Observations of the Disk/Jet Coupling of MAXI J1820+070 During its Descent to Quiescence

Abstract

Black hole X-ray binaries in the quiescent state (Eddington ratios typically $\lesssim$10${}^{-5}$) display softer X-ray spectra (photon indices $\Gamma \sim 2$) compared to higher-luminosity black hole X-ray binaries in the hard state ($\Gamma \sim 1.7$). However, the cause of this softening, and its implications for the underlying accretion flow, are still uncertain. Here, we present quasi-simultaneous X-ray and radio spectral monitoring of the black hole X-ray binary MAXI J1820$+$070 during the decay of its 2018 outburst and of a subsequent re-flare in 2019, providing an opportunity to monitor a black hole X-ray binary as it actively transitions into quiescence. We probe 1-10 keV X-ray luminosities as low as $L_{\mathrm{X}}\sim 4\times 10^{32}$ erg s${}^{-1}$, equivalent to Eddington fractions of $\sim 4\times 10^{-7}$. During its decay towards quiescence, the X-ray spectrum of MAXI J1820$+$070 softens from $\Gamma \sim 1.7$ to $\Gamma \sim 2$, with the softening taking $\sim 30$d, and completing at $L_{\mathrm{X}}\approx 10^{34}$ erg s${}^{-1}$ ($\approx 10^{-5}{L}_{\mathrm{Edd}}$). While the X-ray spectrum softens, the radio spectrum generally remains flat/inverted throughout the decay. We also find that MAXI J1820$+$070 follows a radio ($L_{\mathrm{R}}$) -- X-ray luminosity correlation of the form $L_{\mathrm{R}}\propto L_{\mathrm{X}}^{0.52\pm 0.07}$, making it the fourth black hole system to follow the so-called `standard track' unbroken over several (in this case, four) decades in $L_{\mathrm{X}}$. Comparing the radio/X-ray spectral evolution(s) with the $L_{\mathrm{R}}$ -- $L_{\mathrm{X}}$ plane, we find that the X-ray softening is consistent with X-rays produced by Comptonization processes in a radiatively inefficient accretion flow. We generally disfavor X-ray emission originating solely from within the jet, with the possible exception of X-rays produced via synchrotron self-Compton processes.

19 pages, 5 figure, 1 appendix. Accepted for publication in ApJ

References in corpus (30)

• X-ray Properties of Black-Hole Binaries
• HI4PI: A full-sky HI survey based on EBHIS and GASS
• Some Aspects of Measurement Error in Linear Regression of Astronomical Data
• Modelling the behaviour of accretion flows in X-ray binaries
• The All-Sky Automated Survey for Supernovae (ASAS-SN) Light Curve Server v1.0
• Advection-Dominated Accretion and the Black Hole Event Horizon
• The corona contracts in a black-hole transient
• A Long, Hard Look at the Low-Hard State in Accreting Black Holes
• 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
• An extremely powerful long-lived superluminal ejection from the black hole MAXI J1820+070
• A radio parallax to the black hole X-ray binary MAXI J1820+070
• Revisiting the radio/X-ray flux correlation in the black hole V404 Cyg: from outburst to quiescence
• The binary mass ratio in the black hole transient MAXI J1820+070
• A Black Hole Nova Obscured by an Inner Disk Torus
• The 2015 Decay of the Black Hole X-ray Binary V404 Cygni: Robust Disk-Jet Coupling and a Sharp Transition into Quiescence
• The Soft State of the Black Hole Transient Source MAXI J1820+070: Emission from the Edge of the Plunge Region?
• Relativistic X-ray jets from the black hole X-ray binary MAXI J1820+070
• The Quiescent X-ray Spectrum of Accreting Black Holes
• Spectral differences between the jets in `radio loud' and `radio quiet' hard state black hole binaries
• Constraints on Relativistic Jets in Quiescent Black Hole X-ray Binaries from Broadband Spectral Modeling
• X-ray dips and a complex UV/X-ray cross-correlation function in the black hole candidate MAXI J1820+070
• A timing study of MAXI J1820+070 based on Swift/XRT and NICER monitoring in 2018/19
• Bright mini-outburst ends the 12-year long activity of the black hole candidate Swift J1753.5-0127
• On the Radio/X-ray Correlation in Microquasars
• The First Simultaneous X-Ray/Radio Detection of the First Be/BH System MWC 656
• Up and Down the Black Hole Radio/X-ray Correlation: the 2017 mini-outbursts from Swift J1753.5-0127
• Radio & X-ray detections of GX 339--4 in quiescence using MeerKAT and Swift
• Radio Variability from a Quiescent Stellar Mass Black Hole Jet
• The black hole X-ray transient Swift J1357.2-0933 as seen with Swift and NuSTAR during its 2017 outburst

Cited by in corpus (14)

• Observations of a black hole X-ray binary indicate formation of a magnetically arrested disk
• Modelling correlated variability in accreting black holes: the effect of high density and variable ionisation on reverberation lags
• The hybrid radio/X-ray correlation of the black hole transient MAXI J1348-630
• Chasing the break: Tracing the full evolution of a black hole X-ray binary jet with multi-wavelength spectral modeling
• Multiwavelength observations of MAXI J1820+070 during its outburst decay and subsequent mini-outburst
• Seven reflares, a mini-outburst and an outburst : High amplitude optical variations in the black hole X-ray binary Swift J1910.2-0546
• Quasi-Simultaneous Radio/X-ray Observations of the Candidate Transitional Millisecond Pulsar 3FGL J1544.6-1125 During its Low-Luminosity Accretion-Disc State
• A quantitative explanation of the radio--X-ray correlation in black-hole X-ray binaries
• Multiwavelength Observations of the Black Hole X-ray Binary MAXI J1820$+$070 in the Rebrightening Phase
• The role of outflows in black-hole X-ray binaries
• Evolution of Accretion Disk Structure of the Black Hole X-ray Binary MAXI J1820$+$070 during the Rebrightening Phase
• The Accretion-Ejection Connection in the Black Hole X-ray Binary MAXI J1820$+$070
• Large optical modulations during 2018 outburst of MAXI J1820+070 reveal evolution of warped accretion disc through X-ray state change
• The black hole X-ray binary MAXI J1348$-$630 in quiescence