[Loops] [1207.4665] X-raying hot plasma in solar active regions with the SphinX spectrometer

[Fabio Reale]

Dear colleagues
      please find at the following link the preprint of a work accepted 
for publication in Astronomy & Astrophysics, showing the detection of a 
minor but significant very hot (~ 7MK) component in quiescent active 
regions, with the SphinX instrument on-board CORONAS-PHOTON:

http://arxiv.org/abs/1207.4665

This hot component is invariably present both at high and low emission 
regimes, i.e. even excluding resolvable microflares.
The abstract is below.
Best regards
Fabio Reale

X-raying hot plasma in solar active regions with the SphinX spectrometer

M. Miceli, F. Reale, S. Gburek, S. Terzo, M. Barbera, A. Collura, J. 
Sylwester, M. Kowalinski, P. Podgorski, M. Gryciuk

The detection of very hot plasma in the quiescent corona is important 
for diagnosing heating mechanisms. The presence and the amount of such 
hot plasma is currently debated. The SphinX instrument on-board 
CORONAS-PHOTON mission is sensitive to X-ray emission well above 1 keV 
and provides the opportunity to detect the hot plasma component. We 
analyzed the X-ray spectra of the solar corona collected by the SphinX 
spectrometer in May 2009 (when two active regions were present). We 
modelled the spectrum extracted from the whole Sun over a time window of 
17 days in the 1.34-7 keV energy band by adopting the latest release of 
the APED database. The SphinX broadband spectrum cannot be modelled by a 
single isothermal component of optically thin plasma and two components 
are necessary. In particular, the high statistics and the accurate 
calibration of the spectrometer allowed us to detect a very hot 
component at ~7 million K with an emission measure of ~2.7 x 10^44 
cm^-3. The X-ray emission from the hot plasma dominates the solar X-ray 
spectrum above 4 keV. We checked that this hot component is invariably 
present both at high and low emission regimes, i.e. even excluding 
resolvable microflares. We also present and discuss a possible 
non-thermal origin (compatible with a weak contribution from 
thick-target bremsstrahlung) for this hard emission component. Our 
results support the nanoflare scenario and might confirm that a minor 
flaring activity is ever-present in the quiescent corona, as also 
inferred for the coronae of other stars.

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Dr. Fabio Reale, Ph.D.
Professore Associato
Dipartimento di Fisica, Universita` di Palermo
P.za Parlamento 1, 90134 Palermo - ITALY
Tel: +39 091 233 237
Fax: +39 091 233 444
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