RESIK & Diogeness NEWS

Data gaps due to missing telemetry: ~ 8 h.

Note, that the link to the catalogue page  is now: http://www.cbk.pan.wroc.pl/resik_catalogue.htm.

RESIK and RHESSI Observations of the Thermal Component of Flare X-ray Emission

RHESSI continues to observe X-ray emission in the 3 keV to 17 MeV energy range from solar flares. Recently a special volume of Solar Physics (vol. 210) was dedicated to a description of the RHESSI mission and some early results. Many of the flares RESIK has seen were also observed by RHESSI, and the observations from both are of great interest in getting flare X-ray fluxes in the region spanning the soft and hard X-ray ranges. This region has been recognized to be of immense interest understanding the relation of the flare non-thermal component (from energetic electrons accelerated in the flare impulsive phase) and thermal component (from very hot plasma, with temperatures up to several tens of MK).

The lower end of RHESSI's spectral energy range (about 3 keV) overlaps with RESIK channels #1 and #2 (wavelength range for an on-axis flare in first order is 3.37 - 4.33 Ǻ or 2.86 - 3.68 keV) offering a highly useful means of cross-calibration. For intense flares, RHESSI often has attenuators in place in front of its nine detectors to reduce the detector counting-rate at low energies (less than 10 keV) to prevent saturation. However, the exact amount of attenuation is somewhat uncertain and knowledge of the continuum at about 3 keV which RESIK sees in its channel #1 and #2 spectra in first order will enable this uncertainty to be much reduced. Also, flares seen by RESIK in 3^rd order diffraction, when Fe XXV line emission at about 1.85Ǻ (6.7 keV) is often a prominent feature, will help to get a cross-calibration at this energy also as RHESSI sees the Fe lines with a 1 keV FWHM resolution on top of the continuum.

We are making preliminary investigations of flares when both RESIK and RHESSI were operating in order to do some cross-calibrations of this type. The April 21, 2002 flare offers the possibility of suitable data for this purpose. Figure 1 shows RESIK channels #1 and #2 spectra, plotted by JS in the unfamiliar guise of being plotted against energy (keV), not wavelength (in Ǻ). The time interval was 03:25:30 - 03:28:41 UT.

Figure 1. RESIK spectra plotted along the energy. This kind of presentation will be used for purposes of direct comparison with RHESSI spectra (see the text for more details).

Figure 2 shows the RHESSI spectrum derived by Brian Dennis (RHESSI Group at GSFC) over an interval close by in time (03:07:44 - 03:08:44 UT) with the RESIK channels 1 and 2 spectra overplotted. RHESSI was in Earth shadow for times just after this interval. Most likely for this slowly decaying event there is not too much change in the flux between 03:08 and 03:25 UT. The agreement of the continuum fluxes to better than a factor 2 shows that the RESIK and RHESSI calibrations are close to expected.

Work will be reported on this in future issues of the RESIK Weekly.

Figure 2. RHESSI and RESIK energy spectra plotted together. Note rather good match except for the slope of the continua. The spectra plotted have NOT been measured simultaneously, however close in time.


Prepared by: Ken Phillips phillips@stars.gsfc.nasa.gov, Janusz Sylwester js@cbk.pan.wroc.pl, Barbara Sylwester bs@cbk.pan.wroc.pl, Brian Dennis Brian.R.Dennis.1@gsfc.nasa.gov