Yesterday was all about understanding FFTs. I think I understand less than I did before. More precisely, I don't understand IDL's FFT routine and how to adjust the x-axis to view the power spectrum correctly. I will attempt to learn.

I spent a while yesterday trying to figure out how to overwrite the x and y columns in an event list before realizing that I wasn't trying to make a light curve. I had wanted to input integers increasing by 1 in the x column and sin(x) values in the y column to create a sinusoidal curve with a known period. I would replace those position coordinates into the event file and run the file through the FFT code Sandy and I have been working on, just to see if the FFT would give us a peak at the correct frequency.

However, Sandy pointed out that I should be modifying the time column. We couldn't figure out a way to create a periodic time column using a function, so I calculated out 16 events (2 pulses) by hand.

Today I finished my code to replace the time column in an event list and save that list. However, the MWRFITS IDL procedure only saved the events and not the GTIs, which are also needed by the wt_fft_evt program. So, after all that work writing a new code, I simply opened the event list in fv (FITS viewer) and changed the columns like it was a spreadsheet. So easy!

When I ran the test event list through the wt_fft_evt program, I could clearly see the periodicity in the light curve, but the power spectrum was weird. I'm not sure if this was a consequence of my time values, binning values, or the code itself, but no matter what I did, I couldn't get a clear spike at the correct frequency to appear in the power spectrum. This is worrisome. I'll have to look into this more closely on Monday.