Sphinx measurements of the 2009 solar minimum x-ray emission

TL;DR

The paper reports on SphinX measurements of the 2009 solar minimum X-ray emission, revealing extremely low flux levels and characterizing the coronal conditions during this deep solar minimum.

Contribution

It provides detailed spectral analysis of the quiet Sun during the 2009 minimum, highlighting the dominance of coronal structures over confined features in X-ray emission.

Findings

X-ray flux was exceptionally low during 2009 minimum

Coronal temperatures ranged from 1.7 to 1.9 MK

Solar X-ray luminosity was lower than most nearby K and M dwarfs

Abstract

The SphinX X-ray spectrophotometer on the CORONAS-PHOTON spacecraft measured soft X-ray emission in the 1-15 keV energy range during the deep solar minimum of 2009 with a sensitivity much greater than GOES. Several intervals are identified when the X-ray flux was exceptionally low, and the flux and solar X-ray luminosity are estimated. Spectral fits to the emission at these times give temperatures of 1.7-1.9 MK and emission measures between 4 x 10^47 cm^-3 and 1.1 x 10^48 cm^-3. Comparing SphinX emission with that from the Hinode X-ray Telescope, we deduce that most of the emission is from general coronal structures rather than confined features like bright points. For one of 27 intervals of exceptionally low activity identified in the SphinX data, the Sun's X-ray luminosity in an energy range roughly extrapolated to that of ROSAT (0.1-2.4 keV) was less than most nearby K and M dwarfs.