Volume 612, April 2018
|Number of page(s)||15|
|Published online||07 May 2018|
Energy distribution of relativistic electrons in the kiloparsec scale jet of M 87 with Chandra
Max-Planck-Institut für Kernphysik,
P.O. Box 103980,
2 ZAH, Institut für Theoretische Astrophysik, Heidelberg University, Philosophenweg 12, 69120 Heidelberg, Germany
3 Dublin Institute for Advanced Studies, 31 Fitzwilliam Place, Dublin 2, Ireland
4 Gran Sasso Science Institute, 7 viale Francesco Crispi, 67100 L’Aquila (AQ), Italy
5 MEPHI, Kashirskoe shosse 31, 115409 Moscow, Russia
Accepted: 24 January 2018
The X-ray emission from the jets in active galactic nuclei (AGN) carries important information on the distributions of relativistic electrons and magnetic fields on large scales. We reanalysed archival Chandra observations on the jet of M 87 from 2000 to 2016 with a total exposure of 1460 kiloseconds to explore the X-ray emission characteristics along the jet. We investigated the variability behaviours of the nucleus and the inner jet component HST-1, and confirm indications for day-scale X-ray variability in the nucleus contemporaneous to the 2010 high TeV γ-ray state. HST-1 shows a general decline in X-ray flux over the last few years consistent with its synchrotron interpretation. We extracted the X-ray spectra for the nucleus and all knots in the jet, showing that they are compatible with a single power law within the X-ray band. There are indications that the resultant X-ray photon index exhibit a trend, with slight but significant index variations ranging from ≃ 2.2 (e.g. in knot D) to ≃ 2.4−2.6 (in the outer knots F, A, and B). When viewed in a multiwavelength context, a more complex situation can be seen. Fitting the radio to X-ray spectral energy distributions (SEDs) assuming a synchrotron origin, we show that a broken power-law electron spectrum with break energy Eb around 1 (300 μG/B)1/2 TeV allows a satisfactory description of the multiband SEDs for most of the knots. However, in the case of knots B, C, and D we find indications that an additional high-energy component is needed to adequately reproduce the broad-band SEDs. We discuss the implications and suggest that a stratified jet model may account for the differences.
Key words: X-rays: galaxies / galaxies: individual: M 87 / radiation mechanisms: non-thermal
© ESO 2018
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