A Very Large Glitch in PSR J1806-2125

PSR J1806-2125 is a pulsar discovered in the Parkes multibeam pulsar survey with a rotational period of 0.4s and a characteristic age of 65kyr. Between MJDs 51462 and 51894 this pulsar underwent an increase in rotational frequency of $\Delta \nu/\nu \approx 16 \times 10^{-6}$. The magnitude of this glitch is approximately 2.5 times greater than any previously observed in any pulsar and 16 times greater than the mean glitch size. This letter gives the parameters of the glitch and compares its properties to previously observed events. The existence of such large and rare glitches offers new hope for attempts to observe thermal X-ray emission from the internal heat released following a glitch, and suggests that pulsars which previously have not been observed to glitch may do so on long timescales.