A half ring of ionized circumstellar material trapped in the magnetosphere of a white dwarf merger remnant

Many white dwarfs are observed in compact double white dwarf binaries, and through the emission of gravitational waves, a large fraction are destined to merge. The merger remnants that do not explode in a Type Ia supernova are expected to initially be rapidly rotating and highly magnetized. In this work, we present our discovery of the variable white dwarf ZTF J200832.79+444939.67, hereafter ZTF J2008+4449, as a likely merger remnant showing signs of circumstellar material without a stellar or substellar companion. The nature of ZTF J2008+4449 as a merger remnant is supported by its physical properties: it is hot (35 500 ± 300 K) and massive (1.12 ± 0.03 M ⊙ ), rapidly rotating with a period of ≈6.6 minutes, and likely possesses exceptionally strong magnetic fields (∼400−600 MG) at its surface. Remarkably, we detect a significant period derivative of (1.80 ± 0.09)×10 −12 s/s, indicating that the white dwarf is spinning down, and a soft X-ray emission that is inconsistent with photospheric emission. As the presence of a mass-transferring stellar or brown dwarf companion is excluded by infrared photometry, the detected spin-down and X-ray emission could be tell-tale signs of a magnetically driven wind or of interaction with circumstellar material, possibly originating from the fallback of gravitationally bound merger ejecta or from the tidal disruption of a planetary object. We also detect Balmer emission, which requires the presence of ionized hydrogen in the vicinity of the white dwarf, showing Doppler shifts as high as ≈2000 km s −1 . The unusual variability of the Balmer emission on the spin period of the white dwarf is consistent with the trapping of a half ring of ionized gas in the magnetosphere of the white dwarf.

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Journal
Astronomy and Astrophysics
Published
2025-12-12
DOI
https://doi.org/10.1051/0004-6361/202556432
Citations
1
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Gamma-ray bursts and supernovae
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article
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1.15
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article

A half ring of ionized circumstellar material trapped in the magnetosphere of a white dwarf merger remnant

J. C. Raymond, Scott J. Kenyon, Jeremy Heyl, A. Kawka et al.
1 citations
Astronomy and Astrophysics
Gamma-ray bursts and supernovae
1.15
article

A half ring of ionized circumstellar material trapped in the magnetosphere of a white dwarf merger remnant

J. C. Raymond, Scott J. Kenyon, Jeremy Heyl, A. Kawka, Antonio C. Rodriguez, M. J. Graham, J. J. Hermes, Ilaria Caiazzo, Kareem J. El-Badry, Stephen Justham, Paula Szkody, Lilia Ferrario, Frank J. Masci, Josiah Purdum, S. Vennes, D. T. Wickramasinghe, A. J. Drake, Abhishek Desai, Rüdiger Pakmor, Tim Cunningham, Jan van Roestel, Eric C. Bellm, Jim Fuller, Thomas A. Prince, Viraj Karambelkar, Kevin B. Burdge, Steven L. Groom, David R. Miller, S. R. Kulkarni, Richard G. Dekany, Boris T. Gänsicke, Ingrid Pelisoli, Zach Vanderbosch, Andrei A. Cristea
article en
1 citations

Abstract

Many white dwarfs are observed in compact double white dwarf binaries, and through the emission of gravitational waves, a large fraction are destined to merge. The merger remnants that do not explode in a Type Ia supernova are expected to initially be rapidly rotating and highly magnetized. In this work, we present our discovery of the variable white dwarf ZTF J200832.79+444939.67, hereafter ZTF J2008+4449, as a likely merger remnant showing signs of circumstellar material without a stellar or substellar companion. The nature of ZTF J2008+4449 as a merger remnant is supported by its physical properties: it is hot (35 500 ± 300 K) and massive (1.12 ± 0.03 M ⊙ ), rapidly rotating with a period of ≈6.6 minutes, and likely possesses exceptionally strong magnetic fields (∼400−600 MG) at its surface. Remarkably, we detect a significant period derivative of (1.80 ± 0.09)×10 −12 s/s, indicating that the white dwarf is spinning down, and a soft X-ray emission that is inconsistent with photospheric emission. As the presence of a mass-transferring stellar or brown dwarf companion is excluded by infrared photometry, the detected spin-down and X-ray emission could be tell-tale signs of a magnetically driven wind or of interaction with circumstellar material, possibly originating from the fallback of gravitationally bound merger ejecta or from the tidal disruption of a planetary object. We also detect Balmer emission, which requires the presence of ionized hydrogen in the vicinity of the white dwarf, showing Doppler shifts as high as ≈2000 km s −1 . The unusual variability of the Balmer emission on the spin period of the white dwarf is consistent with the trapping of a half ring of ionized gas in the magnetosphere of the white dwarf.

Astronomy and AstrophysicsVol. 706
Australian National University (AU), California Institute of Technology (US), University of British Columbia (CA), Institute of Science and Technology Austria (AT), University of Washington (US), Australian Mathematical Sciences Institute (AU), University of Warwick (GB), Architecture Technology Corporation (United States) (US), Max Planck Institute for Astrophysics (DE), Center for Astrophysics Harvard & Smithsonian (US), Astronomical Institute of the Slovak Academy of Sciences (SK), International Centre for Radio Astronomy Research (AU), Infrared Processing and Analysis Center (US), Optica (US), Massachusetts Institute of Technology (US), University of Amsterdam (NL)
Openalex Percentile: Top 14%
Gamma-ray bursts and supernovae
1.15
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