GB6 J1058+5628: A new quasi-periodic BL Lac object from the asiago plate archive

摘要

We present the historic photographic light curves of three little known blazars (two BL Lac objects and one FSRQ), GB6 J1058+5628, GB6 J1148+5254, and GB6 J1209+4119, spanning a time interval of about 50 years, mostly built using the Asiago plate archive. All objects show evident long-term variability, over which short-term variations are superposed. One source, GB6 J1058+5628, showed a marked quasi-periodic variability of 1 mag on timescale of about 6.3 years, making it one of the few BL Lac objects with a quasi-periodic behavior.