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 19 th and 20 th , 1998  330 MHz observations made September 15 th , 16 th , 19 th , and 20 th , 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] Sept. 15 th Sept. 16th Sept. 19th S [Jy] Sept. 20th

74 N/A N/A 4.96 ±0.30

4.71 ±0.30

S [Jy] Average

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

I

 

E E



Max Min



B



F

(

 

c

)

dE



E



a

   1 

E E

0 

JUST j(E,



,L)

the energy dependence of    

b

 Radial (L) dependence governed by diffusion theory, of which the controllable parameters are the diffusion coefficient

D 0

, and the loss term, t

0

.

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