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          Institute: MPI für Kernphysik     Collection: High-Energy Astrophysics     Display Documents

ID: 281519.0, MPI für Kernphysik / High-Energy Astrophysics
Dynamics and high-energy emission of the flaring HST-1 knot in the M 87 jet
Authors:Stawarz, Lucasz; Aharonian, Felix; Kataoka, J.; Ostrowski, M.; Siemiginowska, A.; Sikora, M.
Research Context:radiation mechanisms: non-thermal: shock waves: galaxies: active: galaxies: jets: galaxies: individual: M 87
Date of Publication (YYYY-MM-DD):2006-07
Title of Journal:Monthly Notices of the Royal Astronomical Society
Journal Abbrev.:MNRAS
Volume:Online early
Sequence Number of Article:1365-2966.2006.10525.x
Copyright:2006 The Authors. Journal compilation © 2006 RAS
Review Status:Peer-review
Audience:Experts Only
Abstract / Description: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.
Free Keywords:radiation mechanisms: non-thermal: shock waves: galaxies: active: galaxies: jets: galaxies: individual: M 87
External Publication Status:published
Document Type:Article
Affiliations:MPI für Kernphysik/Group of W. Hofmann/High Energy Astrophysics (F. Aharonian)
External Affiliations:AC(Department of Physics, Tokyo Institute of Technology, 2-12-1, Ohokayama, Meguro, Tokyo 152-8551, Japan), AD(Obserwatorium Astronomiczne, Uniwersytet Jagielloński, ul. Orla 171, 30-244 Kraków, Poland
Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, USA
Centrum Astronomiczne im. M. Kopernika, ul. Bartycka 18, 00-716 Warszawa, Poland
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