Observations of Doppler Shifts of X-Ray Lines in Solar Flare Spectra Based on DIOGENESS Spectrometer Data
The idea of measurement of X-ray lines Doppler shifts in spectra of the Sun, applied in DIOGENESS spectrometer, was previously developed and verified in rocket experiment with RDR X-ray Dopplerometer (Vertical-11 Rocket, 1981). Upon the obtained results two X-ray DIOGENESS spectrometers have been manufactured; the first one was operated aboard the CORONAS-I satellite (launch in 1994), while the second was operated aboard the CORONAS-F.
The idea of measurement of X-ray lines Doppler shifts in spectra of the Sun, applied in DIOGENESS spectrometer, was previously developed and verified in rocket experiment with RDR X-ray Dopplerometer (Vertical-11 Rocket, 1981) . Upon the obtained results two X-ray DIOGENESS spectrometers have been manufactured; the first one was operated aboard the CORONAS-I satellite (launch in 1994) , while the second was operated aboard the CORONAS-F. The general view of the instrument is shown in Fig. 1.
The concept of spectrometer which can operate as the Dopplerometer system is based on mounting of two identical crystals fixed at the precise angular position against each other at the α angle and attached to rocking table. The crystals scan the spectrum in opposite directions, i.e., in the direction of increasing and decreasing wavelengths. When the incidence angle reaches the value \(\theta =\alpha /2\), the same wavelength is measured in both spectra. Figure 2 shows a basic scheme of Dopplerometer measurements.
The angle α between the crystals should be selected in a manner to ensure the simultaneous registration of selected intense spectral line from radiation source staying at rest relative to Dopplerometer. In case of the presence of a source moving along the line toward the instrument, the Doppler effect occurs, which causes the change in wavelengths. The spectral line in such a case will not be observed in both spectra simultaneously. The angle of table rotation between the detected lines in both spectra will represent a measure of Doppler shift and speed of the source along the line of sight.
DIOGENESS spectrometer parameters
2d spacing (Å)
Principal lines in range
Full Width at Half Maximum (FWHM) (arcsec)
The spectra from all crystals were registered by double proportional counters with beryllium entrance windows of the 145 μm thickness, filled with argon under the pressure of ∼ 0.5 atm. Physical connection of two gas detector chambers (working and control ones) ensured the identity of gas parameters in the whole double counter. The window of detector control chamber was covered with55Fe radioactive isotope emitting reference radiation at the energy of 5.9 keV. This ensured the constant energy gain of detector electronic system.
There was the multi-slit collimator attached to the rocking table. The narrow (FWHM = 10′ ′) transmission window of collimator scanned the disc of the Sun along the direction of spectrometer dispersion. Transmitted radiation was registered in two wavelengths ranges (2–4 keV and 4–8 keV), by the proportional counter. It was expected that the scans would give the localization of radiation source on the Sun, but, unfortunately, the operation of this detector terminated early during a flight.
The rocking motion of table-collimator system with 1 arcmin s−1 angular velocity was actuated by the step motor which rotated back and forth the Archimedian spiral-shaped disc, against which the arm with collimator was pressed by a spring. The full scan in one direction required 40,000 motor steps.
Till mid September 2001, when the device stopped its operation, probably because of the mechanical damage of spectrometer drive, hundreds of spectra of solar flares above M1 class (according to GOES classification) have been obtained. The observations of the highest quality are that obtained on August 25, 2001 (4 × 30 spectra), when a strong flare of 3B optical flare importance occurred on the Sun. According to X-ray radiation the intensity of this event has reached X5.3 class. Figure 3 (bottom) illustrates the time evolution of X-ray radiation of this flare. For comparison the X-ray measurements in two standard ranges measured by GOES satellite detectors are also provided. The continuum level evolution is similar as seen with DIOGENESS spectrometer: on the regular shape of the continuum the groups of strong X-ray emission lines, recorded in turn in two opposite directions along the dispersion plane, are notable in a form of narrow spikes.
Ca XIX ion resonance line is effectively formed in a hot plasma with the temperature above 7 MK only. The maximum of efficiency occurs at ∼ 20 MK. In the given flare the plasma had such a temperature in the very initial phase of the event, during the rise phase. The sulfur and silicon lines are formed in a lower temperature plasmas. DIOGENESS spectrometer was not designed for operation in Dopplerometer arrangement for a spectral range including the lines of these elements. However, the knowledge about device geometry has allowed to analyze, for S XV and Si XIII ion lines, their shift relative to the position of imaginary bisector of angle between the crystals. The results obtained in such a manner are also shown in Fig. 8, qualitatively they coincide with the data obtained for calcium ion lines.
The works with DIOGENESS spectrometer have been carried out in the Solar Physics Laboratory of the Space Research Center of Polish Academy of Sciences in Wrocław (Poland), with the support of Polish Scientific Research Fund (project 1.PO3D.017.29 and 2011/01/B/ST9/05861).
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