Four Years of Extreme Ultraviolet Observations of Markarian 421: II.   Temporal Analysis
  The Extreme Ultraviolet Explorer (EUVE) satellite accumulated ~one million seconds of public data between 1994 and 1997 for the BL Lacertae object Markarian 421. This is the second of two papers in which we present the results of spectral and temporal analysis of this EUVE data set. We analyze in the present paper the imaging data by means of power spectrum and structure function techniques, while the spectral analysis is presented in a companion paper. We find for MRK 421 a power spectrum with slope -2.14 +- 0.28 with a break at ~3 days. This is the first time that a break in the power spectrum of a BL Lacertae object has been found. We also find evidence of non-stationarity for MRK 421 EUV emission 
Ilaria Cagnoni (1 and 2), Antonella Fruscione (2) and Iossif E.   Papadakis (3) ((1) SISSA, Trieste, Italy (2) Harvard-Smith...