SETI bioastro: Have we detected the most luminous ULX so far?

From: LARRY KLAES (ljk4_at_msn.com)
Date: Mon Jul 24 2006 - 20:13:08 PDT

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    Astrophysics, abstract
    astro-ph/0607501

    From: Giovanni Miniutti [view email]

    Date (v1): Fri, 21 Jul 2006 12:54:52 GMT (781kb)
    Date (revised v2): Mon, 24 Jul 2006 12:11:42 GMT (783kb)

    Have we detected the most luminous ULX so far?

    Authors: G. Miniutti (1), G. Ponti (2,3), M. Dadina (3), M. Cappi (3), G.
    Malaguti (3), A.C. Fabian (1), P. Gandhi (1,4) ((1) Institute of Astronomy,
    Cambridge; (2) Dip. di Astronomia, Univ. di Bologna; (3) IASF/INAF Bologna;
    (4) ESO, Santiago)

    Comments: MNRAS Letters in press; minor correction at the end of Section2

    We report the XMM-Newton detection of a moderately bright X-ray source
    superimposed on the outer arms of the inactive spiral galaxy MCG-03-34-63
    (z=0.0213). It is clearly offset from the nucleus (by about 19'') but well
    within the D25 ellipse of the galaxy, just along its bar axis. The field has
    also been observed with the HST enabling us to compute a lower limit of > 94
    on the X-ray to optical flux ratio which, together with the X-ray spectrum
    of the source, argues against a background AGN. On the other hand, the
    detection of excess X-ray absorption and the lack of a bright optical
    counterpart argue against foreground contamination. Short-timescale
    variability is observed, ruling out the hypothesis of a particularly
    powerful supernova. If it is associated with the apparent host galaxy, the
    source is the most powerful ULX detected so far with a peak luminosity of
    1.35x10^41 erg/s in the 0.5-7 keV band. If confirmed by future
    multi-wavelength observations, the inferred bolometric luminosity (about
    3x10^41 erg/s) requires a rather extreme beaming factor (larger than 115) to
    accommodate accretion onto a stellar-mass black hole of 20 solar masses and
    the source could represent instead one of the best intermediate-mass black
    hole candidate so far. If beaming is excluded, the Eddington limit implies a
    mass of >2300 solar masses for the accreting compact object.

    http://arxiv.org/abs/astro-ph/0607501


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