Motter, Juliana Cristina

Cross-entropy: a new method to study jet kinematics.

Author list: Juliana C. Motter & Zulema Abraham

VLBI images of blazars are characterized by the presence of jets that have enhanced emission regions and seem to recede from the central core with apparently superluminal velocities. It is still under discussion if the movement of these jet components is ballistic or not, although it is well established that different components of the same jet may have different velocities. The determination of these velocities depends strongly on the identification of the same components (which are frequently superimposed) at different epochs, and also on a reliable model for their positions. There are many procedures to identify these components, which are in general taken as two-dimensional gaussians. Commonly, these procedures are subjective in the sense that they depend on initial conditions. Recently, Caproni, Monteiro & Abraham (2011) adopted the method Cross-entropy (CE) that allows the fitting of an unlimited number of components and determines their parameters without the need of initial conditions. In this work we used this method to analyze the images of the quasar 3C 279 obtained in 15 GHz by the VLBA between 1995 and 1999. In addition to the stationary core we identified six components that move with ballistic motion and velocities between 0.15 < µ < 0.25 mas/yr.