Radio-observations of fragment (A) comet Shoemaker-Levy 9
with Swiss amateur radio telescope
On July the 16th 1994 Jupiter was tracked automatically with our amateur radio telescope 'Ricken Süd' within hours on the wavelength 0,7m (432MHz). The telescope is a 10m parabola antenna fully computer controlled. The feed is a short Yagi mounted in the focal plane. A very expensive low noise GaAsFET preamp is fixed between antenna and receiver. Our receiver is a commercial one set to wide fm with a bandwidth of 180KHz. The detector is a quadratic demodulator or multiplier with low pass filter of 0,2sec and a fet-opamp as backend. The recorded signals did not show any special signature until 19:53 UT. But at about 19:54 UT the radio noise increased drastically. Two minutes later at about 19:56 UT the noise level returned slowly to nominal level. The opticians recorded the event at about 19:58 UT (according to local press information). The reason why the radio noise was recorded before the optical event is up to now not clear to me. It may be that we did not record the crash itself but the motion of charged particles in Jupiter's magnetosphere prior the physical crash (synchrotron radiation). In the picture below we see the radio signal in digits recorded with an A/D-converter with 12 digits resolution and a sample rate of 0,1sec. The abscissa shows the time in minutes after 19:00 UT (21:00 local summer time). The A/D-converter is also a commercial plug-in card in a AT personal computer. The software is home brewed written in Turbo Pascal. Comparisons with measurements on Taurus A two hours earlier showed, that the antenna excess noise was about 15 to 20 Kelvin's. The plot shown below was a bit filtered with an FFT- and IFFT procedure to enhance the interesting variations.
On the basis of the measured antenna temperature of 15 to 20 Kelvin's the thermal or synchrotron noise temperature in the radio range can be estimated to about
where W A means the beam angle of the antenna and W pla means the angle of planet Jupiter. This high temperature in my opinion is not the crash temperature but it may be that this high temperature is synchrotron in its nature as mentioned above. The opticians (in local press) told, that the crash temperature was 30'000 Kelvin's in minimum. We are anxious to hear about professional interpretations of this event.