IXPE Live Tracker
NASA's Imaging X-ray Polarimetry Explorer, launched 9 December 2021 on a SpaceX Falcon 9 from Kennedy Space Center. The world's first X-ray polarimetry mission, measuring the direction of vibrating X-ray light waves to reveal the geometry and magnetic-field structure of black holes, neutron stars, magnetars and active galactic nuclei. Built in partnership with the Italian Space Agency (ASI).
IXPE Maps Magnetic Geometry of Magnetar 4U 0142+61
A new IXPE polarisation measurement of magnetar 4U 0142+61 reveals a surface magnetic-field geometry consistent with a bare quark-matter surface rather than an atmospheric one. The result constrains models of the most extreme magnetic fields in the universe.
The First X-ray Polarimetry Mission Ever Flown
IXPE opened up a whole new dimension of information in X-ray astronomy. Every previous X-ray telescope measured position, energy and arrival time. IXPE adds polarisation, the direction in which the X-ray light waves are vibrating, which encodes the geometry and magnetic-field structure of the source.
Three Co-Aligned Polarimeters
IXPE carries three identical X-ray telescopes, each with its own mirror module and its own gas pixel detector. Three redundant measurements per source give the sensitivity needed for the tiny polarisation signals in astrophysical X-rays.
Five Years of X-ray Polarimetry
What IXPE Has Actually Measured
Nearly five years of X-ray polarimetry has already rewritten the geometry of black hole accretion, magnetar magnetic fields, and blazar jets.
IXPE vs Chandra, NuSTAR and XMM
IXPE measures a different property (polarisation) at lower spatial resolution than Chandra, NuSTAR or XMM. All four together give a complete picture of X-ray sources.
| Telescope | Waveband | Mirror | Orbit | Launched |
|---|---|---|---|---|
| IXPE | X-ray polarimetry (2, 8 keV) | 3 × 24-shell, 4 m FL | Equatorial LEO ~545 km | Dec 2021 |
| Chandra | Soft X-ray (0.1, 10 keV) | 1.2 m Wolter grazing | HEO 14k, 133k km | Jul 1999 |
| NuSTAR | Hard X-ray (3, 79 keV) | 2 × multilayer, 10 m FL | LEO ~545 km | Jun 2012 |
| XMM-Newton | Soft X-ray (0.1, 12 keV) | 3 co-aligned mirrors | HEO 6k, 100k km | Dec 1999 |
Why X-ray Polarimetry Took So Long
Astronomers have measured optical, radio and infrared polarisation for decades. X-ray polarisation was the missing piece: theory predicted it would encode the geometry of accretion flows, jets and neutron-star magnetic fields, but every previous instrument that tried was defeated by low photon counts and detector background. IXPE finally cracked it in 2021 using Italian-built gas pixel detectors that measure the direction of the photoelectron liberated by each incoming X-ray.
Why the equatorial orbit
IXPE's polarimeters are extremely sensitive to charged-particle background. Its 0.23-degree near-equatorial orbit at 600 km stays below the outer Van Allen belts and, critically, never crosses the South Atlantic Anomaly, the pocket where the inner belt dips low over the Atlantic. That gives IXPE almost continuous observing time with the cleanest background of any X-ray mission.
The Italian partnership
The three gas pixel detectors that make IXPE unique were built by the Italian Space Agency (ASI) and INAF-IAPS in Rome, drawing on two decades of laboratory work on X-ray polarimeters that no other space agency chose to fly. Without the Italian detectors, IXPE would not exist.
What comes next
No successor X-ray polarimeter is scheduled before the 2030s. The natural follow-up, a mission that combines Chandra's spatial resolution with IXPE's polarimetric sensitivity, is a design goal for the next generation of X-ray flagships (AXIS, Lynx or an ESA equivalent).
IXPE, Frequently Asked
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