PSJ2107-1611: a new wide-separation, quadruply imaged lensed quasar with flux ratio anomalies

TL;DR

The paper reports the discovery of a new quadruply imaged lensed quasar with flux ratio anomalies, identified using neural networks and confirmed through multi-wavelength observations, providing a valuable system for studying quasar structure and lensing effects.

Contribution

This work introduces a novel neural network-based method for discovering wide-separation quadruply lensed quasars and presents the first detailed analysis of PSJ2107-1611, highlighting flux ratio anomalies.

Findings

Discovery of PSJ2107-1611 with flux ratio anomalies

Optical/near-IR flux ratios inconsistent with smooth mass models

Radio flux ratios compatible with smooth macromodel

Abstract

We report the discovery of PSJ2107-1611, a fold-configuration 4.3"-separation quadruply lensed quasar with a bright lensed arc. It was discovered using a convolutional neural network on Pan-STARRS gri images of pre-selected quasar candidates with multiple nearby Pan-STARRS detections. Spectroscopic follow-up with EFOSC2 on the ESO 3.58m New Technology Telescope reveals the source to be a quasar at z = 2.673, with the blended fold image pair showing deformed broad lines relative to the other images. The flux ratios measured from optical to near-infrared imaging in the Canada-France-Hawaii Telescope Legacy Survey, Pan-STARRS, the Legacy Surveys, and the Vista Hemisphere Survey are inconsistent with a smooth mass model as the fold pair images are about 15 times too faint. Variability, time delay effects, and reddening are ruled out through multiple-epoch imaging and color information. The system is marginally resolved in the radio in the Very Large Array Sky Survey S-band, where it has a 10 mJy detection. The radio flux ratios are compatible with the smooth mass macromodel. This system offers a unique tool for future studies of quasar structure with strong and microlensing. A more detailed analysis of follow-up with JWST/MIRI, VLT/MUSE, VLT/ERIS, and data from the European Very Long Baseline Interferometer will be presented in an upcoming paper.