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The buried Balmer-edge signatures from quasars
In our previous paper, we reported the detection of a Balmer edgeabsorption feature in the polarized flux of one quasar (Ton202). We havenow found similar Balmer edge features in the polarized flux of fourmore quasars (4C09.72, 3C95, B21208+32, 3C323.1), and possibly a fewmore, out of 14 newly observed with the Very Large Telescope and theKeck Telescope. In addition, we also re-observed Ton202, but we did notdetect such a dramatic feature, apparently due to polarizationvariability (the two observations are 1 yr apart). The polarizationmeasurements of some quasars are affected by an interstellarpolarization in our Galaxy, but the measurements have been corrected forthis effect reasonably well.As the broad emission lines are essentially unpolarized and thepolarization is confined only to the continuum in the five quasarsincluding Ton202 in both epochs, the polarized flux is considered tooriginate interior to the broad emission-line region. The Balmer edgefeature seen in the polarized flux is most simply interpreted as anintrinsic spectral feature of the quasar ultraviolet/optical continuum,or the `Big Blue Bump' emission. In this case, the edge feature seen inabsorption indeed indicates the thermal and optically thick nature ofthe continuum emitted. However, we also discuss other possibleinterpretations.
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