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Periodic Structure in the Megaparsec-scale Jet of PKS 0637–752

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Abstract

  • We present 18 GHz Australia Telescope Compact Array imaging of the megaparsec-scale quasar jet PKS 0637–752 with angular resolution ~0farcs58. We draw attention to a spectacular train of quasi-periodic knots along the inner 11'' of the jet, with average separation ~1.1 arcsec (7.6 kpc projected). We consider two classes of model to explain the periodic knots: those that involve a static pattern through which the jet plasma travels (e.g., stationary shocks) and those that involve modulation of the jet engine. Interpreting the knots as re-confinement shocks implies the jet kinetic power Q jet ~ 1046 erg s–1, but the constant knot separation along the jet is not expected in a realistic external density profile. For models involving modulation of the jet engine, we find that the required modulation period is 2 × 103 yr yr yr 5 yr. The lower end of this range is applicable if the jet remains highly relativistic on kiloparsec scales, as implied by the IC/CMB model of jet X-ray emission. We suggest that the periodic jet structure in PKS 0637–752 may be analogous to the quasi-periodic jet modulation seen in the microquasar GRS 1915 105, believed to result from limit cycle behavior in an unstable accretion disk. If variations in the accretion rate are driven by a binary black hole, the predicted orbital radius is 0.7 pc <~ a <~ 30 pc, which corresponds to a maximum angular separation of ~0.1-5 mas.

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  • 2012

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