P2160 crab single pulses


    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:

Total power versus time (.ps) (.pdf):

List of pulses greater than 1% of Tsys:  This lists all of the pulses from the bottom plot that exceeded .01 Tsys. The columns are : hh:mm:ss.ssss utc time, PolA total power, polB total power. If there were contiguous time samples above .01 Tsys then only the first was listed (since the time constant could cause many samples to be included). PolB had many more entries than polA. When the pulsar became active, TsysA was higher than TsysB do to the nebulas polarized power. This may have affected the .01 threshold for inclusion in the list.

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 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): 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):  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.

To do:

processing: x101/030611/tim.pro