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Major Milestones In X-ray Astronomy

In September, 1949, a team led by Herbert Friedman of the Naval Research Laboratory detected weak X-ray emission from the solar corona, the hot outer layers of the Sun's atmosphere. Their experiment consisted of a collection of small Geiger counters aboard a captured German V-2 rocket. It took more than a decade before a greatly improved detector discovered X-rays coming from sources beyond the solar system.

In 1962, a team of scientists under the direction of Riccardo Giacconi at American Science and Engineering in Cambridge, MA., used a small X-ray detector aboard an Aerobee rocket to discover Scorpius X-1, the first source of X-rays outside our solar system. Forty years later, over 100,000 X-ray sources have been detected, the most distant of which is 13 billion light years from Earth. This extraordinary leap in sensitivity has been due, in large part, to the development of telescopes that can focus X-rays.

The first imaging X-ray telescope was made by Giacconi and collaborators. It was flown on a small sounding rocket in October 1963 and made crude images of hot spots in the upper atmosphere of the sun. This telescope was about the same diameter and length as the optical telescope Galileo used in 1610. Over a period of 380 years, optical telescopes improved in sensitivity by 100 million times from Galileo's telescope to the Hubble Space Telescope. Remarkably, the Chandra X-ray Observatory represents a comparable leap in sensitivity over Giacconi's 1963 telescope, yet it took only 36 years!

X-ray Astronomy Time Line
V2 Rocket Credit: NRL Date: September, 1949 Vehicle/Mission: V-2 rocket Agency/Country: Naval Research Laboratory Instruments/Detectors: Geiger counters Mirror Description: No mirrors Highlights: Detection of X-ray emission from the solar corona.
Aerobee Rocket Credit: USAF Museum Date: June 18, 1962 (350 seconds) Vehicle/Mission: Aerobee Rocket Agency/Country: USAF Instruments/Detectors: Proportional counter (2 -10 keV) Mirror Description: No mirrors Highlights: Discovery of Scorpius X-1, the first cosmic X-ray source and X-ray background, a signal appearing to come from all directions, possibly a truly diffuse emission and possibly due to many sources, too faint to be resolved individually. (Reference: R. Giacconi, H. Gursky, F. R. Paolini, and B. B. Rossi, "Evidence for x Rays From Sources Outside the Solar System," Physical Review Letters, 1 December 1962, Volume 9, pp. 439-443)
Terrier-Sandhawk rocket Credit: Lawrence Livermore Laboratory & Sandia Laboratories Date: 1963 to 1970 Vehicle/Mission: Numerous rocket and balloon flights Agency/Country: Various agencies Instruments/Detectors: Proportional counters (0.2 -10 keV) / scintillation counters (10 -40 keV) Mirror Description: No mirrors, except for a small solar X-ray telescope with the resolution of a few arc min Highlights: First X-ray pictures of the sun. Discovery of 40 extra-solar X-ray sources, including X-ray stars, the Crab Nebula pulsar, supernova remnants, and the galaxy M87.
Uhuru Date: December 1970 to March 1973 Vehicle/Mission: Uhuru X-ray satellite Agency/Country: NASA Instruments/Detectors: Proportional counters (2 -20 keV) Mirror Description: No mirrors Highlights: Uhuru, the first satellite dedicated to the observation of cosmic X-ray sources, was equipped with a sensitive proportional counter attached to a viewing pipe to locate the sources. It expanded the number of known sources to more than 400, showed that X-ray stars are neutron stars or black holes accreting matter from companions in binary star systems, and discovered X-rays from hot gas in galaxy clusters.
The Vela-5B Satellite Credit: Los Alamos National Laboratory Date: May 1969 to June 1979 Vehicle/Mission: Vela Satellites Agency/Country: Department of Defense (DOD) Instruments/Detectors: Scintillation counters (3 -40 keV) Mirror Description: No mirrors Highlights: Discovery of gamma ray bursts, X-ray bursters
ANS Date: August 1974 to July 1976 Vehicle/Mission: Astronomy Netherlands Satellite (ANS) Agency/Country: The Netherlands Instruments/Detectors: Proportional counters (2 -40 keV), crystal spectrometer Mirror Description: No mirrors Highlights: Discovery of X-ray bursters, more X-ray binaries
Ariel V Date: October 1974 to March 1980 Vehicle/Mission: Ariel V Agency/Country: United Kingdom Instruments/Detectors: Proportional counters (2 -10 keV) Mirror Description: No mirrors Highlights: Discovery of black hole X-ray nova A0620-00; brightest X-ray source ever seen
SAS-3 Date: May 1975 to April 1980 Vehicle/Mission: Small Astronomy Satellite-3 (SAS-3) Agency/Country: NASA Instruments/Detectors: Proportional counters (1.5 -10 keV) Mirror Description: No mirrors Highlights: Discovery of X-ray emission from white dwarf SS Cygni; research on X-ray bursters
HEAO-1 Date: August 1977 to January 1979 Vehicle/Mission: High Energy Astronomy Observatory-1 (HEAO -1) Agency/Country: NASA Instruments/Detectors: Proportional counters (0.2 -20 keV) & phoswich scintillators (15 keV -10 MeV) Mirror Description: No mirrors Highlights: Survey used large proportional counters that covered a wide range of X-ray energies. Discovered the Cygnus superbubble, and gathered detailed information on spectra of active galactic nuclei and the X-ray background.
Einstein Date: November 1978 to April 1981 Vehicle/Mission: Einstein X-ray Observatory Agency/Country: NASA Instruments/Detectors: Proportional counters/microchannel plate imager/solid state spectrometer/crystal spectrometer (0.2 -4 keV) Mirror Description: 4 nested mirror pairs with an area of 350 sq cm and a resolution of 3-5 arc sec. Highlights: The first large X-ray telescope with mirrors. Einstein made the first X-ray images of shock waves in supernova remnants, hot gas in galaxies and clusters of galaxies. Einstein also located accurately over 7000 X-ray sources, including stellar coronas, X-ray binaries, galaxies and quasars. It made possible a new way to study the mysterious dark matter that is present in galaxies and clusters of galaxies and showed that most of the X-ray background is probably due to discrete sources.
EXOSAT Date: May 1983 to April 1986 Vehicle/Mission: EXOSAT Agency/Country: European Space Agency Instruments/Detectors: Proportional counters (0.1 -10 keV) Mirror Description: 2 nested mirror pairs with 80 sq cm area and 18 arc sec resolution Highlights: Discovery of quasi-periodic oscillations from neutron stars and black holes, surveys of variability of wide variety of galactic and extragalactic sources.
ROSAT Date: June 1990 to February 1999 Vehicle/Mission: Roentgensatellite (ROSAT) Agency/Country: Germany Instruments/Detectors: Proportional counters/microchannel plate imager (0.1 -2.5 keV) Mirror Description: 4 nested mirror pairs with 1140 sq cm area and 3 arc sec resolution Highlights: ROSAT expanded the number of known X-ray sources to 125,000 and proved to be especially valuable for investigating the multi-million degree gas present in the upper atmospheres of many stars, made the first detection of radiation from the hot surface of a neutron star, and comets. It resolved 70% of soft X-ray background, and made an extensive catalogue of galaxy clusters.
ASCA Date: 1993 to July 2000 Vehicle/Mission: Advanced Satellite for Cosmology and Astrophysics (ASCA) Agency/Country: Japan Instruments/Detectors: Proportional counters/CCDs (0.4 -12 keV) Mirror Description: 120 nested foil mirrors with 1300 sq cm area and resolution of 180 arc sec Highlights: The ASCA X-ray observatory with low resolution mirrors, and the first large CCD detectors, was especially designed to study the detailed spectra of X-ray sources in supernova remnants, active galactic nuclei and galaxy clusters. Found first evidence of the gravitational redshift due to the strong gravitational field around a black hole.
RXTE Date: December 1995 to present Vehicle/Mission: Rossi X-ray Timing Explorer (RXTE) Agency/Country: NASA Instruments/Detectors: Proportional counters (2 -50 keV) and scintillation counters (15 -200 keV) Mirror Description: No mirrors Highlights: Although RXTE does not have focusing X-ray mirrors, it has the unique capability to study rapid time variability in the emission of cosmic X-ray sources over a wide band of X-ray energies, and has made valuable contributions to our understanding of the behavior of matter in the vicinity of neutron stars and black holes. Extremely rapid variability observed by RXTE may be evidence for the dragging of space by strong gravity in the vicinity of black holes.
BeppoSAX Date: April 1996 to April 2002 Vehicle/Mission: BeppoSAX Agency/Country: Italy & The Netherlands Instruments/Detectors: Proportional counters (0.1 -10 keV), scintillation counters (3 -120 keV) and phoswich detectors (15 -300 keV) Mirror Description: No mirrors Highlights: BeppoSAX is the first X-ray mission with a scientific payload covering more than three decades of energy - from 0.1 to 300 keV, with moderate imaging capability. BeppoSAX has proved to be especially useful for wide band spectra of active galactic nuclei, and for studying gamma-ray bursts by determining their positions with an unprecedented precision and monitoring their X-ray afterglow.
Chandra X-ray Observatory Date: July 1999 to present Vehicle/Mission: Chandra X-ray Observatory Agency/Country: NASA Instruments/Detectors: High Resolution Imager/CCDs, grating spectrometers (0.1 -10 keV) Mirror Description: 4 nested pairs with 1145 sq cm area and 0.5 arc sec resolution. Highlights: Chandra's unique sensitivity and precision have made possible significant advances in many areas of astronomy. Of particular importance are discoveries relating to the life cycles of stars, the number and nature of black holes in the universe, the generation by neutron stars of high energy matter and anti-matter particles, and the formation and evolution of galaxies. Chandra has traced the distribution of elements such as oxygen, neon, silicon and iron in supernova remnants, and made spectacular images of the pulsar wind nebulas in the Crab Nebula and Vela supernova remnant. Chandra observations have revealed the presence of many previously undetected stellar black holes in nearby galaxies, including a possible new class of intermediate mass black holes. Chandra's detailed spectral studies of the activity of supermassive black holes in the centers of galaxies have detected winds coming from the centers of galaxies, and X-ray jets hundreds of thousands of light years in length that can be traced back to the central supermassive black holes. Very long Chandra exposures have shown that there may be twice as many active supermassive black holes in the universe as previously thought. Chandra is enabling astronomers to study how clusters of galaxies are formed and how they change with time, and to investigate the nature of the dark matter that comprises most of the mass of the universe.
XMM-Newton Date: December 1999 to present Vehicle/Mission: XMM-Newton Agency/Country: European Space Agency Instruments/Detectors: CCD cameras and spectrometers (0.1 - 12 keV) Mirror Description: 3 modules each with 58 wafer-thin mirrors for a total area of 4300 sq cm and a resolution of 5 arc sec Highlights: With its large collecting area, spectrometers and moderate resolution, XMM-Newton is especially designed to make detailed studies of the spectra of supernova remnants, accretion disks around black holes, stars and other types of sources. Notable achievements have been to accurately measure the energy budget of radiation from a black-hole accretion disk, the detection of heavy elements in the spectrum of the afterglow of a gamma-ray burst, the mapping of elements in supernova remnants, and detailed spectra of active galactic nuclei.
HETE-2 Date: October 2000 to present Vehicle/Mission: High Energy Transient Explorer (HETE-2) Agency/Country: USA, Japan, France, and Italy Instruments/Detectors: X-ray cameras & gamma-ray detectors (0.5 -400 keV) Mirror Description: No mirrors Highlights: Detection and localization of gamma-ray bursts, and a possible new type of X-ray burst that may be related to gamma-ray bursts.

Disclaimer: This material is being kept online for historical purposes. Though accurate at the time of publication, it is no longer being updated. The page may contain broken links or outdated information, and parts may not function in current web browsers. Visit chandra.si.edu for current information.