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|Title:||An ultraluminous X-ray microquasar in NGC 5408?|
Fender, R. P.
Hannikainen, D. C.
Read, A. M.
Stevens, I. R.
|Publisher:||Royal Astronomical Society (RAS)|
|Citation:||Monthly Notices of the Royal Astronomical Society, 2006, 368 (4), pp. 1527-1539|
|Abstract:||We studied the radio source associated with the ultraluminous X-ray source in NGC 5408 (LX≈ 1040 erg s−1). The radio spectrum is steep (index ≈−1), consistent with optically thin synchrotron emission, not with flat-spectrum core emission. Its flux density (≈0.28 mJy at 4.8 GHz, at a distance of 4.8 Mpc) was the same in the March 2000 and December 2004 observations, suggesting steady emission rather than a transient outburst. However, it is orders of magnitude higher than expected from steady jets in stellar-mass microquasar. Based on its radio flux and spectral index, we suggest that the radio source is either an unusually bright supernova remnant, or, more likely, a radio lobe powered by a jet from the black hole (BH). Moreover, there is speculative evidence that the source is marginally resolved with a radius ∼30 pc. A faint H ii region of similar size appears to coincide with the radio and X-ray sources, but its ionization mechanism remains unclear. Using a self-similar solution for the expansion of a jet-powered electron–positron plasma bubble, in the minimum-energy approximation, we show that the observed flux and (speculative) size are consistent with an average jet power ≈ 7 × 1038 erg s−1∼ 0.1LX∼ 0.1LEdd, an age ≈105 yr, a current velocity of expansion ≈80 km s−1. We briefly discuss the importance of this source as a key to understand the balance between luminosity and jet power in accreting BHs.|
|Rights:||This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society ©: 2006 the authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. Deposited with reference to the publisher’s archiving policy available on the SHERPA/RoMEO website.|
|Appears in Collections:||Published Articles, Dept. of Physics and Astronomy|
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