RX J0852.0-4622 (also known as G266.2−1.2) is a recently discovered supernova remnant. The distance to this object is controversial, but some scientists argue that the supernova remnant is only 650-700 light years away, and exploded comparatively recently, only about 1400 years ago. The remnant is located in the southern sky in the constellation Vela ("sail"), and sits (in projection) inside the much larger and older Vela Supernova Remnant. For this reason, RX J0852.0-4622 is often referred to as Vela Junior.
X-ray astronomers and gamma-ray astronomers of the Max Planck Institute for Extraterrestrial Physics in Garching, Germany, discovered this supernova remnant in 1998 (Nature, Vol. 396, 12 November 1998).
If the remnant is indeed young and nearby, its corresponding supernova should have been visible from the Earth in about the year 1250. One difficulty with this interpretation is that there are no contemporary written reports of any supernova at that time or in that part of the sky.