Late last year the Crab pulsar glitched. It was the biggest glitch we've ever seen in that source since it was discovered in 1968. Today our paper on how we @jodrellbank detected and measured the glitch came out. Here's a summary. (1/19) 
The Crab pulsar sits in the centre of this Supernova remnant. It was formed in AD 1054 in the supernova that created this nebula. It's one of the youngest pulsars we know of. (2/19)
We observe the Crab every day for 11 hours at Jodrell Bank using the 42-ft telescope. None of the other ~850 pulsars we routinely time get this much attention. (3/19)
The rotation of pulsars is exceptionally stable. Clock-like, in fact. And we can measure it to very high precision. On 4 Nov 2017, the Crab was spinning once every 33.7418002331(4) milliseconds. That bracketed 4 is the error on the last digit. (4/19)
We can also measure its rotation slowing down. On that day its rotation period was increasing by 36 nanoseconds per day or 13 microseconds per year. 4 days later though, its smooth spin-down was interrupted. (5/19)
On the 8th of Nov, its rotation period, abruptly decreased - that is, it was suddenly rotating much faster. This is a known as a glitch and is the Crab's 25th such event, and it's the biggest seen so far. More than twice the size of the previous largest in March 2004.(6/19)
What causes glitches? We think there's a superfluid in the star that doesn't slow down with the crust from which we observe the radio emission. This means the fluid interior becomes a 'reservoir' of angular momentum. (7/19)
For reasons we don't fully understand yet, the fluid and the crust can suddenly exchange angular momentum. The fluid slows down and the crust speeds up - and we observe this as a glitch. Models predict this should happen in just minutes. (8/19)
This shows the Nov 2017 glitch in the data. Panel (A): Before the glitch the radio pulses were arriving at Earth when we expected (i.e. the residuals were zero). Then they suddenly started arriving progressively earlier than we expected. The pulsar had glitched. (9/19)
Glitches happen really quickly. Normally we don't see the spin-up itself. Before the glitch we see it spinning at one rate, and then after the glitch we see it spinning at another. We don't see the change happen. In other words, the spin-up is normally "unresolved". (10/19)
Panel (C) is the interesting one. That shows the change in the spin-rate and also shows that we've resolved part of the spin-up (that curvy bit after the dashed line). It took several days. This is highly unusual. (11/19)
By contrast, the Vela pulsar, when it glitches, (mostly of similar size to this one) does so in just seconds. Why are they different? We don't know. It's possible that delayed spin-ups are common but we don't usually see them because we don't observe for long enough. (12/19)
So we could measure the glitch properly, we checked that the amount of 'stuff' between us and the pulsar hadn't changed too much near the glitch. The pulsar is in a nebula and so the amount of stuff in the way (mostly electrons) can change quickly and affect the timing.(13/19)
This plot shows a measure of the electron density along the line-of-sight to the pulsar. There are no sharp changes near the glitch (dashed line). All is well.(14/19)
This is the pulse profile for the Crab pulsar. It has three components. We wanted to know if the power in each of these components had changed because of the glitch. If it had, it would suggest a link between the interior and the magnetic field. We saw no change. (15/19)
Despite promising hints of a change to the X-ray flux from the Crab as measured by the Swift X-ray telescope, it turned out there was none - the X-ray flux appears steady over the glitch. (16/19)
This big glitch happened after a long time without any glitches. We think there might be a relationship between the size of a glitch and how long it's been since the last one. We only have 20 data points though. We can only wait for more glitches to confirm/refute this.(17/19)
We've been watching the Crab to see how it recovers from the glitch. This can take years. However, a few days ago we found the Crab had glitched again! This time a small one. Its recovery from the large one has been interrupted! We keep watching, for 11 hours, every day.(18/19)
And here's the link to our paper - Click the PDF link to download it! arxiv.org/abs/1805.05110 (19/19). End of astronomy spam!
