IXPE Detection of Highly Polarized X-Rays from the Magnetar 1E 1841-045

The Imaging X-ray Polarimetry Explorer (IXPE) observed for the first time highly polarized X-ray emission from the magnetar 1E 1841-045, targeted after a burst-active phase in 2024 August. To date, IXPE has observed four other magnetars during quiescent periods, highlighting substantially different polarization properties. 1E 1841-045 exhibits a high, energy-dependent polarization degree, which increases monotonically from approximate to 15% at 2-3 keV up to approximate to 55% at 5.5-8 keV, while the polarization angle, aligned with the celestial north, remains fairly constant. The broadband spectrum (2-79 keV) obtained by combining simultaneous IXPE and NuSTAR data is well modeled by a blackbody and two power-law components. The unabsorbed 2-8 keV flux (approximate to 2 x 10-11 erg cm-2 s-1) is about 10% higher than that obtained from archival XMM-Newton and NuSTAR observations. The polarization of the soft, thermal component does not exceed approximate to 25%, and may be produced by a condensed surface or a bombarded atmosphere. The intermediate power law is polarized at around 30%, consistent with predictions for resonant Compton scattering in the star magnetosphere; meanwhile, the hard power law exhibits a polarization degree exceeding 65%, pointing to a synchrotron/curvature origin.