Analysis of Quiescent Corona X-ray Spectra from SphinX during the 2009 Solar Minimum

• Main Authors: Sylwester, B, Sylwester, J, Siarkowski, M, Phillips, K. J. H, Podgorski, P, Gryciuk, M
• Format: Journal Article
• Language: English
• Published: 10-12-2019
• Subjects: Physics - Solar and Stellar Astrophysics
• DOI: 10.48550/arxiv.1912.03082

The SphinX X-ray spectrophotometer on the {\em CORONAS-PHOTON}\/ mission
observed the 1~--~15\,keV X-ray spectrum of the spatially integrated solar
corona during the deep minimum of 2009, when solar activity was exceptionally
low. Its sensitivity for energies $> 1.2$\,keV was higher than that of any
other solar X-ray spectrometer in orbit at the time, including the detectors on
GOES. Using much improved instrumental data than was used previously, we
analyzed SphinX spectra in 576 intervals for which there was no discernible
activity (NA), 40 intervals when there were X-ray brightenings (B), and sixteen
intervals when there were micro-flares with peak emission less than GOES A1
(F). An instrumental background spectrum, formed over 34 hours of spacecraft
night-time periods and including electronic noise and particle radiation, was
subtracted from the solar spectra. Theoretical spectra were used to deduce
temperatures on an isothermal assumption for the NA, B, and F intervals (1.69,
1.81, and 1.86\,MK respectively). Differential emission measure (DEM) analysis
for the same spectra revealed a "cooler" component (log\,$T = 6.2$ or $T
\approx 1.6$\,MK) in each case, but with a second hotter component having a
less well-defined peak temperature varying from $\approx 2.5$ to $\approx
3.5$\,MK (log\,$T = 6.4$ and 6.55) and an emission measure between two and
three orders smaller than that of the cooler component. These results are
similar to those obtained at times just after solar minimum with the EVE
instrument. A very hot component that might indicate the signature of
nano-flare heating of the corona is not evident in SphinX data.