When eROSITA's eyes are closed, scintillating events can still be seen. They are caused by high-energy particles, such as Galactic cosmic rays or energetic solar particles. These can penetrate the shielding made of 3 centimetres of copper, and hit the sensitive area of the pnCCD camera. In addition, these particles can also interact with the camera housing and create a variety of secondary particles, forming showers of events that are accompanied by X-ray emission.
Usually, these events are rejected on-board, to save telemetry for the actual eROSITA science. On special occasions and for a short amount of time, full images with all events are beamed to ground, to see the full glory of space environment at the Lagrange point L2. The animation shows 140 such images, with total exposure of only 7 seconds, taken on the evening of 1st April 2020.
The Sun's 11-year activity cycle modulates the Galactic Cosmic Rays, and at the current solar minium the protecting magnetic fields are weakest. eROSITA could recently see a decline of this particle background, expected for the start of the new solar cycle. But also variations on the order of 27 days are visible, maybe coupled to solar rotation.
M. Freyberg et al., "SRG/eROSITA in-flight background at L2", Proc. SPIE 11444,
https://doi.org/10.1117/12.2562709© M. Freyberg/MPE