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