X-ray polarimetry is the measurement of the

polarization Polarization or polarisation may refer to: Mathematics *Polarization of an Abelian variety, in the mathematics of complex manifolds *Polarization of an algebraic form, a technique for expressing a homogeneous polynomial in a simpler fashion by ...

X-ray An X-ray (also known in many languages as Röntgen radiation) is a form of high-energy electromagnetic radiation with a wavelength shorter than those of ultraviolet rays and longer than those of gamma rays. Roughly, X-rays have a wavelength ran ...

s from astronomical sources. This technique provides information about emission mechanisms, magnetic field structures, and source geometry that cannot be obtained through traditional X-ray

spectroscopy Spectroscopy is the field of study that measures and interprets electromagnetic spectra. In narrower contexts, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectro ...

imaging Imaging is the representation or reproduction of an object's form; especially a visual representation (i.e., the formation of an image). Imaging technology is the application of materials and methods to create, preserve, or duplicate images. ...

, or

timing Timing is the tracking or planning of the spacing of events in time. It may refer to: * Timekeeping, the process of measuring the passage of time * Synchronization, controlling the timing of a process relative to another process * Time metrolo ...

observations.

History

Polarization Polarization or polarisation may refer to: Mathematics *Polarization of an Abelian variety, in the mathematics of complex manifolds *Polarization of an algebraic form, a technique for expressing a homogeneous polynomial in a simpler fashion by ...

of X-rays was found in 1904 by

Charles Glover Barkla Charles Glover Barkla (7 June 1877 – 23 October 1944) was an English physicist who received the Nobel Prize in Physics in 1917 for his discovery of characteristic X-rays. Life Barkla was born in Widnes, England, to John Martin Barkla, a sec ...

Astronomical X-ray source Astrophysical X-ray sources are astronomical objects with physical properties which result in the emission of X-rays. Several types of astrophysical objects emit X-rays. They include galaxy clusters, black holes in active galactic nuclei (AGN ...

s were found in 1962, by

Riccardo Giacconi Riccardo Giacconi ( , ; October 6, 1931 – December 9, 2018) was an Italian-American Nobel Prize-winning astrophysicist who laid down the foundations of X-ray astronomy. He was a professor at the Johns Hopkins University. Biography Born in ...

and

Bruno Rossi Bruno Benedetto Rossi ( , ; 13 April 1905 – 21 November 1993) was an Italian-American experimental physicist. He made major contributions to particle physics and the study of cosmic rays. A 1927 graduate of the University of Bologna, he ...

. X-ray polarimetry was first used in astronomy in 1968 when Robert Novick, working with

Roger Angel James Roger Prior Angel (born February 7, 1941) is a British-American astrophysicist known for his contributions to astronomy and the design and fabrication of large optics for telescopes, solar power and other applications. He developed the spi ...

and

Martin C. Weisskopf Martin C. Weisskopf (born April 21, 1942) until his retirement from NASA in at the end of May, 2022, was project scientist for NASA's Chandra X-ray Observatory and Chief Scientist for X-ray Astronomy in the Space Sciences Department at NASA's Mars ...

Columbia University Columbia University in the City of New York, commonly referred to as Columbia University, is a Private university, private Ivy League research university in New York City. Established in 1754 as King's College on the grounds of Trinity Churc ...

, launched the first

sounding rocket A sounding rocket or rocketsonde, sometimes called a research rocket or a suborbital rocket, is an instrument-carrying rocket designed to take measurements and perform scientific experiments during its sub-orbital flight. The rockets are often ...

experiment to measure polarization from

Scorpius X-1 Scorpius X-1 is an X-ray source located roughly 9000 light years away in the constellation Scorpius. Scorpius X-1 was the first extrasolar X-ray source discovered, and, aside from the Sun, it is the strongest apparent non-transient source of X-ra ...

using a lithium

Compton scattering Compton scattering (or the Compton effect) is the quantum theory of high frequency photons scattering following an interaction with a charged particle, usually an electron. Specifically, when the photon hits electrons, it releases loosely bound e ...

polarimeter, though this initial attempt yielded only upper limits. The first successful detection came from the

Crab Nebula The Crab Nebula (catalogue designations M1, NGC 1952, Taurus A) is a supernova remnant and pulsar wind nebula in the constellation of Taurus (constellation), Taurus. The common name comes from a drawing that somewhat resembled a crab with arm ...

using improved rocket-borne instruments that combined lithium scattering polarimeters with Bragg crystal polarimeters. This measurement, reporting 15±5% polarization at 156±10°, confirmed the

synchrotron radiation Synchrotron radiation (also known as magnetobremsstrahlung) is the electromagnetic radiation emitted when relativistic charged particles are subject to an acceleration perpendicular to their velocity (). It is produced artificially in some types ...

origin of the Crab's X-ray emission.

Ariel 5 Ariel 5 (or UK 5) was a joint British and American space telescope dedicated to observing the sky in the X-ray band. It was launched on 15 October 1974 from the San Marco platform in the Indian Ocean and operated until 1980. It was the penultima ...

satellite with a spectro-polarimeter was launched in 1974; the OSO-8 satellite, launched in 1975, carried two graphite crystal polarimeters and made the most significant early measurement, detecting 19±1% polarization from the Crab Nebula at 156.4±1.4°, well above the theoretical limit for

thermal radiation Thermal radiation is electromagnetic radiation emitted by the thermal motion of particles in matter. All matter with a temperature greater than absolute zero emits thermal radiation. The emission of energy arises from a combination of electro ...

(higher than the

Chandrasekhar limit The Chandrasekhar limit () is the maximum mass of a stable white dwarf star. The currently accepted value of the Chandrasekhar limit is about (). The limit was named after Subrahmanyan Chandrasekhar. White dwarfs resist gravitational collapse pr ...

of 12%).

Techniques

Early X-ray polarimeters used two main approaches: #Scattering polarimeters exploit the polarization dependence of

in materials like lithium #Crystal polarimeters use

Bragg diffraction In many areas of science, Bragg's law — also known as Wulff–Bragg's condition or Laue–Bragg interference — is a special case of Laue diffraction that gives the angles for coherent scattering of waves from a large crystal lattice. It descr ...

from mosaic crystals, typically pyrolytic graphite, at 45° incidence angles Modern instruments employ photoelectric polarimeters that image the tracks of photoelectrons ejected during

photoelectric The photoelectric effect is the emission of electrons from a material caused by electromagnetic radiation such as ultraviolet light. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physic ...

absorption. The direction of the photoelectron track correlates with the incident X-ray polarization direction. These detectors use either

gas electron multiplier A gas electron multiplier (GEM) is a type of gaseous ionization detector used in nuclear and particle physics and radiation detection. All gaseous ionization detectors are able to collect the electrons released by ionizing radiation, guiding them ...

s with pixelated readouts or

time projection chamber In physics, a time projection chamber (TPC) is a type of particle detector that uses a combination of electric fields and magnetic fields together with a sensitive volume of gas or liquid to perform a three-dimensional reconstruction of a particle ...

Missions and instruments

After OSO-8, X-ray polarimetry experienced a 40-year gap due to the mismatch between polarimetry requirements and the development of focusing X-ray optics. * Spectrum Roentgen-Gamma - a Soviet spacecraft planned with the American-Italian Stellar X-ray Polarimeter on board, cancelled in 1988 * Gravity and Extreme Magnetism Small Explorer - cancelled in 2012 * PoGOLite (2013) / PoGO+ (2018) - balloon-borne hard X-ray polarimeter that observed the Crab and

Cygnus X-1 Cygnus X-1 (abbreviated Cyg X-1) is a galactic X-ray source in the constellation Cygnus and was the first such source widely accepted to be a black hole. It was discovered in 1964 during a rocket flight and is one of the ...

Imaging X-ray Polarimetry Explorer Imaging X-ray Polarimetry Explorer, commonly known as IXPE or SMEX-14, is a space observatory with three identical telescopes designed to measure the polarization of cosmic X-rays of black holes, neutron stars, and pulsars. The observatory, ...

(IXPE) - launched December 2021, uses gas pixel detectors at the focus of three X-ray telescopes.

, who took part in first sounding rocket experiments with Novick, is the PI of the mission. *

XPoSat 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 operat ...

(X-ray Polarimeter Satellite) - Indian space probe launched in 2024 * Enhanced X-ray Timing and Polarimetry mission (eXTP) - planned Chinese mission with four polarimetry telescopes, planned to be launched in 2027

Scientific applications

Different astronomical objects can emit X-rays with specific polarization patterns. These signatures can provide data for measurements that can be done by other methods, for example "in accreting millisecond pulsars ... variations of the polarization angle with the pulsar phase allow us to measure source inclination and magnetic obliquity ...

hich Ij () is a village in Golabar Rural District of the Central District in Ijrud County, Zanjan province, Iran Iran, officially the Islamic Republic of Iran (IRI) and also known as Persia, is a country in West Asia. It borders Iraq ...

give a possibility to measure NS mass-radius relation from the pulse profiles with a much better accuracy". For different objects, X-ray polarimetry allows to measure different properties:

black hole A black hole is a massive, compact astronomical object so dense that its gravity prevents anything from escaping, even light. Albert Einstein's theory of general relativity predicts that a sufficiently compact mass will form a black hole. Th ...

spin measurements through polarization rotation in curved spacetime;

neutron star A neutron star is the gravitationally collapsed Stellar core, core of a massive supergiant star. It results from the supernova explosion of a stellar evolution#Massive star, massive star—combined with gravitational collapse—that compresses ...

magnetic field geometry and emission regions;

active galactic nuclei An active galactic nucleus (AGN) is a compact region at the center of a galaxy that emits a significant amount of energy across the electromagnetic spectrum, with characteristics indicating that this luminosity is not produced by the stars. Such e ...

jet structures and accretion disk properties;

supernova remnant A supernova remnant (SNR) is the structure resulting from the explosion of a star in a supernova. The supernova remnant is bounded by an expanding shock wave, and consists of ejected material expanding from the explosion, and the interstellar mat ...

s and

pulsar wind nebula A pulsar wind nebula (PWN, plural PWNe), sometimes called a plerion (derived from the Greek "πλήρης", ''pleres'', meaning "full"), is a type of nebula sometimes found inside the shell of a supernova remnant (SNR), powered by winds generate ...

e magnetic field configurations. The polarization degree and angle depend on the physical processes producing the X-rays and the geometry of the emitting region, making it complementary to other observational techniques.

References

{{reflist X-ray astronomy

History

Techniques

Missions and instruments

Scientific applications

Further reading

References