WanYun Wu | Searcharxiv

arXiv2026

The First X-Ray Polarimetry of the Typical Accretion Disk Corona Source 4U 1822-37

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 $5.6\pm0.8\%$ and $11.6\pm1.7\%$, respectively, and the difference is significant ($>3\sigma$). 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 $21.3\pm6.1\%$, 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.

astro-ph.HE↗

arXiv2025

Highly Polarized Intrinsic Emission and its Orthogonal Counterpart in Vela X-1

Vela X-1 is one of the most archetypal wind-fed X-ray pulsars (XRPs), and the emergence of its orthogonal polarization states reveals distinctive polarimetric properties. Using data from Imaging X-ray Polarimetry Explorer (IXPE) observations of Vela X-1, we perform a polarization analysis of Vela X-1 using a triple power-law spectral model absorbed by varying column densities, successfully isolating two physically distinct orthogonal polarized components. The first polarized component corresponds to emission from the accretion mound surface that is not obscured by the wind clumps, with its polarization degree (PD) exceeding 30\%. In specific phase intervals, the PD reaches $50.9 \pm 10.7\%$. This marks the first detection of such highly polarized neutron star emission in an XRP. The second polarized component likely originates from complex physical processes within or near the accretion mound, with its PD showing a potential negative correlation with column density. Furthermore, by rotating the predicted polarization angle (PA) of the first polarized component by 90$^\circ$, we successfully achieve separate fitting and simultaneous fitting of the two orthogonal polarization states using the rotating vector model (RVM).

astro-ph.HE↗