The Possible Origins of the $VR$ Magnification Ratios of Q0957+561AB

Abstract

Abstract. We present V R magnification ratios of the double quasar Q0957+561AB, which are inferred from frames taken with the 2.56m Nordic Optical Telescope. From two different photometric techniques (pho2comC and psf phot) and a reasonable range for the time delay in the system (415-430 days), we find optical continuum ratios depending on the wavelength. These chromatic ratios are consistent with either differential extinction in a dust system or gravitational microlensing in the deflector. Although the dusty scenario is only viable for a compact dust cloud in the line of sight to the A component, the possible values for the differential extinction and the ratio of total to selective extinction in the V band are surprisingly reasonable. To decide on the true origin of the anomalous ratios (extinction, microlensing or a mixed scenario), we are carrying out new monitoring campaigns and planning detailed observations from the best ground-based and space telescopes.