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G. Fossati (Rice University), R.A. Edelson (UCLA)
We present the result of a week-long simultaneous monitoring of the blazar Mrk421 at 2-60~keV X-rays (with RXTE) and TeV gamma-rays (with Whipple). The source shows strong variations in both bands, which are highly correlated, with no evidence of a non-zero interband lag. The upper limit based on the full dataset is 15 min. This lends further support to the standard model in which the same electrons produce the X-rays by synchrotron emission and then scatter photons to produce the gamma-rays by inverse Compton scattering. During the best observed individual flare the gamma-rays flux scales approximately quadratically with X-ray flux, suggesting that the scattering occurs in the Thompson regime. However, the slope of the X-ray/TeV fluxes correlation seems to change during the second half of the campaign, towards a linear relationship. It is interesting to note that this change accompanies the progressive hardening observed in the X-ray band. We will discuss the astrophysical consequences of these new findings in the context of the competing models for the jet emission in blazars.
(GF has been supported by NASA grants NAG5-11796 and NAG5--11853.)
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Bulletin of the American Astronomical Society,
© 2003. The American Astronomical Soceity.