Event-by-Event Errors: Using Covariance to Enhance the Fermi Sky

In the standard ground-based processing of Fermi LAT data, a detailed fit is done for each photon event. In addition to the best estimate of the direction, this also provides an estimate of the two-dimensional errors. Although this event-by-event error information in basic form has been included in the standard data release, it has not yet been utilized in science analysis because more development work is required. We show here the characteristics of these covariant errors when projected back onto the sky and discuss the potential science returns, including source finding, localization, and image analysis.