The First X-Ray Polarimetry of the Typical Accretion Disk Corona Source 4U 1822-37
WanYun Wu, Fei Xie, YuShan Ling
arXiv:2608.24292v2 Announce Type: replace
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.arXiv:2608.24292v2 Announce Type: replace
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.

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