Gandhi, P. orcid.org/0000-0003-3105-2615, Borowski, E.S. orcid.org/0009-0002-6989-1019, Byrom, J. et al. (44 more authors) (2025) Rapid mid-infrared spectral-timing with JWST: GRS 1915+105 during a MIR–bright and X-ray–obscured state. Monthly Notices of the Royal Astronomical Society, 537 (2). pp. 1385-1403. ISSN 0035-8711
Abstract
We present mid-infrared (MIR) spectral-timing measurements of the prototypical Galactic microquasar GRS 1915+105. The source was observed with the Mid-Infrared Instrument (MIRI) onboard JWST in June 2023 at a MIR luminosity LMIR ≈ 1036 erg s−1 exceeding past IR levels by about a factor of 10. In contrast, the X-ray flux is much fainter than the historical average, in the source’s now–persistent ‘obscured’ state. The MIRI low-resolution spectrum shows a plethora of emission lines, the strongest of which are consistent with recombination in the hydrogen Pfund (Pf) series and higher. Low amplitude (∼ 1%) but highly significant peak-to-peak photometric variability is found on timescales of ∼ 1,000 s. The brightest Pf (6–5) emission line lags the continuum. Though difficult to constrain accurately, this lag is commensurate with light-travel timescales across the outer accretion disc or with expected recombination timescales inferred from emission line diagnostics. Using the emission line as a bolometric indicator suggests a moderate (∼ 5–30 % Eddington) intrinsic accretion rate. Multiwavelength monitoring shows that JWST caught the source close in-time to unprecedentedly bright MIR and radio long-term flaring. Assuming a thermal bremsstrahlung origin for the MIRI continuum suggests an unsustainably high mass-loss rate during this time unless the wind remains bound, though other possible origins cannot be ruled out. PAH features previously detected with Spitzer are now less clear in the MIRI data, arguing for possible destruction of dust in the interim. These results provide a preview of new parameter space for exploring MIR spectral-timing in XRBs and other variable cosmic sources on rapid timescales.
Metadata
Item Type: | Article |
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Authors/Creators: |
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Copyright, Publisher and Additional Information: | © 2025 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited. |
Keywords: | infrared: general; X-rays: binaries |
Dates: |
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Institution: | The University of Sheffield |
Academic Units: | The University of Sheffield > Faculty of Science (Sheffield) > School of Mathematical and Physical Sciences |
Funding Information: | Funder Grant number SCIENCE AND TECHNOLOGY FACILITIES COUNCIL ST/V000853/1 |
Depositing User: | Symplectic Sheffield |
Date Deposited: | 20 Feb 2025 11:19 |
Last Modified: | 20 Feb 2025 11:19 |
Published Version: | https://doi.org/10.1093/mnras/staf036 |
Status: | Published |
Publisher: | Oxford University Press (OUP) |
Refereed: | Yes |
Identification Number: | 10.1093/mnras/staf036 |
Related URLs: | |
Open Archives Initiative ID (OAI ID): | oai:eprints.whiterose.ac.uk:223598 |