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Discrete knot ejection from the jet in a nearby low-luminosity active galactic nucleus, M81∗

Nature Physics volume 12, pages 772–777 (2016)Cite this article

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Abstract

Observational constraints of the relativistic jets from black holes have largely come from the most powerful and extended jets1,2, leaving the nature of the low-luminosity jets a mystery3. M81∗ is one of the nearest low-luminosity jets and it emitted an extremely large radio flare in 2011, allowing us to study compact core emission with unprecedented sensitivity and linear resolution. Using a multiwavelength campaign, we were able to track the flare as it re-brightened and became optically thick. Simultaneous X-ray observations indicated that the radio re-brightening was preceded by a low-energy X-ray flare at least 12 days earlier. Associating the time delay (tdelay) between the two bands with the cooling time in a synchrotron flare4,5, we find that the magnetic field strength was 1.9 < B < 9.2 G, which is consistent with magnetic field estimate from spectral energy distribution modelling6, B < 10.2 G. In addition, Very Long Baseline Array observations at 23 GHz clearly illustrate a discrete knot moving at a low relativistic speed of vapp/c = 0.51 ± 0.17 associated with the initial radio flare. The observations indicate radial jet motions for the first time in M81∗. This has profound implications for jet production, as it means radial motion can be observed in even the lowest-luminosity AGN, but at slower velocities and smaller radial extents (≍104 RG).

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Figure 1: Radio flare spectral energy distribution.
Figure 2: X-ray flare.
Figure 3: High-resolution radio knot motion.
Figure 4: Changes in knot position and brightness.
Figure 5: Constraints on orientation.
Figure 6: VLBA 16 January 2012 (MJD 55943) observations.

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Acknowledgements

A.L.K. acknowledges support provided by NASA through an Einstein Postdoctoral Fellowship (grant number PF4-150125) awarded by the Chandra X-ray Center, which is operated by the Smithsonian Astrophysical Observatory for NASA under contract NAS8-03060.

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Authors and Affiliations

  1. Department of Physics, Stanford University, 382 Via Pueblo Mall, Stanford, California 94305, USA

    Ashley L. King

  2. Department of Astronomy, University of Michigan, 1085 S. University Avenue, Ann Arbor, Michigan 48109-1107, USA

    Jon M. Miller, Kayhan Gültekin & Mark T. Reynolds

  3. Department of Physics and Astronomy, York University, Toronto, M3J 1P3 Ontario, Canada

    Michael Bietenholz & Norbert Bartel

  4. Hartebeesthoek Radio Observatory, PO Box 443, Krugersdorp 1740, South Africa

    Michael Bietenholz

  5. National Radio Astronomical Observatory, PO Box O, Socorro, New Mexico 87801, USA

    Amy Mioduszewski

  6. NRC Dominion Radio Astrophysical Observatory, Penticton, British Columbia V2A 6J9, Canada

    Michael Rupen

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  1. Ashley L. King
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  2. Jon M. Miller
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Contributions

A.L.K. led the data reduction and analysis, with contributions from J.M.M., M.B. and A.M. K.G., M.T.R., M.R. and N.B. contributed to discussion and interpretation.

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Correspondence to Ashley L. King.

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The authors declare no competing financial interests.

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King, A., Miller, J., Bietenholz, M. et al. Discrete knot ejection from the jet in a nearby low-luminosity active galactic nucleus, M81∗. Nature Phys 12, 772–777 (2016). https://doi.org/10.1038/nphys3724

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