RHESSI Hard X-ray Imaging Spectroscopy and the Electron Acceleration Rate

Details RHESSI Hard X-ray Imaging Spectroscopy and the Electron Acceleration Rate RHESSI Hard X-ray Imaging Spectroscopy and the Electron Acceleration Rate

May 2007

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007aas...210.9316x&link_type=abstract

American Astronomical Society Meeting 210, #93.16; Bulletin of the American Astronomical Society, Vol. 39, p.213

Astronomy and Astrophysics

Astronomy

Scientific paper

We present empirical results for the specific acceleration rate (particles s-1 per ambient particle) of bremsstrahlung-producing electrons during solar flares. Hard X-ray images from several M-class limb events, observed by the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) were studied, from which we determined the source "size" by forward-fitting to the source visibilities in different energy bands. A nonthermal collisional model with an extended "dense acceleration region" was introduced and used to fit the source sizes as a function of photon energy. This fitting program yielded both the number density n and length L of the acceleration region, and hence the column density N = nL. We found that the variation of N from event to event (or from subintervals within the same event) was correlated very well with the hard X-ray intensities I(ɛ). Using standard thick-target formulae, we converted I(ɛ) to Ψ(E>ɛ), the electron acceleration rate, and we multiplied N by the cross-sectional area of the source to get f, number of particles in the acceleration region. Taking the ratio Ψ/f gives the fraction of the available electrons are accelerated each second. Our results show that the value of this quantity is (5.1 ± 0.2) × 10-3 s-1. We critically compare this with the predictions of both large-scale sub-Dreicer and stochastic acceleration models.

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