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Peer-reviewedCC BY 4.0Monthly Notices of the Royal Astronomical Society

A Multi-Wavelength Picture of the Surprisingly Short 2024/25 Outburst from EXO 0748–676

  • Amy H Knight1
  • Lauren Rhodes2,3
  • Noel Castro Segura4
  • Douglas J K Buisson5
  • Aru Beri6,7
  • David M Russell8
  • Kevin Alabarta9
  • Maria C Baglio9
  • Jakob van den Eijnden10
  • Matthew J Middleton7
  • Payaswini Saikia11
  • Chris Done1
2 more authors
  • Rob Fender12,13
  • Fraser Lewis14,15
15 affiliations
  1. 1Durham University Centre for Extragalactic Astronomy, Department of Physics, , South Road, Durham DH1 3LE ,
  2. 2Trottier Space Institute at McGill, 3550 Rue University , Montreal, Quebec H3A 2A7 ,
  3. 3McGill University, 3600 Rue University Department of Physics, , Montreal, Quebec H3A 2T8 ,
  4. 4Gibbet Hill Road, University of Warwick Department of Physics, , Coventry, CV4 7AL ,
  5. 5Independent Researcher
  6. 6Indian Institute of Astrophysics , Koramangala II Block, Bangalore 560034 ,
  7. 7University of Southampton Department of Physics and Astronomy, , Highfield, Southampton SO17 1BJ ,
  8. 8Center for Astrophysics and Space Science (CASS) , New York University Abu Dhabi, PO Box 129188 Abu Dhabi ,
  9. 9INAF, Osservatorio Astronomico di Brera , Via E. Bianchi 46, I-23807 Merate (LC) ,
  10. 10Anton Pannekoek Institute for Astronomy, Universiteit van Amsterdam , Science Park 904, NL-1098 XH Amsterdam ,
  11. 11Yale University Department of Astronomy, , PO Box 208101, New Haven, CT 06520-8101 ,
  12. 12The University of Oxford Astrophysics, Department of Physics, , Keble Road, Oxford, OX1 3RH ,
  13. 13University of Cape Town Department of Astronomy, , Private Bag X3, Rondebosch 7701 ,
  14. 14Faulkes Telescope Project , Cardiff, Wales ,
  15. 15The Schools’ Observatory, Astrophysics Research Institute, Liverpool John Moores University , 146 Brownlow Hill, Liverpool L3 5RF ,
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Abstract

After sixteen years in quiescence, EXO 0748–676 unexpectedly returned to outburst in March 2024. However, in stark contrast to its previous outburst (1985 - 2008), EXO 0748–676 returned to quiescence in January 2025, after ∼10 months in outburst. Here, we collate data from nine observing facilities, covering wavelengths from radio to X-ray, to provide the first multi-wavelength study of the 2024/25 outburst. Unlike the 1985 outburst, both the rise and decay are fully captured at X-ray and optical wavelengths. The light curves do not exhibit the hallmarks of a canonical transient low-mass X-ray binary outburst. Instead, the X-ray and optical fluxes remain reasonably stable during the 2024/25 outburst. The wealth of optical data of EXO 0748-676 reveals a skewed optical phase curve and an irradiation-dominated optical light curve which lasts until the onset of hydrogen recombination in the outer disc at ∼11000K, triggering a rapid fade at the end of the outburst. X-ray observations by XMM-Newton and NICER revealed that EXO 0748–676 was heavily obscured early on, with spectra exhibiting a dampened soft X-ray contribution. We find that a spectral model including a clumpy, ionised absorber describes the obscuration, although the exact cause of the early-time obscuration remains uncertain. X-ray colour analysis indicates that EXO 0748–676 spent most of the ∼10 month outburst in a faint, hard state. EXO 0748-676 increased marginally in brightness towards the end of the outburst, but never entered a soft spectral state. This behaviour is characteristic of a failed transition outburst.

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Cite

BibTeXRIS
BibTeX
@article{knight2026multiwavelength,
  title = {{A Multi-Wavelength Picture of the Surprisingly Short 2024/25 Outburst from EXO 0748–676}},
  author = {Amy H Knight and Lauren Rhodes and Noel Castro Segura and Douglas J K Buisson and Aru Beri and David M Russell and Kevin Alabarta and Maria C Baglio and Jakob van den Eijnden and Matthew J Middleton and Payaswini Saikia and Chris Done and Rob Fender and Fraser Lewis},
  journal = {Monthly Notices of the Royal Astronomical Society},
  year = {2026},
  month = oct,
  doi = {10.1093/mnras/stag2056},
  url = {https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2056/9005954},
  note = {CC BY 4.0},
}
RIS
TY  - JOUR
TI  - A Multi-Wavelength Picture of the Surprisingly Short 2024/25 Outburst from EXO 0748–676
AU  - Amy H Knight
AU  - Lauren Rhodes
AU  - Noel Castro Segura
AU  - Douglas J K Buisson
AU  - Aru Beri
AU  - David M Russell
AU  - Kevin Alabarta
AU  - Maria C Baglio
AU  - Jakob van den Eijnden
AU  - Matthew J Middleton
AU  - Payaswini Saikia
AU  - Chris Done
AU  - Rob Fender
AU  - Fraser Lewis
PY  - 2026
DA  - 2026/10/31
JO  - Monthly Notices of the Royal Astronomical Society
DO  - 10.1093/mnras/stag2056
UR  - https://academic.oup.com/mnras/advance-article/doi/10.1093/mnras/stag2056/9005954
AB  - After sixteen years in quiescence, EXO 0748–676 unexpectedly returned to outburst in March 2024. However, in stark contrast to its previous outburst (1985 - 2008), EXO 0748–676 returned to quiescence in January 2025, after ∼10 months in outburst. Here, we collate data from nine observing facilities, covering wavelengths from radio to X-ray, to provide the first multi-wavelength study of the 2024/25 outburst. Unlike the 1985 outburst, both the rise and decay are fully captured at X-ray and optical wavelengths. The light curves do not exhibit the hallmarks of a canonical transient low-mass X-ray binary outburst. Instead, the X-ray and optical fluxes remain reasonably stable during the 2024/25 outburst. The wealth of optical data of EXO 0748-676 reveals a skewed optical phase curve and an irradiation-dominated optical light curve which lasts until the onset of hydrogen recombination in the outer disc at ∼11000K, triggering a rapid fade at the end of the outburst. X-ray observations by XMM-Newton and NICER revealed that EXO 0748–676 was heavily obscured early on, with spectra exhibiting a dampened soft X-ray contribution. We find that a spectral model including a clumpy, ionised absorber describes the obscuration, although the exact cause of the early-time obscuration remains uncertain. X-ray colour analysis indicates that EXO 0748–676 spent most of the ∼10 month outburst in a faint, hard state. EXO 0748-676 increased marginally in brightness towards the end of the outburst, but never entered a soft spectral state. This behaviour is characteristic of a failed transition outburst.
SN  - 0035-8711
SN  - 1365-2966
ER  -