THE FIRST LOW-MASS BLACK HOLE X-RAY BINARY IDENTIFIED in QUIESCENCE OUTSIDE of A GLOBULAR CLUSTER

B. E. Tetarenko, A. Bahramian, R. M. Arnason, J. C.A. Miller-Jones, S. Repetto, C. O. Heinke, T. J. MacCarone, L. Chomiuk, G. R. Sivakoff, J. Strader, F. Kirsten, W. Vlemmings

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Abstract

The observed relation between the X-ray and radio properties of low-luminosity accreting black holes (BHs) has enabled the identification of multiple candidate black hole X-ray binaries (BHXBs) in globular clusters (GCs). Here, we report an identification of the radio source VLA J213002.08+120904 (aka M15 S2), recently reported in Kirsten et al., as a BHXB candidate. They showed that the parallax of this flat-spectrum variable radio source indicates a - + 2.2 0.30.5 kpc distance, which identifies it as lying in the foreground of the GC M15. We determine the radio characteristics of this source and place a deep limit on the X-ray luminosity of ∼4 × 1029 erg s.1. Furthermore, we astrometrically identify a faint red stellar counterpart in archival Hubble images with colors consistent with a foreground star; at 2.2 kpc, its inferred mass is 0.1-0.2Me. We rule out that this object is a pulsar, neutron star X-ray binary, cataclysmic variable, or planetary nebula, concluding that VLA J213002.08+120904 is the first accreting BHXB candidate discovered in quiescence outside of a GC. Given the relatively small area over which parallax studies of radio sources have been performed, this discovery suggests a much larger population of quiescent BHXBs in our Galaxy, 2.6 ± 104-1.7 × 108 BHXBs at 3× confidence, than has been previously estimated (∼102-104) through population synthesis.

Original languageEnglish
Article number10
JournalAstrophysical Journal
Volume825
Issue number1
DOIs
StatePublished - Jul 1 2016

Keywords

  • X-rays: binaries
  • black hole physics
  • radio continuum: general
  • stars: individual (VLA J213002.08+120904)

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    Tetarenko, B. E., Bahramian, A., Arnason, R. M., Miller-Jones, J. C. A., Repetto, S., Heinke, C. O., MacCarone, T. J., Chomiuk, L., Sivakoff, G. R., Strader, J., Kirsten, F., & Vlemmings, W. (2016). THE FIRST LOW-MASS BLACK HOLE X-RAY BINARY IDENTIFIED in QUIESCENCE OUTSIDE of A GLOBULAR CLUSTER. Astrophysical Journal, 825(1), [10]. https://doi.org/10.3847/0004-637X/825/1/10