from astropy.io import fits
import numpy as np

psf_fits = fits.open('cat_IRAC1_519.psf')
dat = psf_fits[1].data[0][0]
dat[dat<0] = 0
dat = dat / np.sum(dat)
hdul = fits.HDUList([fits.PrimaryHDU(data=dat)])
hdul.writeto('IRAC1_519_psf.fits',overwrite=True)