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Astron. Astrophys. 320, L33-L36 (1997)

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Letter to the Editor

SXR Coronal Flashes

S. Koutchmy 1, H. Hara 2, Y. Suematsu 2 and K. Reardon 3

1 Institut d'Astrophysique de Paris, C.N.R.S., 98 bis Bd Arago, F-75014 Paris, France, associated with the Paris VI University
2 National Astronomical Observatory, Mitaka, 181 Tokyo, Japan
3 Osservatorio di Capodimonte, via Moiariello 16, I-80131 Napoli, Italy

Received 5 December 1996 / Accepted 7 January 1997

Abstract

We provide evidence for the existence of a new type of soft X-ray (SXR) brightening event that we call coronal flashes. The phenomenon was observed on deep time series taken with the SXT of Yohkoh in the north polar coronal hole, near the sunspot minimum. Events last as short as 1.5 mn and the corresponding SXR flux span the range of energies, from single pixel brightenings corresponding to fluxes of about 1024 erg but barely surpassing the level of the noise, to higher and more smeared multiple px brightenings still orders of magnitude smaller than the known small SXR bright points and/or transient brightenings. The typical occurrence rate of flashes is 1 event/arcmin2 /5mn with a 1/2 mn integration time. At least part of the coronal flashes are recurrent and some of them could be associated with a SXR jet; it is not clear what is their optical counterpart.

Key words: Solar corona; MHD; SXR; jets; bright points; brightening events; reconnections; magnetic dissipation; nano-flare; flash; flare.

Send offprint requests to: S. Koutchmy

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© European Southern Observatory (ESO) 1997

Online publication: June 30, 1998
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