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Title:
A Revisit of the Masuda Flare
Authors:
Liu, Rui; Xu, Yan; Wang, Haimin
Affiliation:
AA(Space Weather Research Laboratory, Center for Solar-Terrestrial Research, NJIT), AB(Space Weather Research Laboratory, Center for Solar-Terrestrial Research, NJIT), AC(Space Weather Research Laboratory, Center for Solar-Terrestrial Research, NJIT)
Publication:
Solar Physics, Volume 269, Issue 1, pp.67-82 (SoPh Homepage)
Publication Date:
03/2011
Origin:
SPRINGER
Keywords:
Flares, dynamics, Flares, energetic particles, Flares, impulsive phase, Flares, spectrum
Abstract Copyright:
(c) 2011: Springer Science+Business Media B.V.
DOI:
10.1007/s11207-010-9688-z
Bibliographic Code:
2011SoPh..269...67L

Abstract

We revisit the flare that occurred on 13 January 1992, which is now universally termed the ``Masuda flare''. The new analysis is motivated not just by its uniqueness despite the increasing number of coronal observations in hard X-rays, but also by the improvement of Yohkoh hard X-ray image processing, which was achieved after the intensive investigations on this celebrated event. Using an uncertainty analysis, we show that the hard X-ray coronal source is located closer to the soft X-ray loop by about 5000 km (or 7 arcsec) in the re-calibrated Hard X-ray Telescope (HXT) images than in the original ones. Specifically, the centroid of the M1-band (23 - 33 keV) coronal source is above the maximum brightness of the Soft X-ray Telescope (SXT) loop by 5000±1000 km (9600 km in the original data) and above the apex of the SXT loop represented by the 30% brightness contour by 2000±1000 km (˜ 7000 km in the original data). The change is obviously significant, because most coronal sources are above the thermal loop by less than 6 arcsec. We suggest that this change may account for the discrepancy in the literature, i.e., the spectrum of the coronal emission was reported to be extremely hard below ˜ 20 keV in the pre-calibration investigations, whereas it was reported to be considerably softer in the literature after the re-calibration done by Sato, Kosugi, and Makishima ( Pub. Astron. Soc. Japan 51, 127, 1999). Still, the coronal spectrum is flatter at lower energies than at higher energies, due to the lack of a similar, co-spatial source in the L-band (14 - 23 keV), for which a convincing explanation is absent.
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