IXPE Detection of Highly Polarized X-Rays from the Magnetar 1E 1841-045
Michela Rigoselli, Roberto Taverna, S. Mereghetti, Roberto Turolla, G. L. Israel, Silvia Zane, Lorenzo Marra, Fabio Muleri, A. Borghese, F. Coti Zelati, Davide De Grandis, M. Imbrogno, Ruth Kelly, P. Esposito, N. Rea
Abstract
Abstract 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 ≈15% at 2–3 keV up 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 (≈2 × 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 ≈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.