Structure of the Accretion Disk in the Lensed Quasar Q2237+0305 from Multi-Epoch and Multi-Wavelength Narrow Band Photometry

We present estimates for the size and the logarithmic slope of the disk temperature profile of the lensed quasar Q2237+0305, independent of the component velocities. These estimates are based on six epochs of multi-wavelength narrowband images from the Nordic Optical Telescope. For each pair of lensed images and each photometric band, we determine the microlensing amplitude and chromaticity using pre-existing mid-IR photometry to define the baseline for no microlensing magnification. A statistical comparison of the combined microlensing data (6 epochs $\times$ 5 narrow bands $\times$ 6 image pairs) with simulations based on microlensing magnification maps gives Bayesian estimates for the half-light radius of $R_{1/2}=8.5^{+7.5}_{-4.0}\sqrt{ \langle M \rangle/0.3\, M_\odot}$ light-days, and $p=0.95\pm0.33$ for the exponent of the logarithmic temperature profile $T\propto R^{ -1/p}$. This size estimate is in good agreement with most recent studies. Other works based on the study of single microlensing events predict smaller sizes, but could be statistically biased by focusing on high-magnification events.