-energy gamma rays (above 100 MeV) with the Fermi Large Area Telescope (LAT) during its first four years of operation. Interestingly, all flares are associated with fairly fast Coronal Mass Ejections (CMEs) and are not all powerful X-ray flares. 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 gamma-ray emission over 13 hours, and the 2011 June 7 M2.5 flare, which was followed by gamma-ray emission lasting for 2 hours. We compare the Fermi-LAT data with X-ray and proton data measurements from GOES and RHESSI. We argue that a hadronic origin of the gamma rays is more likely than a leptonic origin and find that the energy spectrum of the proton distribution softens after the 2011 March 7 flare, favoring a scenario with continuous acceleration at the flare site. This work suggests that proton acceleration in solar flares is more common than previously thought, occurring for even modest X-ray flares, and for longer durations.

Domaines: Phénomènes cosmiques de haute energie [astro-ph.HE]; Phénomènes cosmiques de haute energie [astro-ph.HE]

Markus Ackermann, Marco Ajello, A. Albert, A. Allafort, Luca Baldini, et al.. High-Energy Gamma-Ray Emission From Solar Flares: Summary of Fermi LAT Detections and Analysis of Two M-Class Flares. The Astrophysical Journal, 2013, 787, pp.15. ⟨10.1088/0004-637X/787/1/15⟩. ⟨in2p3-01016748⟩