A search for electron cyclotron maser emission from compact binaries

Abstract

Unipolar induction (UI) is a fundamental physical process, which occurs when a conducting body transverses a magnetic field. It has been suggested that UI is operating in RX J0806+15 and RX J1914+24, which are believed to be ultra-compact binaries with orbital periods of 5.4 min and 9.6 min respectively. The UI model predicts that those two sources may be electron cyclotron maser sources at radio wavelengths. Other systems in which UI has been predicted to occur are short period extra-solar terrestrial planets with conducting cores. If UI is present, circularly polarised radio emission is predicted to be emitted. We have searched for this predicted radio emission from short period binaries using the VLA and ATCA. In one epoch we find evidence for a radio source, coincident in position with the optical position of RX J0806+15. Although we cannot completely exclude that this is a chance alignment between the position of RX J0806+15 and an artifact in the data reduction process, the fact that it was detected at a significance level of 5.8 sigma and found to be transient, suggests that it is more likely that RX J0806+15 is a transient radio source. We find an upper limit on the degree of circular polarisation to be ~50%. The inferred brightness temperature exceeds 10^18 K, which is too high for any known incoherent process, but is consistent with maser emission and UI being the driving mechanism. We did not detect radio emission from ES Cet, RX J1914+24 or Gliese 876.Comment: Accepted for publication MNRA

SPH Simulations of Direct Impact Accretion in the Ultracompact AM CVn Binaries

“…To first order the timescale for orbital evolution is that which gravitational radiation predicts, consistent with the observed rates of period change (Strohmayer 2002;Hakala et al 2003;Strohmayer 2004;Ramsay et al 2005;Ramsay, Cropper, & Hakala 2006). Ramsay et al (2007) note that the UI model predicts radio emission, which they detected at the 5.8-σ level along the line of sight to HM Cnc, but which was not detected in observations of V407 Vul. The major problem with this model is the phasing of the optical versus X-ray light curves, because the X-ray spots are on the meridian facing the secondary, this model predicts a phase offset of ∼0.5, whereas the observed phase offset is ∼0.2 for both V407 Vul and HM Cnc (Barros et al 2007).…”

“…The absence of a hard component in the spectrum as well as the absence of polarization are further long-standing problems with this model (Cropper et al 2004). The unipolar inductor model appears to allow consistency with all of the observations -including the reported detection of radio emission (Ramsay et al 2007) -except the relative phasing of the optical and X-ray light curves. In the UI model the ∼50 eV hot spots on the surface of the primary white dwarf are found along the meridian that passes through the line of centers, and the optical light curve results from the heated face of the secondary star.…”

“…The unipolar-inductor (UI) model proposed by Wu et al (2002) and discussed most recently in the context of V407 Vul and HM Cnc by Dall'Osso et al (2006, 2007 and Ramsay et al (2007) is the stellar analog of behavior observed in the Jupiter-Io system. As Io moves through Jupiter's magnetic field, charge separation occurs, and because the environment is a weak plasma, an emf is established from the far point of Io as observed from Jupiter, along the magnetic field lines in both directions to Jupiter's atmosphere in both hemispheres, and from the planet back to the near side of Io (Goldreich & Lynden-Bell 1969).…”

The Coherent Radio Emission from the RS CVn Binary HR 1099

“…In these systems, the authors suggest that unipolar induction (UI) could be a driving mechanism, comparable to that which drives the Jupiter-Io decametric emission. Evidence for such emission has been detected in the candidate double degenerate system RX J0806+15 (Ramsay et al 2007).…”

Phase connecting multi-epoch radio data for the ultracool dwarf TVLM 513-46546

“…This mechanism is also the source of certain classes of solar and stellar bursts (Melrose & Dulk 1982;Bingham et al 2001;. It was also suggested to be operational in the magnetic chemically peculiar star CU Vir where 100% circularly polarized, bright and highly directive radio bursts were detected (Kellett et al 2007;Trigilio et al 2007), and for the compact binary RX J080 6.3+1527 (Ramsay et al 2007). …”