Radio Variability from a Quiescent Stellar Mass Black Hole Jet

Abstract

Relativistic outflows are believed to be a common feature of black hole X-ray binaries at the lowest accretion rates, when they are in their `quiescent' spectral state. However, we still lack a detailed understanding of how quiescent jet emission varies with time. Here we present 24 years of archival radio observations (from the Very Large Array and the Very Long Baseline Array) of the black hole X-ray binary V404 Cygni in quiescence (totalling 150 observations from 1.4 -- 22 GHz). The observed flux densities follow lognormal distributions with means and standard deviations of (<log f_nu>, sigma) = (-0.53, 0.19) and (-0.53, 0.30) at 4.9 and 8.4 GHz, respectively (where f_nu is the flux density in units of mJy). As expected, the average radio spectrum is flat with a mean and standard deviation of (<alpha_r >, sigma_alpha_r)= (0.02, 0.65) where f_nu \propto nu^alpha_r. We find that radio flares that increase the flux density by factors of 2 -- 4 over timescales as short as <10 min are commonplace, and that long-term variations (over 10--4000 day timescales) are consistent with shot noise impulses that decay to stochastic variations on timescales <10 days (and perhaps as short as tens of minutes to several hours). We briefly compare the variability characteristics of V404 Cygni to jetted active galactic nuclei, and we conclude with recommendations on how to account for variability when placing quiescent black hole X-ray binary candidates with radio luminosities comparable to V404 Cygni (L_r ~ 1e28 erg/s) onto the radio/X-ray luminosity plane.

21 pages, 9 figures, 3 tables. Accepted for publication in ApJ

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• Accretion and Outflow in V404 Cyg
• Radio & X-ray detections of GX 339--4 in quiescence using MeerKAT and Swift
• Observations of the Disk/Jet Coupling of MAXI J1820+070 During its Descent to Quiescence
• The variable radio counterpart of Swift J1858.6-0814
• Comprehensive coverage of particle acceleration and kinetic feedback from the stellar mass black hole V404 Cygni
• Ultra-deep ATCA imaging of 47 Tucanae reveals a central compact radio source
• Toward a Larger Sample of Radio Jets from Quiescent Black Hole X-ray Binaries
• ALMA observations of A0620-00: fresh clues on the nature of quiescent black hole X-ray binary jets
• Parameters of the Galactic Spiral Density Wave from Masers with Parallax Errors Less Than 10%
• The flickering radio jet from the quiescent black hole X-ray binary A0620-00
• Exploration of faint X-ray and radio sources in the massive globular cluster M14: A UV-bright counterpart to Nova Ophiuchus 1938
• The black hole X-ray binary MAXI J1348$-$630 in quiescence
• On the origin of core radio emissions from black hole sources in the realm of relativistic shocked accretion flow