Pulsar PSR B0656 -14, the Monogem ring, and the origin of the "knee" in the primary cosmic-ray spectrum

The Monogem ring is a bright, diffuse, 25° diameter supernova remnant easily visible in soft X-ray images of the sky. Projected within the ring is a young radio pulsar, PSR B0656 +14. An association between the remnant and pulsar has been considered but was seemingly ruled out by the direction and magnitude of the pulsar proper motion and by a distance estimate that placed the pulsar twice as far from Earth as the remnant. Here we show that in fact the pulsar was born very close to the center of the expanding remnant, both in distance and in projection. The inferred pulsar and remnant ages are in good agreement. The conclusion that the pulsar and remnant were born in the same supernova explosion is nearly inescapable. The remnant distance and age aie in remarkable concordance with the predictions of a model for the primary cosmic-ray energy spectrum in which the "knee" feature is produced by a single dominant source.