Rapid mid-infrared spectral timing with JWST: GRS 1915+105 during an MIR-bright and X-ray-obscured state

Creators: Gandhi, P.¹; Borowski, E. S.²; Byrom, J.¹; Hynes, R. I.²; Maccarone, T. J.³; Shaw, A. W.⁴; Adegoke, O. K.⁵; Altamirano, D.¹; Baglio, M. C.⁶; Bhargava, Y.⁷; Britt, C. T.⁸; Buckley, D. A. H.⁹; Buisson, D. J. K.¹⁰; Casella, P.¹¹; Segura, N. Castro¹²; Charles, P. A.^{1, 13}; Corral-Santana, J. M.¹⁴; Dhillon, V. S.^{15, 16}; Fender, R.¹³; Gúrpide, A.¹; Heinke, C. O.¹⁷; Igl, A. B.²; Knigge, C.¹; Markoff, S.¹⁸; Mastroserio, G.¹⁹; McCollough, M. L.²⁰; Middleton, M.¹; Miller, J. M.²¹; Miller-Jones, J. C. A.²²; Motta, S. E.²³; Paice, J. A.²⁴; Pawar, D. D.²⁵; Plotkin, R. M.²⁶; Pradhan, P.²⁷; Ressler, M. E.²⁸; Russell, D. M.²⁹; Russell, T. D.³⁰; Santos-Sanz, P.³¹; Shahbaz, T.^{16, 32}; Sivakoff, G. R.¹⁷; Steeghs, D.¹²; Tetarenko, A. J.³³; Tomsick, J. A.³⁴; Vincentelli, F. M.¹; George, M.¹; Gurwell, M.²⁰; Rao, R.²⁰; JWST Timing Consortium

1. University of Southampton
2. Louisiana State University
3. Texas Tech University
4. Butler University
5. California Institute of Technology
6. INAF-Osservatorio Astronomico di Brera, Via Bianchi 46, I-23807 Merate (LC), Italy
7. Tata Institute of Fundamental Research
8. Space Telescope Science Institute
9. South African Radio Astronomy Observatory
10. Independent
11. INAF-Osservatorio Astronomico di Roma, via Frascati 33, I-00078 Monteporzio Catone (RM), Italy
12. University of Warwick
13. University of Sheffield
14. Instituto de Astrofísica de Canarias
15. University of Oxford
16. European Southern Observatory
17. University of Alberta
18. University of Amsterdam
19. University of Milan
20. Harvard-Smithsonian Center for Astrophysics
21. University of Michigan–Ann Arbor
22. Curtin University
23. Brera Astronomical Observatory
24. Durham University
25. Department of Physics, R. J. College, Mumbai 400086, India
26. University of Nevada Reno
27. Embry–Riddle Aeronautical University
28. Jet Propulsion Lab
29. New York University Abu Dhabi
30. INAF—IASF Palermo, via Ugo La Malfa, 153, I-90146 Palermo, Italy
31. Instituto de Astrofísica de Andalucía
32. University of La Laguna
33. University of Lethbridge
34. University of California, Berkeley

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 an MIR luminosity L_(MIR) ≈ 10³⁶ erg s⁻¹ exceeding past infrared 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 per cent) but highly significant peak-to-peak photometric variability is found on time-scales of ∼1000 s. The brightest Pf (6–5) emission line lags the continuum. Though difficult to constrain accurately, this lag is commensurate with light-travel time-scales across the outer accretion disc or with expected recombination time-scales inferred from emission-line diagnostics. Using the emission line as a bolometric indicator suggests a moderate (⁠∼5–30 per cent 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. Polycyclic aromatic hydrocarbon 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 X-ray binaries and other variable cosmic sources on rapid time-scales.

Copyright and License

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.

Acknowledgement

We are grateful to the mission and instrument teams at STScI for their patience and expert help with our numerous queries, especially MIRI scientist S. Kendrew and staff astronomers I. Wong and G. Sloan. We also thank the anonymous referee for their time and their review.

PG acknowledges funding from The Royal Society (SRF\R1\241074). PG and MER thank UKRI Science and Technology Facilities Council (STFC) for support. AJT acknowledges the support of the Natural Sciences and Engineering Research Council of Canada (NSERC; funding reference number RGPIN-2024-04458). TJM acknowledges support from JWST-GO-01586.002. RIH and ESB acknowledge support from JWST-GO-01586.007. JAT acknowledges support from JWST-GO-01586.010-A. TS and FMV acknowledge financial support from the Spanish Ministry of Science, Innovation and Universities (MICIU) under grant PID2020-114822GB-I00. JAP acknowledges support from STFC consolidated grant ST/X001075/1. RMP acknowledges support from NASA under award no. 80NSSC23M0104. DDP acknowledges the support from ISRO (India), under the ISRO RESPOND programme. The work of MER was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. MCB and TDR acknowledge support from the INAF-Astrofit fellowship. GRS and COH were supported by NSERC Discovery Grants RGPIN-2021-0400 and RGPIN-2023-04264, respectively. DMR was supported by Tamkeen under the NYU Abu Dhabi Research Institute grant CASS. PS-S acknowledges financial support from the Spanish I + D + i Project PID2022-139555NB-I00 (TNO-JWST) and the Severo Ochoa Grant CEX2021-001131-S, both funded by MCIN/AEI. VSD acknowledges support by the Science and Technology Facilities Council (grant ST/V000853/1). SM was supported by a European Research Council (ERC) Synergy Grant ‘BlackHolistic’ grant no. 10107164.

Line identification benefited from the compilation v3.00b4 presented in van Hoof (2018).⁶cloudy calculations were performed with version c23.01 (Chatzikos et al. 2023).

This work is based on observations made with the NASA/ESA/CSA JWST. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with programme #1586 (Gandhi et al. 2021). Support for programme #1586 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127.

This research has made use of the NASA/IPAC Infrared Science Archive, which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology. The DOI of the Spitzer Enhanced IRS Products is 10.26131/IRSA399.

This research has made use of MAXI data provided by RIKEN, JAXA, and the MAXI team.

This research has made use of data and/or software provided by the High Energy Astrophysics Science Archive Research Center (HEASARC), which is a service of the Astrophysics Science Division at NASA/GSFC.

This study is based on observations with ISO, an ESA project with instruments funded by ESA Member States (especially the PI countries: France, Germany, the Netherlands, and the United Kingdom) and with the participation of ISAS and NASA.

PG is grateful to G. J. Ferland for help with cloudy and to S. F. Hönig, J. Hernandez-Santisteban, and J. H. Matthews for discussions at the initial stages of analysis.

This study is dedicated to the memory of our colleague, Tomaso Belloni.

Data Availability

The core data analysed herein are publicly available in telescope archives. The JWST data may be found using the programme identifier 1586 and 1033. The NEOWISE, MAXI, and Rossi X-ray Timing Explorer (RXTE) data are similarly publicly available. AMI data can be made available upon reasonable request to the coauthors.

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