Tom's discussion about pulsars brought back some memories...

Many pulsars exhibit skipped pulses.  And one curiosity that I didn't see
mentioned in Tom's discussion is that some pulsars even exhibit behavior
reminiscent of the "sawtooth jitter" so evident in the PPS outputs of most
GPS receivers.  See figures 12-11 & 12-12 in "An Introduction to Radio
Astronomy" (2nd edition) by Burke and Graham-Smith.  The first ed also
contains the basic plot (as figure 12-8 in this case), but whose explanation
is not as up-to-date).

For a deeper treatment of pulsars, also see
      https://www.cv.nrao.edu/course/astr534/PDFnew.shtml
by Condon and Ransom (both of NRAO).

The above two references are the best Radio Astronomy tomes I've yet seen..

Pulsar timing has been (and still is) a very big deal in radio astronomy,
as it
is key to verification of certain points of Einstein's General Theory of
Relativity.

Here are two web sites in which audio recordings of various pulsar
sounds (made with larger radio telescopes) are presented.

https://www.youtube.com/watch?v=uHEVo-LkDrQ
(You may ignore the video part, even though it's "cute", but the
audio portion is a fine example of the pulse to pulse variations
exhibited by many pulsars, all wrapped up in one pulsar)

http://www.jb.man.ac.uk/pulsar/Education/Sounds/0329_stack.mp4
(I think this is the best overall site, giving quality recordings of a
fair number of different pulsars)

Dana






On Fri, Apr 13, 2018 at 2:54 AM, Tom Van Baak <t...@leapsecond.com> wrote:

> Amazing news... 1.2.3.
>
> 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:
>
> http://theconversation.com/captured-radio-telescope-
> records-a-rare-glitch-in-a-pulsars-regular-pulsing-beat-94815
>
> And also the official Nature article with all the juicy, peer-reviewed
> details:
>
> https://rdcu.be/LfP0
>
> 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.
>
> /tvb
>
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