Optical spectroscopy of SDSS J004054.65-0915268: three possible scenarios for the classification. A z ~ 5 BL Lacertae, a blue FSRQ, or a weak emission line quasar

Optical spectroscopy of SDSS J004054.65-0915268: three possible scenarios for the classification. A z ~ 5 BL Lacertae, a blue FSRQ, or a weak emission line quasar