Magnetars are neutron stars with ultra-strong magnetic fields that are about a quadrillion times greater than the magnetic field of Earth. These huge magnetic fields are thought to be produced when an rapidly rotating neutron star is formed by the collapse of the core of a massive star. Magnetars emit bright X-rays and show erratic periods of activity, with the emission of bursts and flares which can release in just one second an amount of energy millions of times greater than our Sun emits in one year. Polarization measurements could provide information on their magnetic fields and surface properties. Astronomers using NASA’s Imaging X-ray Polarimetry Explorer (IXPE) focused on 1E 1841-045, a magnetar located in the supernova remnant (SNR) Kes 73 nearly 28,000 light-years from Earth. The results are presented in two papers published in the Astrophysical Journal Letters.
An artist’s impression of a magnetar. Image credit: NASA’s Goddard Space Flight Center / S. Wiessinger.
Magnetars are a type of young neutron star — a stellar remnant formed when a massive star reaches the end of its life and collapses in on itself, leaving behind a dense core roughly the mass of the Sun, but squashed down to the size of a city.
Neutron stars display some of the most extreme physics in the observable Universe and present unique opportunities to study conditions that would otherwise be impossible to replicate in a laboratory on Earth.
The 1E 1841-045 magnetar was observed to be in a state of outburst by NASA’s Swift, Fermi, and NICER telescopes on August 21, 2024.
A few times a year, the IXPE team approves requests to interrupt the telescope’s scheduled observations to instead focus on unique and unexpected celestial events.
When 1E 1841-045 entered this brighter, active state, scientists decided to redirect IXPE to obtain the first-ever polarization measurements of a flaring magnetar.
Magnetars have magnetic fields several thousand times stronger than most neutron stars and host the strongest magnetic fields of any known object in the Universe.
Disturbances to their extreme magnetic fields can cause a magnetar to release up to a thousand times more X-ray energy than it normally would for several weeks.
This enhanced state is called an outburst, but the mechanisms behind them are still not well understood.
Through IXPE’s X-ray polarization measurements, scientists may be able to get closer to uncovering the mysteries of these events.
Polarization carries information about the orientation and alignment of the emitted X-ray light waves; the higher the degree of polarization, the more the X-ray waves are traveling in sync, akin to a tightly choreographed dance performance.
Examining the polarization characteristics of magnetars reveals clues about the energetic processes producing the observed photons as well as the direction and geometry of the magnetar magnetic fields.
This illustration depicts IXPE’s measurements of X-ray polarization emitting from 1E 1841-045. Image credit: Michela Rigoselli / Italian National Institute of Astrophysics.
The IXPE results, aided by observations from NASA’s NuSTAR and NICER telescopes, show that the X-ray emissions from 1E 1841-045 become more polarized at higher energy levels while still maintaining the same direction of propagation.
A significant contribution to this high polarization degree comes from the hard X-ray tail of 1E 1841-045, an energetic magnetospheric component dominating the highest photon energies observed by IXPE.
Hard X-rays refer to X-rays with shorter wavelengths and higher energies than soft X-rays.
Although prevalent in magnetars, the mechanics driving the production of these high energy X-ray photons are still largely unknown.
Several theories have been proposed to explain this emission, but now the high polarization associated with these hard X-rays provide further clues into their origin.
“This unique observation will help advance the existing models aiming to explain magnetar hard X-ray emission by requiring them to account for this very high level of synchronization we see among these hard X-ray photons,” said Rachael Stewart, a Ph.D. student at George Washington University and lead author of the first paper.
“This really showcases the power of polarization measurements in constraining physics in the extreme environments of magnetars.”
“It will be interesting to observe 1E 1841-045 once it has returned to its quiescent, baseline state to follow the evolution of its polarimetric properties,” added Dr. Michela Rigoselli, an astronomer at the Italian National Institute of Astrophysics and lead author of the second paper.
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Rachael Stewart et al. 2025. X-Ray Polarization of the Magnetar 1E 1841-045. ApJL 985, L35; doi: 10.3847/2041-8213/adbffa
Michela Rigoselli et al. 2025. IXPE Detection of Highly Polarized X-Rays from the Magnetar 1E 1841-045. ApJL 985, L34; doi: 10.3847/2041-8213/adbffb
