To RHESSI collaborators:

On August 13, RHESSI resumed normal operations collecting solar X-ray and gamma-ray data, following the successful completion of the "anneal" procedure to rejuvenate the RHESSI detectors from the effects of radiation damage. The detectors were heated up from their operating temperature of ~120 K to ~100 deg C (373 K), held at that temperature for ten days, and then cooled back down. The entire procedure took seven weeks.

Over the past two weeks, we have been evaluating the instrument performance and optimizing its settings. All nine detectors have recovered from the effects of radiation damage, providing hard X-ray (>~20 keV) imaging spectroscopy at the nominal angular resolution of ~2 arcsec and spectral resolution of ~1 keV. For soft X-ray (~3–20 keV) observations, five of the nine detectors can be used, which include the smallest and largest angular scales, but the other four detectors cannot be used at present because they are currently unable to electronically segment into separate front and rear volumes. The primary impact is a reduction in image quality below 20 keV. Such an outcome was expected, and these detectors may segment in the future.

We now look forward to future solar activity. If you have any questions about this past anneal or the current status of the instrument, please feel free to contact me.

Albert Shih RHESSI Deputy Mission Scientist

————— Albert Y. Shih Solar Physics Laboratory, Code 671 NASA Goddard Space Flight Center Greenbelt, MD 20771 Office: 301-286-1843