Although not designed primarily as a polarimeter , the Fermi -Large Area Telescope ( LAT ) has the potential to detect high degrees of linear polarization from some of the brightest gamma-ray sources .
To achieve the needed accuracy in the reconstruction of the event geometry , low-energy ( \leq 200 MeV ) events converting in the silicon detector layers of the LAT tracker have to be used .
We present preliminary results of the ongoing effort within the LAT collaboration to measure gamma-ray polarization .
We discuss the statistical and systematic uncertainties affecting such a measurement .
We show that a 5 \sigma minimum detectable polarization ( MDP ) of \approx 30 - 50 \% could be within reach for the brightest gamma-ray sources as the Vela and Crab pulsars and the blazar 3C 454.3 , after 10 years of observation .
To estimate the systematic uncertainties , we stack bright AGN , and use this stack as a test source .
LAT sensitivity to polarization is estimated comparing the data to a simulation of the expected unpolarized emission of the stack .
We measure a 5 \sigma sensitivity limit corresponding to a polarization degree of \approx 37 \% .
This is in agreement with a purely statistical estimate , suggesting that the systematic errors are likely to be small compared to the statistical ones .