P2160 crab single pulses

mar06

links:
Oscillation frequency versus hour angle (0 to 10Hz) (.gif):
Oscillation frequency versus hour angle (0 to 2 Hz) (.gif):

Intro:

Project p2160 is looking at giant pulses from the crab pulsar with high time resolution using a fancy oscilloscope. On previous days an oscillation was seen in the total power output while tracking the source (which includes the nebula). On 11mar06 cband high was used to look at the crab. While the crab was tracked, a separate total power time series was taken with a 500 Mhz bandwidth centered at 7000 Mhz and a 1 millisecond time constant to check out the oscillations. The plots show the results:

The oscillations:

To look at the change in the total power oscillations, the spectrum of the total power was computed in 100 second sections (we ended up with 90 100 second sections). For each 100 seconds of data the following was done:

The 100 seconds of data was normalized to the median value.
A 1st order polynomial was removed.
A hanning window was applied and then the data was transformed : abs(fft(tpAN)).
An image was made of the oscillation frequency versus hour angle.

The maximum value of the oscillation was about 1% of Tsys. If we were looking at a point source, then a pointing error could put the point source on the edge of the beam. Any small oscillations could then cause a large change in the power from the source. Since the nebula is extended, it must depend on the gradient across the nebula. Vertical oscillations could also move us in focus.

The crab is at 21 Dec so the za goes down to about 3 degrees before the azimuth swings around (you see this where the total power switches from polA to polB in the first set of plots.

Oscillation frequency versus hour angle (0 to 10Hz) (.gif):
Oscillation frequency versus hour angle (0 to 10Hz) (.ps) (.pdf):

This shows 0 to 10 hz versus hour angle. There is a high frequency oscillation around 5.8 hz when the dome is at high za. It moves toward lower frequency as the telescope approaches transit and the reappears on the other side of transit. If the oscillation is in azimuth, then the amplitude of the oscillation should decrease as you move towards za=0 since on the sky, the displacement goes at Ampl*sin(za). But this does not change the frequency.

Oscillation frequency versus hour angle (0 to 2 Hz) (.gif):
Oscillation frequency versus hour angle (0 to 2 Hz) (.ps) (.pdf):

This blows up the horizontal scale to 0 to 2 hz. The .35 Hz and .55 Hz oscillation frequencies have previously been measured an motion oscillations during the hurricanes (more info). The .35 hz oscillation remains fixed. The .55 hz oscillation changes frequency with hour angle. The .87 Hz frequency peaks up at az=120 and 240 deg (tower 4 and tower 8).

Table of oscillation frequencies
freq (Hz)	Notes
.34	Frequency does not change with az,za. During hurricanes saw .35 (georges , .354 jeanne using tiedown tensions and pitch tilt sensors.
.5 to .61	Frequency varies with az,za. Highest frequency at transit Largest amplitude at high za Looks like there is a 2nd set of frequencies (that are weaker) about .07 hz lower in frequency. Seen in georges(at .57) jeanne (at .55) data.
.87	Frequency does not change with az,za Strong peaks at az=120, 240 which line up with tower 4 and tower 8.
5.8 to 0?	5.8 hz at high za then decreases towards 0. start to loose it around 4 hz. comes back from low freq back up to 5.8 hz after transit.

To do:

See if the amplitude of the oscillation frequency correlates with the motion of the tiedowns.

I looked at the td data and there is no obvious correlation with the motion of the tiedowns and the oscillations.

Track a continuum point source with a pointing offset and see what the oscillations look like. This will remove the uncertainty in the variation of the nebulas power (since it is extended and when the horn oscillates we're not sure how the power varies).

processing: x101/060311/tim.pro

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