A First Close Look at the Balmer Edge Behavior of the Quasar Big Blue Bump

We have found for the first time a Balmer edge feature in the polarized flux spectrum of a quasar (Ton 202). The edge feature is seen as a discontinuity in the slope, rather than as a discontinuity in the absolute flux. Since the polarized flux contains essentially no broad emission lines, it is considered to arise interior to the broad emission line region, showing the spectrum with all the emissions outside the nucleus scraped off and removed. Therefore, the polarized flux spectrum is likely to reveal features intrinsic to the Big Blue Bump emission. In this case, the existence of the Balmer edge feature, seen in absorption in the shorter wavelength side, indicates that the Big Blue Bump is indeed thermal and optically thick.