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

Abstract

The SphinX X-ray spectrophotometer on the 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 B. Sylwester bs@cbk.pan.wroc.pl J. Sylwester SOLA: SphinX_quietSun.tex; 11 December 2019; 1:36; p. 1 B. Sylwester et al.revealed a "cooler" component (log T = 6.2 or T ≈ 1.6 MK) in each case, but with a second hotter component having a less well-defined peak temperature varying from ≈ 2.5 to ≈ 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.

Observations of the Quiet Sun During the Deepest Solar Minimum of the Past Century with Chandrayaan-2 XSM -- Elemental Abundances in the Quiescent Corona

“…However, there are small variations in temperature and emission measure, which are correlated with the variations in X-ray flux. Sylwester et al (2019) reported isothermal temperatures of ∼1.69 MK for the quiescent corona using X-ray spectroscopic observations in a similar energy range using SphinX observations during the 2009 solar minimum, which is lower than the estimates from XSM. They also noted that the isothermal fit does not explain the observed spectra completely and had shown the presence of higher temperature components with DEM analysis, unlike in the present case where the XSM spectra in the range of 1.3 -2.3 keV is consistent with isothermal models.…”

Observations of the Quiet Sun During the Deepest Solar Minimum of the Past Century with Chandrayaan-2 XSM -- Sub-A Class Microflares Outside Active Regions

“…We also note that the 16 microflares observed by SphinX show a systematically lower temperature and higher EM compared to the microflares observed by XSM as well as NuSTAR. One possible reason for this observation may be the difference in analysis procedure followed for SphinX data where the flare spectra were fitted with a single temperature model without subtracting or separately modelling the pre-flare emission (Sylwester et al 2019). While the microflares observed by SphinX and XSM occupy slightly different regions in the temperature-EM parameter space, the fact that they fall along the same isoflux line shows that they should be of similar nature.…”

“…While the microflares observed by SphinX and XSM occupy slightly different regions in the temperature-EM parameter space, the fact that they fall along the same isoflux line shows that they should be of similar nature. (Sylwester et al 2019) and NuSTAR (Kuhar et al 2018), respectively. Parameter space of active region (AR) events observed by RHESSI (Hannah et al 2008) and SphinX (Gryciuk et al 2017) are shown with orange and gray shades, respectively.…”

“…While this ambiguity does not arise at X-ray energies where the emission arises from higher temperature plasma, there are very few observations due to the technical limitations involved. There have been only a handful of X-ray microflares detected in the quiet Sun with Yokoh SXT (Krucker et al 1997), SphinX (Sylwester et al 2019), andNuSTAR (Kuhar et al 2018). Hence, no statistical studies of quiet Sun X-ray microflares have been possible so far.…”

“…The error bars represent 1σ uncertainties. Magneta squares and red filled circles correspond to QS microflares observed by SphinX(Sylwester et al 2019) and NuSTAR(Kuhar et al 2018), respectively. Parameter space of active region (AR) events observed by RHESSI(Hannah et al 2008) and SphinX(Gryciuk et al 2017) are shown with orange and gray shades, respectively.…”