HXT_FSP is the same as HXS_FSP, but for HXT spectra. See HXS_FSP for a
better description. Index and data come from an hda file.
IDL> HXT_FSP, index, data, fit_pars
HXTBOX_FSP fits spectra to a given box, chosen by LCUR_IMAGE, for a set of HXT images in the HXI structure; index and data come from and hxi file of deconvolved images.
IDL> HXTBOX_FSP, index, data, fit_pars