[time-nuts] How good is your ADEV at 10E7 seconds? :)
jim77742 at gmail.com
Sat Nov 18 06:06:41 EST 2017
Approximately 6% of pulsars "glitch" and yes these (typically young)
pulsars are poor time standards. The glitching is most likely caused by
unpinning of vortices in the superfluid outer core. This causes a momentum
transfer from the core to the crust - and a speed-up. The Vela pulsar (freq
of ~11 Hz) is the most famous of the glitching pulsars as it glitches
regularly (approximately every three years). The last glitch of Vela (Dec
2016) had a deltaF/F of about 1.4E-6.
However millisecond pulsars are completely different. They spin at hundreds
of Hz, typically don't glitch, and PSR J0437-4715 will give many atomic
clocks a run for their money. It has an error in its period (5.75 ms) of
9.9E-17 and an error in its period derivative of 9E-26. The idea was to
monitor an array of millisecond pulsars and use this to detect
gravitational waves. For many years it was a race between LIGO and the
pulsar array to find GW. LIGO won.
Incidentally, LIGO has looked for GW coming from a pulsar. Vela was chosen
as its frequency is in the LIGO sweet spot. Nothing was found however (
https://arxiv.org/pdf/1104.2712.pdf) - but this was 7 years ago.
On 18 November 2017 at 13:24, Bob kb8tq <kb8tq at n1k.org> wrote:
> There are a number of papers on pulsars as time standards. The gotcha
> in the observed data (that has been measured over long time periods) has
> been random frequency jumps. Put another way, 10 million seconds and
> beyond *is* the problem. It’s going to take a *lot* of monitoring for a
> very long
> time to convince people that a specific pulsar is a good idea.
> > On Nov 17, 2017, at 8:54 PM, Hal Murray <hmurray at megapathdsl.net> wrote:
> > Context is the what-next portion of a recent LIGO talk. For those of you
> > that missed it (or didn't pay enough attention), on Aug 17th, they got
> > data from a pair of neutron stars. 1.7 seconds later, the Fermi
> > got a gamma ray burst. Within a day, the optical guys had found a new
> > Over the next days and weeks, they got data over the whole spectrum,
> radio to
> > X-rays. (There were 70 observatories lined up to pounce. Everybody
> > in on the action.)
> > LIGO only works for roughly the audio spectrum. At the low and high
> > the noise goes up. Lots of people are working on how to build gear that
> > work at other wavelengths.
> > One proposal is to monitor pulsars. There might be stuff leftover from
> > big bang with a period of a year or so. If you can get good timing from
> > pulsar, you might be able to see it. I suspect that will take "good"
> > to a scale that would astonish most time-nuts.
> > --
> > These are my opinions. I hate spam.
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