Detection of Superluminal Motion in the X-Ray Jet of M87

Bradford Snios, Paul. E. J. Nulsen, Ralph P. Kraft, C. C. Cheung, Eileen T. Meyer, William R. Forman, Christine Jones, Stephen S. Murray

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22 Citations (Scopus)


Chandra HRC observations are investigated for evidence of proper motion and brightness changes in the X-ray jet of the nearby radio galaxy M87. Using images spanning 5 yr, proper motion is measured in the X-ray knot HST-1, with a superluminal apparent speed of 6.3 +/- 0.4c, or 24.1 +/- 1.6 mas yr(-1), and in Knot D, with a speed of 2.4 +/- 0.6c. Upper limits are placed on the speeds of the remaining jet features. The X-ray knot speeds are in excellent agreement with existing measurements in the radio, optical, and ultraviolet. Comparing the X-ray results with images from the Hubble Space Telescope indicates that the X-ray and optical/UV emitting regions co-move. The X-ray knots also vary by up to 73% in brightness, whereas there is no evidence of brightness changes in the optical/UV. Using the synchrotron cooling models, we determine lower limits on magnetic field strengths of similar to 420 mu G and similar to 230 mu G for HST-1 and Knot A, respectively, consistent with estimates of the equipartition fields. Together, these results lend strong support to the synchrotron cooling model for Knot HST-1, which requires that its superluminal motion reflects the speed of the relativistic bulk flow in the jet.

Original languageEnglish
Article number8
Number of pages9
JournalThe Astrophysical Journal
Issue number1
Publication statusPublished - 1 Jul 2019
Externally publishedYes


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