High-frequency observations and spectrum of the jet in M 87
This review collects the current fund of ground-based observations at v>1014 Hz which allows to determine the overall synchrotron spectrum of the jet in M 87 very accurately. Beyond knot D (at 3″ distance from the core), the spectrum is characterized by a straight power-law S v ∼ v −0.66 which cuts off steeply at some frequency v c The optically observed spectral variations along the jet are caused by changes in the cutoff frequency between v c =4×1015 Hz and v c =7 × 1014 Hz, while the power-law index between 1010 and 1014 Hz stays amazingly constant at α PL =−0.66±0.02. We demonstrate that an ubiquitous particle distribution function N(E)∼E −2.32 which cuts off steeply at a maximum energy E c =106 m e c 2, together with local variations of the magnetic field strength, accounts well for both the observed variation of v c and the apparent brightness distribution along the jet (i.e. the “knots”). The global particle spectrum might even be maintained into the inner lobes — albeit the eastern, “un-jetted” side seems to contain a steeper particle spectrum N(E) ∼ E −2.65. Thus, permanent particle re-acceleration seems required all along the jet and in the inner lobes.
Recent high-resolution observations with the HST (spatial scale ≲ 0″.1) seem to support this general behaviour of the kpc jet beyond knot D. However in the inner 300 pc from the core, rapidly evolving optical features with deviating synchrotron spectra are found. A careful analysis of their time-dependence (on time-scales comparable to the synchrotron loss-time τ syn ⋍ 10 years) might eventually help to understand the nature of the particle acceleration process. The X-ray emission from the jet is most likely of synchrotron origin. It seems to arise from compact substructures where locally the maximum particle energy is boosted above its steady state value to E c >5 × 106 m e c 2.
KeywordsSurface Brightness Radio Galaxy Extragalactic Radio Source Synchrotron Spectrum High Surface Brightness
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- Carilli, C.L. and Harris, D.E. (eds.) 1996: “Cygnus A — Study of a Radio Galaxy”, Cambridge University Press, Cambridge U.K.Google Scholar
- Curtis, H.D. 1918, Lick Obs. Publ. 13, 11Google Scholar
- Meisenheimer, K., Röser, H.-J. and Schlötelburg, M. 1989b, in E. Meurs and R. Fosbury (eds.): Extranuclear Activity in Galaxies, ESO Proceedings Garching.Google Scholar
- Neumann, M. 1994: PhD Thesis, University of Heidelberg.Google Scholar
- Owen, F.N., Hardee, P.E. and Bignell 1980, Astrophys. J. (Lett.) 239, L11Google Scholar
- Perez-Fournon, I., Colina, L., Gonzalez-Serrano, J.I. and Biermann, P.L. 1988, Astrophys. J. (Lett.) 329, L81Google Scholar
- Schlötelburg, M., Meisenheimer, K. and Röser, H.-J. 1988, Astron. Astrophys. (Lett.) 202, L23Google Scholar
- Shklovsky, I.S. 1953, Doklady Akad. Nauk. U.S.S.R. 90, 983Google Scholar