|Description:|| The binary system AR Sco contains an M star and the only known radio-pulsing white dwarf. The system shows emission from radio to X-rays, likely dominated by synchrotron radiation. The mechanism of how most of the emission is produced remains unclear and two competing scenarios have been proposed: collimated outflows and direct interaction between the magnetospheres of the white dwarf and the M star.|
We conducted a radio observation with the Australian Long Baseline Array (LBA) on 20 Oct 2016 at 8.5 GHz to study the compactness of the radio emission and discern between the two proposed scenarios. Simultaneous data with the Australian Telescope Compact Array (ATCA) were also recorded for a direct comparison of the obtained flux densities.
We have observed that AR Sco shows radio emission compact on milliarcsecond angular scales (less than four solar radii). As it can be seen in the picture, the emission is orbitally modulated, with an average flux density of around 6.5 mJy. A comparison with the simultaneous ATCA data shows that no flux is resolved out on mas scales, implying that the radio emission is produced in this compact region. Additionally, the obtained radio light-curves on hour timescales are consistent with the optical light-curve. This points to the fact that the radio emission in AR Sco is likely produced in the magnetosphere of the M star or the white dwarf, and we do not see evidence for a radio outflow or collimated jets significantly contributing to the radio emission.
This work has been accepted for publication in A&A: Marcote, Marsh, Stanway, Paragi, and Blanchard (2017, arXiv:1705.00600).