@ARTICLE{2018ApJ...867..122J,
       author = {Jin, Meng and Petrosian, Vahe and Liu, Wei and Nitta, Nariaki V. and Omodei, Nicola and Rubio da Costa, Fatima and Effenberger, Frederic and Li, Gang and Pesce-Rollins, Melissa and Allafort, Alice and Manchester, Ward IV},
        title = "{Probing the Puzzle of Behind-the-limb γ-Ray Flares: Data-driven Simulations of Magnetic Connectivity and CME-driven Shock Evolution}",
      journal = {The Astrophysical Journal},
     keywords = {magnetohydrodynamics: MHD, methods: numerical, Sun: corona, Sun: coronal mass ejections: CMEs, Sun: flares, Sun: X-rays, gamma rays, Astrophysics - Solar and Stellar Astrophysics},
         year = "2018",
        month = "Nov",
       volume = {867},
       number = {2},
          eid = {122},
        pages = {122},
     abstract = "{Recent detections of high-energy γ-rays from behind-
        the-limb (BTL) solar flares by the Fermi Gamma-ray Space
        Telescope pose a puzzle and challenge on the particle
        acceleration and transport mechanisms. In such events, the
        γ-ray emission region is located away from
        the BTL flare site by up to tens of degrees in heliographic
        longitude. It is thus hypothesized that particles are
        accelerated at the shock driven by the coronal mass ejection
        (CME) and then travel from the shock downstream back to the
        front side of the Sun to produce the observed
        γ-rays. To test this scenario, we performed
        data-driven, global magnetohydrodynamics simulations of the CME
        associated with a well-observed BTL flare on 2014 September 1.
        We found that part of the CME-driven shock develops magnetic
        connectivity with the γ-ray emission region,
        facilitating transport of particles back to the Sun. Moreover,
        the observed increase in γ-ray flux is
        temporally correlated with (1) the increase of the shock
        compression ratio and (2) the presence of a quasi-perpendicular
        shock over the area that is magnetically connected to the
        γ-ray emitting region, both conditions
        favoring the diffusive shock acceleration (DSA) of particles.
        These results support the above hypothesis and can help resolve
        another puzzle, i.e., long-duration (up to 20 hr)
        γ-rays flares. We suggest that, in addition
        to DSA, stochastic acceleration by plasma turbulence may also
        play a role, especially in the shock downstream region and
        during the early stage when the shock Alfv{'e}n Mach number is
        small.}",
          doi = {10.3847/1538-4357/aae1fd},
archivePrefix = {arXiv},
       eprint = {1807.01427},
 primaryClass = {astro-ph.SR},
       adsurl = {https://ui.adsabs.harvard.edu/abs/2018ApJ...867..122J},
      adsnote = {Provided by the SAO/NASA Astrophysics Data System}
}