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

TL;DR

This study provides a detailed six-year analysis of interstellar scintillation of the radio-loud magnetar XTE J1810-197 across multiple frequencies, revealing insights into the scattering environment and interstellar medium properties.

Contribution

It offers the first comprehensive multi-frequency ISS characterization of XTE J1810-197, including scattering screen location and arc properties, extending understanding of magnetar scintillation at high frequencies.

Findings

Scintillation decorrelation time shorter than magnetar spin period.

Scattering screen located within the Sagittarius Arm at 1.6 kpc.

Detection of the highest-frequency scintillation arc to date.

Abstract

We present a comprehensive interstellar scintillation (ISS) study of the radio-loud magnetar XTE~J1810$-$197, based on six years of multi-frequency monitoring (2018$-$2024) with the Shanghai Tian Ma Radio Telescope (TMRT) at 7.0, 8.6, and 14.0~GHz. The scintillation parameters--decorrelation bandwidth $\Delta\nu_{\rm d}$, decorrelation time $\Delta\tau_{\rm d}$, and drift rate $dt/d\nu$--are fully characterized. Our measured $\Delta\tau_{\rm d}$ implies $\Delta\tau_{\rm d} < 4$~s at 575-725~MHz under a Kolmogorov spectrum, which is shorter than the magnetar's 5.54~s spin period. This result naturally explains the previously reported absence of pulse-to-pulse coherence at these frequencies. Kinematic modeling locates the dominant scattering screen at $1.6\pm0.1$~kpc away from the Earth, within the Sagittarius Arm. The screen coincides with the HII region JCMTSE~J180921.2$-$201932 and is unrelated to the magnetar's 2018 outburst suggested by earlier studies. A scintillation arc detected at 14.0~GHz represents the highest-frequency arc observed to date. The asymmetry of arcs is linearly correlated with a dispersion-measure gradient across the screen ($r = 0.959$, $p < 10^{-8}$). We also measure its refractive scintillation timescale, which is only $1.21\pm0.19$~d. Clear DISS 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 and provide a precise probe of the ionized interstellar medium in the Sagittarius Arm.