Gone with the Wind: JWST-MIRI Unveils a Strong Outflow from the Quiescent Stellar-mass Black Hole A0620-00
Abstract We present new observations of the black hole X-ray binary A0620-00 using the Mid-Infrared (MIR) Instrument on the James Webb Space Telescope, during a state where the X-ray luminosity is 9 orders of magnitude below Eddington, and coordinated with radio, near-infrared, and optical observations. The goal is to understand the nature of the excess MIR emission originally detected by Spitzer redward of 8 μ m. The stellar-subtracted MIR spectrum is well modeled by a power law with a spectral index of α = 0.72 ± 0.01, where the flux density scales with frequency as F ν ∝ ν α . The spectral characteristics, along with rapid variability—a 40% flux flare at 15 μ m and 25% achromatic variability in the 5–12 μ m range—rule out a circumbinary disk as the source of the MIR excess. The Low Resolution Spectrometer reveals a prominent emission feature at 7.5 μ m, resulting from the blend of three hydrogen recombination lines. While the contribution from partially self-absorbed synchrotron radiation cannot be ruled out, we argue that thermal bremsstrahlung from a warm (a few tens of thousands of Kelvin) wind accounts for the MIR excess; the same outflow is responsible for the emission lines. The inferred mass outflow rate indicates that the system’s low luminosity is due to a substantial fraction of the mass supplied by the donor star being expelled through a wind rather than accreted onto the black hole.
Authors
- F. Vincentelli (ORCID: https://orcid.org/0000-0002-1481-1870)
- Fraser Lewis (ORCID: https://orcid.org/0000-0003-3352-2334)
- P. Casella (ORCID: https://orcid.org/0000-0002-0752-3301)
- R. P. Fender (ORCID: https://orcid.org/0000-0002-5654-2744)
- D. M. Russell (ORCID: https://orcid.org/0000-0002-3500-631X)
- Sera Markoff (ORCID: https://orcid.org/0000-0001-9564-0876)
- J. M. Mïller (ORCID: https://orcid.org/0000-0003-2869-7682)
- Joseph M. Michail (ORCID: https://orcid.org/0000-0003-3503-3446)
- F. J. Cowie (ORCID: https://orcid.org/0009-0009-0079-2419)
- Richard M. Plotkin (ORCID: https://orcid.org/0000-0002-7092-0326)
- Gabriele Cugno (ORCID: https://orcid.org/0000-0001-7255-3251)
- J. C. A. Miller‐Jones (ORCID: https://orcid.org/0000-0003-3124-2814)
- P. Gandhi (ORCID: https://orcid.org/0000-0003-3105-2615)
- M. C. Baglio (ORCID: https://orcid.org/0000-0003-1285-4057)
- Fan Zou (ORCID: https://orcid.org/0000-0002-4436-6923)
- Alexandra Veledina (ORCID: https://orcid.org/0000-0002-5767-7253)
- Elena Gallo (ORCID: https://orcid.org/0000-0001-5802-6041)
- Zihao Zuo (ORCID: https://orcid.org/0009-0000-8524-8344)
Publication Details
- Journal
- The Astrophysical Journal
- Published
- 2025-09-24
- DOI
- https://doi.org/10.3847/1538-4357/adf6b9
- Citations
- 3
- Primary Topic
- Astrophysical Phenomena and Observations
- Type
- article
- Field-Weighted Citation Impact
- 3.46
Funders
- National Science Foundation
- National Aeronautics and Space Administration
- New York University Abu Dhabi
- Space Telescope Science Institute
- UK Research and Innovation
- Royal Society
- European Commission
- Nuclear Safety and Security Commission
- NordForsk
- Tamkeen
- HORIZON EUROPE Framework Programme