2025-06-05 NASA
Michela Rigoselli/Italian National Institute of Astrophysics
＜関連情報＞
- https://www.nasa.gov/missions/ixpe/nasas-ixpe-obtains-first-x-ray-polarization-measurement-of-magnetar-outburst/
- https://iopscience.iop.org/article/10.3847/2041-8213/adbffa
- https://iopscience.iop.org/article/10.3847/2041-8213/adbffb
マグネター1E 1841-045のX線偏光 X-Ray Polarization of the Magnetar 1E 1841−045
Rachael Stewart, George A. Younes, Alice K. Harding, Zorawar Wadiasingh, Matthew G. Baring, Michela Negro, Tod E. Strohmayer, Wynn C. G. Ho, Mason Ng, Zaven Arzoumanian,…
The Astrophysical Journal Letters Published: 2025 May 28
DOI:10.3847/2041-8213/adbffa
Abstract
We report on IXPE and NuSTAR observations beginning 40 days after the 2024 outburst onset of magnetar 1E 1841−045, marking the first IXPE observation of a magnetar in an enhanced state. Our spectropolarimetric analysis indicates that both a blackbody (BB) plus double power-law (PL) and a double blackbody plus power-law spectral model fit the phase-averaged intensity data well, with a hard PL tail (Γ = 1.19 and 1.35, respectively) dominating above ≈5 keV. For the former model, we find the soft PL (the dominant component at soft energies) exhibits a polarization degree (PD) of ≈30% while the hard PL displays a PD of ≈40%. Similarly, the cool BB of the 2BB+PL model possesses a PD of ≈15% and a hard PL PD of ≈57%. For both models, each component has a polarization angle (PA) compatible with celestial north. Model-independent polarization analysis supports these results, wherein the PD increases from ≈15% to ≈70% in the 2–3 keV and 6–8 keV ranges, respectively, while the PA remains nearly constant. We find marginal evidence for phase-dependent variability of the polarization properties, namely a higher PD at phases coinciding with the hard X-ray pulse peak. We compare the hard X-ray PL to the expectation from resonant inverse Compton scattering (RICS) and secondary pair cascade synchrotron radiation from primary high-energy RICS photons; both present reasonable spectropolarimetric agreement with the data, albeit the latter does so more naturally. We suggest that the soft PL X-ray component may originate from a Comptonized corona in the inner magnetosphere.
マグネター1E 1841-045からの高偏光X線のIXPE検出 IXPE Detection of Highly Polarized X-Rays from the Magnetar 1E 1841-045
Michela Rigoselli, Roberto Taverna, Sandro Mereghetti, Roberto Turolla, Gian Luca Israel, Silvia Zane, Lorenzo Marra, Fabio Muleri, Alice Borghese, Francesco Coti Zelati,…
The Astrophysical Journal Letters Published: 2025 May 28
DOI:10.3847/2041-8213/adbffb
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.
