Transcript 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.

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)
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).
.
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?
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
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 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
AR UMa was in a
low state during the
GMRT Observations
Orbital Phase
High State Comparison Spectrum
AR UMa “Sleeping”
AR UMa
---- VLA
6 hours --- covering 3 Orbital Cycles
VLA 8.635 GHz Light Curve
800
600
400
200
0
0.70
0.75
0.80
0.85
UT DATE (August 31, 2008)
0.90
0.95
Phase Resolved 8.4 MHz Light Curve
of AR UMa
700
600
500
400
300
200
100
0
0.00
0.20
0.40
0.60
Orbital Phase
0.80
1.00
GMRT 50cm map of AR UMa
Detected during a very low accretion state
Orbital Phase
Ultra-relativistic electrons in Jupiter's
radiation belts (Bolton et al. 2002)
Neutral Wind Dynamo
Charged particles, especially electrons, get trapped in Jupiter's
magnetosphere. Electrons spiral along magnetic field lines bouncing back
and forth between the magnetic poles by the well known magnetic mirror
effect. There must be a supply of electrons injected into Jupiter's
magnetosphere and there must be a way to accelerate these electrons to
MeV energies. An additional observation clarifies how this might occur.
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 which
accelerate the electrons to Mev energies. These fast moving electrons
become trapped in Jupiter's magnetosphere and dissipate their energy as
Synchrotron radiation.
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.
Future Prospects
The VLA is currently being retrofitted with new
receivers, correlators, and electronics.
The Extended Very Large Array (EVLA) is
essentially a new telescope using the VLA
dishes. Its 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