English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We present the results of a detailed temporal analysis of the bright BL Lacobject Mrk 421 using the three available long timing mode observations by theEPIC PN camera. This detector mode is characterized by its long life time andis largely free of photon pile-up problems. The source was found in differentintensity and variability states differing by up to more than a factor of threein count rate. A time resolved cross correlation analysis between the soft andhard energy bands revealed that the characteristics of the correlated emission,with lags of both signs, change on time scales of a few thousand seconds.Individual spectra, resolved on time scales of a few hundread seconds, can bequite well fitted by a broken power law. We find significant spectralvariations on time scales as short as 500-1000 sec. Both the hard and the softband spectral indices show a non-linear correlation with the source flux. Acomparison of the observed light curves with numerical results fromrelativistic hydrodynamic computer simulations of the currently favoredshock-in-jet models indicates that any determination of the jet's physicalparameters from `simple' emission models must be regarded with caution: at anytime we are seeing the emission from several emission regions distinct in spaceand time, which are connected by the complex hydrodynamic evolution of thenon-uniform jet.Comment: 16 pages, 16 figures. Accepted for publication in A&

XMM-Newton timing mode observations of Mrk 421