Astro-C, renamed Ginga (Japanese for 'galaxy') on 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
- study time variabilities from milliseconds to years for all types of
X-ray sources, and
- study the spectra of sources. After a highly
successful mission, the Ginga satellite reentered the Earth's atmosphere
on 1 November 1991.
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
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
V0332+53, and Cep X-4.
- A large number of pulsar transients in the galactic ridge were observed.