Deep radio imaging of 47 Tuc identifies the peculiar X-ray source X9 as a new black hole candidate.
In: Monthly Notices of the Royal Astronomical Society, Jg. 453 (2015-11-11), Heft 4, S. 3918-3931
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Zugriff:
We report the detection of steady radio emission from the known X-ray source X9 in the globular cluster 47 Tuc. With a double-peaked C iv emission line in its ultraviolet spectrum providing a clear signature of accretion, this source had been previously classified as a cataclysmic variable. In deep ATCA (Australia Telescope Compact Array) imaging from 2010 and 2013, we identified a steady radio source at both 5.5 and 9.0 GHz, with a radio spectral index (defined as Sν ∝ να) of α = −0.4 ± 0.4. Our measured flux density of 42 ± 4 μJy beam−1 at 5.5 GHz implies a radio luminosity (νLν) of 5.8 × 1027 erg s−1, significantly higher than any previous radio detection of an accreting white dwarf. Transitional millisecond pulsars, which have the highest radio-to-X-ray flux ratios among accreting neutron stars (still a factor of a few below accreting black holes at the same LX), show distinctly different patterns of X-ray and radio variability than X9. When combined with archival X-ray measurements, our radio detection places 47 Tuc X9 very close to the radio/X-ray correlation for accreting black holes, and we explore the possibility that this source is instead a quiescent stellar-mass black hole X-ray binary. The nature of the donor star is uncertain; although the luminosity of the optical counterpart is consistent with a low-mass main-sequence donor star, the mass transfer rate required to produce the high quiescent X-ray luminosity of 1033 erg s−1 suggests the system may instead be ultracompact, with an orbital period of order 25 min. This is the fourth quiescent black hole candidate discovered to date in a Galactic globular cluster, and the only one with a confirmed accretion signature from its optical/ultraviolet spectrum. [ABSTRACT FROM AUTHOR]
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Deep radio imaging of 47 Tuc identifies the peculiar X-ray source X9 as a new black hole candidate.
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Autor/in / Beteiligte Person: | Miller-Jones, J. C. A. ; Strader, J. ; Heinke, C. O. ; Maccarone, T. J. ; van den Berg, M. ; Knigge, C. ; Chomiuk, L. ; Noyola, E. ; Russell, T. D. ; Seth, A. C. ; Sivakoff, G. R. |
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Zeitschrift: | Monthly Notices of the Royal Astronomical Society, Jg. 453 (2015-11-11), Heft 4, S. 3918-3931 |
Veröffentlichung: | 2015 |
Medientyp: | academicJournal |
ISSN: | 0035-8711 (print) |
DOI: | 10.1093/mnras/stv1869 |
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