ALMA observations of A0620–00: fresh clues on the nature of quiescent black hole X-ray binary jets

Abstract

We report on ALMA continuum observations of the black hole X-ray binary A0620-00, at an X-ray luminosity nine orders of magnitude sub-Eddington. The system was significantly detected at 98 GHz (at 44 ± 7 µJy) and only marginally at 233 GHz (20 ± 8 µJy), about 40 days later. These results suggest either an optically thin sub-mm synchrotron spectrum, or highly variable sub-mm jet emission on month timescales. Although the latter appears more likely, we note that, at the time of the ALMA observations, A0620-00 was in a somewhat less active optical-IR state than during all published multi-wavelength campaigns when a flatspectrum, partially self-absorbed jet has been suggested to extend from the radio to the mid-IR regime. Either interpretation is viable in the context of an internal shock model, where the jet's spectral shape and variability are set by the power density spectrum of the shells' Lorentz factor fluctuations. While strictly simultaneous radio-mm-IR observations are necessary to draw definitive conclusions for A0620-00, the data presented here, in combination with recent radio and sub-mm results from higher luminosity systems, demonstrate that jets from black hole X-ray binaries exhibit a high level of variability -either in flux density or intrinsic spectral shape, or both -across a wide spectrum of Eddington ratios. This is not in contrast with expectations from an internal shock model, where lower jet power systems can be expected to exhibit larger fractional variability owing to an overall decrease in synchrotron absorption.

Scale-invariance of black hole accretion: modelling emission from a black hole X-ray binary with relativistic accretion flow simulations

“…Although our simulation does not include a large scale jet -the radio observations of A0620-00 still constrain some properties of an eventual jet model. Given that the observed radio emission is at the level of F10GHz ≈ 15−50 [µJy] (Gallo et al 2019), any extended jet originating from our magnetized disk model should produce a spectrum Fν ∼ ν −p with slightly inverted slope p = 0.3−0.17 to match the observations.…”

“…There are only a few other known black hole systems in strongly sub-Eddington state: XTE J1118+480 (LX/L Edd = 4×10 −9 , Gallo et al 2014), Swift J1357.2-0933 (LX/L Edd = 4×10 −9 − 3×10 −8 , Armas Padilla et al 2014;Plotkin et al 2016), and Sgr A* associated with supermassvie black hole in the center of our Galaxy (LX/L Edd < 10 −10 , Baganoff et al 2003). Besides optical/NIR and X-ray monitoring, A0620-00 system is frequently observed in radio (Gallo et al 2006) and recently Atacama Large Millimeter Array has detected the millimeter counterpart of the system (Gallo et al 2019).…”

Multi-wavelength emission from magnetically arrested disks around isolated black holes

“…Although IBH-MADs cannot produce detectable radio signals, compact jets are highly likely launched by MADs (Tchekhovskoy et al 2011). Such jets may produce radio signals as detected from a few quiescent X-ray binaries (e.g., Hynes et al 2009;Gallo et al 2019). The radio luminosity correlates with X-ray luminosity in the low-hard state: L R ∼ 1.4 × 10 29 L 0.61 X,35 erg s −1 (Gallo et al 2014).…”

The Disk Veiling Effect of the Black Hole Low-Mass X-ray Binary A0620-00

“…However, their luminosity alone is orders of magnitude lower than the observed optical luminosity (Zurita et al 2003). Regarding to the non-stellar continuum emission, jets of quiescent black holes can contribute significant flickering variabilities in the OIR bands (e.g., Dinçer et al 2018;Gallo et al 2019). However, this component follows a steep spectrum, i.e., stronger at redder optical and infrared bands (Dinçer et al 2018).…”