Multiwavelength Observations of Radio-quiet Quasars with Weak Emission
  Lines
  We present radio and X-ray observations, as well as optical light curves, for
a subset of 26 BL Lac candidates from the Sloan Digital Sky Survey (SDSS)
lacking strong radio emission and with z<2.2. Half of these 26 objects are
shown to be stars, galaxies, or absorbed quasars. We conclude that the other 13
objects are Active Galactic Nuclei (AGN) with abnormally weak emission
features; ten of those 13 are definitively radio-quiet, and, for those with
available optical light curves, their level of optical flux variability is
consistent with radio-quiet quasars. We cannot exclude the possibility that
some of these 13 AGN lie on the extremely radio-faint tail of the BL Lac
distribution, but our study generally supports the notion that all BL Lac
objects are radio-loud. These radio-quiet AGN appear to have intrinsically weak
or absent broad emission line regions, and, based on their X-ray properties, we
argue that some are low-redshift analogs to weak line quasars (WLQs). SDSS BL
Lac searches are so far the only systematic surveys of the SDSS database
capable of recovering such exotic low-redshift WLQs. There are 71 more z<2.2
radio-quiet BL Lac candidates already identified in the SDSS not considered
here, and many of those might be best unified with WLQs as well. Future studies
combining low- and high-redshift WLQ samples will yield new insight on our
understanding of the structure and formation of AGN broad emission line
regions.
