Solar Flares During Deep Solar Minimum as Observed Simultaneously by SphinX and RHESSI

Mrozek Tomasz, mrozek@astro.uni.wroc.pl, Solar Physics Division, Space Research Centre, Polish Academy of Sciences, Poland
Gburek Szymon, Solar Physics Division, Space Research Centre, Polish Academy of Sciences
Siarkowski Marek, Solar Physics Division, Space Research Centre, Polish Academy of Sciences
Sylwester Barbara, Solar Physics Division, Space Research Centre, Polish Academy of Sciences
Sylwester Janusz, Solar Physics Division, Space Research Centre, Polish Academy of Sciences
Gryciuk Magdalena, Solar Physics Division, Space Research Centre, Polish Academy of Sciences
Kepa Anna, Solar Physics Division, Space Research Centre, Polish Academy of Sciences

Abstract
In 2008-2009, we experienced the deepest solar minimum in the last 100 years. The sunspots were rarely visible as well as associated active events like flares or Coronal Mass Ejections. In Februrary 2009, Polish X-ray spectrometer SphinX begun observations of the Sun in the energy range of 1.0-15 keV. The observations continued until December 2009 when SphinX was turned off due to problems with the satelite's power supply. SphinX was almost 100 times more sensitive than GOES X-ray Flux Monitor. The instrument provided us with observations of hundreds of very small flares and X-ray brightenings. The silicon PIN diode detectors used in the experiment were carefully calibrated on the ground. For that we used Synchrotron Radiation Source BESSY II. The SphinX energy range overlaps with the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) energy range. For the present investigation, we have chosen a group of solar flares observed simultaneously by SphinX and RHESSI and performed spectroscopic analysis of observations wherever possible. It was found that the RHESSI and SphinX spectra are consistent with each other thus, the common observations should provide insight into the physics of weakest solar flares as the common spectral range extends above 1 keV. From the analysis of thermal part of the spectra we obtained the temperature (T) and emission measure (EM) and the analysis of time evolution of the parameters was performed. It was found that the quality of the spectral fits to RHESSI data may be significantly improved when the SphinX data are taken into account.