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TOPIC: NGC 6251

Blobrana

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Posts: 131433

Date: Feb 7 16:47 2012

2FGLJ1629.4+8236	Permalink

Title: Suzaku X-ray Imaging of the Extended Lobe in the Giant Radio Galaxy NGC6251 Associated with the Fermi-LAT Source 2FGLJ1629.4+8236 Authors: Y. Takeuchi, J. Kataoka, L. Stawarz, Y. Takahashi, K. Maeda, T. Nakamori, C. C. Cheung, A. Celotti, Y. Tanaka, T. Takahashi We report the results of a Suzaku X-ray imaging study of NGC6251, a nearby giant radio galaxy with intermediate FR I/II radio properties. Our pointing direction was centred on the gamma -ray emission peak recently discovered with Fermi-LAT around the position of the north-west radio lobe 15 arcmin offset from the nucleus. After subtracting two "off-source" pointings adjacent to the radio lobe, and removing possible contaminants in the XIS field of view, we found significant residual X-ray emission most likely diffuse in nature. The spectrum of the excess X-ray emission is well fit by a power law with photon index \Gamma = 1.90 ± 0.15 and a 0.5 - 8 keV flux of 4 x 10^{-13} erg cm^{-2} s^{-1}. We interpret this diffuse X-ray emission component as being due to inverse-Compton up-scattering of the cosmic microwave background photons by ultrarelativistic electrons within the lobe, with only a minor contribution from the beamed emission of the large-scale jet. Utilizing archival radio data for the source, we demonstrate by means of broad-band spectral modelling that the -ray flux of the Fermi-LAT source 2FGL J1629.4+8236 may well be accounted for by the high-energy tail of the inverse-Compton continuum of the lobe. Thus, this claimed association of gamma-rays from the north-west lobe of NGC6251, together with the recent Fermi-LAT imaging of the extended lobes of Centaurus A, indicates that particles may be efficiently (re-)accelerated up to ultrarelativistic energies within extended radio lobes of nearby radio galaxies in general. Read more (746kb, PDF) __________________

Blobrana

L

Posts: 131433

Date: Sep 30 03:41 2011

NGC 6251	Permalink

Title: The Suzaku View of the Disk-Jet Connection in the Low Excitation Radio Galaxy NGC 6251 Authors: D. A. Evans (1, 2), A. C. Summers (2), M. J. Hardcastle (3), R. P. Kraft (1), P. Gandhi (4), J. H. Croston (5), J. C. Lee (1) ((1) Harvard-Smithsonian Centre for Astrophysics, Cambridge, MA, (2) Elon University, Elon, NC, (3) School of Physics, Astronomy and Mathematics, University of Hertfordshire, Hatfield, UK, (4) Institute of Space and Astronautical Science (ISAS), Japan Aerospace Exploration Agency, Sagamihara, Japan, (5) School of Physics and Astronomy, University of Southampton, Southampton, UK) We present results from an 87-ks Suzaku observation of the canonical low-excitation radio galaxy (LERG) NGC 6251. We have previously suggested that LERGs violate conventional AGN unification schemes: they may lack an obscuring torus and are likely to accrete in a radiatively inefficient manner, with almost all of the energy released by the accretion process being channelled into powerful jets. We model the 0.5-20 keV Suzaku spectrum with a single power law of photon index \Gamma=1.82^{+0.04}_{-0.05}, together with two collisionally ionised plasma models whose parameters are consistent with the known galaxy- and group-scale thermal emission. Our observations confirm that there are no signatures of obscured, accretion-related X-ray emission in NGC 6251, and we show that the luminosity of any such component must be substantially sub-Eddington in nature. Read more (769kb, PDF) __________________

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