Radio Observations of Cataclysmic Variables

Paul A. Mason (University of Texas at El Paso) (University of Texas at El Paso)

(New Mexico State University at Doña Ana)(New Mexico State University at Doña Ana)

With thanks to Collaborators:

S. Howell (NOAO)

T. Harrison (NMSU)

K.P. Singh, V. Girish (TIFR-Mumbai)

Saika (NCRA-GMRT)

M. Claussen (NRAO)

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. (e.g. 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). Note: The reported discovery of a CV from radio data, FIRSTJ1023, is actually a pulsar (Thorstensen).

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Radio StudiesDespite 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 MGAM 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?

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

Radio StudiesIsolated fast rotating red dwarf flare stars Isolated fast rotating red dwarf flare stars cannot account for the persistent radio flux density cannot account for the persistent radio flux density seen in AM Her and AR UMaseen in AM Her and AR UMa

So a binary with a magnetic WD is necessary, So a binary with a magnetic WD is necessary, but but observations of V471 Tau as well as low states of observations of V471 Tau as well as low states of AM Her and AR UMa show thatAM Her and AR UMa show that radio emission radio emission does not require high-state accretion.does not require high-state accretion.

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

Multiwavelength campaignMultiwavelength campaign AR UMa AR UMa

Phased-resolved VLA 6hr light-curve @ 3.6 cm

Snapshots @VLA 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 9th 2008

Orbital Phase

AR UMa was in a low state during the GMRT Observations

High State Comparison SpectrumHigh State Comparison Spectrum

AR UMa “Sleeping”AR UMa “Sleeping”

VLA 8.635 GHz Light Curve

0

200

400

600

800

0.70 0.75 0.80 0.85 0.90 0.95

UT DATE (August 31, 2008)

AR UMa ---- VLA

6 hours --- covering 3 Orbital Cycles

Phase Resolved 8.4 MHz Light Curve Phase Resolved 8.4 MHz Light Curve of AR UMaof AR UMa

Orbital Phase

Orbital Phase

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

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

Charged particles, especially electrons, get trapped in Jupiter's Charged particles, especially electrons, get trapped in Jupiter's magnetosphere. Electrons spiral along magnetic field lines bouncing back magnetosphere. Electrons spiral along magnetic field lines bouncing back and forth between the magnetic poles by the well known magnetic mirror and forth between the magnetic poles by the well known magnetic mirror effect. There must be a supply of electrons injected into Jupiter's effect. There must be a supply of electrons injected into Jupiter's magnetosphere and there must be a way to accelerate these electrons to magnetosphere and there must be a way to accelerate these electrons to MeV energies. An additional observation clarifies how this might occur. MeV energies. An additional observation clarifies how this might occur. There is a correlation between the Solar UV flux and the JSR. Both criteria 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 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 Jupiter to expand by heating, resulting in a partially ionized wind. As the partial plasma expands into the magnetosphere of Jupiter, neutral atoms partial plasma expands into the magnetosphere of Jupiter, neutral atoms impede the flow of protons while the electrons move forward. The separation impede the flow of protons while the electrons move forward. The separation of the electrons from the protons set up strong electric fields which of the electrons from the protons set up strong electric fields which accelerate the electrons to Mev energies. These fast moving electrons accelerate the electrons to Mev energies. These fast moving electrons become trapped in Jupiter's magnetosphere and dissipate their energy as become trapped in Jupiter's magnetosphere and dissipate their energy as Synchrotron radiation.Synchrotron radiation.

Neutral Wind DynamoNeutral Wind Dynamo

Neutral Wind DynamoNeutral 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.

Future ProspectsFuture ProspectsThe VLA is currently being retrofitted with new The VLA is currently being retrofitted with new receivers, correlators, and electronics. receivers, correlators, and electronics.

The Extended Very Large Array (EVLA) is The Extended Very Large Array (EVLA) is essentially a new telescope using the VLA essentially a new telescope using the VLA dishes. Its will have its bandwidth increased by dishes. Its will have its bandwidth increased by a factor of 80 and will increase continuum a factor of 80 and will increase continuum sourcesource sensitivity by a factor of 5-20 depending sensitivity by a factor of 5-20 depending on the frequency.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 VLBA will provide the first spatially resolved observation of any CVresolved observation of any CV