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arXiv · 2606.18127

Detailed Timing, Spectral, and Polarimetric Analysis of Magnetar 1RXS J170849.0-400910

Rachael Stewart·George Younes·Alice Harding·Hoa Dinh Thi·Matthew Baring·Zorawar Wadiasingh·Michela Negro·Alex Van Kooten
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Abstract

We present a broadband timing, spectral, and polarimetric study of the magnetar 1RXS~J170849.0-400910 using XMM-Newton, NuSTAR, and IXPE. The pulse morphology evolves strongly across 0.5-70 keV. Below 3 keV, the emission is dominated by a broad soft pulse with a leading shoulder that develops into a faint interpulse near 3 keV, while the pulse fraction remains $\approx$25%. The profile becomes increasingly double-peaked between 3 and 20 keV and returns to a single peak at higher energies. The pulse fraction dips to $\sim$20% near 4 keV and rises to $\sim$42% above 25 keV. The phase-averaged spectrum is well described by an absorbed blackbody plus two power-laws, with $kT=0.468\pm0.003$ keV, $Γ_{\rm soft}=2.63\pm0.04$, and $Γ_{\rm hard}=0.5\pm0.1$. Phase-resolved spectroscopy reveals distinct soft and hard pulse components. The thermal modulation is driven primarily by a factor of $\sim$5 variation in projected emitting area, whereas the soft power-law exhibits two peaks with different phase and energy evolution, suggesting distinct emission regions or mechanisms. The 10-70 keV flux is strongly anticorrelated with the soft power-law photon index, linking spectral hardening to the hard pulse. The polarization degree also varies strongly with phase and energy. In the 2-3 keV band, it is anticorrelated with the intensity profile, consistent with magnetized-atmosphere emission, whereas in the 4-8 keV band it reaches $64\pm10$% during the nonthermal power-law-dominated peak. This high polarization can be reproduced by magnetospheric quantum pair-synchrotron emission. Together, these results reveal an intricate, phase-dependent superposition of emitting regions and radiative processes whose complexity emerges only through broadband, phase-resolved spectropolarimetry.

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Rachael Stewart, George Younes, Alice Harding, Hoa Dinh Thi, Matthew Baring, Zorawar Wadiasingh, Michela Negro, Alex Van Kooten. 2026-06-16. Detailed Timing, Spectral, and Polarimetric Analysis of Magnetar 1RXS J170849.0-400910. https://arxiv.org/abs/2606.18127

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