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Publication - Professor Mark Birkinshaw

    Variability and Proper Motion of X-ray Knots in the Jet of Centaurus A


    Snios, B, Wykes, S, Nulsen, PEJ, Kraft, RP, Meyer, ET, Birkinshaw, M, Worrall, DM, Hardcastle, MJ, Roediger, E, Forman, WR & Jones, C, 2018, ‘Variability and Proper Motion of X-ray Knots in the Jet of Centaurus A’. Astrophysical Journal.


    We report results from Chandra observations analyzed for evidence of
    variability and proper motion in the X-ray jet of Centaurus A. Using data
    spanning 15 years, collective proper motion of 11.3±3.3 mas yr−1, or
    0.68±0.20c, is detected for the fainter X-ray knots and other substructure
    present within the jet. The three brightest knots (AX1A, AX1C, and BX2) are
    found to be stationary to an upper limit of 0.10c. Brightness variations up
    to 27% are detected for several X-ray knots in the jet. For the fading knots,
    BX2 and AX1C, the changes in spectral slope expected to accompany synchrotron
    cooling are not found, ruling it out and placing upper limits of ≃80 μG for each of their magnetic field strengths. Adiabatic expansion can
    account for the observed decreases in brightness. Constraints on models for the
    origin of the knots are established. Jet plasma overrunning an obstacle is
    favored as the generator of stationary knots, while moving knots are likely
    produced either by internal differences in jet speed or the late stages of jet
    interaction with nebular or cloud material.

    Full details in the University publications repository