X-ray charge-coupled devices (CCDs) are the workhorse detectors of modernX-ray astronomy. Typically covering the 0.3-10.0 keV energy range, CCDs areable to detect photoelectric absorption edges and K shell lines from mostabundant metals. New CCDs also offer resolutions of 30-50 (E/dE), which issufficient to detect lines in hot plasmas and to resolve many lines shaped bydynamical processes in accretion flows. The spectral capabilities of X-ray CCDshave been particularly important in detecting relativistic emission lines fromthe inner disks around accreting neutron stars and black holes. One drawback ofX-ray CCDs is that spectra can be distorted by photon "pile-up", wherein two ormore photons may be registered as a single event during one frame time. We haveconducted a large number of simulations using a statistical model of photonpile-up to assess its impacts on relativistic disk line and continuum spectrafrom stellar-mass black holes and neutron stars. The simulations cover therange of current X-ray CCD spectrometers and operational modes typically usedto observe neutron stars and black holes in X-ray binaries. Our results suggestthat severe photon pile-up acts to falsely narrow emission lines, leading tofalsely large disk radii and falsely low spin values. In contrast, oursimulations suggest that disk continua affected by severe pile-up are measuredto have falsely low flux values, leading to falsely small radii and falselyhigh spin values. The results of these simulations and existing data appear tosuggest that relativistic disk spectroscopy is generally robust against pile-upwhen this effect is modest.
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