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 K) and massive (1. 12 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. 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. 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
Cristea et al. (Mon,) studied this question.