Dynamics and high-energy emission of the flaring HST-1 knot in the M 87 jet

By L. Stawarz, F. Aharonian, J. Kataoka, M. Ostrowski, Aneta Siemiginowska, M. Sikora. 2006

134 citations recorded by the source corpus.

Stimulated by recent observations of a giant radio-to-X-ray synchrotron flare from Hubble Space Telescope (HST)-1, the innermost knot of the M 87 jet, as well as by the detection of a very high energy γ-ray emission from M 87, we investigated the dynamics and multiwavelength emission of the HST-1 region. We study thermal pressure of the hot interstellar medium in M 87 and argue for the presence of a gaseous condensation in its central parts. We postulate that this additional feature is linked to the observed central stellar cusp of the elliptical host. Interaction of the jet with such a feature is likely to result in the formation of a stationary converging/diverging reconfinement/reflected shock structure in the innermost parts of the M 87 jet. We show that for a realistic set of the outflow parameters, a stationary and a flaring part of the HST-1 knot located ∼100 pc away from the active centre can be associated with the decelerated portion of the jet matter placed immediately downstream of the point where the reconfinement shock reaches the jet axis. We discuss a possible scenario explaining a broad-band brightening of the HST-1 region related to the variable activity of the central core. In particular, we show that assuming a previous epoch of the high central black hole activity resulting in ejection of excess particles and photons down along the jet, one may first expect a high-energy flare of HST-1 due to inverse-Comptonization of the nuclear radiation, followed after a few years by an increase in the synchrotron continuum of this region. The synchrotron flare itself could be accompanied by a subsequent inverse-Compton brightening due to upscattering of the ambient (mostly starlight) photons. If this is the case, then the recently observed order-of-magnitude increase in the knot luminosity in all spectral bands could be regarded as an unusual echo of the order-of-magnitude outburst that had happened previously (and could be eventually observed some ∼40 yr ago) in the highly relativistic active core of the M 87 radio galaxy. We show that very high energy γ-ray fluxes expected in a framework of the proposed scenario are consistent with the observed ones.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/b0f7f8323f4d656b9e631eae141f6c1b46987fbe

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In Astronomy and Astrophysics

1. F. Tavecchio
2. G. Ghisellini
3. Bing Zhang
4. D. Harris
5. C. Dermer
6. L. Maraschi
7. E. Orlando
8. J. Finke

In Nuclear and High Energy Physics

1. F. Tavecchio
2. G. Ghisellini
3. D. Harris
4. C. Dermer
5. L. Maraschi
6. J. Finke
7. E. Orlando
8. A. Reimer

Citations in the corpus

• Gamma-ray binaries and related systems (2013, background): “Recollimation shocks have also been invoked to explain the radio brightening of ejecta moving through (nearly) standing shocks in M87 and blazars (Stawarz et al. 2006; Bromberg & Levinson 2009; Agudo et al. 2011).”
• Production of TeV Gamma Radiation in the Vicinity of the Supermassive Black Hole in the Giant Radio Galaxy M87 (2007, background): “…TeV γ-ray production range from large scale structures of the kpc jet (Stawarz et al. 2005) to a compact peculiar hot spot (the so-called HST -1 knot) at a distance 100 pc along the jet (Stawarz et al. 2006) and inner (sub-parsec) parts of the jet (Georganopoulos et al. 2005; Reimer et al. 2005).”
• First M87 Event Horizon Telescope Results. V. Physical Origin of the Asymmetric Ring (2019, unknown): “…the jet width profile (Asada & Nakamura 2012; Hada et al. 2013; Nakamura et al. 2018), the total jet power at kilo-parsec scale (Owen et al. 2000; Stawarz et al. 2006), the jet power (e.g., Kino et al. 2014, 2015), the core shift (Hada et al. 2011), and the symmetric limb-brightening structure…”
• Spine–sheath layer radiative interplay in subparsec‐scale jets and the TeV emission from M87 (2008, background): “This extreme phenomenlogy is described by Stawarz et al. (2006) on the assumption that HST-1 marks the recollimation shock of the jet.”
• Superluminal Radio Features in the M87 Jet and the Site of Flaring TeV Gamma-Ray Emission (2007, background): “…our X-ray observations establish flux doubling timescalestvar of 0.14 yrs (Harris et al. 2006), which constrainsRvar < ctvarδ ≈ 0.022δ pc. Recently, Stawarz et al. (2006) showed that the position of the HST-1 knot agrees with the expected location of a ‘reconfinement nozzle’ formed within the…”
• MAGIC DISCOVERY OF VERY HIGH ENERGY EMISSION FROM THE FSRQ PKS 1222+21 (2011, background): “An alternative possibility is that the jet experiences a strong recollimation forming a small emitting nozzle (e.g. Nalewajko & Sikora 2009) as already suggested for M87 and PKS 2155- 304 (e.g. Bromberg & Levinson 2009; Stawarz et al. 2006).”
• FERMI LARGE AREA TELESCOPE GAMMA-RAY DETECTION OF THE RADIO GALAXY M87 (2009, background): “This knot is more compact than knot A, and its IC emission is expected to be further enhanced by the increased energy densities of the surrounding circumnuclear and galactic photon fields, as well of the comoving synchrotron radiation (Stawarz et al. 2006).”