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 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 cosmic X-rays of black holes, neutron stars, and pulsars. The observatory, which was launched on 9 December 2021, is an international collaboration between NASA and the Italian Space Agency (ASI). It is part of NASA's Explorers program, which designs low-cost spacecraft to study heliophysics and astrophysics. The mission will study exotic astronomical objects and permit mapping of the magnetic fields of

black hole A black hole is a region of spacetime where gravitation, gravity is so strong that nothing, including light or other Electromagnetic radiation, electromagnetic waves, has enough energy to escape it. The theory of general relativity predicts t ...

s, neutron stars,

pulsar A pulsar (from ''pulsating radio source'') is a highly magnetized rotating neutron star that emits beams of electromagnetic radiation out of its magnetic poles. This radiation can be observed only when a beam of emission is pointing toward Ea ...

s, supernova remnants, magnetars,

quasar A quasar is an extremely Luminosity, luminous active galactic nucleus (AGN). It is pronounced , and sometimes known as a quasi-stellar object, abbreviated QSO. This emission from a galaxy nucleus is powered by a supermassive black hole with a m ...

s, and active galactic nuclei. The high-energy X-ray radiation from these objects' surrounding environment can be polarized oscillating in a particular direction. Studying the polarization of X-rays reveals the physics of these objects and can provide insights into the high-temperature environments where they are created.

Overview

The IXPE mission was announced on 3 January 2017 and was launched on 9 December 2021. The international collaboration was signed in June 2017, when the Italian Space Agency (ASI) committed to provide the X-ray

detectors. The estimated cost of the mission and its two-year operation is US$188 million (the launch cost is US$50.3 million). The goal of the IXPE mission is to expand understanding of high-energy astrophysical processes and sources, in support of NASA's first science objective in astrophysics: "Discover how the universe works". By obtaining X-ray polarimetry and polarimetric imaging of cosmic sources, IXPE addresses two specific science objectives: to determine the radiation processes and detailed properties of specific cosmic X-ray sources or categories of sources; and to explore

general relativistic General relativity, also known as the general theory of relativity and Einstein's theory of gravity, is the geometric theory of gravitation published by Albert Einstein in 1915 and is the current description of gravitation in modern physics. G ...

and

quantum effects Quantum mechanics is a fundamental theory in physics that provides a description of the physical properties of nature at the scale of atoms and subatomic particles. It is the foundation of all quantum physics including quantum chemistry, ...

in extreme environments. During IXPE's two-year mission, it will study targets such as active galactic nuclei,

s, pulsar wind nebulae, magnetars, accreting X-ray binaries, supernova remnants, and the Galactic Center. The spacecraft was built by Ball Aerospace & Technologies. The principal investigator is Martin C. Weisskopf of NASA

Marshall Space Flight Center The George C. Marshall Space Flight Center (MSFC), located in Redstone Arsenal, Alabama (Huntsville postal address), is the U.S. government's civilian rocketry and spacecraft propulsion research center. As the largest NASA center, MSFC's first ...

; he is the chief scientist for X-ray astronomy at NASA's Marshall Space Flight Center and project scientist for the Chandra X-ray Observatory spacecraft. Other partners include the McGill University, Massachusetts Institute of Technology (MIT), Roma Tre University,

Stanford University Stanford University, officially Leland Stanford Junior University, is a private research university in Stanford, California. The campus occupies , among the largest in the United States, and enrolls over 17,000 students. Stanford is consider ...

, OHB Italia and the University of Colorado Boulder.

Objectives

The technical and science objectives include: * Improve polarization sensitivity by two orders of magnitude over the X-ray

polarimeter A polarimeter is a scientific instrument used to measure the angle of rotation caused by passing polarized light through an optically active substance.Orbiting Solar Observatory 8 * Provide simultaneous spectral, spatial, and temporal measurements * Determine the geometry and the emission mechanism of active galactic nuclei and microquasars * Find the magnetic field configuration in magnetars and determine the magnitude of the field * Find the mechanism for X-ray production in

s (both isolated and accreting) and the geometry * Determine how particles are accelerated in pulsar wind nebula

Telescopes

The space observatory features three identical telescopes designed to measure the

of cosmic X-rays. The polarization-sensitive detector was invented and developed by Italian scientists of the Istituto Nazionale di AstroFisica (INAF) and the Istituto Nazionale di Fisica Nucleare (INFN) and was refined over several years.

Principle

IXPE's payload is a set of three identical imaging X-ray polarimetry systems mounted on a common optical bench and co-aligned with the pointing axis of the spacecraft. Each system operates independently for redundancy and comprises a mirror module assembly that focuses X-rays onto a polarization-sensitive imaging detector developed in Italy. The focal length is achieved using a deployable boom. The Gas Pixel Detectors (GPD) rely on the anisotropy of the emission direction of

photoelectrons The photoelectric effect is the emission of electrons when electromagnetic radiation, such as light, hits a material. Electrons emitted in this manner are called photoelectrons. The phenomenon is studied in condensed matter physics, and solid st ...

produced by polarized photons to gauge with high sensitivity the polarization state of X-rays interacting in a gaseous medium. Position-dependent and energy-dependent polarization maps of such synchrotron-emitting sources will reveal the magnetic-field structure of the X-ray emitting regions. X-ray polarimetric imaging better indicates the magnetic structure in regions of strong electron acceleration. The system is capable to resolve point sources from surrounding nebular emission or from adjacent point sources.

Launch profile

IXPE was launched on 9 December 2021 on a SpaceX Falcon 9 ( B1061.5) from LC-39A at NASA's Kennedy Space Center in Florida. The relatively small size and mass of the observatory falls well short of the normal capacity of SpaceX's Falcon 9 launch vehicle. However, Falcon 9 had to work to get IXPE into the correct orbit because IXPE is designed to operate in an almost exactly equatorial orbit with a 0° inclination. Launching from

Cape Canaveral , image = cape canaveral.jpg , image_size = 300 , caption = View of Cape Canaveral from space in 1991 , map = Florida#USA , map_width = 300 , type =Cape , map_caption = Location in Florida , location ...

, which is located 28.5° above the

equator The equator is a circle of latitude, about in circumference, that divides Earth into the Northern and Southern hemispheres. It is an imaginary line located at 0 degrees latitude, halfway between the North and South poles. The term can als ...

, it was physically impossible to launch directly into a 0.2° equatorial orbit. Instead, the rocket needed to launch due east into a parking orbit and then perform a plane, or inclination, change once in space, as the spacecraft crossed the equator. For Falcon 9, this meant that even the tiny IXPE likely still represented about 20–30% of its maximum theoretical performance () for such a mission profile, while the same launch vehicle is otherwise able to launch about to the same orbit IXPE was targeting when no plane change is needed, while recovering the first stage booster. IXPE is the first satellite dedicated to measuring the polarization of X-rays from a variety of cosmic sources, such as

s and neutron stars. The orbit hugging the equator will minimize the X-ray instrument's exposure to radiation in the South Atlantic Anomaly, the region where the inner Van Allen radiation belt comes closest to Earth's surface.

Operations

IXPE is built to last for two years. After that it may be retired and deorbited or given an extended mission. After launch and deployment of the IXPE spacecraft, NASA pointed the spacecraft at 1ES 1959+650, a black hole, and SMC X-1, a pulsar, for calibration. After that the spacecraft observed its first science target, Cassiopeia A. A first-light image of Cassiopeia A was released on 11 January 2022. 30 targets are planned to be observed during IXPE's first year. IXPE communicates with Earth via a ground station in Malindi, Kenya. The ground station is owned and operated by the Italian Space Agency. At present mission operations for IXPE are controlled by the Laboratory for Atmospheric and Space Physics (LASP).

Results

In May 2022 the first study of IXPE hinted the possibility of vacuum birefringence on

4U 0142+61 4U 0142+61 is a magnetar at an approximate distance of from Earth, located in the constellation Cassiopeia. In an article published in ''Nature'' on April 6, 2006, Deepto Chakrabarty ''et al.'' of MIT revealed that a circumstellar disk ...

and in August another study looked at centaurus A measuring low polarization degree, suggesting that the X-ray emission is coming from a scattering process rather than arising directly from the accelerated particles of the jet.

Gallery

File:IXPE-space-telescope-drawing.png, Diagram of IXPE's structure File:IXPE deploying.webm, Animation of the IXPE deployment process File:This image from NASA’s Imaging X-ray Polarimetry Explorer maps the intensity of X-rays coming from the observatory’s first target, the supernova Cassiopeia A.png, IXPE X-ray image of the supernova remnant Cassiopeia A

References

{{Orbital launches in 2021 Space telescopes X-ray telescopes NASA satellites orbiting Earth Explorers Program Spacecraft launched in 2021