A demonstration of STIX hard X-ray imaging spectroscopy capabilities for an X-class flare (SOL2021-10-28)
From RHESSI Wiki
| Nugget | |
|---|---|
| Number: | 426 |
| 1st Author: | Andrea BATTAGLIA, Hannah COLLIER, |
| 2nd Author: | and Säm KRUCKER |
| Published: | 7 February 2021 |
| Next Nugget: | TBD |
| Previous Nugget: | A solar flare driven by thermal conduction observed in mid-infrared |
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Contents |
Introduction
The Solar Orbiter observatory, launched just two years ago, carries a hard X-ray imager (STIX)] that now extends RHESSI's hard X-ray record. Although not as powwerful as RHESSI in some regards, STIX has remarkable advantages - it approaches the Sun closely, and it can observe stereoscopically when combined with Earth-bound instruments.
This Nugget reports on the first X-class flare observed, SOL2021-10-28.
Calibration
STIX consists of two-grid shadow optics, as did RHESSI, but with the innovation of Moiré patterns. Its sophisticated simplicity required much effort on in-flight calibration of the amplitudes and phases of the visibility functions provided by the grids (Ref. [1]) SOL2021-10-28, as luck would have it, occurred at a solar radial distance outside the nominal operating window (within 0.75 AU), and so the alignment in the analysis below is ad hoc, but all future observations will have proper STIX aspect solutions.
The flare
At the time of the flare, Solar Orbiter was rather far away from the Sun (0.80 AU), but the viewing angle was only 4 degrees away from the Sun-Earth line. This small separation angle makes the comparison with observations taken from Earth relatively straightforward, but somewhat limited due to projection effects. However, for emissions originating from a single height layer, the images can be rotated from one vantage point to another precisely. In particular STIX can be compared accurately with UV observations of the flare ribbons provided by SDO/AIA. On the other hand, emission from flares loops, which have complicated 3-dimensional structures, cannot be coaligned accurately. Therefore, STIX and AIA images are best compared in a two-panel figure showing the images side by side, with the chromospheric emissions being shown in both panels, as in Figure 1
References
[1] Massa 21, Battaglia 21
| RHESSI Nugget Date | 7 February 2021 + |
| RHESSI Nugget First Author | Andrea BATTAGLIA, Hannah COLLIER, + |
| RHESSI Nugget Index | 426 + |
| RHESSI Nugget Second Author | and Säm KRUCKER + |
