Polarized X-rays reveal two hot spots on a newly found magnetar
Observations show that the source’s X-ray polarization changes across its six-second rotation, pointing to a complex surface geometry.
Editorial illustration — not from the study.
The Imaging X-ray Polarimetry Explorer observed the source from July 6 to 8, 2026, after its discovery by the Einstein Probe Wide-field X-ray Telescope on June 28. The X-ray spectrum is consistent with two thermal emitting regions on the magnetar’s surface, with temperatures of about 0.5 and 1 kiloelectronvolts.
Across the observation, the average polarization was about 7%, detected at more than four standard deviations. When the data were sorted by the star’s rotation and X-ray energy, the polarization reached about 63% at energies between 4 and 7.5 kiloelectronvolts, while remaining below about 30% at lower energies. The polarization angle swung continuously from −90 to +90 degrees during one rotation.
Two polarized emitting regions
The IXPE data detected polarized X-ray emission from EP J223759.5+531421 with more than 4σ confidence. The phase- and energy-averaged polarization degree was about 7%, with a polarization angle of roughly −2 degrees east of celestial north.
The two thermal components had different polarization behavior, with the hotter component more strongly polarized. In phase-folded data, the polarization degree reached about 63% in the 4–7.5 keV band near the secondary pulse peak, but did not exceed about 30% at lower energies. The polarization angle changed continuously through a full rotational cycle and was well described by a rotating-vector model.
The results point to a geometry in which the warmer component may come from two regions on opposite sides of the star, possibly in a magnetically condensed state. The hotter component may instead arise from a smaller region covered by an atmosphere.
What the changing angle shows
Polarization records the direction in which X-ray light is oriented, adding information that ordinary X-ray brightness and temperature measurements do not provide. Here, its changing angle and strong energy dependence distinguish the two emitting components and provide evidence about how they are arranged on the magnetar’s surface.
The observations therefore offer a way to test models of magnetar emission geometry, while the proposed two-cap and smaller-atmosphere arrangement remains an interpretation of the data rather than a direct image of the surface.
Evidence and caveats
The findings come from a targeted IXPE observation lasting about 200 kiloseconds, with roughly 60,000 net source counts, combined with about 10 kiloseconds of simultaneous Einstein Probe data. The source was analyzed by energy and rotational phase, and its polarization-angle variation was compared with a rotating-vector model.
The surface geometry is inferred from spectral and polarization models; the observations do not directly resolve the emitting regions. The abstract describes the two-cap and atmospheric interpretation as possible or likely, so it remains model-dependent. The results also come from this follow-up observation of one newly discovered source.
// Source
The Astrophysical Journal Letters · 2026 · DOI: 10.3847/2041-8213/aeb4aa
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