Modelling the continuous radio outbursts in AE Aquarii

Abstract

In this paper an attempt is made to simulate the non-thermal radio spectrum of the enigmatic nova-like variable AE Aquarii. Earlier radio studies of AE Aquarii suggested that the radio flares originate from expanding synchrotron-emitting clouds in terms of a van der Laan process. Recent studies also indicate that expanding blob-like propeller-ejected outflow from the system may be the source of the optical flares from AE Aquarii. In this paper we model the radio to infrared flares from AE Aquarii in highly magnetized blob-like propeller-ejected outflow. We showed that the secondary star can possess surface magnetic fields of the order of B0 2000 G. Through turbulence and subsequent reconnection, magnetic flux can be pinched off into a fraction of the mass transfer flow from the secondary star. These fields can be highly twisted, resulting in localized regions where the blob plasma is magnetically dominated, i.e. β = (8π nkBT /B 2 ) 1), mechanisms such as shock drift acceleration and magnetic pumping can further energize electrons, in regions where β 1, to energies of the order of γ → 20. It was shown that the total integrated flux during outbursts, over the frequency range from 1 to 50 000 GHz, can be the result of several (∼10‐20), initially highly magnetized (B0 ∼ 2000‐3000 G) synchrotron-emitting blobs in different stages of their evolution. The simulated spectrum corresponding to B0 ≈ 2000 G (∼20 blobs), showed that a peak flux of Sν ∼ 148 mJy is produced at ν ∼ 1805 GHz (∼166 µm), while a spectrum corresponding to B0 ≈ 3000 G (∼10 blobs), results in a peak synchrotron flux of Sν ∼ 134 mJy at ν ∼ 2410 GHz (∼125 µm). In terms of a multiflare van der Laan superposition, these are obtained where the spectrum changes from a typical self-absorbed Sν ∝ ν α to Sν ∝ ν −(δ−1)/2 . In terms of the scenarios described above, this may place the latest detection (5σ level) at ν = 3333 GHz (Sν ≈ 113 mJy), already in the optically thin part of the spectrum.