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XMM-Newton Science Analysis System

epreject (epreject-5.18.1) [xmmsas_20211130_0941-20.0.0]

Background: motivation for developing this procedure

The EPIC-pn fast timing mode was designed so that a time resolution of 0.029 milliseconds can be achieved. This mode is important for observing bright variable sources with a very high time resolution. Up to now the it has only been possible to use the spectra down to 300 eV in this mode. Below this energy the data is affected by so-called soft flares which are caused by stack overflows generated by high energy particles.

These so-called soft flares have sharp rise (from 0 counts/sec to several thousand counts/sec in $\sim$ 0.10-0.15 sec) then decaying back to 0 counts/sec slightly slower in about 0.3-0.4 sec). In some cases (extremely bright flares) they can lead to a FIFO overflow thus causing a small gap in the data of about $\sim$ 0.08 sec. These gaps are statistically handled by the SAS in epframes

In this task we provide a method to mitigate the effect these flares have on the data for flagging such soft flare events so that they can later be screened off the data.

With this method it at last becomes possible to use the spectral information in the data down to the lowest energies detectable in this mode, i.e. 200 eV. This is particularly interesting for timing studies of isolated neutron stars, X-ray Binaries and other variable objects, such as magnetic CVs, with very soft spectra.

XMM-Newton SOC -- 2021-11-30