Tom Van Baak
2018-04-13 07:54:08 UTC
1) Many of you know that pulsars are weird astronomical sources of periodic signals. Some are so accurate that they rival atomic clocks for stability! True, but I don't have a 100 foot antenna at home so I'll take their word for it. Plus, you have to account for a myriad of PhD-level corrections: from earth's rotation to general relativity. And, like quartz or rubidium clocks, pulsars drift (as they gradually slow down). Precision timing is not easy. If you poke around the web you can find numerous articles describing their detection and measurement and exploring their use as reference clocks, both here and potentially for deep-space timekeeping.
2) If you do a lot of clock measurement at home then you know the dark side of working with precision clocks. There are signal quality issues, measurement resolution issues, reference stability limitations, offset, drift, phase jumps, frequency jumps, missed or extra cycles, glitches, etc. For example, quartz oscillators (depending on make / model / luck) can exhibit frequency jumps; i.e., without warning they just change frequency without your permission. Ok, maybe not by a lot, but enough to notice; perhaps enough to cause trouble to any naive GPSDO PID algorithm that assumes steady state from the oscillator you thought was stable.
3) Now the exciting part! Fellow time-nut Jim Palfreyman studies pulsars. You've seen postings from him now and then over the years. It turns out Jim is the first person to catch a pulsar in the act of a frequency jump. After 3 years of continuous searching! This is really cool. Just amazing. You can't get more time nutty than this. And it just got published in Nature. It's a perfect never-give-up, i-eat-nanoseconds-for-breakfast, time nut thing to do. I am so impressed.
To quote Jim:
On December 12, 2016, at approximately 9:36pm at night, my phone
goes off with a text message telling me that Vela had glitched. The
automated process I had set up wasn't completely reliable - radio
frequency interference (RFI) had been known to set it off in error.
So sceptically I logged in, and ran the test again. It was genuine!
The excitement was incredible and I stayed up all night analysing the data.
What surfaced was quite surprising and not what was expected. Right
as the glitch occurred, the pulsar missed a beat. It didn't pulse.
Here is a very readable description of his discovery:
And also the official Nature article with all the juicy, peer-reviewed details:
So congratulations to Jim. I will think of him next time my 10811A quartz oscillator does a frequency jump or next time my 60 Hz mains frequency monitor skips a cycle...
If you have comments or questions feel free to send them to Jim directly (see Cc: address). Perhaps he can summarize the questions and his answers in a posting to time-nuts soon.
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