Burst-induced spin variations in the accreting magnetic white dwarf PBC J0801.2–4625

Abstract

PBC J0801.2–4625 is an intermediate polar with a primary spin frequency of 66.08 d⁻¹ and an unknown orbital period. The long-term All Sky Automated Survey for Supernovae (ASAS-SN) light curve of this system reveals four bursts, all of which have similar peak amplitudes (∼2 mag) and durations (∼2 d). In this work, we primarily study the timing properties of this system’s 2019 February burst, which was simultaneously observed by both ASAS-SN and the Transiting Exoplanet Survey Satellite (TESS). Pre-burst, a frequency of 4.064 ± 0.002 d⁻¹(5.906 ± 0.003 h period), likely attributed to the binary orbit, is identified in addition to previous measurements for the white dwarf’s spin. During the burst, however, we find a spin frequency of 68.35 ± 0.28 d⁻¹. Post-burst, the spin returns to its pre-brust value but with a factor 1.82 ± 0.05 larger amplitude. The burst profile is double-peaked, and we estimate its energy to be 3.3 × 10³⁹ erg. We conclude that the burst appears most consistent with thermonuclear runaway (i.e. a’micronova’), and suggest that the spin variations may be an analogue to burst oscillations (i.e.’micronova oscillations’). However, we also note that the above findings could be explained by a dwarf nova outburst. With the available data, we are unable to distinguish between these two scenarios.

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