Near-infrared emission lines trace the state-independent accretion disc wind of the black hole transient MAXI J1820+070

Abstract

The black hole transient MAXI J1820+070 displayed optical P-Cyg profiles and other wind-related emission line features during the hard state of its discovery outburst. We present near-infrared (nIR) spectroscopy covering the different accretion states of the system during this event. Our 8-epoch data set (VLT/X-shooter) reveals strong variability in the properties of the nIR emission lines. This includes the presence of absorption troughs and extended emission line wings with kinetic properties that are remarkably similar to those inferred from the wind signatures observed in optical emission lines, indicating that they are most likely tracing the same accretion disc wind. Unlike the optical features, these nIR signatures are not exclusive of the hard state, as they are also witnessed across the soft state with similar observational properties. This supports the presence of a relatively steady outflow during the entire outburst of the system, and represents the first detection of an accretion disc wind in a black hole soft state at energies other than X-rays. We discuss the visibility of the wind as a function of the spectral band and the potential of nIR spectroscopy for wind studies, in particular during luminous accretion phases.

Accepted for publication in A&A Letters

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• Discovery of optical outflows and inflows in the black hole candidate GRS 1716-249
• X-ray polarization from accretion disk winds
• The Evolution of Rapid Optical/X-ray Timing Correlations in the Initial Hard State of MAXI J1820+070
• The origin of optical emission lines in the soft state of X-ray binary outbursts: the case of MAXI J1820+070
• Gamma-ray observations of MAXI J1820+070 during the 2018 outburst
• Optical and near-infrared spectroscopy of the black hole transient 4U 1543-47 during its 2021 ultra-luminous state
• Comprehensive Radio Monitoring of the Black Hole X-ray Binary Swift J1727.8$-$1613 during its 2023$-$2024 Outburst
• MeerKAT radio observations of the neutron star low-mass X-ray binary Cen X-4 at low accretion rates
• Unveiling optical signatures of outflows in accreting white dwarfs
• Multiwavelength Observations of the Black Hole X-ray Binary MAXI J1820$+$070 in the Rebrightening Phase
• Evolution of Accretion Disk Structure of the Black Hole X-ray Binary MAXI J1820$+$070 during the Rebrightening Phase
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