... flspec computes the spectrum of the background fluctuations in EPIC Imaging data. ... Once the 'flatfielded' image is free from detected sources, its pixels are binned according to the input parameter binsize and classified as 'positive' (if they have more counts than the median in the image) and 'negative' pixels (less counts than the median). ... Once created, positive and negative spectra are subtracted to obtain the 'fluctuations' spectrum in each annular region. ...