Parsec-scale jet properties of the gamma-ray quasar 3C 286

Abstract

The quasar 3C 286 is one of two compact steep-spectrum sources detected by the Fermi/Large Area Telescope. Here, we investigate the radio properties of the parsec(pc)-scale jet and its (possible) association with the gamma-ray emission in 3C 286. The Very Long Baseline Interferometry (VLBI) images at various frequencies reveal a one-sided core–jet structure extending to the south-west at a projected distance of ∼1 kpc. The component at the jet base showing an inverted spectrum is identified as the core, with a mean brightness temperature of 2.8 × 10⁹ K. The jet bends at about 600 pc (in projection) away from the core, from a position angle of −135° to −115°. Based on the available VLBI data, we inferred the proper-motion speed of the inner jet as 0.013 ± 0.011 mas yr⁻¹ (β_app = 0.6 ± 0.5), corresponding to a jet speed of about 0.5 c at an inclination angle of 48° between the jet and the line of sight of the observer. The brightness temperature, jet speed and Lorentz factor are much lower than those of gamma-ray-emitting blazars, implying that the pc-scale jet in 3C 286 is mildly relativistic. Unlike blazars in which gamma-ray emission is in general thought to originate from the beamed innermost jet, the location and mechanism of gamma-ray emission in 3C 286 may be different as indicated by the current radio data. Multiband spectrum fitting may offer a complementary diagnostic clue of the gamma-ray production mechanism in this source.