Image Flux Ratios of Gravitationally Lensed HS 0810+2554 with High Resolution Infrared Imaging


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We report near simultaneous imaging using LMIRCam on the LBTI of the quadruply imaged lensed quasar HS 0810+2554 at wavelengths of 2.16, 3.7 and $4.78~mu$m with a Full Width Half Max (FWHM) spatial resolution of $0^{primeprime}!!.13$, $0^{primeprime}!!.12$ and $0^{primeprime}!!.15$ respectively, comparable to HST optical imaging. In the $rm{z} = 1.5$ rest frame of the quasar, the observed wavelengths correspond to 0.86, 1.48, and $1.91~mu$m respectively. The two brightest images in the quad, A and B, are clearly resolved from each other with a separation of $0.187^{primeprime}$. The flux ratio of these two images (A/B) trends from 1.79 to 1.23 from 2.16 to $4.78~mu$m. The trend in flux ratio is consistent with the $2.16~mu$m flux originating from a small sized accretion disk in the quasar that experiences only microlensing. The excess flux above the contribution from the accretion disk at the two longer wavelengths originates from a larger sized region that experiences no microlensing. A simple model employing multiplicative factors for image B due to stellar microlensing $(m)$ and sub-structure millilensing $(M)$ is presented. The result is tightly constrained to the product $mtimes M=1.79$. Given the observational errors, the 60% probability contour for this product stretches from $m= 2.6$, $M = 0.69$ to $m= 1.79$, $M = 1.0$, where the later is consistent with microlensing only.

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