XMM-Newton Science Analysis System
epexposure (epexposure-0.16) [xmmsas_20211130_0941-20.0.0]
Because of telemetry limits an exposure might be programmed such that not all
frames will be transmitted. This info is stored as quadrant specific periodic
housekeeping parameters An_CHOP (see Table 1).
These chopper parameters (normally 0) control the number of frames
excluded from the onboard analysis before one is
analysed and sent to telemetry.
The livetime due to such discarded frames is represented by the factor
As the chopper parameter and thus the associated livetime
is constant for a specific exposure the values
be stored in the keywords An_CHOP and AX_FC3
in the CCD specific EXPOSURE
extension to be addressed by higher SAS tasks.
If one is just interested in a correct count rate then it is sufficient
to divide the rate by FC3.
XMM-Newton SOC -- 2021-11-30