Cool Stars 14 - Submitted Abstract # 237
This version created on 05 October 2006

Alternative solar paradigms for stellar X-ray activity


H. Hudson, University of California, Berkeley
G. Micela, Osservatorio Astronomico di Palermo

Solar flares generally have a well-defined spectral morphology as seen
in soft X-rays (< 10  keV) hard X-rays (> 10  keV).  This consists of
the Neupert effect, relating coronal energization (soft X-rays) to
non-thermal energy release (hard X-rays), plus the "soft-hard-soft"
hard X-ray spectral variation.  Such a pattern predicts a negligible
"true" non-thermal hard X-ray flux from a stellar flare, which would
scale such that a flare with an emission measure of 10^55 cm^-3, at a
distance of 100  pc, would produce a non-thermal hard X-ray flux of
order 6 x 10^-10  ph(cm^2 sec keV)^-1 at 35 keV.  With this scaling a
stellar hard X-ray flare would be difficult to observe.  Other solar
patterns of behavior do exist, though, and these might apply to other
environments.  We describe these different morphologies, which include
the "extended flare" pattern, often marked by meter-wave Type IV radio
bursts and a gradually flattening hard X-ray spectrum;  the filament
eruption/coronal mass ejection (CME) phenomenon;  and the "impulse
response" flare type originally described by White et al.  (1992).
RHESSI observations have recently revealed another candidate, a
coronal hard X-ray source on the order of 0.3 R_sun in diameter and in
height, which does not match the "extended flare" morphology.  We
discuss these patterns as they may extrapolate to a stellar
application, illustrating the solar morphology with RHESSI hard X-ray
and gamma-ray data.

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