Mon. Not. R. Astron. Soc., 445, 290-300 (2014/November-3)
The radio/X-ray domain of black hole X-ray binaries at the lowest radio luminosities.
GALLO E., MILLER-JONES J.C.A., RUSSELL D.M., JONKER P.G., HOMAN J., PLOTKIN R.M., MARKOFF S., MILLER B.P., CORBEL S. and FENDER R.P.
Abstract (from CDS):
We report on deep, coordinated radio and X-ray observations of the black hole X-ray binary XTE J1118+480 in quiescence. The source was observed with the Karl G. Jansky Very Large Array for a total of 17.5 h at 5.3 GHz, yielding a 4.8±1.4 µJy radio source at a position consistent with the binary system. At a distance of 1.7 kpc, this corresponds to an integrated radio luminosity between 4 and 8x1025erg/s, depending on the spectral index. This is the lowest radio luminosity measured for any accreting black hole to date. Simultaneous observations with the Chandra X-ray Telescope detected XTE J1118+480 at 1.2x10–14erg/s/ cm2 (1-10 keV), corresponding to an Eddington ratio of ∼ 4x10–9 for a 7.5 M☉ black hole. Combining these new measurements with data from the 2005 and 2000 outbursts available in the literature, we find evidence for a relationship of the form ℓr = α+βℓX (where ℓ denotes logarithmic luminosities), with β = 0.72±0.09. XTE J1118+480 is thus the third system - together with GX339-4 and V404 Cyg - for which a tight, non-linear radio/X-ray correlation has been reported over more than 5 dex in ℓX. Confirming previous results, we find no evidence for a dependence of the correlation normalization of an individual system on orbital parameters, relativistic boosting, reported black hole spin and/or black hole mass. We then perform a clustering and linear regression analysis on what is arguably the most up-to-date collection of coordinated radio and X-ray luminosity measurements from quiescent and hard-state black hole X-ray binaries, including 24 systems. At variance with previous results, a two-cluster description is statistically preferred only for random errors ≲ 0.3 dex in both ℓr and ℓX, a level which we argue can be easily reached when the known spectral shape/distance uncertainties and intrinsic variability are accounted for. A linear regression analysis performed on the whole data set returns a best-fitting slope β = 0.61±0.03 and intrinsic scatter σ0 = 0.31±0.03 dex.
© 2014 The Authors Published by Oxford University Press on behalf of the Royal Astronomical Society (2014)
accretion, accretion discs - black hole physics - methods: statistical - ISM: jets and outflows - radio continuum: general - X-rays: binaries
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