The long period radio transient ASKAP J1448-68 is a cataclysmic variable

Abstract

Wide-field time-domain radio surveys have recently unveiled a new class of Galactic radio emitter: long period radio transients (LPTs). Despite the rapid pace of discovery, their origins remain poorly understood, with two main theories emerging: slowly spinning magnetars or binary white dwarfs (WDs) with magnetic interactions. All three LPTs with well-characterised optical counterparts are WDs in binary systems, but even within that class there is diversity, with one accreting and two detached systems. In this Letter, we show that the LPT ASKAP J1448-68 is a cataclysmic variable (CV)---a WD accreting from a low-mass companion---with a spectroscopic orbital period consistent with the radio pulse period, and specifically, potentially consistent with being a polar. Unlike the other known LPT CV, ASKAP J1448-68 does not exhibit the He II emission that is a hallmark of magnetic CVs in their high accretion states. We also present new optical time-series and infrared photometric observations, showing flickering at the 10% level and suggesting a possible period bouncer origin. This identification of ASKAP J1448-68 adds to the small sample of characterised LPT counterparts, and shows that LPTs can arise from WD binaries with a range of accretion states.