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Scientists conducted the first X-ray polarimetry observations of the accretion disk corona source 4U 1822-37 using the IXPE telescope, revealing unusually high polarization that varies significantly with energy. The polarization degree was 5.6% at lower energies (2-5 keV) and doubled to 11.6% at higher energies (5-8 keV), with distinct behavioral patterns during the orbital eclipse phase. These findings suggest that soft and hard X-ray emissions originate from spatially separated regions, with the observed polarization angle rotations likely caused by asymmetric scattering from structural features like bulges or clumps in the accretion disk.
Why it matters
This research provides new insights into the geometry and emission mechanisms of low-mass X-ray binary systems, helping astronomers better understand how matter behaves in extreme gravitational environments around compact objects. The distinct polarization signatures at different energies offer a novel diagnostic tool for mapping the spatial structure of accretion systems that cannot be resolved through conventional imaging.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Abstract: We report the first Imaging X-ray Polarimetry Explorer (IXPE) observations of the typical accretion disk corona (ADC) source 4U 1822-37, covering 44 orbital cycles, together with simultaneous Swift-XRT data. The polarization degree (PD) of this source is found to be higher than typical low-mass X-ray binary (LMXB) values and exhibits a significant energy dependence. Within the 2–5~keV and 5–8~keV bands, PD remains constant, with average values of (5.6pm0.8%) and (11.6pm1.7%), respectively, and the difference is significant ((>3sigma)). Orbital phase-resolved analysis reveals that during the companion eclipse, the PD in the 2–5~keV band drops from a significantly non-zero value to a level consistent with zero, while the polarization angle (PA) remains unchanged. In contrast, the PD in the 5–8~keV band shows a marginal rising trend, reaching (21.3pm6.1%), and the PA exhibits a periodic rotation of (30^circ) before the eclipse. In addition, the PA rotates by (40^circ) with increasing neutral absorption on a three-day timescale. These results suggest that the soft and hard emission in the 2–8~keV band may originate from regions with different spatial distributions, with the high PD implying a scattering contribution. The PA rotation is likely linked to scattering geometry asymmetries caused by a bulge or clumps.
Source: The First X-Ray Polarimetry of the Typical Accretion Disk Corona Source 4U 1822-37