  Lowest-order cumulants provide important information on the shape of the
emission source in femtoscopy. For the simple case of noninteracting identical
particles, we show how the fourth-order source cumulant can be determined from
measured cumulants in momentum space. The textbook Gram-Charlier series is
found to be highly inaccurate, while the related Edgeworth series provides
increasingly accurate estimates. Ordering of terms compatible with the Central
Limit Theorem appears to play a crucial role even for nongaussian
distributions.
