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Astron. Astrophys. 342, 124-130 (1999)

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5. Conclusions

We summarize the main results of the presented BeppoSAX observations of Mkn 421 as follows:

  • Mkn 421 was observed in a quiescent state, with an average 2-10 keV flux of [FORMULA] erg cm-2 s-1. It exhibited flux variation by a factor [FORMULA]2 on timescales as short as a few [FORMULA] s

  • an energy threshold between different variability patterns can be set at [FORMULA]3-4 keV. The 3-10 keV vs. 0.1-3 keV HR increases with increasing flux up to [FORMULA] erg cm-2 s-1 and then "saturates" to a constant level

  • the average 0.1-40 keV spectrum exhibits a gradual steepening with energy. This effect is foreseen by the SSC scenario, where the X-rays originate as synchrotron radiation from a relativistic population of electrons in the jet. If the proper (albeit admittedly phenomenological) continuum model is adopted, no soft X-ray absorption feature is required, with a 10 eV upper limit on the equivalent width of any [FORMULA] resonance absorption line

  • the observed spectral dynamics can be explained as a hardening of the high-energy (i.e. : [FORMULA]4 keV) spectrum, above a relatively invariant soft X-ray emission. This can be due to an increase of the injected electron flux or of the extension of the injection region, possibly in connection with phases of higher nuclear activity.

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© European Southern Observatory (ESO) 1999

Online publication: December 22, 1998