  The Wide Field Imager (WFI), one of two instruments on ESA's next large X-ray
mission Athena, is designed for imaging spectroscopy of X-rays in the range of
0.2 to 15 keV with a large field of view and high count rate capability. The
focal plane consists of back-illuminated DEPFET (Depleted p-channel field
effect transistor) sensors that have a high radiation tolerance and provide a
near Fano-limited energy resolution. To achieve this, a very low noise readout
is required, about 3 electrons ENC at beginning of life is foreseen. This makes
the device very susceptible to any radiation induced worsening of the readout
noise. The main mechanism of degradation will be the increase of dark current
due to displacement damage caused primarily by high energy protons. To study
the expected performance degradation, a prototype detector module with fully
representative pixel layout and fabrication technology was irradiated with 62.4
MeV protons at the accelerator facility MedAustron in Wiener Neustadt. A total
dose equivalent to 3.3 $\textstyle{10^{9}}$ 10-MeV protons/$\mathrm{cm^{2}}$
was applied in two steps. During, in-between and after the irradiations the
detector remained at the operating temperature of 213 K and was fully biased
and operated. Data was recorded to analyze the signal of all incident
particles. We report on the increase of dark current after the irradiation and
present the current related damage rate at 213 K. The effect of low temperature
annealing at 213 K , 236 K, 253 K, 273 K, and 289 K is presented.
