Gamma-Ray Solar Flares and In Situ Particle Acceleration

Abstract

At present two concurrent paradigms of solar energetic particle (SEP) origin exist: acceleration directly in the flare site or by the shock wave of coronal mass ejection (CME). Active discussions on a relative role of flares and coronal mass ejections for SEP acceleration and propagation are continuous until now. In my opinion only future observations of solar high energy γ–emission with better spectral, spatial and temporal resolution may clarify this issue. In my report I discuss possible signatures of the flare and shock acceleration processes. What is a picture provided by the current instruments? What can we expect to observe with a perfect instrument in high energy gamma rays in one or another case on a time scale of impulsive and long decay flare phases?

Extreme solar events

“…More recently, Gopalswamy et al (2021) argued, on the basis of corrected values for both N c-ray (based on the visibility of limb events) and N SEP (based on the effect of flare latitude on SEP propagation) in the de Nolfo et al sample, that the two parameters are highly correlated (r = 0.77). The ''flare vs. shock'' debate for the largest highenergy SEP events (e.g., Vashenyuk et al 2011;McCracken et al 2012;Grechnev et al 2015;Cliver 2016;Bazilevskaya 2017;Klein and Dalla 2017;Kocharov et al 2018;Struminsky 2018;Kouloumvakos et al 2020;Kocharov et al 2020Kocharov et al , 2021Hutchinson et al 2022) is far from over and will continue to inform understanding of SEP acceleration at the Sun.…”