The RHESSI Flare Image Archive, located in the flare_images_v2 directory, contains image cube FITS files that can be used with RHESSI image object software, converted to map structures via hsi_fits2map, or read by any standard FITS reader.

The Visibility Forward Fit (VF) algorithm reconstructs solar flare X-ray and gamma-ray sources by fitting a parametric model directly to RHESSI’s visibility data. Instead of producing a pixel-based image, VF assumes a small number of simple source components (such as circular or elliptical Gaussians) and optimizes their parameters to best match the observed visibilities. This method provides precise source positions, sizes, and fluxes, making it ideal for quantitative analysis, though it does not capture complex or extended structures.

VF FITS files follow the naming convention hsi_imagecube_vf_YYYYMMDD_HHMM_xxxxx.fits, where YYYYMMDD and HHMM represent the observation date and start time (UTC), xxxxx indicates the bin size identifier, and .fits denotes the standard Flexible Image Transport System format.