[time-nuts] Pulsars, clocks, and time nuts (Jim Palfreyman)

Bill Hawkins bill.iaxs at pobox.com
Sat Apr 14 01:04:57 EDT 2018


It seems that pulsars are rotating stellar objects that have no reason
to change their rotation, except to decay.
Ruling out causes from the stellar object, one is left with things that
might be orbiting the object and their ability to absorb the pulse that
is aimed at us. One could move further out to the extremely low
probability that some interstellar object absorbed the pulse. This
doesn't explain the sawtooth, unless one of those orbiting bodies is
affecting the rotation rate of the pulsar, such as a binary star.

Disclaimer: I know very little about radio astronomy, but I've read a
lot of hard science fiction.

Bill Hawkins


-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces at febo.com] On Behalf Of Dana
Whitlow
Sent: Friday, April 13, 2018 8:39 AM
To: Tom Van Baak; Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Pulsars, clocks, and time nuts (Jim Palfreyman)

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 <tvb at 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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