Pulsar Timing Accuracy: Fractional Instability to 10^-15

[mersecske]

I've read the following statement:
"Fractional instability of some pulsars is comparable with the one of atomic standards
and reaches the level 10^{-15}"
This was the first sentence of the paper of Alexander Rodin:
Detection of GW by pulsar timing
But no citation in there.
1) Could you give me some citations?
2) 10^{-15} is the real physical dispersion at the place of the pulsar,
or an error due to physical effects during the sign propagation,
or a measurement error on the Earth?

 

[bcrowell]

This is not a complete answer to your question, but pulsars are subject to "starquakes," and this is one limit on their perfection as clocks.