RHESSI News Item

We are very pleased to announce that HESSI Is now operational. It detected its first flare, a C2 flare early on Tuesday morning, February 12, starting at 0214 UT. All nine detectors are cooled to about 75 K, the high voltages are on at their full level, and all detectors are operating nominally. So far, we have seen modulation in the detector behind the coarsest grid. The spacecraft is balanced and spinning at 14 rpm about an axis within about 0.1 degrees of the Solar Aspect System axis. We should get accurate aspect information once the data from the SAS and the Roll Angle System are fully analyzed. The instrument was launched with all of the thin shutters fixed in place so we have significant attenuation below ~10 keV. Once we have seen a few flares, we will activate the shutter system, thus allowing weaker flares to be detected and larger flares to be recorded without saturation. Additional calibrations and tweaking of the systems are still ongoing but we expect to be able to record every flare visible to us and to have full imaging spectroscopy capabilities by applying the new calibrations to the data retroactively.

With HESSI now operational, we encourage all solar observatories to participate as much as possible in making joint observations of solar activity.

 - Bob Lin and Brian Dennis