According to my book, each magnetic pole of some pulsars is more like a rotating circular array of sub-poles, where the direction of induced radiation varies from sub-pole posetion to sub-pole position. And only a small range of sub-pole positions out of the group happens to point in the direction of the Earth.
A reason for a general slowdown is energy lost to the radiation. But the glitches, in the case of the Vela pulsar at least, involve steps upward in spin rate, although nowhere near enough to cancel the overall slowing trend. The authors of "Introduction to Radio Astronomy" do a much better job of explaining the sawtooth effect than my clumsy attempt. Robert L. Forward, I suspect. Dana On Sat, Apr 14, 2018 at 12:04 AM, Bill Hawkins <bill.i...@pobox.com> wrote: > 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-boun...@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 <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 > > > > _______________________________________________ > > time-nuts mailing list -- email@example.com To unsubscribe, go to > > https://www.febo.com/cgi-bin/ mailman/listinfo/time-nuts and follow > > the instructions there. > > > _______________________________________________ > time-nuts mailing list -- firstname.lastname@example.org To unsubscribe, go to > https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- email@example.com > To unsubscribe, go to https://www.febo.com/cgi-bin/ > mailman/listinfo/time-nuts > and follow the instructions there. > _______________________________________________ time-nuts mailing list -- firstname.lastname@example.org To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.