RHESSI's 15th Anniversary
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=== Introduction === | === Introduction === | ||
- | On Sunday, February 5, 2017, the Reuven Ramaty High Energy Solar | + | On Sunday, February 5, 2017, the [https://en.wikipedia.org/wiki/Reuven_Ramaty Reuven Ramaty] High Energy Solar |
- | Spectroscopic Imager (RHESSI), a highly successful SMEX mission, | + | Spectroscopic Imager (RHESSI), a highly successful |
- | + | [https://explorers.gsfc.nasa.gov/smex.html SMEX] mission, | |
- | RHESSI was designed to study | + | completed its 15th year in orbit. |
- | solar flares through imaging spectroscopy observations of the X-ray and | + | RHESSI was designed to study energy release and particle acceleration in |
+ | [https://solarscience.msfc.nasa.gov/flares.shtml solar flares] through imaging spectroscopy observations of the X-ray and | ||
gamma-ray emissions of these energetic events, the most powerful | gamma-ray emissions of these energetic events, the most powerful | ||
explosions in the solar system. | explosions in the solar system. | ||
These electrons and ions carry a predominant part of the released energy | These electrons and ions carry a predominant part of the released energy | ||
- | in a flare (e.g. Ref. [1]), and only RHESSI at present can provide | + | in a flare (e.g. Ref. [1]), and only RHESSI, at present, can provide |
imaging spectroscopy in this spectral domain (see the RHESSI | imaging spectroscopy in this spectral domain (see the RHESSI | ||
[https://hesperia.gsfc.nasa.gov/rhessi3/index.html home page]). | [https://hesperia.gsfc.nasa.gov/rhessi3/index.html home page]). | ||
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these high-energy photons, and only the transient activity appears (and with | these high-energy photons, and only the transient activity appears (and with | ||
a highly non-spherical distribution). | a highly non-spherical distribution). | ||
+ | Our [http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=Hard_X-ray_Emission_from_Partially_Occulted_Solar_Flares previous Nugget} | ||
+ | also discussed this distribution from a different perspective. | ||
[[File:292f1.png|500px|thumb|center| | [[File:292f1.png|500px|thumb|center| | ||
Figure 1: Map of the RHESSI quick-look flare catalog, displayed as angular | Figure 1: Map of the RHESSI quick-look flare catalog, displayed as angular | ||
- | elongations (ie, not heliographic). | + | elongations (ie, not [https://en.wikipedia.org/wiki/Stonyhurst_Observatory heliographic coordinates]). |
This huge sample, obtained from 15 years of hard X-ray imaging, has remarkable | This huge sample, obtained from 15 years of hard X-ray imaging, has remarkable | ||
smoothness on binning at 30 arc sec. (Courtesy Paulo Simões). | smoothness on binning at 30 arc sec. (Courtesy Paulo Simões). |
Revision as of 11:02, 15 February 2017
Nugget | |
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Number: | 292 |
1st Author: | Brian Dennis, Säm Krucker |
2nd Author: | and Albert Shih |
Published: | 14 February 2017 |
Next Nugget: | Eclipses |
Previous Nugget: | Partial Occultation |
List all |
Contents |
Introduction
On Sunday, February 5, 2017, the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), a highly successful SMEX mission, completed its 15th year in orbit. RHESSI was designed to study energy release and particle acceleration in solar flares through imaging spectroscopy observations of the X-ray and gamma-ray emissions of these energetic events, the most powerful explosions in the solar system. These electrons and ions carry a predominant part of the released energy in a flare (e.g. Ref. [1]), and only RHESSI, at present, can provide imaging spectroscopy in this spectral domain (see the RHESSI home page).
During this interval of roughly 2/3 of a 22-year Hale Cycle, RHESSI has recorded over 114,000 Xray events, 41 of them with gamma-ray emission above 300 keV. Figure 1 displays the catalog as a mean image of the hard X-ray Sun, quite striking in the sense that the body of the Sun actually is dark for these high-energy photons, and only the transient activity appears (and with a highly non-spherical distribution). Our [http://sprg.ssl.berkeley.edu/~tohban/wiki/index.php?title=Hard_X-ray_Emission_from_Partially_Occulted_Solar_Flares previous Nugget} also discussed this distribution from a different perspective.
The present
RHESSI's systems are ageing but still quite functional, and able to provide imaging spectroscopy routinely as before. The operational procedures have changed slightly in that we normally operate only two of the nine Ge detectors, in order to help the cryocooler's cooling performance. This still lets us make images and spectra such as those illustrated in Figure 2.
These very recent observations demonstrate RHESSI's continuing capability, now augmented by many new facilities such as EOVSA for microwaves and IRIS in the UV. To these and all of the other new and soon-to-appear facilities, RHESSI continues to supply the only hard X-ray imaging spectroscopy.
RHESSI's other activities
RHESSI's other pastimes include analysis of transient gamma-ray flashes (TGFs) from the Earth's atmosphere, produced by lightning. Also, data from its optical solar aspect system has been used for the most accurate measurements of solar oblateness and mean photospheric temperature distribution ever made, with continually incrementing precision as the mission continues (Ref. [2]). All of the data and the analysis software have been made immediately available to the scientific community resulting in over 1,000 refereed papers that utilize RHESSI observations, with more than 100 in the last year alone. They are now cited over 4,000 times per year.
The future
The RHESSI spacecraft and instrument continue to operate well, as described above. The mission has no expendables and reentry is not predicted to occur until 2021 at the earliest. The slowly rising detector temperatures, resulting from the gradually decreasing cryocooler efficiency, is a matter of concern and has led us to operate only two of the nine detectors during periods of low solar activity. This minimizes the temperature increase. When major activity reappears, RHESSI can operate with full capability on short notice. We expect to be able to maintain RHESSI's unique hard X-ray imaging spectroscopy capability for the foreseeable future.
References
[1] "Global Energetics of Solar Flares: V. Energy Closure in Flares and Coronal Mass Ejections"
[2] "A Large Excess in Apparent Solar Oblateness Due to Surface Magnetism"
RHESSI Nugget Date | 14 February 2017 + |
RHESSI Nugget First Author | Brian Dennis, Säm Krucker + |
RHESSI Nugget Index | 292 + |
RHESSI Nugget Second Author | and Albert Shih + |