X-ray telescopes operating principle. Physical encyclopedic dictionary - X-ray telescope. Gamma telescopes

An X-ray telescope is a telescope designed to observe distant objects in the X-ray spectrum. To operate such telescopes typically require them to be raised above the Earth's atmosphere, which is opaque to X-rays. Therefore, telescopes are placed on high-altitude rockets or satellites.

Optical design

Due to their high energy, X-ray quanta are practically not refracted in matter (hence, it is difficult to make lenses) and are not reflected at any angle of incidence except the shallowest (about 90 degrees).

The limited capabilities of X-ray optics result in a narrower field of view compared to telescopes operating in the UV and visible light ranges.

Story

The invention of the first telescope is often attributed to Hans Lipperschlei of Holland, 1570-1619, but he was almost certainly not the discoverer. Most likely, his merit is that he was the first to make the new telescope device popular and in demand. It was also he who applied for a patent in 1608 for a pair of lenses placed in a tube. He called the device a spyglass. However, his patent was rejected because his device seemed too simple.

Long before him, Thomas Digges, an astronomer, tried to magnify stars in 1450 using a convex lens and a concave mirror. However, he did not have the patience to finalize the device, and the half-invention was soon conveniently forgotten. Today Digges is remembered for his description of the heliocentric system.

By the end of 1609, small telescopes, thanks to Lipperschlei, became common throughout France and Italy. In August 1609, Thomas Harriot refined and improved the invention, allowing astronomers to view craters and mountains on the Moon.

The big breakthrough came when Italian mathematician Galileo Galilei learned of a Dutchman's attempt to patent a lens tube. Inspired by the discovery, Halley decided to make such a device for himself. In August 1609, it was Galileo who made the world's first full-fledged telescope. At first, it was just a spotting scope - a combination of spectacle lenses, today it would be called a refractor. Before Galileo, most likely, few people thought of using this entertainment tube for the benefit of astronomy. Thanks to the device, Galileo himself discovered mountains and craters on the Moon, proved the sphericity of the Moon, discovered four satellites of Jupiter, the rings of Saturn and made many other useful discoveries.

To today's person, the Galileo telescope will not seem special; any ten-year-old child could easily build a much better instrument using modern lenses. But the Galileo telescope was the only real working telescope of the day with 20x magnification, but with a small field of view, a slightly blurry image and other shortcomings. It was Galileo who opened the age of the refractor in astronomy - the 17th century.

Time and the development of science made it possible to create more powerful telescopes that made it possible to see much more. Astronomers began to use lenses with longer focal lengths. The telescopes themselves turned into large, heavy pipes in size and, of course, were not convenient to use. Then tripods were invented for them. Telescopes were gradually improved and refined. However, its maximum diameter did not exceed several centimeters - it was not possible to produce large lenses.

By 1656, Christian Huyens made a telescope that magnified observed objects 100 times; its size was more than 7 meters, with an aperture of about 150 mm. This telescope is already considered to be at the level of today's amateur telescopes for beginners. By the 1670s, a 45-meter telescope had already been built, which further magnified objects and provided a wider angle of view.

But even ordinary wind could serve as an obstacle to obtaining a clear and high-quality image. The telescope began to grow in length. The discoverers, trying to get the most out of this device, relied on the optical law they discovered - a decrease in the chromatic aberration of a lens occurs with an increase in its focal length. To eliminate chromatic interference, researchers made telescopes of incredible lengths. These pipes, which were then called telescopes, reached 70 meters in length and caused a lot of inconvenience in working with them and setting them up. The shortcomings of refractors forced great minds to look for solutions to improve telescopes. The answer and a new method were found: collecting and focusing the rays was done using a concave mirror. The refractor was reborn into a reflector, completely freed from chromaticism.

This merit belongs entirely to Isaac Newton, it was he who was able to give new life to telescopes with the help of a mirror. His first reflector had a diameter of only four centimeters. And he made the first mirror for a telescope with a diameter of 30 mm from an alloy of copper, tin and arsenic in 1704. The image became clear. By the way, his first telescope is still carefully preserved in the Astronomical Museum in London.

But for a long time, opticians could not make full-fledged mirrors for reflectors. The year of birth of a new type of telescope is considered to be 1720, when the British built the first functional reflector with a diameter of 15 centimeters. It was a breakthrough. In Europe, there is a demand for portable, almost compact telescopes two meters long. They began to forget about the 40-meter refractor tubes.

The two-mirror system in the telescope was proposed by the Frenchman Cassegrain. Cassegrain was unable to fully implement his idea due to the lack of technical ability to invent the necessary mirrors, but today his drawings have been implemented. It was the Newtonian and Cassegrain telescopes that are considered the first “modern” telescopes, invented at the end of the 19th century. By the way, the Hubble Space Telescope works exactly on the principle of the Cassegrain telescope. And Newton's fundamental principle using a single concave mirror has been used at the Special Astrophysical Observatory in Russia since 1974. The heyday of refractor astronomy occurred in the 19th century, when the diameter of achromatic lenses gradually increased. If in 1824 the diameter was still 24 centimeters, then in 1866 its size doubled, in 1885 the diameter became 76 centimeters (Pulkovo Observatory in Russia), and by 1897 the Ierka refractor was invented. It can be calculated that over 75 years the lens has increased at the rate of one centimeter per year.

By the end of the 18th century, compact, convenient telescopes came to replace bulky reflectors. Metal mirrors also turned out to be not very practical - they are expensive to produce and also fade over time. By 1758, with the invention of two new types of glass: light - crown and heavy - flint, it became possible to create two-lens lenses. This was successfully taken advantage of by the scientist J. Dollond, who made a two-lens lens, later called the Dollond lens.

After the invention of achromatic lenses, the victory of the refractor was absolute; all that remained was to improve lens telescopes. They forgot about concave mirrors. They were brought back to life by the hands of amateur astronomers. William Herschel, English musician who discovered the planet Uranus in 1781. His discovery has not been equal in astronomy since ancient times. Moreover, Uranus was discovered using a small homemade reflector. The success prompted Herschel to begin making larger reflectors. Herschel himself fused mirrors from copper and tin in his workshop. The main work of his life was a large telescope with a mirror with a diameter of 122 cm. This is the diameter of his largest telescope. The discoveries were not long in coming; thanks to this telescope, Herschel discovered the sixth and seventh satellites of the planet Saturn. Another, no less famous, amateur astronomer, English landowner Lord Ross, invented a reflector with a mirror with a diameter of 182 centimeters. Thanks to the telescope, he discovered a number of unknown spiral nebulae. The Herschel and Ross telescopes had many disadvantages. Mirror metal lenses turned out to be too heavy, reflected only a small part of the light falling on them and became dim. A new perfect material for mirrors was required. This material turned out to be glass. French physicist Leon Foucault tried to insert a mirror made of silvered glass into a reflector in 1856. And the experience was a success. Already in the 90s, an amateur astronomer from England built a reflector for photographic observations with a glass mirror 152 centimeters in diameter. Another breakthrough in telescope construction was obvious.

This breakthrough could not have happened without the participation of Russian scientists. I'M IN. Bruce became famous for developing special metal mirrors for telescopes. Lomonosov and Herschel, independently of each other, invented a completely new telescope design in which the primary mirror tilts without a secondary one, thereby reducing light loss.

The German optician Fraunhofer put the production and quality of lenses on the conveyor belt. And today at the Tartu Observatory there is a telescope with a intact, working Fraunhofer lens. But the refractors of the German optician were also not without a flaw - chromatism.

It was only towards the end of the 19th century that a new method for producing lenses was invented. Glass surfaces began to be treated with a silver film, which was applied to a glass mirror by exposing grape sugar to silver nitrate salts. These fundamentally new lenses reflected up to 95% of the light, in contrast to the old bronze lenses, which reflected only 60% of the light. L. Foucault created reflectors with parabolic mirrors, changing the shape of the surface of the mirrors. In the late 19th century, Crossley, an amateur astronomer, turned his attention to aluminum mirrors. The concave glass parabolic mirror with a diameter of 91 cm that he purchased was immediately inserted into the telescope. Today, telescopes with such huge mirrors are installed in modern observatories. While the growth of the refractor slowed, development of the reflecting telescope gained momentum. From 1908 to 1935, various observatories around the world built more than one and a half dozen reflectors with a lens larger than that of Yerk. The largest telescope is installed at the Mount Wilson Observatory, its diameter is 256 centimeters. And even this limit will soon be doubled. An American giant reflector was installed in California; today it is more than fifteen years old.

More than 30 years ago in 1976, USSR scientists built a 6-meter BTA telescope - the Large Azimuthal Telescope. Until the end of the 20th century, the BTA was considered the world's largest telescope. The inventors of the BTA were innovators in original technical solutions, such as a computer-guided alt-azimuth installation. Today, these innovations are used in almost all giant telescopes. At the beginning of the 21st century, the BTA was pushed into the second ten large telescopes in the world. And the gradual degradation of the mirror over time - today its quality has fallen by 30% of its original value - turns it only into a historical monument to science.

The new generation of telescopes includes two large 10-meter twin telescopes KECK I and KECK II for optical infrared observations. They were installed in 1994 and 1996 in the USA. They were collected thanks to the help of the W. Keck Foundation, after which they are named. He provided more than $140,000 for their construction. These telescopes are the size of an eight-story building and weigh more than 300 tons each, but they operate with the highest precision. The operating principle is a main mirror with a diameter of 10 meters, consisting of 36 hexagonal segments, working as one reflective mirror. These telescopes are installed in one of the optimal places on Earth for astronomical observations - in Hawaii, on the slope of the extinct volcano Manua Kea 4,200 m high. By 2002, these two telescopes, located at a distance of 85 m from each other, began to operate in interferometer mode, giving the same angular resolution as an 85 meter telescope. The history of the telescope has come a long way - from Italian glass makers to modern giant satellite telescopes. Modern large observatories have long been computerized. However, amateur telescopes and many devices such as Hubble are still based on the operating principles invented by Galileo.

Ground-based observations in transparency windows are carried out using conventional optical telescopes and special IR telescopes. Special IR telescopes have less intrinsic radiation and are equipped with an oscillating secondary mirror and are installed in high mountain areas. Four special infrared telescopes are installed on the top of the extinct volcano Mauna Kea. (Hawaiian Islands). At an altitude of 4200 m above sea level: French with a mirror diameter D = 375 cm; English, D = 360 cm; telescope of the US National Astronautics and Space Administration - NASA, D = 300 cm; telescope of the University of Hawaii, D = 224 cm.

X-ray (ri) telescopes

RI detectors:

In 1978, an oblique incidence X-ray telescope with a resolution of 2ʺ was launched on the HEAO-B satellite (Einstein Observatory) in the USA. Several thousand X-ray sources received (until 1986)

Gamma telescopes.

In area soft gamma radiation(GI), used scintillation telescope.

In area hard GI– telescope with track detector. The trajectory of each charged particle formed during absorption - photons - is recorded. The detector can be spark chamber and drift chamber. In a spark chamber, a spark breakdown develops along the trajectory of a particle that ionizes atoms. A chain of sparks reproduces the trajectory of a particle. In a drift chamber, the position of the trajectory is determined by the time of electron drift from the particle track to neighboring electrodes.

In area intermediate GI – the efficiency of scintillation and track detectors decreases.

In area ultra-high GI– by recording Cherenkov radiation, which is generated by electrons and positrons of a shower of particles accompanying the absorption of an ultra-high energy photon in the atmosphere.

Note: Cherenkov - Vavilov radiation(1934) – emission of electromagnetic waves by an electric charge carrier moving at speed , exceeding the phase " U» speed of electromagnetic waves in matter. . The Cherenkov–Vavilov effect occurs if n> 1;

Neutrino telescopes

In the USSR: in the Caucasus at the Baksan Neutrino Observatory; in a salt mine in Artemovsk at a depth of 600 m of water equivalent; in Italy, USA.

Registration principle: liquid scintillation detectors - registers the resulting positrons, the movement of which is accompanied by a flash.

Major observatories and largest telescopes in the world

OBSERVATORY(from Latin observator - observer), a specialized scientific institution equipped to conduct astronomical, physical, meteorological, etc. research. There are currently more than 500 observatories in the world, most of them in the northern hemisphere of the Earth.

Table 2. Main observatories of the world.

Observatory	Brief information
Abastumani Astrophysical Observatory	Founded in 1932 on Mount Kanobili (1650m) near Abastumani in Georgia. In 1937, observations began on the first Soviet 33-cm reflector (observations were carried out on it since 1932 in the old tower) with the first Soviet photometer. The first director was Evgeniy Kirillovich Kharadze. In the early 50s, a 70-cm meniscus telescope and other instruments were installed. In 1980, the observatory's largest 125-cm fully automated reflecting telescope was installed.
Algonquin Observatory	Astronomical radio observatory in Ontario (Canada). The main instrument is a 46-meter telescope with a fully steerable antenna.
Allegheny Observatory	Research Observatory of the University of Pittsburgh in Pennsylvania (USA). The modern observatory buildings were built in 1912, but work on its creation began in 1858 by several Pittsburgh businessmen. Encouraged by the sight of Comet Donati that year, they formed the Allegheny Telescope Association and purchased a 33-centimeter refractor. In 1867, both the telescope and the observatory were transferred to Western University of Pennsylvania, the predecessor of the University of Pittsburgh. The first full-time director was Samuel Pierpont Langley, who was succeeded by James E. Keeler, one of the founders of the Astrophysical Journal and later director of the Lick Observatory. In 1912, three telescopes were installed in the observatory building. The very first 33 cm refractor is now used primarily for educational purposes and for testing. The other two (76 cm Tau Refractor and 79 cm Keeler Memorial Refractor) continue to be used for scientific research.
Anglo-Australian Observatory (AAO)	The observatory, co-located with Siding Spring Observatory (New South Wales, Australia), is jointly funded by the Australian and UK governments. The observatory is managed by the Anglo-Australian Telescope Directorate (DAAT), which was formed in the early 1970s when the 3.9-metre Anglo-Australian Telescope was built with an equatorial installation. Routine observations began in 1975. It was the first computer-controlled telescope. Together with this universal telescope, many different instruments are used, which led to important scientific discoveries and made it possible to obtain spectacular photographs of the southern sky. In 1988, DAAT received at its disposal the English 1.2-meter Schmidt telescope (put into operation in 1973 and during for some time under the jurisdiction of the Royal Edinburgh Observatory), which began to be used by many astronomers. Popular Schmidt telescopes produce high-quality large-format photographs (6.4° × 6.4°). Most of the telescope's operating time is devoted to long-term sky surveys.
Aresib Observatory	Radio Astronomy Observatory in Puerto Rico. The pit with a diameter of 305 m fits well into the natural fold of the hilly area south of Arecibo. The telescope, whose construction was completed in 1963, is operated by the National Ionospheric and Astronomy Center at Cornell University (USA). The reflective surface cannot move, but radio sources can be tracked by moving the focal receiver along a special support structure. In 1997, this telescope was modernized. The telescope's footprint is larger than all other radio telescopes in the world combined. With such a large surface area, the telescope can detect weaker signals than any other radio telescope
Dominion Astrophysical Observatory	Observatory of the National Research Council of the Canadian Center for Optical Astronomy, located near Victoria (British Columbia). It is part of the Institute of Astrophysics named after. Herzberg. It was founded by J.S. Plaskett, and in 1918 a 1.85-meter telescope began operating there, to which a 1.2-meter telescope was added in 1962. In 1988, the Canadian Astronomical Data Center was created there.
United States Naval Observatory	The observatory owns astrographic telescopes located in Mount Anderson, near Flagstaff, Arizona, in Black Birch, New Zealand, and in Washington. The observatory was founded in 1830 and received its current name in 1842. For fifty years it was located in what is now the Lincoln Memorial. In 1893, the observatory was moved to its current location (next to the official residence of the Vice President). The largest telescope located here is a 66-centimeter refractor, operating since 1873, with the help of which Asaph Hall discovered the moons of Mars Phobos and Deimos in 1877. Other instruments include a 30cm Elvan Clark Refractor, two 61cm reflectors and a 15cm meridian circle. The largest telescope owned by the observatory is the 1.5-meter Astrometric Reflector in Flagstaff. Using this instrument, James Christie discovered Pluto's moon Charon in 1978. At its Arizona site, the observatory has an optical interferometer, the Experimental Marine Optical Interferometer, which was the largest telescope of its type when it went into operation in 1995. The United States Naval Observatory houses one of the richest astronomical libraries in the world. The Observatory compiles and publishes astronomical yearbooks for the navy, aviation and the international directory "Visible Places of Fundamental Stars".
High Altitude Observatory	Solar Physical Observatory and Research Institute in Colorado, USA. Founded in 1940 under the auspices of the Harvard College Observatory and now a branch of the National Center for Atmospheric Research. Equipment for studying the Sun is also located in other ground-based centers and on satellites.
Main Astronomical Observatory of the Academy of Sciences of Ukraine	Founded in 1944 (12 km south of Kyiv, h=180m above sea level). Opened in 1949 A consolidated catalog of coordinates of several thousand reference points on the visible surface of the Moon has been compiled. It has an observational astronomical base in the Elbrus region on Terskol peak (h=3100m) with 40-cm, 80-cm and 2-meter telescopes. Main instruments: 19 cm large vertical circle, dual wide-angle 12 cm astrograph, 70 cm reflecting telescope (1959), 44 cm solar horizontal telescope (1965) and other instruments. Since 1985, the Observatory has been publishing the scientific journal “Kinematics and Physics of Celestial Bodies”, and since 1953 it has been publishing “Izvestia of the State Administrative Okrug of the Academy of Sciences of the Ukrainian SSR”. The first director was Alexander Yakovlevich Orlov (1880-1954) in 1944-1948 and 1950-1951.
European Southern Observatory (ESO)	The European Research Organization was founded in 1962. ESO members are eight countries - Belgium, Denmark, France, Germany, Italy, the Netherlands, Sweden and Switzerland. The organization's headquarters are in Garching near Munich in Germany, and its observatory is in La Silla in Chile.
Crimean Astrophysical Observatory (CrAO)	Ukrainian observatory located in Crimea near Simeiz. Founded in 1908 near Simeiz as a branch of the Pulkovo Observatory, but completely destroyed with the outbreak of war in 1941. By Decree of the USSR Government of June 30, 1945, it was transformed into an independent scientific institution - the Crimean Astrophysical Observatory of the USSR Academy of Sciences. In 1946, construction of the observatory began on a new, more convenient location in the village of Mangush (Nauchny village, 12 km from Bakhchisarai). The first large instrument was an astrograph with a 40 cm lens, installed in the summer of 1946 in Simeizm, where observations continued. The first director was G.A. Shine (1892-1956), then in 1952 he was replaced by A. B. Severny (1913-1987). Commissioned in 1950. Here in 1961 the largest telescope in Europe with a 264 cm mirror, F = 10 m was installed, and in 1981 a 125 cm telescope for photographic observations was installed. One of the best tower solar telescopes in the world was also installed here in 1954, and a powerful 22-meter millimeter-wave radio telescope was installed in 1966.
National Radio Astronomy Observatory (NRAO)	An association of organizations conducting radio astronomy work in the United States under the auspices of a private consortium of universities, Associated Universities Inc. The association receives funding under a consortium agreement with the US National Science Foundation. The telescopes used by NRAO are located at three different locations. This is a "Very Large Array" (VLA - Abbr. Very Large Array. A radio telescope consisting of 27 antennas, each 25 m in diameter, operating using the method of aperture synthesis based on the earth's rotation. Located in Socorro, New Mexico, this telescope is the largest world's largest aperture synthesis telescope. This array of antennas is arranged in a "Y" shape, each arm of which is 21 km long. The antennas are electronically interconnected, resulting in the array operating as a single system of 351 radio interferometers that conduct simultaneous observations. The maximum available resolution of a radio telescope at a wavelength of 1.3 cm is 0.05 arcseconds. However, in practice, most observations are made at a wavelength of 6 cm with a resolution of one arcsecond, since this greatly reduces the time required to construct radio maps) , the millimeter-wave telescope at Kitt Peak, as well as the 42-meter antenna and interferometer of the Green Bank Telescope, located in Green Bank (West Virginia). Built in 1962, the 92-meter dish antenna was completely out of order by 1988. The construction of its “successor” - the 100-meter Telescope was completed in 1998. This is the world's largest parabolic antenna with fully automated control. The 43-meter parabolic antenna, launched in 1965, is still the world's largest equatorial telescope. There is also a radio interferometer consisting of three 26-meter parabolic antennas, two of which can move along a 1.6 km long track). NRAO is headquartered in Charlottesville, Virginia.
Pulkovo Observatory	The observatory near St. Petersburg in Russia, organized back in 1718 as the St. Petersburg Observatory and the St. Petersburg Academy of Sciences, had the only observatory built in the city center in 1760. It has been in Pulkovo since 1835. On August 19, 1839, the Pulkovo Observatory came into operation at the Pulkovo Heights (75m above sea level). Construction began on June 21, 1835, 70 km south of St. Petersburg according to the design of A.P. Bryullov (1798-1877), developed in 1834. On July 3, 1835, the building of the Main Observatory was laid. 07/02/1838 - establishment of the Pulkovo Observatory at the Academy of Sciences. The history of the observatory is connected, in particular, with the history of the Struve family, six members of which became famous astronomers. Vasily Yakovlevich Struve was the director of the observatory from 1839 to 1862, and his son Otto Vasilyevich Struve was from 1862 to 1889, who built an astrophysical laboratory in 1886, and in 1890-1895 F.A. Bredikhin strengthened astrophysical research at the observatory and equipped it with appropriate instruments. The observatory became the “astronomical capital of the world” for creating the most accurate star catalogs of fundamental stars: 1865, 1885, 1905 and 1930, accurately measuring the position of 8700 pairs of double stars, and determining the main astronomical constants. From the very beginning, the observatory contained, at that time, the world's largest 38 cm (15 inch) refracting telescope, made by J. Flaunhofer's students - Merz and Mahler, and in 1888, the world's largest 30 inch (76 cm) refracting telescope, made by American optician A. Clark. It was the Pulkovo Observatory that was one of the first to use photography in astrometry. In 1920, an exact time service was organized, and in 1924, an international time service committee was established at the observatory. In 1932, the Sun Service was organized. The buildings of that time were destroyed during the Second World War, but were subsequently restored to their original form in 1954. The opening took place on May 21, 1954. The observatory was significantly expanded and equipped with the latest instruments. A 65cm refractor telescope (F=10.4m), the largest in the USSR, was installed. Observational bases in the Caucasus and Pamirs, Kislovodsk mountain astronomical station, in Blagoveshchensk (latitudinal laboratory on the Amur), expedition in Bolivia (since 1983). Research: astrometry, radio astronomy, astronomical instrumentation, extra-atmospheric astronomy, etc. The Observatory publishes “Proceedings” (since 1893), “Izvestia” (since 1907), “Solar Data” (since 1954) and others.

Figure 46. Pulkovo Observatory

X-ray telescope(eng. X-ray telescope, XRT) - a telescope designed for observing distant objects in the X-ray spectrum. To operate such telescopes typically require them to be raised above the Earth's atmosphere, which is opaque to X-rays. Therefore, telescopes are placed on high-altitude rockets or on artificial Earth satellites.

Optical design

Due to their high energy, X-ray quanta are practically not refracted in matter (hence, it is difficult to make lenses) and are not reflected at any angle of incidence except the most flat (88-89 degrees to the normal).

X-ray telescopes can use several methods to focus beams. The most commonly used telescopes are Voltaire telescopes (with grazing incidence mirrors), aperture coding, and modulation (oscillating) collimators. The limited capabilities of X-ray optics result in a narrower field of view compared to telescopes operating in the UV and visible light ranges.

Mirrors

The use of X-ray mirrors for extrasolar astronomy requires simultaneously:

the ability to determine the initial direction of the X-ray photon using two coordinates and
sufficient detection efficiency.

Mirrors can be made of ceramic or metal foil. The most commonly used materials for grazing incidence X-ray mirrors are gold and iridium. The critical reflection angle strongly depends on the photon energy. For gold and an energy of 1 keV, the critical angle is 3.72°.

Aperture coding

Many X-ray telescopes use aperture coding to produce images. In this technology, a mask in the form of a lattice of alternating transparent and opaque elements in a special way is installed in front of the matrix detector (for example, a square mask in the form of a Hadamard matrix). This focusing and imaging element weighs less than other X-ray optics (hence why it is often used on satellites), but requires more post-processing to produce an image.

Telescopes

Exosat

Exosat carries two low-energy Wolter I X-ray telescopes with imaging capabilities. Focal plane can be installed

Hard X-ray telescopes

See OSO 7 OSO 7)

On board Seventh Orbital Solar Observatory(OSO 7) was a hard-range X-ray telescope. Characteristics: energy range 7 - 550 keV, field of view 6.5° effective area ~64 cm²

Telescope FILIN

The FILIN telescope installed at the Salyut-4 station consisted of three gas proportional counters with a total working area of 450 cm², energy range 2-10 keV, and one with a working area of 37 cm², energy range 0.2-2 keV. The field of view was limited by a slit collimator with a half-width of 3° x 10°. The instruments included photocells mounted outside the station along with sensors. The measuring modules and power supply were located inside the station.

Calibration of sensors against ground sources was carried out in parallel with flight operations in three modes: inertial orientation, orbital orientation and survey. Data were collected in four energy ranges: 2-3.1 keV, 3.1-5.9 keV, 5.9-9.6 keV and 2-9.6 keV on large detectors. The small sensor had limiters set at levels of 0.2, 0.55, 0.95 keV.

Telescope SIGMA

The SIGMA hard X-ray and low-energy gamma-ray telescope covers the range 35-1300 keV with an effective area of 800 cm² and a maximum sensitivity field of view of ~5° × 5°. Maximum angular resolution 15 arc minutes Energy resolution - 8% at 511 keV. By combining an encoding aperture and position-sensitive sensors based on Anger camera principles, the telescope is capable of imaging.

X-ray telescope ART-P

Focusing X-ray telescope

The Broadband X-ray Telescope (BBXRT) was launched into orbit by Space Shuttle Columbia (STS-35) as part of the ASTRO-1 payload. BBXRT was the first focusing telescope operating in the wide energy range of 0.3-12 keV with an average energy resolution of 90 eV at 1 keV and 150 eV at 6 keV. Two co-directional telescopes with a segmented solid-state Si(Li) spectrometer each (detectors A and B), consisting of five pixels. The overall field of view is 17.4' in diameter, the field of view of the central pixel is 4' in diameter. Total area: 765 cm² at 1.5 keV, 300 cm² at 7 keV.

HEAO-2

The world's first orbital observatory with mirrors with grazing reflection of X-ray photons. Launched in 1978. The effective area is about 400 sq.cm at an energy of 0.25 keV and about 30 sq.cm at an energy of 4 keV.

Chandra

XMM-Newton

Spectr-RG

XRT on Swift spacecraft (MIDEX mission)

The telescope tube with a diameter of 508 mm is made of two sections of graphite fibers and cyanide esters. The outer layer of graphite fibers is designed to reduce the longitudinal coefficient of thermal expansion, while the internal complex tube is lined on the inside with an aluminum foil vapor barrier to prevent water vapor or epoxy contaminants from entering the telescope. The XRT contains a front part, surrounded by mirrors and holding the shutter assembly and celestial navigation unit, and a rear part, holding the focal plane camera and internal optical screen.

The mirror module contains 12 nested Wolter I grazing incidence mirrors mounted on the front and rear crosspieces. Passively heated mirrors are gold-plated nickel shells with a length of 600 mm and a diameter of 191 to 300 mm.

The X-ray imager has an effective area of 120 cm2 at 1.15 keV, a field of view of 23.6 x 23.6 arcminutes and an angular resolution (θ) of 18 arcseconds at half-power diameter (HPD). The sensitivity of the detector is 2⋅10 −14 erg cm −2 s −1 10 4 seconds. Point spread function (PSF) of the mirror - 15 arc seconds HPD at focus (1.5 keV). The mirror is slightly defocused for a more uniform PSF across the entire field of view, resulting in an instrument PSF of 18 arc seconds.

Normal incidence X-ray telescope

History of X-ray telescopes

The first X-ray telescope was used to observe the Sun. The first image of the Sun in the X-ray spectrum was obtained in 1963, using a telescope mounted on a rocket.

Notes

X-ray Telescopes(English) . NASA (2013). Retrieved August 10, 2018.
Hoff H. A. Exosat - the new extrasolar x-ray observatory (undefined) // J Brit Interplan Soc (Space Chronicle).. - 1983. - August (vol. 36, no. 8). - pp. 363-367.

x-ray telescope

device for studying time and spectrum. St. in the sources of space. x-ray radiation, as well as to determine the coordinates of these sources and construct their images.

Existing radio waves operate in the energy range  X-ray photons. radiation from 0.1 to hundreds of keV, i.e. in the wavelength range from 10 nm to hundredths of nm. To carry out astronomical observations in this region of wavelengths, X-rays are raised beyond the Earth's atmosphere on rockets or satellites, since X-rays. radiation is strongly absorbed by the atmosphere. Radiation with >20 keV can be observed from altitudes of ~30 km from balloons.

RT allows: 1) to register X-rays with high efficiency. fo-

tones; 2) separate events corresponding to the impact of photons of the required energy range from signals caused by the influence of charges. h-ts and gamma photons; 3) determine the direction of arrival of the x-rays. radiation.

In RT for the range 0.1-30 keV, the photon detector is proportional counter, filled with a gas mixture (Ar+CH4, Ar+CO2 or Xe+CO2). X-ray absorption photon by a gas atom is accompanied by the emission of a photoelectron (see. photoelectron emission), Auger electrons

Rice. 1. a—X-ray diagram. telescope with a slit collimator; b — telescope operation in scanning mode.

(cm. Auger effect) and fluorescent photons (see Fluorescence). The photoelectron and Auger electron quickly lose their energy to ionize the gas; fluorescent photons can also be quickly absorbed by the gas due to photoelectric effect. In this case, the total number of electron-ion pairs formed is proportional. energy x-ray photon. Thus, the X-ray energy is restored by the current pulse in the anode circuit. photon.

Under normal conditions, R. t. is irradiated by powerful flows of charges. h-ts and gamma photons decomp. energies, which the X-ray detector records together with X-rays. photons from the radiation source under study. To highlight x-rays. photons from the general background, the anti-coincidence method is used (see. Coincidence method). Arrival x-ray photons are also recorded by the shape of the electrical impulse they create. current, since the charger. h-ts give signals that are longer in time than those caused by x-rays. photons.

To determine the direction of the x-ray. The source is a device consisting of a slit collimator and a star sensor rigidly attached to it on the same frame. A collimator (set of plates) limits the X-ray field of view and transmits x-rays. photons traveling only in a small solid angle (~10-15 square degrees). X-ray a photon passing the collimator (Fig. 1,a) is recorded at the top. counter volume. The resulting current pulse is up in the circuit. anode

passes through the anti-coincidence circuit (since there is no prohibiting signal from the lower anode) and is fed to the analyzer to determine the time and energy. characteristic of a photon. The information is then transmitted via telemetry to Earth. At the same time, information from the star sensor about the brightest stars that fall into its field of view is transmitted. This information makes it possible to establish the position of the RT axes in the production at the moment of photon arrival.

When the RT operates in scanning mode, the direction to the source is determined as the position of the RT, at which the counting speed reaches its maximum. Angle The resolution of RT with a slit collimator or a similar cellular collimator is several tens of arc minutes.

Significantly better angle. resolution (~ several tens of seconds) have RT with modulation. collimators (Fig. 2, A). Modular the collimator consists of two (or more) one-dimensional wire grids installed between the detector and the slit collimator, for which the latter is raised above the detector to a height of ~1 m and observations are carried out in either scanning mode (Fig. 1b) or rotation relative to the axis, perpendicular to the mesh plane. The wires in each collimator grid are installed parallel to each other at a distance equal to the diameter of the wire. Therefore, when the source moves across R.’s field of view, shadows from the top. wires slide along the bottom. grid, falling either on the wires, and then the counting rate is maximum, or between them, and then it is minimal (background).

Angle distribution of R.t. counting rate with modulation. collimator (click response function) is shown in Fig. 2, b. For n-grid modulation. collimator angle between adjacent maxima 0=2 n-1 r, where r= d/l- ang. resolution of R. t. In most cases, R. t. with modulation. collimators provide accurate localization of x-rays. sources, sufficient for their identification with celestial objects emitting in other electromagnetic ranges. waves

With modular The encoder technique begins to compete with collimators. aperture, allowing to obtain r<1". В Р. т. с кодиров. апертурой поле зрения перекрывается экраном, обладающим неоднородным пропусканием по всей площади. Детектор излучения в таком Р. т. позиционно-чувствительный, т. е. кроме энергии рентг. фотона измеряют и координаты точки, где он был зарегистрирован. При таком экране точечный источник излучения, находящийся на бесконечности, даёт распределение скорости счёта по поверхности детектора, соответствующее функции пропускания экрана.

Rice. 2. a - X-ray device. telescope with modulation collimator; b - ang. counting rate distribution.

X-ray source position. radiation in the field of view of the RT is determined by the position of the maximum correlation. functions between the obtained count rate distribution over the detector surface and the screen transmittance function.

In the energy range >15 keV, crystals are used as RT detectors. scintillators NaI (Tl) (see. Scintillation counter); to suppress charging background. h-ts of high energies and gamma photons are installed on anti-coincidence with the first crist. scintillators CsI(Tl). To limit the field of view in such radios, active collimators are used—cylinders of scintillators connected to anti-coincidence with NaI(Tl) scintillators.

In the energy range from 0.1 to several. keV radiation technologies are the most effective, in which radiation incident on a focusing mirror is focused at small angles (Fig. 3). The sensitivity of such a radiation t. is ~10 3 times higher than the radiation t. of other designs due to its ability to collect radiation. area and directed to a small detector, which significantly increases the signal-to-noise ratio. X-ray t., built according to this scheme, gives a two-dimensional image of the x-ray source.

Rice. 3. X-ray focusing diagram. telescope.

radiation similar to conventional optical. telescope. To construct an image in a focusing RT, position-sensitive proportions are used as detectors. cameras, microchannel detectors, and charge-coupled devices (CCDs). Angle the resolution in the first case is determined by ch. arr. spaces. camera resolution is ~1", microchannel detectors and CCDs give 1-2" (for beams close to the axis). With spectrometric In research, PP detectors and Bragg crystals are used. spectrometers and diffraction position-sensitive gratings detectors. Space X-ray sources radiations are very diverse. X-ray radiation from the Sun was discovered in 1948 in the USA from a rocket that lifted Geiger counters to the top layers of the atmosphere. In 1962, the first X-ray source was discovered by the group of R. Giacconi (USA), also from a rocket. radiation outside the Solar System - “Scorpio X-1”, as well as diffuse X-ray background, apparently extragalactic. origin. By 1966, as a result of experiments on rockets, approx. 30 discrete x-rays. sources. With the launch into orbit of a series of specials. Satellite satellites (“UHURU”, “Ariel”, “SAS-3”, “Vela”, “Copernicus”, “HEAO”, etc.) with R. t. dec. Hundreds of roentgens have been discovered. sources (galactic and extragalactic, extended and compact, stationary and variable). Mn. of these sources have not yet been identified with sources manifesting themselves in optical and other electromagnetic ranges radiation. Among the identified galaxies. objects: close binary star systems, one of the components of which is X-ray. pulsar; single pulsars(Crab, Vela); leftovers supernovae(extended sources); temporary (transient) sources that sharply increase the luminosity in x-rays. range and again fading over a period of time ranging from several. minutes to several minutes months; so-called B a r s t e r s are powerful flashing X-ray sources. radiation with a characteristic flash time of the order of several. seconds To identified extragalactic. objects include nearby galaxies (Magellan clouds and the Andromeda Nebula), radio galaxies Virgo-A (M87) and Centaurus-A (NGC 5128), quasars (in particular, 3S 273), Seyfert and other galaxies with active nuclei; Galaxy clusters are the most powerful sources of X-rays. radiation in the Universe (in them, hot intergalactic gas with a temperature of 50 million K is responsible for the radiation). The vast majority of space x-ray sources of phenomena objects completely different from those that were known before the beginning of X-rays. astronomy, and above all they are distinguished by their enormous energy release. Luminosity of galactic x-ray sources reaches 10 36 -10 38 erg/s, which is 10 3 -10 5 times higher than the energy release of the Sun over the entire wavelength range. In extragalactic sources, luminosity up to 10 45 erg/s was recorded, which indicates the unusual nature of the radiation mechanisms manifested here. In close binary star systems, for example, as the main. The energy release mechanism considers the flow of matter from one component (giant star) to another (neutron star or black hole)- disk accretion, when a substance falling on a star forms a disk near this star, where the substance, due to friction, heats up and begins to radiate intensely. Among the probable hypotheses for the origin of diffuse X-rays. background, along with the assumption of thermal radiation hot intergalactic gas, the reverse is considered Compton effect e-nov on IR photons emitted by active galaxies, or on photons relict radiation. Observational data from the HEAO-B satellite indicate that a significant contribution (>35%) to diffuse X-rays. the background is provided by distant discrete sources, Ch. arr. quasars.

X-ray astronomy, ed. R. Giacconi, H. Gursky, Dordrecht—Boston, 1974; Shklovsky I.S., Stars: their birth, life and death, 2nd ed., M., 1977; Kaplan S.A., Pikelner S.B., Physics of the interstellar medium, M., 1979.

N. S. Yamburenko.

"Earth and Universe" 1993 No. 5

STAGES OF DEVELOPMENT OF X-RAY ASTRONOMY

The Earth's atmosphere is opaque to X-rays. Therefore, X-ray astronomy was born along with rocket technology: in 1948, with the help of photographic plates raised by a V-2 rocket to an altitude of about 160 km, R. Barnight from the Naval Laboratory (USA) discovered X-ray radiation from the Sun. In 1962, replacing the photographic plate with a Geiger counter, astronomers discovered a second X-ray source, this time beyond the solar system - it was Sco X-1. The naming system adopted in those years was simple: “Sco X-1” means the brightest (1) x-ray (X-ray) source in the constellation Scorpius (Sco). The third object of X-ray astronomy, discovered in 1963, was the famous Crab Nebula in the constellation Taurus (Tau X-1).

In the 1960s, X-ray detectors were mostly carried above the atmosphere on geophysical rockets; their vertical flight lasted only a few minutes, so during this period only about 40 sources were plotted on the X-ray sky maps. But in the 70s, sensitive X-ray detectors began to be placed on artificial Earth satellites, the most famous of which are Uhuru, ANS, Copernicus, OSO-7, SAS-3. This was followed by the launch of large spacecraft - HEAO-1, Einstein, Astron, Granat, Rosat, equipment at the Salyut-4 and -7, Skylab, and Mir stations. Although the work of each of them brought interesting astrophysical information, the most important stages in the development of X-ray astronomy were the launches of the first high-sensitivity X-ray detector, Uhuru, in 1970 and the first X-ray reflecting telescope, Einstein, in 1978 (had high sensitivity and high angular resolution of 2-4"). With their help, X-ray binary stars, X-ray pulsars and flare sources, normal stars with hot coronas, active galactic nuclei and intergalactic gas in galaxy clusters were discovered. In the 80s and early 90s Many powerful instruments were already operating in orbit, but their characteristics remained traditional (Earth and Universe, 1989, No. 5, p. 30.- Ed.).

The next major advance in X-ray astronomy is expected in 1998 with the launch of AXAF's new orbital observatory, the Advanced X-ray Astrophysics Facility.

Back in the 70s, American astronomers conceived the idea of creating four large orbital observatories capable of covering the entire scale of electromagnetic waves, with the exception of radio. In May 1990, HST was launched into orbit - the Hubble Space Telescope, operating in the optical and near ultraviolet ranges (Earth and Universe, 1987, No. 4, p. 49). Then, in April 1991, GRO - Gamma Ray Observatory - was launched. Next in line is the AXAF X-ray observatory, followed by the infrared observatory SIRTF (Space Infrared Telescope Facility).

However, the last two projects are now undergoing significant revision. The fact is that the production of the first observatories was very expensive: HST cost $5.55 billion, and GRO cost $600 million. Moreover, each of the satellites was put into orbit with the help of specially organized expeditions on the Space Shuttle. . Errors in the manufacture of the HST telescope and general economic difficulties forced NASA to reconsider the budget for promising astrophysics projects. First of all, it was decided to abandon the Shuttle or the powerful Titan rocket, which were required to launch heavy observatories. Orbital observatories must become lighter so that they can be launched by cheap, expendable Atlas-type rockets.

For the SIRTF infrared observatory, this means reducing the diameter of the main mirror from 85 to 70 cm, almost halving the size of the satellite, and reducing its minimum lifetime from five to three years. True, recently new, very sensitive detectors of infrared radiation have appeared, which should compensate for the reduction in the area of the telescope mirror. NASA scientists hope that they will be able to launch an infrared observatory before the year 2000.

Even more radical changes are coming to the AXAF project. The observatory was initially conceived as a satellite 17 m long and weighing 15 tons; the wingspan of the solar panels was supposed to be 26 m. Now, instead of one large satellite, it is planned to make two smaller ones: the main one (14 m long and weighing about 6 tons) will house the main X-ray telescope, the second will be equipped with X-ray spectrometers. The launch of the X-ray observatory was originally planned for 1987. Now they say 1998. What do astronomers expect from the AXAF observatory?

IS IT POSSIBLE TO PLAN OPENINGS?

It turns out that it is possible! Especially if you know what you are looking for. This is exactly the situation in X-ray astronomy now: it is well known what the parameters of an X-ray telescope should be in order to use it to make long-awaited discoveries in the field of cosmology and relativistic astrophysics. However, it was not possible to create such a tool for a long time.

There are two fundamentally different types of X-ray detectors: proportional quantum counters with collimators and X-ray telescopes with a focusing system and image detectors 1 . The first of them was used on Uhuru, the second on Einstein.

1 In reality, many more different types of X-ray detectors have been created, but we want to show the fundamental difference between them.

A proportional counter is a modern version of a Geiger counter, i.e. a gas-filled tube with two electrodes - positive and negative. An X-ray quantum, flying into the tube through a window covered with a thin film, ionizes the gas, and the electrodes collect the resulting ions and electrons. By measuring the resulting current pulse, it is possible to determine the energy of the detected quantum: they are approximately proportional to each other (hence the name of the counter). Proportional counters are capable of recording quanta in a wide energy range - from 1 to 30 eV, and have good spectral resolution, i.e. they determine the energy of a quantum with an accuracy of 15-20%. However, the proportional counter itself is similar to a photographic plate without a lens: it registers quanta coming from all directions. If there is a signal, it means that somewhere in front of the counter there is a source of X-ray radiation, but where exactly is unknown.

To determine the direction to the source, shadow collimators are used, which give free access to the counter only to quanta coming from a certain direction, and obscure the counter from all other quanta. Continuing the analogy with a photographic plate, we can say that by placing it at the bottom of a deep well or a long pipe, we are able to fix the direction of bright sources like the Sun: as soon as they are on the axis of our “collimator”, the plate turns black. However, you cannot image an object with such a tool: its angular resolution is low, and its sensitivity is low. After all, it records all quanta passing through this “collimator” - both quanta from the source and the sky background. And in the X-ray range the sky is quite bright. The situation is reminiscent of daytime observation of stars from the surface of the Earth: only bright sources are visible to the naked eye - the Sun, Moon, Venus - and the stars fade in the radiance of the daytime sky. The collimator is helpless here (remember: the stars are not visible during the day from the bottom of a deep well!), but an optical system - a telescope - can help. It creates an image of a piece of the sky and makes it possible to observe the star separately from the background.

An X-ray lens, if constructed, allows the counter to isolate the source from the background. And if you place many small counters at the focus of an X-ray lens, then they, like grains of photographic emulsion, will build a picture of the X-ray sky, and a “colored” picture if these counters correctly perceive the energy of the incident photons.

Unfortunately, creating an X-ray lens is very difficult: hard quanta penetrate deep into the lens material without being refracted or reflected. Only the lowest-energy X-ray quanta, falling very gently onto a well-polished metal surface, are reflected from it according to the laws of geometric optics. Therefore, an X-ray lens, which is a combination of a paraboloid and a hyperboloid of rotation, is very similar to a slightly conical tube. Usually, in order to intercept more quanta, several lenses of different diameters are made, but with the same focal length, and they are strengthened coaxially like a nesting doll. Then all images are added in the focal plane and mutually enhanced. An X-ray quantum detector placed in this plane records their coordinates and transmits them to a computer, which synthesizes the image.

Effective area and spectral range of the main mirror of the AXAF telescope in comparison with the Einstein Space Observatory telescope

A telescope with a mirror diameter of 60 cm was installed at the Einstein Observatory. However, the effective area of the complex mirror strongly depended on the energy of incoming quanta: for soft X-ray quanta with an energy of 0.25 keV it was 400 cm 2 and decreased to 30 cm 2 for quanta with energy 4 keV. And the telescope was generally unsuitable for recording even harder quanta.

This is very sad, since it is hard quanta that carry unique information. Every astronomer knows how important it is to record the spectral line of a chemical element: its intensity indicates the content of the element, and its position in the spectrum indicates the speed of movement of the source (Doppler effect). However, there are almost no lines in the X-ray spectra; Typically, the spectrum of hot interstellar gas contains only one line of iron with a quantum energy of about 7 keV. Many astrophysicists dream of getting images of “their” objects in it. For example, galaxy researchers could use them to determine the content of heavy elements in the hot coronas of stellar systems and in intergalactic gas; they could measure the speed of galaxy clusters and directly determine the distance to them, which would make it possible to clarify the Hubble constant and the age of the Universe. Unfortunately, the Einstein Observatory telescope is not capable of operating in the 7 keV region: its sensitivity is limited to the range of 0.1 4-4 keV.

The ROSAT X-ray observatory (“Roentgen Satellite”), launched in June 1990, created mainly by German specialists, although it has a higher sensitivity than the Einstein, its operating range is relatively small: 0.1÷2 keV. The angular resolution of ROSAT (4") is approximately the same as that of Einstein (2"÷4").

But the telescope of the AXAF observatory will be able to construct an image in the range of 0.14-10 keV and at the same time give the resolution of a good optical telescope (0.5"). Moreover, taking into account that its composite mirror will have a diameter of 1.2 m , when observing point sources, AXAF will be almost a hundred times more sensitive than Einstein. This means that it will have access to almost a thousand times more space for studying sources of a known type. And how many fundamentally new objects will be discovered? One can only guess. ..

In addition, AXAF will be equipped with a high-resolution crystalline Bragg spectrometer, making it possible to determine the energy of quanta with an accuracy higher than 0.1%. The operating principle of this device is similar to an optical diffraction grating, but since the wavelength of X-ray radiation is very small, the role of a diffraction grating for it in a Bragg spectrograph is played by a natural crystal, the distance between the layers of atoms in which is close to the wavelength of X-ray radiation.

THIRD STAGE OF X-RAY ASTRONOMY

In the book by P.R. Amnuel “The Sky in X-Rays” (M.: Nauka, 1984) an interesting analogy is given between X-ray and optical astronomy. Viewing the X-ray sky from the Uhuru satellite was similar to viewing the night sky with the naked eye. Indeed, the brightest “star” object in the sky - Venus - is 10 thousand times brighter than the faintest 6t star accessible to the eye; This is the same ratio of fluxes from the brightest X-ray source Sco X-1 and the faintest source discovered by Uhuru. The launch of a telescope at Einstein Observatory, 100 times more sensitive than Uhuru, was equivalent to the appearance of a modest, amateur-level optical telescope that could see stars up to 11 m. And another 100 times more sensitive AXAF will be similar to a good professional telescope, for which stars up to 16 m are available.

Each new orbiting observatory makes its own important contribution to astronomy. Even instruments with traditional parameters are capable of collecting a large array of unique information and making many discoveries; An example of this is the Russian observatory “Granat” (Earth and Universe, 1993, No. 1, p. 17.- Red.). It is even more important to create devices with unique characteristics, each of which will give a breakthrough in science. Just one example: before the launch of the GRO observatory, only two pulsars were recorded in the gamma-ray range - Crab and Vela - but now there are about 500 of them! Therefore, astrophysicists are eagerly awaiting the start of operation of new large observatories in orbit.