The giant outburst of EXO 2030+375
In 2021, the high-mass X-ray binary EXO 2030+375 underwent a giant X-ray outburst, the first since 2006, that reached a peak flux of ∼600 mCrab (3–50 keV). The goal of this work is to study the spectral evolution over the course of the outburst, search for possible cyclotron resonance scattering features (CRSFs), and to associate spectral components with the emission pattern of the accretion column. We used broadband spectra taken with the Nuclear Spectroscopic Telescope Array ( NuSTAR ), the Neutron Star Interior Composition Explorer (NICER), and Chandra near the peak and during the decline phase of the outburst. We describe the data with established empirical continuum models and perform pulse-phase-resolved spectroscopy. We compare the spectral evolution with pulse phase using a proposed geometrical emission model. We find a significant spectral hardening toward lower luminosity, a behavior that is expected for super-critical sources. The continuum shape and evolution cannot be described by a simple power-law model with exponential cutoff; it requires additional absorption or emission components. We can confirm the presence of a narrow absorption feature at ∼10 keV in both NuSTAR observations. The absence of harmonics puts into question the interpretation of this feature as a CRSF. The empirical spectral components cannot be directly associated with identified emission components from the accretion column.
Authors
- Pragati Pradhan (ORCID: https://orcid.org/0000-0002-1131-3059)
- J. Wilms (ORCID: https://orcid.org/0000-0003-2065-5410)
- Brent West (ORCID: https://orcid.org/0009-0007-1219-7508)
- Jakob Stierhof (ORCID: https://orcid.org/0000-0001-9537-7887)
- E. Sokolova-Lapa (ORCID: https://orcid.org/0000-0001-7948-0470)
- P. Kretschmar (ORCID: https://orcid.org/0000-0001-9840-2048)
- P. Thalhammer (ORCID: https://orcid.org/0000-0001-6269-2821)
- R. Staubert
- Peter A. Becker (ORCID: https://orcid.org/0000-0002-3718-1293)
- R. Rothschild
- M. T. Wolff (ORCID: https://orcid.org/0000-0002-4013-5650)
- Joel B. Coley (ORCID: https://orcid.org/0000-0001-7532-8359)
- Christian Malacaria (ORCID: https://orcid.org/0000-0002-0380-0041)
- Ralf Ballhausen (ORCID: https://orcid.org/0000-0002-1118-8470)
- K. Pottschmidt (ORCID: https://orcid.org/0000-0002-4656-6881)
- Felix Fürst
Institutions
- Vassar College (US)
- United States Naval Research Laboratory (US)
- Goddard Space Flight Center (US)
- Howard University (US)
- George Mason University (US)
- Friedrich-Alexander-Universität Erlangen-Nürnberg (DE)
- United States Naval Academy (US)
- University of California San Diego (US)
- European Space Astronomy Centre (ES)
- Astrophysics Science Division (US)
- Massachusetts Institute of Technology (US)
- University of Maryland, College Park (US)
- University of Maryland, Baltimore County (US)
- University of Tübingen (DE)
- Embry–Riddle Aeronautical University (US)
- International Space Science Institute (CH)
Publication Details
- Journal
- Astronomy and Astrophysics
- Published
- 2024-08-01
- DOI
- https://doi.org/10.1051/0004-6361/202348595
- Citations
- 3
- Primary Topic
- Astrophysical Phenomena and Observations
- Type
- article
- Field-Weighted Citation Impact
- 0.99
Funders
- National Aeronautics and Space Administration
- California Institute of Technology
- Deutsche Forschungsgemeinschaft
- Nuclear Safety and Security Commission
- Jet Propulsion Laboratory
- Goddard Space Flight Center
- Office of Naval Research