Interstellar Scintillation of the Radio-Loud Magnetar XTE J1810–197

Abstract In this Letter, we present a comprehensive interstellar scintillation (ISS) study of the radio-loud magnetar XTE J1810–197 based on six years (2018–2024) of multifrequency monitoring (7.0, 8.6, and 14.0 GHz) with the Shanghai Tian Ma Radio Telescope. Scintillation parameters such as decorrelation bandwidth Δν_d, decorrelation time Δτ_d, and drift rate dt/dν, are fully characterized by the two-dimensional auto-correlation analysis. The measured Δτ_d is less than 4 s at 575–725 MHz under a Kolmogorov spectrum, which is shorter than the 5.54 s spin period of the magnetar, thereby explaining the previously reported absence of pulse-to-pulse coherence at these frequencies. Kinematic modeling is utilized to locate the dominant scattering screen 1.6±0.1 kpc away from the Earth, within the Sagittarius Arm. The screen coincides with the H ii region JCMTSE J180921.2–201932 and is unrelated to the 2018 outburst of the magnetar, as suggested by earlier studies. The scintillation arc detected at 14.0 GHz is the highest-frequency arc observed to date. The arc asymmetry is linearly correlated with the dispersion-measure gradient across the screen (r = 0.959, p < 10⁻⁸). Further, we measure its refractive scintillation timescale, which is only 1.21 ± 0.19 d. Clear diffractive interstellar scintillation at 14 GHz effectively resolves the debate over a possible strong-to-weak scattering transition at this frequency. These results extend the ISS characterization of magnetars to previously unexplored frequencies, providing a precise probe for ionized interstellar media in the Sagittarius Arm.