Different polarized components of the quasar 3C 286 revealed by FAST

Abstract

3C 286, a well-known radio calibrator, exhibits the stability in both of total flux density (FD) and polarization parameters. However, its stable and luminous interstellar radio signal may encounter interplanetary scintillation (IPS) due to density irregularities in the solar wind within the heliosphere. In this work, we analyze high-time-resolution observations of 3C 286 obtained with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) from 2019 to 2023. Our analysis reveals that IPS affects the polarized flux densities of the Stokes I, Q, and U parameters, whereas Stokes V shows no detectable IPS-induced variations. The IPS variations detected in Stokes I are synchronous with those in Stokes U, while those in Stokes Q exhibit greater randomness. The crosscorrelation function (CCF) results indicate no time delay between Stokes I and U, but a delay of approximately 2.8 seconds between Stokes I and Q. This suggests that the different polarized radio emissions of 3C 286 originate from distinct emission regions, specifically the core and the southwestern jet. Furthermore, the projections of the radio core and jet component onto the scintillation screen at 1 AU yield a solar wind plasma speed of $\sim 637$ km/s.

Figures (6)

• Figure 1: The original temporally averaged bandpass spectra (black solid lines) and corresponding baselines (red dashed lines) fitted by ArPLS algorithm for AA ( a), BB ( b), CR ( c), and CI ( d).
• Figure 2: Long-term monitoring of quasar 3C 286 from 2019 to 2023 with FAST. Shown are the deviations of the total flux density (a), linear polarization (b), circular polarization (c), and linear polarization position angle (d) from their respective best-estimated mean values. The error bars indicate the fluctuations of time series on second timescales, which are attributed to IPS caused by solar wind turbulence.
• Figure 3: The light curves of total flux density ( a), linear polarization ( b), circular polarization ( c), and polarization position angle ( d) of 3C 286 from the FAST observations conducted on September 30, 2022. The comparison with Figure \ref{['fig:LC']} shows that while FD and LP remain stable, the liner polarization position angle exhibits larger apparent fluctuations due to uncorrelated IPS-induced variations in Stokes $Q$ and $U$. The scintillation index of FD in panel a is $m=0.018$.
• Figure 4: The averaged flux densities and dynamic spectra of Stokes I ( a), Q ( b), U ( c), and V ( d) from the FAST observations conducted on September 30, 2022. The obscured horizontal stripes indicate the RFIs mask. Stokes U shows variations coherent with Stokes I, while Stokes Q, although exhibiting some similar variations in some time intervals, primarily manifests as relatively stochastic fluctuations. The Stokes V is near zero for all observation.
• Figure 5: From left to right: the ACF results of Stokes I, Q and U. The bold red dashed curves represent Gaussian fits, and the horizontal red dashed lines mark the e-folding level. The derived characteristic timescales are $\tau_I$ = 0.206 s, $\tau_Q$ = 0.560 s, and $\tau_U$ = 0.187 s. The scintillation indices of Stokes I, Q, and U are $m_I = 0.018$, $m_Q = 0.079$, and $m_U = 0.020$, respectively.