A Seyfert Nucleus in BL Lacertae

We have obtained spectroscopic observations of the broad Ha line in BL Lacertae over a period of 30 months. These data show that the line equivalent width is anti-correlated with the continuum flux implying that the broad line emission is not powered primarily by synchrotron emission from the relativistic jet. The most probable explanation is that the broad line region in BL Lacertae is photoionized by continuum emission from an accretion disk which at optical wavelengths is dominated by the Doppler beamed synchroton continuum.