Deep radio imaging of 47 Tuc identifies the peculiar X-ray source X9 as a new black hole candidate
| Autor: | Craig O. Heinke, Jay Strader, Gregory R. Sivakoff, Christian Knigge, James Miller-Jones, Eva Noyola, Thomas D. Russell, Thomas J. Maccarone, Laura Chomiuk, M. van den Berg, Anil C. Seth |
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| Přispěvatelé: | API (FNWI) |
| Rok vydání: | 2015 |
| Předmět: |
High Energy Astrophysical Phenomena (astro-ph.HE)
Physics Astrophysics::High Energy Astrophysical Phenomena FOS: Physical sciences Cataclysmic variable star White dwarf Astronomy Astronomy and Astrophysics Astrophysics::Cosmology and Extragalactic Astrophysics Astrophysics Luminosity Black hole Neutron star X-shaped radio galaxy Space and Planetary Science Millisecond pulsar Globular cluster Astrophysics::Solar and Stellar Astrophysics Astrophysics - High Energy Astrophysical Phenomena Astrophysics::Galaxy Astrophysics |
| Zdroj: | Monthly Notices of the Royal Astronomical Society, 453(4), 3918-3931. Oxford University Press |
| ISSN: | 1365-2966 0035-8711 |
| Popis: | 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 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 $S_{\nu}\propto\nu^{\alpha}$) of $\alpha=-0.4\pm0.4$. Our measured flux density of $42\pm4$ microJy/beam at 5.5 GHz implies a radio luminosity ($\nu L_{\nu}$) of 5.8e27 erg/s, 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 X-ray luminosity), 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 1e33 erg/s suggests the system may instead be ultracompact, with an orbital period of order 25 minutes. 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. Comment: 15 pages, 6 figures, accepted for publication in MNRAS |
| Databáze: | OpenAIRE |
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