Detection of a Peculiar Drift in the Nuclear Radio Jet of the TeV Blazar Markarian 501

Mrk 501 is one of the most prominent TeV-emitting blazars and belongs to class high synchrotron peaked (HSP) blazars. The Doppler factors derived from jet kinematics are much too low provide sufficient beaming for detected high-energy emission (the so-called Lorentz factor crisis). This BL Lac object also a prime example misaligned AGN with an approximately 90∘ difference in orientation between inner parsec-scale kpc-scale structure. We have performed detailed analysis pc-scale kinematics, based on 23 years VLBA observations (at 15 GHz) find, addition robustly consolidating already claimed stationary features hinted absence component ejections, significant drift outer nuclear jet. two outermost move somewhat higher but still subluminal speeds. Albeit, they orthogonally jet, which itself does not partake drifting motion. effect this intriguing that appears strongly curved at first (1995) then straighten out (2018). To our knowledge, time orthogonal swing just part has been observed. discuss possible physical nature turning maneuver. In addition, we report evidence emission, likely originates spine–sheath