2025ApJ...986...78B

AR Scorpii, the so-called white dwarf (WD) pulsar, contains a rapidly rotating magnetic WD (P_spin = 117.0564 s) interacting with a cool, red dwarf (RD) companion in a 3.56 hr orbit. It is a strong radio source with an inverted spectral index between 1 and 200 GHz that is indicative of synchrotron emission. This paper presents the first submillimeter observations of AR Scorpii using the Submillimeter Array, helping to fill a critical gap in the spectral energy distribution (SED) between 10 and 600 GHz. The average flux densities at 220 and 345 GHz are 124 and 86 mJy, respectively. The lower than expected flux density at 345 GHz suggests a break in the synchrotron emission at about 200 GHz. A periodogram analysis of the 220 GHz observations shows a modulation with an amplitude of ≈6% at a period of 58.26 s or at twice the spin frequency of the WD. This modulation is the first direct detection of the WD spin period at radio frequencies and implies that the synchrotron emission arises near the WD and and not from an interaction with the photosphere of the RD. A fit to the SED shows that the synchrotron emission arises from a small, low-density region with a magnetic field of 43 MG at a distance of 0.6 orbital radii from the WD. This result implies that AR Scorpii contains a weakly magnetic WD (∼15 MG) and not a strongly magnetic WD (∼500 MG) as previously asserted.