Abstract
During the rising phase of the radio burst of August 30, 2002, at ∼1328 UT a short pulse with a duration of approximately 4 s was observed. Here we present a multiwavelength analysis, including microwave and X-ray. Its background-subtracted radio spectrum ranges only from 2.5 to 12 GHz with a maximum flux density of approximately 900 s.f.u. at 7 GHz and a steep optically thin spectral index α ∼ 8. The hard X-ray pulse emission above the background in the range of 10-150 keV observed by RHESSI is coincident in time with the microwave observation. Hard X-ray images reveal very compact (∼10) footpoint sources. A distribution of accelerated electrons represented by a double power law, with δ E < 250 keV = 5.3 and δ E ≥ 250 keV = 13, was used to compute the expected gyrosynchrotron and thick target bremsstrahlung fluxes of a homogeneous source. We interpret the very steep electron index above the energy break to represent a high energy cutoff. With these parameters, our results reproduce the observations well. Nevertheless, they pose the still unanswered question about the mechanism that has slectively accelerated these electrons.
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