A persistent bow shock in a diskless magnetised accreting white dwarf

Stellar bow shocks are formed when an outflow interacts with the interstellar medium. In white dwarfs accreting from a binary companion, outflows are associated with either strong winds from the donor star, the accretion disk, or a thermonuclear runaway explosion on the white dwarf surface. To date, only six accreting white dwarfs are known to harbour disk-wind driven bow shocks that are not associated to thermonuclear explosions. Here, we report the discovery of a bow shock associated with a high-proper-motion disk-less accreting white dwarf, 1RXS J052832.5+283824. We show that the white dwarf has a strong magnetic field in the range B~42-45 MG, making RXJ0528+2838 the a bonafide known polar-type cataclysmic variable harbouring a bow shock. The resolved bow shock is shown to be inconsistent with a past thermonuclear explosion, or being inflated by a donor wind, ruling out all accepted scenarios for inflating a bow shock around this system. Modelling of the energetics reveals that the observed bow shock requires a persistent power source with a luminosity significantly exceeding the system accretion energy output. This implies the presence of a powerful, previously unrecognized energy loss mechanism - potentially tied to magnetic activity - that may operate over sufficiently long timescales to influence the course of binary evolution.

💡 Research Summary

The authors report the discovery of a resolved bow‑shock nebula surrounding the high‑proper‑motion, disk‑less, magnetic cataclysmic variable (CV) 1RXS J052832.5+283824 (hereafter RXJ0528+2838). Spectropolarimetric observations and cyclotron harmonic analysis with MUSE confirm that the white dwarf (WD) in this system possesses a strong magnetic field of about 42–45 MG, classifying it as a polar. The bow shock is clearly aligned with the star’s proper motion (south‑east) and exhibits strong stratification: the apex lies at ~3800 AU in Balmer lines, ~2400 AU in