Testing Rate Dependent corrections on timing mode EPIC-pn spectra of the
  accreting Neutron Star GX 13+1
  When the EPIC-pn instrument on board XMM-Newton is operated in Timing mode,
high count rates (>100 cts/s) of bright sources may affect the calibration of
the energy scale, resulting in a modification of the real spectral shape. The
corrections related to this effect are then strongly important in the study of
the spectral properties. Tests of these calibrations are more suitable in
sources which spectra are characterised by a large number of discrete features.
Therefore, in this work, we carried out a spectral analysis of the accreting
Neutron Star GX 13+1, which is a dipping source with several narrow absorption
lines and a broad emission line in its spectrum. We tested two different
correction approaches on an XMM-Newton EPIC-pn observation taken in Timing
mode: the standard Rate Dependent CTI (RDCTI or epfast) and the new, Rate
Dependent Pulse Height Amplitude (RDPHA) corrections. We found that, in
general, the two corrections marginally affect the properties of the overall
broadband continuum, while hints of differences in the broad emission line
spectral shape are seen. On the other hand, they are dramatically important for
the centroid energy of the absorption lines. In particular, the RDPHA
corrections provide a better estimate of the spectral properties of these
features than the RDCTI corrections. Indeed the discrete features observed in
the data, applying the former method, are physically more consistent with those
already found in other Chandra and XMM-Newton observations of GX 13+1.
