IDENTIFICATION OF THE PULSAR PSR1509-58 WITH THE GUEST STAR OF AD 185

ON 7 December 185, astronomers at the imperial observatory of Lo-Yang, in central China, reported a 'guest star' in the southern sky. Their records of its appearance, gradual fading and disappearance constitute the oldest compelling historical account of a supernova. It is widely believed that the remnant of this explosion is MSH14-63, but the identification is problematic, in particular because the position of MSH14-63 with respect to the Sun and the horizon would have made it invisible for some of the time when the guest star was said to be visible. I argue here that the Chinese astronomers actually witnessed the birth of the pulsar PSR1509-58 in the supernova remnant MSH15-52. This is then only the second pulsar, after that in the Crab nebula (PSR0531 + 21), to have a known age. Timing measurements of the age of PSR1509-58 are consistent with its birth approximately 1,800 years ago, and future measurements of the distance to MSH15-52 and its rate of expansion should conclusively establish or disprove this identification.