The SGD will make observations in a region of the spectrum from 60 to 600 keV, a region referred to as the “soft gamma ray” band. In order to be able to extract meaningful information from the data provided by SGD observations, we must understand beforehand how the SGD responds to gamma rays, depending both on their energy and on their direction of incidence. Further, we need to understand how each section of the detector responds to such irradiation. In short, the response of the detector needs to be calibrated. To this end, tests were carried out at ISAS over a period of about one week in February. The tests were conducted using a large thermal tank which maintains its interior at a fixed temperature over an extended period of time. One portion
of the SGD sensor (SGD-S) along with its electronics (SGD-AE) was inserted into the tank where the temperature was maintained at -20 degrees around the clock. This mimics the thermal conditions the SGD will be operating under while on orbit. Graduate students from ISAS, Hiroshima University,
Nagoya University and Shizuoka University all took part, taking turns working the three shifts per day.
During the tests, a variety of different sources of gamma rays were used to irradiate the detector from a variety of different directions with the data being recorded all the while. The three photos depict the large tank, the SGD, and graduate students examining the data. The SGD sensor produced about 40,000 signals, so checking the data was no easy task!
The analysis afterwards of all of this data will be an arduous process, requiring many graduate-student hours of work — in fact, graduate-student months of work!
Now that the experiments have been successfully completed, we await the installation of the two SGD detectors into ASTRO-H.