Student Hera: HERA Timing Tools Extension  Power Spectrum
In the previous exercises you analyzed the light curve data of the source using the method of folding to find the best period. You then verified this period by looking at the folded light curve. Another method of finding the period of a source is to look at its power spectrum. The power spectrum is a plot of how much power there is at each frequency. It is generated using a mathematical procedure (Fourier Transform) that takes a signal (brightness as a function of time, or lightcurve) and turns it into a frequency spectrum (how much power at each frequency). This technique is like using an equalizer to find what frequencies are present in a piece of music. For a periodic source, the power spectrum will show a peak at the best frequency (the inverse of the period), and perhaps several other smaller peaks at other frequencies (there may be more than one periodicity in a source).
To find the power spectrum of GX3012, click on the data set in the Student Hera GUI and select Power Spectrum from the list of XRONOS tools. Click on the "run" button, and you will see a parameter box with the file name and directory filled in. You will need to assign values to the parameters Newbin Time or negative rebinning, Number of Newbins/Interval and Number of Intervals/Frame. You can reuse the values you used when running File Plot or Epoch Fold for these parameters, as a first start. The resulting plot will show a peak at the strongest frequency, as well as smaller peaks at secondary frequencies.
To get rid of the error bars, type "error off" at the PLT> prompt in the powspec Output window, then "p" (to replot). For more detailed description and help with basic plotting commands, go to Plotting Basics.
Exercise E2
