I did a detailed signal analysis of the Crab Pulsar (PSR B0531+21) data file and posted it to my baudline blog.
A strange amplitude modulation, hydrogen has sidebands, two pairs of identical drifting-random-walking signal twins, and cue the Baby Elephant Walk because they're back at 1/3, 2/3, 3/3 with a whole lot of lower level structure.
The strange amplitude modulation visible in both the spectrogram and waveform displays is unique to this data set. This is something new. It has a period of 3.489 seconds. Any idea what is causing it?
I have just sent to JRSETI a document which shows that there is a good chance that what you are seeing here is the effect caused by the immaturity of the Crab Pulsar; it is less than 1000 years old, and I believe that the remnant has yet to reach equilibrium and not only is it flashing its pulses once/twice a revolution, the remnant is actually still oscillating in size. I believe that if you analyse the data over the complete 10minutes (which I did by breaking the supplied files into SETISecond blocks, then averaging each block, to end up with 609 samples of the Crab intensity taken at 1 SETISec intervals) it shows some interesting results. I don't know how to attach pictures to these contributions, but the results suggest that the polar axis is oscillating at slightly higher frequency than the equatorial axis, generating a very characteristic envelope to the time domain intensity distribution. The Fourier transform shows an interesting spike at 3.5 seconds per cycle, which is slightly broadened, which is what you would expect from a relatively solid object which has a different but close polar frequency to equatorial frequency
I have asked JRSETI either to put the document up here if someone knows how to include pictures, else send you a copy (Would have done it myself but I don't know your EMAIL address)
The Crab Pulsar is in the news again:
Researchers have discovered that the Crab Pulsar is emitting gamma rays at energies much higher than expected. This quote sums up why this is important:
"The results are surprising: in contrast to expectations, the pulses are visible at energies of 100GeV and beyond, casting doubt on our current models for how pulsars work."
Dave Robinson has a blog about at http://setiquest.org/blog/low-frequency-analysis-crab-pulsar-data. What is the reason for these low frequency oscillations?
The direction I came to the conclusion that the Crab remnant might be oscillating was thinking about the way that the remnant formed, when the original star went SuperNova it formed a shock wave which has the effect of massively compressing the core of the star - not too unlike the way that laser fusion compresses the fuel pellets - however in the case of the Super Nova there is little or no fusionable material left in the core. What happens after the shock wave has dissipated, I figured that if there is no force continuing the collapse, then the core would probably start to re-expand slightly; providing that the core wasn't so big that it had become a black hole, in which case re-expansion is out of the question. I imagined a balancing act where finally the neutron star would reach equilibrium, where the internal pressure exactly matched the gravitational pull, but I felt it unlikely that the remnant would reach this state immediately, and would oscillate in a damped fashion about this equilibrium position. Of course I have no idea how rapid the oscillation would damp down completely, but felt that there was just a chance that in less than 1000 years, it might still be happening in the Crab remnant. Again I have no idea what the characteristic frequency of a a neutron star might be; so nothing ventured nothing gained, I decided to look to see if there was any evidence for such an oscillation, and to my great surprise, there was this 3.5 second oscillation and the much slower envelop oscillation. Fourier Analysis of the data showed that the slower oscillation was a phantom, there is no component at that frequency, and thus must be caused by multiple frequencies about the 3.5 second period; hence my Blog.
Sigblips is of course right, we must apply the same processing to the other Crab data sets. Alas I have exhausted my monthly allowance, and can't afford to download any more data, until November . But in line with all good scientific theories we can make a prediction; if the Crab is vibrating in the proposed fashion, then the effect will still be there, if it is an instrument fault, it probably won't be.
I looked at the other Crab Pulsar datasets with baudline and commented here:
a much more efficient analysis than I could have generated, as I only have the one set of Crab pulsar results; and with my limited download allowance, it would have taken several months to get the full set from one of the other Crab acquisitions.
Well you have shown that the Crab isn't oscillating, which suggests that there is either an instrumental problem, or I guess interference from another source. It seems a very low frequency for an instrumental fault - although having said that I once had an 'amplifier' that oscillated with a period of about 4 hours, that was a real problem to track down. It looked all the world like the DC level was drifting, maybe with temperature, which led me on a real wild goose chase I don't mind telling you.
I had started a similar analysis of the psrb0329+54 pulsar based on the assumption that if it was an oscillation, this older Pulsar would either have had time to reach equilibrium, else would have oscillated at a much lower level; but you seemed to have saved me a lot of effort. The only problem now is knowing that this Crab sequence has this 3.5 second artifact, how reliable is the higher frequency data?
Keep up the good work