2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/14546We present a detailed Cross Correlation analysis of the light curves of the X-ray bright BL Lac object Mkn 421 observed with $Beppo$SAX period 1997-1998. Monte Carlo simulations are performed in order to estimate the uncertainties. We found that in one occasion the lag is negative.1 page, 1 figure, to be published in the Proc. of the ASCA Symposium "Heating and Acceleration in the Universe", Tokio, March 1999Astrophysicstext