There are scientific questions, which cannot be answered with the time sampling provided by the pn burst mode. In such cases pn timing mode is often requested. Observing the brightest sources with the timing mode may cause pile-up which leads to distorted spectra as well as distorted light curves. Experience shows that such data are often degenerated and their scientific interpretation is seriously hampered.
Brightest sources (with an expected count rate 400 c/s) may be observed in pn timing mode (or modified timing mode) if the case is clearly explained in the proposal scientific justification and if one additional 10 ks exposure in pn burst mode is requested.