Low-Frequency VLA Observations of Jupiter

1
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
2
Jupiters Radio Spectrum

• Below 40 MHz Decametric emission

• Between 50 5000 MHz Synchrotron emission

• Above 15000 MHz Thermal emission

3
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 Jupiters 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 Jupiters 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

4
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)

Jupiters 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
5
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

6
Model Fits

• JUST the energy dependence of j(E,a,L)

• Radial (L) dependence governed by diffusion
  theory, of which the controllable parameters are
  the diffusion coefficient D0, and the loss term,
  t0.

7
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. Jupiters radio spectrum from 74 MHz up to
8 GHz. Icarus 163, 434-448