X-ray Images of Solar Flares from the Solar Maximum Mission/Hard X-ray Burst Spectrometer (SMM/HXRBS)

The HXRBS operated aboard the SMM spacecraft which was launched on February 14, 1980 and re-entered the Earth's atmosphere December 12, 1989. The duty cycle for the HXRBS was about 50% as a result of the circular SMM orbit with an altitude of 500 km and an inclination of 33 degrees. The orbital period was 95 minutes with 60-65 minutes in the Sun and the remainder behind the Earth. In 7 or 8 orbits per day, 5 to 30 minutes of data were lost because the HXRBS high voltage power supplies were commanded off as the satellite passed through the high charged-particle fluxes in the South Atlantic Anomaly. In addition, the HXRBS was turned off occasionally for longer intervals as a result of satellite difficulties. The HXRBS was not affected by the failure of spacecraft fine pointing in November 1980, and other than the exceptions mentioned, has operated almost continuously since launch.

The HXRBS was used primarily to observe the spectra of hard X-ray bursts from solar flares on a time-continuous basis. The instrument was described in detail by Orwig et al. (1980) (see References). Briefly, the X-Ray detector was an actively-shielded CsI(Na) scintillation crystal with a sensitive area of 71 cm**2 and a 40 degree (FWHM) circular field of view. The central crystal is surrounded by shield crystal except for the circular aperture which is kept pointed at the Sun. The aperture admits incoming X-ray photons within a cone of directions with a half-angle of approximately 40 degrees. Photons outside this cone may penetrate the central detector, but not without passing through the shield crystal. The shield and central detector are operated in anti-coincidence, so that collimation is accomplished by discriminating against photons detected in both the shield and central detector. Scintillation pulses due to photons that penetrate the shield are recorded as well as pulses in the central detector. This permits non-solar gamma-ray bursts to be observed as well as solar flares.

Data from the Hard X-ray Burst Spectrometer (HXRBS) consist of the counting rate recorded every 128 ms in each of fifteen pulse-height channels. These channels covered the range 25 to 440 keV immediately after launch and then proceeded to drift slowly to higher energies through the mission. More than 12,000 solar flares and numerous cosmic bursts were observed. For the larger flares, higher time resolution data (1, 5, or 10 ms) is also available with no spectral information.

The main data analysis center and archive is at the Solar Data Analysis Center (SDAC), NASA/GSFC. The entire raw data set has been archived on twenty-five 12' optical disk platters. The time intervals containing flares and surrounding background are also archived separately on three optical disk platters. In addition, spectral analysis was performed on most of the solar flares and the results are stored on one optical disk platter.
The HXRBS counting rate time profiles with 1 s time resolution are available on microfiche for most of the events observed by HXRBS. One plot is given for each event showing the total counting rate integrated over the full energy range of the instrument as a function of time. Copies of these microfiche are stored at the SDAC and the NSSDC (NSSDC Dataset_ID: 80-014A-06B ).

Parameters describing the observed HXRBS events are stored in the extensive SMM flare catalog that resides on the SDAC's MicroVAX computer (SPAN node ISIS). This on-line data base contains extensive data on all the events detected with the SMM instruments and also includes data on those events from other spacecraft, and from ground-based radio and optical observatories, when available. The HXRBS event list has been published as a NASA Technical Memorandum (see References).