(University of Texas at El Paso) (New Mexico State University at Doña Ana) Radio Observations of Cataclysmic Variables Paul A. Mason (University of Texas at El Paso) (New Mexico State University at Doña Ana) With thanks to Collaborators: S. Howell (NOAO) T. Harrison (NMSU) K.P. Singh, V. Girish (TIFR-Mumbai) D.J.Saika (NCRA-GMRT) M. Claussen (NRAO)

Picture credit: M. A. Garlick © 1998 Cataclysmic Variable Binary Stars (CVs) Non-magnetic CVs: About 75% of all CVs do not show any magnetic effects. Accretion occurs via an accretion disk. Picture credit: M. A. Garlick © 1998

Picture credit: M. A. Garlick © 1998 Magnetic Cataclysmic Variables (MCVs) About 25% of known CVs show magnetic effects. Intermediate Polars: Accretion occurs via a partially disrupted accretion disk. Plasma flows onto the white dwarf along magnetic field lines. Polars: Accretion occurs via an accretion stream. Plasma flows onto the white dwarf along magnetic field lines. Picture credit: M. A. Garlick © 1998

Radio Surveys (See Mason and Gray ApJ, 2007 for a detailed review) Surveys of non-magnetic CVs have not found any persistent radio sources. AM Her and AE Aqr were discovered to be radio emitters early in the process of surveying magnetic CVs. (e.g. Chanmugam, and Dulk, 1982). Nearly all of the pre-ROSAT magnetic CVs were observed and found not to be radio emitters. (Bastian 1987, Beasley et al. 1994; Mason, Fisher and Chanmugam 1996). AR UMa was discovered to be a persistent radio source in a recent survey (Mason and Gray, 2007).

Radio Studies Despite decades of searching, there are only 3 persistent radio CVs, but there is also a radio emitting pre-CV, V471 Tau. AR UMa (highest field known for a polar, 230 MG AM Her (prototype polar low (13 MG) field AE Aqr (magnetic propeller Intermediate Polar) V471 Tau (detached wind accreting pre-magnetic CV) So what do these 4 binaries have in common?

Isolated Magnetic WDs are not radio sources Holberg, Oswalt, and Sion (2002) compiled a list of 109 white dwarfs whose best distance estimates place them within 20 pc of the sun. This includes two binary white dwarfs. They state that the sample is likely to be complete out to 13 pc and is 65% complete to 20 pc. Liebert, Bergeron, and Holberg (2003) examined a subset of 11 magnetic white dwarfs within 20 pc. None of these are radio sources. These white dwarfs cover a range of magnetic field strengths from ~0.2 to 320 MG. The radio flux density from a magnetic white dwarf at 13 pc would be a factor of 50 times as great as that detected from AR UMa Radio Studies Isolated Magnetic WDs are not radio sources Holberg, Oswalt, and Sion (2002) compiled a list of 109 white dwarfs whose best distance estimates place them within 20 pc of the sun. This includes two binary white dwarfs. They state that the sample is likely to be complete out to 13 pc and is 65% complete to 20 pc. Liebert, Bergeron, and Holberg (2003) examined a subset of 11 magnetic white dwarfs within 20 pc. None of these are radio sources. These white dwarfs cover a range of magnetic field strengths from ~0.2 to 320 MG. The radio flux density from a magnetic white dwarf at 13 pc would be a factor of 50 times as great as that detected from AR UMa

Isolated fast rotating red dwarf flare stars cannot account for the persistent radio flux density seen in AM Her and AR UMa So a binary with a magnetic WD is necessary, but observations of V471 Tau as well as low states of AM Her and AR UMa show that radio emission does not require high-state accretion. Radio Studies Isolated fast rotating red dwarf flare stars cannot account for the persistent radio flux density seen in AM Her and AR UMa So a binary with a magnetic WD is necessary, but observations of V471 Tau as well as low states of AM Her and AR UMa show that radio emission does not require high-state accretion.

Radio Flare From SS Cyg (Körding et al. 2008). Is it a synchrotron jet?

Multiwavelength campaign AR UMa Phased-resolved VLA 6hr 3.6 cm 3.6cm, 6cm, 20cm GMRT 50cm UBVRI Photometry NMSU 1m Tom Harrison Optical Spectra 2hr WYNN Steve Howell

GMRT: Giant Metrewave Radio Telescope near Pune, India, is currently the largest operating array dedicated primarily to observations in the 21 cm to 6 m wavelength range.

GMRT The design of the GMRT array resembles that of the VLA. Its field of view is determined by the diffraction limit of one 45-m antenna.

Phase resolved B, V, and I light curves of AR UMa obtained March 9 th 2008 Orbital Phase AR UMa was in a low state during the GMRT Observations

High State Comparison Spectrum AR UMa “Sleeping”

AR UMa ---- VLA 6 hours --- covering 3 Orbital Cycles

Phase Resolved 8.4 MHz Light Curve of AR UMa Orbital Phase

GMRT 50cm map of AR UMa Detected during a very low accretion state

Electrons are injected into Jupiter's magnetosphere and there must be a way to accelerate these electrons to MeV energies. There is a correlation between the Solar UV flux and the JSR. Both criteria may be realized if enhanced solar UV flux causes the upper atmosphere of Jupiter to expand by heating, resulting in a partially ionized wind. As the partial plasma expands into the magnetosphere of Jupiter, neutral atoms impede the flow of protons while the electrons move forward. The separation of the electrons from the protons set up strong electric fields accelerating electrons to MeV energies. These electrons dissipate their energy as Synchrotron radiation. This is called a neutral wind dynamo. Jupiter Synchrotron Radiation (JSR)

Ultra-relativistic electrons in Jupiter's radiation belts (Bolton et al. 2002)

Neutral Wind Dynamo A very similar mechanism may be working in the magnetosphere of the secondary of AR UMa, which likely has a wind as evidenced from HST observations. A significant difference is of course the strong magnetic field of the white dwarf in AR UMa. It might be more proper to say the combined primary and secondary magnetosphere of AR UMa. A determination of the position and SED of radio emission will place models on mechanisms

From HST STIS Observations of AR UMa Gänsicke et al. (2001) found P-Cygni profiles that they attribute to a wind from the trailing face of the secondary.

EVLA Prospects The Extended Very Large Array (EVLA) will have its bandwidth increased by a factor of 80 and will increase continuum source sensitivity by a factor of 5-20 depending on the frequency.

AM Her and AR UMa have similar flux densities and distances. By scaling the radio flux density of these polars, the EVLA will be able to detect radio CVs out to 500pc.

Is there a future in radio observations of CVs?

VLBA will provide the first spatially resolved observation of any CV