Abstract
Spatial extension is an important characteristic for correctly associating γ-rayemitting sources with their counterparts at other wavelengths and for obtaining an unbiased model of their spectra. We present a new method for quantifying the spatial extension of sources detected by the Large Area Telescope (LAT), the primary science instrument on the Fermi Gamma-ray Space Telescope (Fermi ). We perform a series of Monte Carlo simulations to validate this tool and calculate