2.8 Development of X-ray Astronomy
75
In the early 1960s, NASA launched the Orbiting Solar Observatory (OSO)
Program, the name of a series of American space telescopes primarily intended
to study the Sun, though they also included important non-solar experiments. There
were eight satellites (OSO 1–8) for the program, launched successfully into the Low
Earth Orbit (LEO) between 1962 and 1975. In March 1967, the OSO-3 was launched
into nearly circular orbit with a mean altitude of 550 km, inclined at 33 degrees to
the equatorial plane. The OSO-3 extensively measured the hard X-ray from solar
flares and the cosmic diffuse X-ray background radiation from 10 to 40 keV, and
particularly detected firstly an extra-solar X-ray source by an observatory satellite,
Scorpius X-1. Thereafter, the OSO-5 launched in January 1969 measured the diffuse
background X-ray radiation from 14 to 200 keV; the OSO-6 launched in August
1969 observed three instances of hard X-ray coincidences with gamma-ray bursts;
the OSO-7 launched in September 1971 observed solar flares in the gamma-ray spectrum and collected data allowed for identification of Vela X-1 as a HMXB; the OSO-8
launched in June 1975 discovered an iron emission line in the X-ray spectrum of a
galaxy cluster.
In addition, the first specific satellite for the purpose of X-ray astronomy, “Uhuru”,
was launched into an initial orbit of about 560 km apogee, 520 km perigee and 3
degrees inclination on December 12, 1970. The satellite was named in recognition
of the hospitality of Kenya where it was launched by the Italian San Marco launch
platform near Mombasa, and operated by the NASA. The payload of Uhuru consisted
of two sets of proportional counters, each with about 840 cm
2 effective area. The
two sets of counters were placed back to back and collimated to FOV 0.52° × 0.52°
and 5.2° × 5.2°, respectively, which were sensitive with more than 10% efficiency to
X-ray photons within 2–20 keV range. Pulse-height analysis in eight energy channels
was used to obtain information on the energy spectrum of the incident photons. The
Uhuru performed the first comprehensive survey of the entire sky for X-ray sources,
with a sensitivity of about 0.001 times the intensity of the Crab nebula. It is a scanning
mission with a spin period of 12 min. The outstanding scientific advances achieved
by the Uhuru are: to discover and study the pulsing accretion-powered binary X-ray
sources, like Centaurus X-3, Vela X-1 and Hercules X-1; to identify Cygnus X-1,
the first strong candidate for an astrophysical black hole; to observe many important
extra-galactic sources. There were four successive versions of the Uhuru catalogue,
in which 4U catalogue, the first comprehensive X-ray catalogue, contains 339 objects
and covers the entire sky in 2–6 keV energy band.
Meanwhile, the Orbiting Astronomical Observatory (OAO) was another space
observation program launched by NASA in the mid-1960s, and consisted of four
satellites, OAO-1, OAO-2, OAO-B and OAO-3. The OAO-3 was a collaborative
effort between the NASA and the British Science Research Council (currently known
as the Science and Engineering Research Council), and carried an X-ray detector
and an ultraviolet telescope. The OAO-3 was launched in 1972 and proved to be
the most successful of the OAO program. To mark the 500th anniversary of the
birth of Nicolaus Copernicus (1473–1543), the OAO-3 was named Copernicus after
launching. The Copernicus operated until 1981 and returned high-resolution spectra
of hundreds of stars along with extensive X-ray observations. Among the significant
75
In the early 1960s, NASA launched the Orbiting Solar Observatory (OSO)
Program, the name of a series of American space telescopes primarily intended
to study the Sun, though they also included important non-solar experiments. There
were eight satellites (OSO 1–8) for the program, launched successfully into the Low
Earth Orbit (LEO) between 1962 and 1975. In March 1967, the OSO-3 was launched
into nearly circular orbit with a mean altitude of 550 km, inclined at 33 degrees to
the equatorial plane. The OSO-3 extensively measured the hard X-ray from solar
flares and the cosmic diffuse X-ray background radiation from 10 to 40 keV, and
particularly detected firstly an extra-solar X-ray source by an observatory satellite,
Scorpius X-1. Thereafter, the OSO-5 launched in January 1969 measured the diffuse
background X-ray radiation from 14 to 200 keV; the OSO-6 launched in August
1969 observed three instances of hard X-ray coincidences with gamma-ray bursts;
the OSO-7 launched in September 1971 observed solar flares in the gamma-ray spectrum and collected data allowed for identification of Vela X-1 as a HMXB; the OSO-8
launched in June 1975 discovered an iron emission line in the X-ray spectrum of a
galaxy cluster.
In addition, the first specific satellite for the purpose of X-ray astronomy, “Uhuru”,
was launched into an initial orbit of about 560 km apogee, 520 km perigee and 3
degrees inclination on December 12, 1970. The satellite was named in recognition
of the hospitality of Kenya where it was launched by the Italian San Marco launch
platform near Mombasa, and operated by the NASA. The payload of Uhuru consisted
of two sets of proportional counters, each with about 840 cm
2 effective area. The
two sets of counters were placed back to back and collimated to FOV 0.52° × 0.52°
and 5.2° × 5.2°, respectively, which were sensitive with more than 10% efficiency to
X-ray photons within 2–20 keV range. Pulse-height analysis in eight energy channels
was used to obtain information on the energy spectrum of the incident photons. The
Uhuru performed the first comprehensive survey of the entire sky for X-ray sources,
with a sensitivity of about 0.001 times the intensity of the Crab nebula. It is a scanning
mission with a spin period of 12 min. The outstanding scientific advances achieved
by the Uhuru are: to discover and study the pulsing accretion-powered binary X-ray
sources, like Centaurus X-3, Vela X-1 and Hercules X-1; to identify Cygnus X-1,
the first strong candidate for an astrophysical black hole; to observe many important
extra-galactic sources. There were four successive versions of the Uhuru catalogue,
in which 4U catalogue, the first comprehensive X-ray catalogue, contains 339 objects
and covers the entire sky in 2–6 keV energy band.
Meanwhile, the Orbiting Astronomical Observatory (OAO) was another space
observation program launched by NASA in the mid-1960s, and consisted of four
satellites, OAO-1, OAO-2, OAO-B and OAO-3. The OAO-3 was a collaborative
effort between the NASA and the British Science Research Council (currently known
as the Science and Engineering Research Council), and carried an X-ray detector
and an ultraviolet telescope. The OAO-3 was launched in 1972 and proved to be
the most successful of the OAO program. To mark the 500th anniversary of the
birth of Nicolaus Copernicus (1473–1543), the OAO-3 was named Copernicus after
launching. The Copernicus operated until 1981 and returned high-resolution spectra
of hundreds of stars along with extensive X-ray observations. Among the significant