A blast from the past: How Cir X-1 became the youngest known X-ray Binary
Sebastian Heinz



Deep Chandra observations of Circinus X-1 reveal the nebula of a young supernova remnant surrounding neutron star X-ray binary. Spectral fits indicate an age of approximately 2600 years for a source distance of 8 kpc, making Circinus X-1 the youngest known X-ray binary. The young age explains the rapid orbital evolution and the extreme swings in X-ray brightness from the accreting neutron star. The fact that Cir X-1 shows type I X-ray bursts, the lack of pulsations, and the presence of jets in this system argue for a very low magnetic field of this young neutron star, suggesting that neutron stars can be born with fields well below the canonical value of 10^12 G.