By Guang Yang
We develop a code, "X-CIGALE", allowing simultaneously fitting of AGN SEDs from X-ray to infrared. X-CIGALE can constrain AGN power even for X-ray undetected sources (using upper limits). With the expected flux upper limit by a ~100 ks Athena exposure, X-CIGALE can tightly constrain the AGN power down to a negligible level for typical galaxies in the distant universe.