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Gas Imaging Spectrometer (GIS)

NSSDCA ID: 1993-011A-02

Mission Name: ASCA
Principal Investigator:Dr. Kazuo Makishima


Two identical Gas Imaging Spectrometer (GIS) detectors were carried by the ASCA spacecraft. The GIS detectors were located in the focal plane of the X-Ray Telescopes (XRT). The GIS was an Imaging Gas Scintillation Propotional Counter (IGSPC). X-ray photons, focused by the mirror, entered the detector through the thin beryllium entrance window into the "drift region" containing the detector gas: xenon with ten percent of helium. The xenon atoms were then ionized by the X-rays, and the photoelectrons produced then drifted into the "scintillation region" which contained the same mixture of gases. The electrons were then accelerated by a strong electric field and excited the xenon atoms. When the xenon atoms de-excited, UV scintillations were produced with intensity proportional to the energy of the original X-rays. These scintillations were then detected by the position sensitive phototube. The GIS was an improved version of the Scintillation Proportional Counter (SPC) experiment on board the Japanese X-Ray mission Tenma. The GIS had an energy resolution of 8% at 5.9 keV at launch and a circular field-of-view with a diameter of 50 arcmin. Between about 1.5 keV and 5 keV the GIS and the Solid-state Imaging Spectrometer (SIS) had similar effective areas of about 150-200 cm**2. Below 1.5 keV the GIS had less effective area than the SIS, while above 5 keV the GIS had greater effective area. The GIS significantly broadened the point spread function of the XRT. The GIS could observe brighter sources and had better temporal resolution than the SIS, but the GIS had poorer angular resolution. The GIS could be operated in 4 different modes: pulse height (PH), multi-channel pulse count (MPC), position calibration (PCAL) and memory-check modes. Guest Observer observations were normally carried out in PH and MPC modes.

Alternate Names

  • GIS

Facts in Brief

Mass: 3.8 kg
Bit rate (avg): 15.2 kbps

Funding Agencies

  • Institute of Space and Aeronautical Science, U of Tokyo Japan
  • NASA-Office of Space Science Applications United States


  • Astronomy: X-Ray

Additional Information

Questions and comments about this experiment can be directed to: Coordinated Request and User Support Office



NameRoleOriginal AffiliationE-mail
Dr. Kazuo MakishimaPrincipal InvestigatorUniversity of

Selected References

  • Tanaka, Y., The ASTRO-D mission, in Observatories in Earth Orbit and Beyond, edited by Y. Kondo, IAU Colloq. 123, Kluwer, 81-87, 1990.
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