Hard X-ray and UV Two-ribbon Flares

Details Hard X-ray and UV Two-ribbon Flares Hard X-ray and UV Two-ribbon Flares

May 2010

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2010aas...21640425c&link_type=abstract

American Astronomical Society, AAS Meeting #216, #404.25; Bulletin of the American Astronomical Society, Vol. 41, p.904

Astronomy and Astrophysics

Astronomy

Scientific paper

It is well known that two-ribbon flares observed in Halpha and UV wavelengths
mostly exhibit compact and localized hard X-ray sources.
The reason is largely unknown. In this paper, we present comprehensive analysis of a two-ribbon flare observed on 2005, January 15 in UV 1600 Å, and the hard X-ray imaging and spectroscopic observations by RHESSI are analyzed. We show that (1) UV brightening is substantially enhanced when the hard X-ray source moves into the location, and during the hard X-ray transit, the UV light curve is temporally correlated with hard X-ray light curve. After the passage of the HXR source, the UV light curve exhibits smooth monotonically decay. (2) We compute the hard X-ray source motion, and decompose it into parallel and perpendicular motion, finding that the parallel motion dominates the rise of the hard X-ray light curve, and the perpendicular motion starts and dominates at the peak of the hard X-ray. The apparent motion speed is 20-40 km/s; we also follow the UV brightening speed following the approach by Qiu (2009), finding that the motion pattern and apparent speed the same as hard X-ray sources; The hard X-ray motion speed during the cooling time of UV would produce a ribbon of length 40", just about the UV ribbon length. (3) We also estimate the cooling time (e-slope) of UV brightening, by deconvolving the UV curve from the hard X-ray curve; which gives 15 - 30 min cooling time. It is, of course, related to the maximum intensity of UV. The above analyses provide evidence that UV brightening is due to beam heating, the thermal origin cannot be excluded, but would produce heating of 1 order of magnitude weaker. The UV ribbon for this event is due to the cooling time.

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