Examples data files used in the niriss_illumflat_notebook_part1.ipynb
Jupyer notebook are found here:
/ifs/jwst/wit/niriss/tsohn/mirage_simulations/NIS-011/jw01086001001_01101_00021_nis_cal.fits
/ifs/jwst/wit/niriss/tsohn/mirage_simulations/NIS-011/jw01086001001_01101_00045_nis_cal.fits
Copy these two files to the same directory as the notebook.