Multiple imaging of the quasar 2005 + 403 formed by anisotropic scattering

Abstract

ABSTRACT We report on the low Galactic latitude (b = 4${_{.}^{\circ}}$3) quasar 2005 + 403, the second active galactic nuclei, in which we detected a rare phenomenon of multiple imaging induced by refractive-dominated scattering. The manifestation of this propagation effect is revealed at different frequencies (≲ 8 GHz) and epochs of Very Long Baseline Array (VLBA) observations. The pattern formed by anisotropic scattering is stretched out along the line of constant Galactic latitude with a local position angle, PA ≈ 40° showing 1–2 sub-images, often on either side of the core. Analysing the multifrequency VLBA data ranging from 1.4 to 43.2 GHz, we found that both the angular size of the apparent core component and the separation between the primary and secondary core images follow a wavelength squared dependence, providing convincing evidence for a plasma scattering origin for the multiple imaging. Based on the Owens Valley Radio Observatory long-term monitoring data at 15 GHz obtained for 2005 + 403, we identified the characteristic flux density excursions occurred in 2019 April and May and attributed to an extreme scattering event (ESE) associated with the passage of a plasma lens across the line of sight. Modelling the ESE, we determined that the angular size of the screen is 0.4 mas and it drifts with the proper motion of 4.4 mas yr−1. Assuming that the scattering screen is located in the highly turbulent Cygnus region, the transverse linear size and speed of the lens with respect to the observer are 0.7 au and 37 km s−1, respectively.