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Issue A&A Volume 402, Number 3, May II 2003 First Science with the ODIN satellite Page(s) 929 - 947 Section Galactic structure and dynamics DOI 10.1051/0004-6361:20030264

A&A 402, 929-947 (2003)
DOI: 10.1051/0004-6361:20030264

Temporal variability of Mrk 421 from XMM-Newton observations

W. Brinkmann¹, I. E. Papadakis^{2, 3}, J. W. A den Herder⁴ and F. Haberl<sup>5

1</sup>  Centre for Interdisciplinary Plasma Science, Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany
²  IESL, FORTH, 711 10 Heraklion, Crete, Greece
³  Physics Department, University of Crete, 710 03 Heraklion, Crete, Greece
⁴  SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
⁵  Max-Planck-Institut für extraterrestrische Physik, Postfach 1312, 85741 Garching, Germany

(Received 12 November 2002 / Accepted 14 February 2003)

Abstract
We present the results of a detailed spectral and temporal analysis of the currently available XMM-Newton observations of the bright BL Lac object Mrk 421 using mainly the EPIC-PN data. The source was found in various intensity states differing by up to a factor of five in count rates. In general, the source is more variable and shows a harder spectrum during higher intensities than when it is in lower states. The spectrum is very complex and cannot be fitted adequately by a broken power law or a continuously curved model. We find that the flux variations on time scales of  few thousand seconds are associated with significant and sometimes very complex spectral changes. The spectral variability rate is not the same in all cases and is correlated with the source flux state: the spectral variations per unit time increase with the source flux. The Cross-Correlation analysis shows that the soft and hard band light curves are often well correlated near zero lag, in other cases the hard band variations lead the soft band variations by typically ~5 min, in two cases we find the soft band leading the hard band variations. The delays appear to be correlated to the flares' duration: the shorter the flare, the smaller the delay.

Key words: BL Lacertae objects: individual: Mrk 421; X-rays: galaxies -- radiation mechanisms: non-thermal

Offprint request: W. Brinkmann, wpb@mpe.mpg.de

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