The very high energy gamma ray spectra of IES 1959+650 and Mrk 421 as measured with the Whipple 10 m telescope


In observations made with the Whipple 10 m telescope, 1ES 1959+650 (z = 0.048) was caught in a high flaring state in May 2002, concurrent with a high X‐ray state, and in June 2002, for which there was no corresponding X‐ray flare. The spectra for both of those occasions are well fitted by a power law of differential spectral index ∼ −2.8. The relative stability of the spectral index for those flares argues strongly in favour of a two‐component model as to the emission zones for the two radiation regimes.

Markarian 421 (z = 0.031) was observed to be in a high flaring state, at levels of ⩾ 3 Crab, during March and April 2004. The average spectrum over this time period shows evidence for a cut‐off in the spectrum at ∼ 5 TeV, similar to a cut‐off seen during an equivalently strong episode of flaring activity in 2001. The continued appearance of this feature indicates a long term stability, either in the physical conditions at the source, or in the intervening medium (such as attenuation on the extra‐galactic infra‐red background radiation).

In AIP Conference Proceedings