(21.9.2018) Some of these triggers are due to the cosmological Gamma-ray Bursts, others to sporadic bursting sources of impulsive high-energy emission within our galaxy such as Soft Gamma-ray Repeaters or accreting binary systems. (…)
This has happened nearly 1200 times during the mission, with most of the triggers arising during the most active part of the solar cycle.

(16.8.2018) The likely cause is hadronic cosmic rays undergoing collisions in the Sun’s atmosphere after being redirected from ingoing to outgoing in magnetic fields, though the exact mechanism is not understood.

(14.8.2018) Our star appears to unleash its most energetic photons during the quiet phase of its 11-year cycle.

(…)

The flux significantly exceeded that predicted by the one and only model that takes on cosmic-ray interactions with solar gas.