While INTEGRAL is designed to measure high-energy photons,
it is also affected by energetic particles, which abound in
the space environment, originating from the Sun or other cosmic
sources and especially those caught in the van Allen radiation
belts around the Earth.
The image shows electron (red) and proton (blue) count-rates as
measured from January til March 2012 by the INTEGRAL Radiation
Environment Monitor (IREM), a small on-board particle detector
safeguarding the INTEGRAL payload.
The regular sharp peaks - every 3 days - are due to the passages of
INTEGRAL on its orbit through the radiation belts. The instruments
are routinely de-activated during these passages during which the
typical radiation dose as observed along the rest of the orbit is
increased by about 4 orders of magnitude.
In addition, one sees the dramatic effects of two radiation storms
caused by powerful solar flares in January and March 2012. The first
"double-punch", starting on 22 January forced the monitor instruments
JEM-X and OMC into inactivity for about 8 days in total, IBIS still
for ~5.5 days while only SPI kept measuring. On the second occasion
in March all instruments had to be put into safe mode, IBIS and SPI
for about 5 days each, the monitors for more than a week.
