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Imaging Spectroscopy on Preflare Coronal Nonthermal Sources Associated with the 2002 July 23 Flare
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Ayumi Asai Submitted: 2009-01-22 19:24
We present a detailed examination on the coronal nonthermal emissions
during the preflare phase of the X4.8 flare that occurred on 2002 July
23.
The microwave (17~GHz and 34~GHz) data obtained with Nobeyama
Radioheliograph, at Nobeyama Solar Radio Observatory and the hard
X-ray (HXR) data taken with {it Reuven Ramaty High Energy Solar
Spectroscopic Imager} obviously showed nonthermal sources that are
located above the flare loops during the preflare phase.
We performed imaging spectroscopic analyses on the nonthermal emission
sources both in microwaves and in HXRs, and confirmed that electrons
are accelerated from several tens of keV to more than 1~MeV even in
this phase.
If we assume the thin-target model for the HXR emission source, the
derived electron spectral indices (sim 4.7) is the same value as
that from microwaves (sim 4.7) within the observational
uncertainties, which implies that the distribution of the accelerated
electrons follows a single power-law.
The number density of the microwave-emitting electrons is, however,
larger than that of the HXR-emitting electrons, unless we assume low
ambient plasma density of about 1.0 x 10^9~cm-3 for the
HXR-emitting region.
If we adopt the thick-target model for the HXR emission source, on the
other hand, the electron spectral index (sim 6.7) is much
different, while the gap of the number density of the accelerated
electrons is somewhat reduced.
Authors: Ayumi Asai, Hiroshi Nakajima, Masumi Shimojo, Takaaki Yokoyama, Satoshi Masuda, Sam Krucker
Projects: RHESSI
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Publication Status: ApJ (accepted)
Last Modified: 2009-01-23 09:36
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