X-ray astronomy is an observational branch of astronomy which deals with the study of X-ray observation and detection from astronomical objects. X-radiation is absorbed by the Earth's atmosphere, so instruments to detect X-rays must be taken to high altitude by balloons, sounding rockets, and satellites. X-ray astronomy uses a type of space telescope that can see x-ray radiation which standard optical telescopes, such as the Mauna Kea Observatories, cannot.
The Fermi Gamma-ray Space Telescope, formerly called the Gamma-ray Large Area Space Telescope (GLAST), is a space observatory being used to perform gamma-ray astronomy observations from low Earth orbit. Its main instrument is the Large Area Telescope (LAT), with which astronomers mostly intend to perform an all-sky survey studying astrophysical and cosmological phenomena such as active galactic nuclei, pulsars, other high-energy sources and dark matter. Another instrument aboard Fermi, the Gamma-ray Burst Monitor, is being used to study gamma-ray bursts and solar flares.
Uhuru was the first satellite launched specifically for the purpose of X-ray astronomy. It was also known as the X-ray Explorer Satellite, SAS-A, SAS 1, or Explorer 42. The observatory was launched on 12 December 1970 into an initial orbit of about 560 km apogee, 520 km perigee, 3 degrees inclination, with a period of 96 minutes. The mission ended in March 1973. Uhuru was a scanning mission, with a spin period of ~12 minutes. It 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.
The Advanced Satellite for Cosmology and Astrophysics was the fourth cosmic X-ray astronomy mission by JAXA, and the second for which the United States provided part of the scientific payload. The satellite was successfully launched on 20 February 1993. The first eight months of the ASCA mission were devoted to performance verification. Having established the quality of performance of all ASCA's instruments, the spacecraft provided science observations for the remainder of the mission. In this phase the observing program was open to astronomers based at Japanese and U.S. institutions, as well as those located in member states of the European Space Agency.
Einstein Observatory (HEAO-2) was the first fully imaging X-ray telescope put into space and the second of NASA's three High Energy Astrophysical Observatories. Named HEAO B before launch, the observatory's name was changed to honor Albert Einstein upon its successfully attaining orbit.
Suzaku was an X-ray astronomy satellite developed jointly by the Institute of Space and Aeronautical Science at JAXA and NASA's Goddard Space Flight Center to probe high-energy X-ray sources, such as supernova explosions, black holes and galactic clusters. It was launched on 10 July 2005 aboard the M-V launch vehicle on the M-V-6 mission. After its successful launch, the satellite was renamed Suzaku after the mythical Vermilion bird of the South.
Tenma, known as ASTRO-B before launch, was a Japanese X-ray astronomy satellite, developed by the Institute of Space and Astronautical Science. It was launched on February 20, 1983, using a M-3S rocket on the M-3S-3 mission.
AstroSat is India's first dedicated multi-wavelength space telescope. It was launched on a PSLV-XL on 28 September 2015. With the success of this satellite, ISRO has proposed launching AstroSat-2 as a successor for AstroSat.
AGILE was an X-ray and gamma ray astronomical satellite of the Italian Space Agency (ASI). Launched in 2007, it de-orbited in February 2024.
Cornelis A. "Neil" Gehrels was an American astrophysicist specializing in the field of gamma-ray astronomy. He was Chief of the Astroparticle Physics Laboratory at NASA's Goddard Space Flight Center (GSFC) from 1995 until his death, and was best known for his work developing the field from early balloon instruments to today's space observatories such as the NASA Swift mission, for which he was the principal investigator. He was leading the WFIRST wide-field infrared telescope forward toward a launch in the mid-2020s. He was a member of the National Academy of Sciences and the American Academy of Arts and Sciences.
The International Astrophysical Observatory "GRANAT", was a Soviet space observatory developed in collaboration with France, Denmark and Bulgaria. It was launched on 1 December 1989 aboard a Proton rocket and placed in a highly eccentric four-day orbit, of which three were devoted to observations. It operated for almost nine years.
The Small Astronomy Satellite 3 was a NASA X-ray astronomy space telescope. It functioned from May 7, 1975 to April 1979. It covered the X-ray range with four experiments on board. The satellite, built by the Johns Hopkins University Applied Physics Laboratory (APL), was proposed and operated by MIT's Center for Space Research (CSR). It was launched on a Scout vehicle from the Italian San Marco launch platform near Mombasa, Kenya, into a low-Earth, nearly equatorial orbit. It was also known as Explorer 53, as part of NASA's Explorer program.
Hitomi, also known as ASTRO-H and New X-ray Telescope (NeXT), was an X-ray astronomy satellite commissioned by the Japan Aerospace Exploration Agency (JAXA) for studying extremely energetic processes in the Universe. The space observatory was designed to extend the research conducted by the Advanced Satellite for Cosmology and Astrophysics (ASCA) by investigating the hard X-ray band above 10 keV. The satellite was originally called New X-ray Telescope; at the time of launch it was called ASTRO-H. After it was placed in orbit and its solar panels deployed, it was renamed Hitomi. The spacecraft was launched on 17 February 2016 and contact was lost on 26 March 2016, due to multiple incidents with the attitude control system leading to an uncontrolled spin rate and breakup of structurally weak elements.
The history of gamma-ray began with the serendipitous detection of a gamma-ray burst (GRB) on July 2, 1967, by the U.S. Vela satellites. After these satellites detected fifteen other GRBs, Ray Klebesadel of the Los Alamos National Laboratory published the first paper on the subject, Observations of Gamma-Ray Bursts of Cosmic Origin. As more and more research was done on these mysterious events, hundreds of models were developed in an attempt to explain their origins.
Gamma-ray astronomy is a subfield of astronomy where scientists observe and study celestial objects and phenomena in outer space which emit cosmic electromagnetic radiation in the form of gamma rays, i.e. photons with the highest energies at the very shortest wavelengths. Radiation below 100 keV is classified as X-rays and is the subject of X-ray astronomy.
X-ray emission occurs from many celestial objects. These emissions can have a pattern, occur intermittently, or as a transient astronomical event. In X-ray astronomy many sources have been discovered by placing an X-ray detector above the Earth's atmosphere. Often, the first X-ray source discovered in many constellations is an X-ray transient. These objects show changing levels of X-ray emission. NRL astronomer Dr. Joseph Lazio stated: " ... the sky is known to be full of transient objects emitting at X- and gamma-ray wavelengths, ...". There are a growing number of recurrent X-ray transients. In the sense of traveling as a transient, the only stellar X-ray source that does not belong to a constellation is the Sun. As seen from Earth, the Sun moves from west to east along the ecliptic, passing over the course of one year through the twelve constellations of the Zodiac, and Ophiuchus.
The history of X-ray astronomy begins in the 1920s, with interest in short wave communications for the U.S. Navy. This was soon followed by extensive study of the earth's ionosphere. By 1927, interest in the detection of X-ray and ultraviolet (UV) radiation at high altitudes inspired researchers to launch Goddard's rockets into the upper atmosphere to support theoretical studies and data gathering. The first successful rocket flight equipped with instrumentation able to detect solar ultraviolet radiation occurred in 1946. X-ray solar studies began in 1949. By 1973 a solar instrument package orbited on Skylab providing significant solar data.
IRS-P3 was a remote sensing satellite launched by ISRO on board of Polar Satellite Launch Vehicle (PSLV) launch vehicle for remote sensing of Earth's natural resources. It also hosted a scientific instrument, the Indian X-ray Astronomy Experiment (IXAE), for the study of X-ray astronomy. The IRS-P3 satellite contained an X-ray astronomy instrument, a C-band transponder and two remote sensing instruments.
ULTRASAT is a space telescope in a smallsat format with a large field of view, 210 square degrees, that will detect and monitor transient astronomical events in the near-ultraviolet (220–280 nm) spectral region. ULTRASAT will observe a large patch of sky, alternating every six months between the southern and northern hemisphere. The satellite will be launched into geosynchronous orbit in early 2026. All ULTRASAT data will be transmitted to the ground in real time. Upon detection of a transient event, ULTRASAT will provide alerts within 20 minutes to other ground-based and space telescopes to be directed to the source for further observation of the event in other wavelength bands.
The X-ray Polarimeter Satellite (XPoSat) is an Indian Space Research Organisation (ISRO) manufactured space observatory to study polarisation of cosmic X-rays. It was launched on 1 January 2024 on a PSLV rocket, and it has an expected operational lifespan of at least five years.
