A Study of Gravitational Lens Chromaticity using Ground-based Narrow Band Photometry

Abstract

We present observations of wavelength-dependent flux ratios for four gravitational lens systems (SDSS~J1650+4251, HE~0435$-$1223, FBQ 0951+2635, and Q~0142$-$100) obtained with the Nordic Optical Telescope. The use of narrowband photometry, as well as the excellent seeing conditions during the observations, allows us to study their chromatic behavior. For SDSS~J1650+4251, we determine the extinction curve of the dust in the $z_L=0.58$ lens galaxy and find that the 2175 Å\ feature is absent. In the case of HE~0435$-$1223, we clearly detect chromatic microlensing. This allows us to estimate the wavelength-dependent size of the accretion disk. We find an R-band disk size of $r_s^R=13\pm 5$ light days for a linear prior on $r_s^R$ and $r_s^R=7\pm 6$ light days for a logarithmic prior. For a power-law size-wavelength scaling of $r_s\propto {\lambda }^p$, we were able to constrain the value of the exponent to $p=1.3\pm 0.3$ for both $r_s^R$ priors, which is in agreement with the temperature profiles of simple thin disk models ($p=4/3$).

35 pages, 13 figures, and 6 tables. Matches accepted version, ApJ in press

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Cited by in corpus (1)

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