JWST/MIRI Spectroscopy of the Quiescent Black Hole X-ray Binary XTE J1118+480: Constraints on Jet and Circumbinary Dust Contributions to the Mid-infrared Emission
Abstract
We report on JWST/MIRI low-resolution spectroscopy ($5−12 μ$m) and imaging ($15−25 μ$m) of the black hole X-ray binary XTE~J1118+480 in quiescence, at an X-ray luminosity nine orders of magnitude sub-Eddington, together with contemporaneous optical monitoring and a radio upper limit of 4.5 μJy at 6 GHz. With the donor subtracted, the $5−12 μ$m continuum is curved, turning over near 6 μm; a single power law is rejected in favor of a 764± 9 K blackbody. Longward of the turnover the spectral index is α= +1.21±0.36, steeper at the 2σ level than the flat to slightly inverted spectrum of a compact jet. Interpreted as synchrotron, the turnover implies equipartition fields of ∼104 G on scales of tens of gravitational radii, but the MIRI photometry at $15−21~μ$m-taken $2.6$ hr before the spectrum-lies $30−90$ per cent above its extrapolation, suggesting a second self-absorbed zone. A single partially self-absorbed jet spectrum can reach the photometry only at the expense of the spectral curvature and the 25.5 μm upper limit, so a steady compact jet is disfavored, although not excluded. Representative self-consistent irradiated-disk models instead reproduce the principal features of the $5−25~μ$m spectral energy distribution, with a directly illuminated dust wall at ≃ 5 binary separations, outside the tidal-truncation radius, and a minimum dust mass of order 1022 g. This is the first spectroscopic evidence, though not yet conclusive, favoring circumbinary dust over a jet in a quiescent black hole X-ray binary.
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BibTeX
@misc{zuo2026jwstmiri,
title = {{JWST/MIRI Spectroscopy of the Quiescent Black Hole X-ray Binary XTE J1118+480: Constraints on Jet and Circumbinary Dust Contributions to the Mid-infrared Emission}},
author = {Zihao Zuo and Elena Gallo and Nuria Calvet and Richard M. Plotkin and David M. Russell and Gabriele Cugno and Rob Fender and Fraser Lewis and Joseph Michail and Jon M. Miller and James C. A. Miller-Jones and Fan Zou},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.36318},
eprint = {2609.36318},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.36318},
}
RIS
TY - UNPB
TI - JWST/MIRI Spectroscopy of the Quiescent Black Hole X-ray Binary XTE J1118+480: Constraints on Jet and Circumbinary Dust Contributions to the Mid-infrared Emission
AU - Zihao Zuo
AU - Elena Gallo
AU - Nuria Calvet
AU - Richard M. Plotkin
AU - David M. Russell
AU - Gabriele Cugno
AU - Rob Fender
AU - Fraser Lewis
AU - Joseph Michail
AU - Jon M. Miller
AU - James C. A. Miller-Jones
AU - Fan Zou
PY - 2026
DA - 2026/09/28
PB - arXiv
DO - 10.48550/arxiv.2609.36318
UR - https://arxiv.org/abs/2609.36318
AB - We report on JWST/MIRI low-resolution spectroscopy ($5−12 μ$m) and imaging ($15−25 μ$m) of the black hole X-ray binary XTE~J1118+480 in quiescence, at an X-ray luminosity nine orders of magnitude sub-Eddington, together with contemporaneous optical monitoring and a radio upper limit of 4.5 μJy at 6 GHz. With the donor subtracted, the $5−12 μ$m continuum is curved, turning over near 6 μm; a single power law is rejected in favor of a 764± 9 K blackbody. Longward of the turnover the spectral index is α= +1.21±0.36, steeper at the 2σ level than the flat to slightly inverted spectrum of a compact jet. Interpreted as synchrotron, the turnover implies equipartition fields of ∼10^4 G on scales of tens of gravitational radii, but the MIRI photometry at $15−21~μ$m-taken $2.6$ hr before the spectrum-lies $30−90$ per cent above its extrapolation, suggesting a second self-absorbed zone. A single partially self-absorbed jet spectrum can reach the photometry only at the expense of the spectral curvature and the 25.5 μm upper limit, so a steady compact jet is disfavored, although not excluded. Representative self-consistent irradiated-disk models instead reproduce the principal features of the $5−25~μ$m spectral energy distribution, with a directly illuminated dust wall at ≃ 5 binary separations, outside the tidal-truncation radius, and a minimum dust mass of order 10^22 g. This is the first spectroscopic evidence, though not yet conclusive, favoring circumbinary dust over a jet in a quiescent black hole X-ray binary.
ER -