Low-Frequency VLA Observations of Jupiter
Imke de Pater, University of California – Berkeley
Brian J. Butler, National Radio Astronomy Observatory
Icarus 163 (2003) 428-433
Presented by Carl Gross
TERPS Conference
College Park, MD
December 7, 2003
Jupiter’s Radio Spectrum
Below ~40 MHz: Decametric emission
Between 50 – 5000 MHz: Synchrotron emission
Above ~15000 MHz: Thermal emission
Physical Background
Why does Jupiter have a magnetic field?
High pressure ionizes hydrogen, forming a layer of plasma
Electrons are free to move freely through the plasma, like a metal, making it liquid
‘metallic’ hydrogen
These electrons move with Jupiter’s rotation, setting up a current, resulting in a
magnetic field
Synchro-what radiation?
Charged particles from the solar wind get trapped and accelerated along magnetic field
lines, emitting synchrotron radiation
Recent observations and computer simulations show that Jupiter’s synchrotron
emission can depend on solar activity, resulting in a time-varying radio
spectrum
As a result, an accurate spectrum can only be obtained with simultaneous observations
Low-Frequency Observations
74 MHz observations made September 19th and 20th, 1998
330 MHz observations made September 15th, 16th, 19th, and 20th, 1998
Observations made with VLA in its B-configuration (74 MHz resolution ~ 2.3 arcmin,
330 MHz resolution ~ 17 arcsec)
Jupiter’s nonthermal flux densities scaled to 4.04 AU
Frequency
[MHz]
S [Jy]
S [Jy]
S [Jy]
S [Jy]
S [Jy]
Sept. 15th
Sept. 16th
Sept. 19th
Sept. 20th
Average
74
N/A
N/A
4.96 ±0.30
4.71 ±0.30
4.84 ±0.16
330
5.15 ±0.06
5.27 ±0.06
5.12 ±0.06
5.02 ±0.06
5.13 ±0.05
Full Radio Spectrum
In an effort to generate and accurate radio spectrum, throughout September 1998, 11
additional flux densities were measured for Jupiter, using 10 different
telescopes
Frequencies range from 74 MHz – 8 GHz
Model Fits
E Max
I  
E Min

j ( E ,  , L) B F ( )dE
c

E 
j ( E )  E 1  
 E0 
b
a
JUST the energy dependence of
j(E,,L)
Radial (L) dependence governed by
diffusion theory, of which the
controllable parameters are the
diffusion coefficient D0, and the loss
term, t0.
Bibliography
de Pater, I., Butler, B.J., 2003. Low-frequency VLA observations of Jupiter. Icarus
163, 428-433
de Pater, I., Bulter, B.J., Green, D.A., Strom, R., Millan, R., Klein, M.J., Bird, M.K.,
Funke, O., Neidhofer, J., Maddalena, R., Sault, R.J., Kesteven, M., Smits,
D.P., Hunstead, R., 2003. Jupiter’s radio spectrum from 74 MHz up to 8
GHz. Icarus 163, 434-448