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Ginga

Ginga

Ginga satellite (Credit: NASA)

The Mission

Astro-C, renamed Ginga (Japanese for 'galaxy') when it reached orbit, was launched from the Kagoshima Space Center on 5 February 1987. It was put into an orbit with an orbital period of ~96 minutes. Ginga was the third Japanese X-ray astronomy mission, following Hakucho and Tenma. It had two main science objectives:

  1. Study the time variability on timescales of milliseconds to years for all types of X-ray sources.
  2. Study the spectra of sources.

After a highly successful mission, the Ginga satellite reentered the Earth's atmosphere on 1 November 1991.

The Instrumentation

Ginga was approximately 1000 x 1000 x 1550 mm in size. It weighed about 420 kg. There were 3 science instruments on board: a large area proportional counter (LAC), an all-sky monitor (ASM), and a gamma-ray burst detector (GBD).

The LAC was the main scientific instrument aboard Ginga. It was designed and built under a Japan-United Kingdom collaboration (ISAS, U. Tokyo, Nagoya U., U. Leicester, Rutherford Appleton Lab). The LAC consisted of 8 identical proportional counters, with a total effective area of ~ 4000 sq-cm. The instrument was sensitive to ~1-37 keV X-ray photons.

The ASM consisted of 2 identical gas proportional counters, and was sensitive to 1-20 keV X-rays. The aim of the ASM was to create an all-sky survey every 1-2 days to look for transient events (for alarm to the LAC) and to collect a long-term record for X-ray sources.

The purpose of the GBD was to detect gamma-ray bursts in the energy range 1 - 400 keV with a high energy resolution. The GBD could also operate as a radiation belt monitor for high particle backgrounds which could harm the other 2 experiments.

The Science Results

Ginga performed approximately 1000 observations of about 350 different objects. The observing program included all known classes of X-ray sources and produced many significant results. Some highlights are:

  • The ASM discovered 2 very bright transients GS2023+338 and GS2000+25.
  • The LAC found cyclotron features in several X-ray pulsars, such as 4U1538-522, V0332+53, and Cep X-4.
  • A large number of pulsar transients in the galactic ridge were observed.

Published: February 1998
Text Reviewed: September 2018