GS 2000+25: The Least Luminous Black Hole X-ray Binary

Abstract

Little is known about the properties of the accretion flows and jets of the lowest-luminosity quiescent black holes. We report new, strictly simultaneous radio and X-ray observations of the nearby stellar-mass black hole X-ray binary GS 2000+25 in its quiescent state. In deep Chandra observations we detect the system at a faint X-ray luminosity of $L_X=1.1_{-0.7}^{+1.0}\times 10^{30}(d/2\mathrm{kpc}{)}^2$ erg s${}^{-1}$ (1-10 keV). This is the lowest X-ray luminosity yet observed for a quiescent black hole X-ray binary, corresponding to an Eddington ratio $L_X/L_{\mathrm{Edd}}\sim 10^{-9}$. In 15 hours of observations with the Karl G. Jansky Very Large Array, no radio continuum emission is detected to a $3\sigma$ limit of $<2.8\mu$Jy at 6 GHz. Including GS 2000+25, four quiescent stellar-mass black holes with $L_X<10^{32}$ erg s${}^{-1}$ have deep simultaneous radio and X-ray observations and known distances. These sources all have radio to X-ray luminosity ratios generally consistent with, but slightly lower than, the low state radio/X-ray correlation for stellar-mass black holes with $L_X>10^{32}$ erg s${}^{-1}$. Observations of these sources tax the limits of our current X-ray and radio facilities, and new routes to black hole discovery are needed to study the lowest-luminosity black holes.

7 pages, 2 figures, accepted for publication in ApJ

References in corpus (9)

• A catalogue of low-mass X-ray binaries in the Galaxy, LMC, and SMC (Fourth edition)
• A radio-emitting outflow in the quiescent state of A0620-00: implications for modelling low-luminosity black hole binaries
• The radio/X-ray domain of black hole X-ray binaries at the lowest radio luminosities
• The Quiescent X-ray Spectrum of Accreting Black Holes
• Constraints on Relativistic Jets in Quiescent Black Hole X-ray Binaries from Broadband Spectral Modeling
• Multiwavelength observations of the black hole X-ray binary A0620-00 in quiescence
• The First Simultaneous X-Ray/Radio Detection of the First Be/BH System MWC 656
• Hibernating black holes revealed by photometric mass functions
• Chandra detection of XTE J1650-500 in quiescence and the minimum luminosity of black hole X-ray binaries

Cited by in corpus (5)

• An X-ray quiet black hole born with a negligible kick in a massive binary within the Large Magellanic Cloud
• A Deep Search for Faint Chandra X-ray Sources, Radio Sources, and Optical Counterparts in NGC 6752
• Toward a Larger Sample of Radio Jets from Quiescent Black Hole X-ray Binaries
• The flickering radio jet from the quiescent black hole X-ray binary A0620-00
• The black hole X-ray binary MAXI J1348$-$630 in quiescence