Weak lensing by minifilament or minivoid as the origin of flux-ratio anomalies in lensed quasar MG0414+0534

We explore the weak lensing effects by ministructures in the line of sight in a quadruply lensed quasar MG0414+0534 that shows an anomaly in the flux ratios. We find that the observed flux-ratio anomaly can be explained by a presence of either a minifilament or a minivoid in the line of sight with a surface mass density of the order of 10^8-9 h^-1 M_⊙ arcsec^-2 without taking into account any subhaloes in the lensing galaxy. The astrometric perturbation by a possible minifilament/minivoid at the primary lens plane is ≲0.001 arcsec and the amplitudes of convergence perturbations due to these perturbers are δκ ∼ 0.004-0.008 at the place of an image that shows anomaly. In order to discriminate models with the line-of-sight ministructures from those with a subhalo(es) in the lensing galaxy, we need to precisely measure the projected convergence and shear perturbations around the lensing galaxy. The differential magnification effect could break the model degeneracy if the source size is ≳100 pc. Observation at the submillimetre band using interferometers will enable us to determine the origin of anomalies in the flux ratios.