Although the Galactic supernova rate is about 2 per century , only few supernova remnants are associated with historical records .
There are a few ancient Chinese records of “ guest stars ” that are probably sightings of supernovae for which the associated supernova remnant is not established .
Here we present an X-ray study of the supernova remnant G7.7 -3.7 , as observed by XMM-Newton , and discuss its probable association with the guest star of 386 CE .
This guest star occurred in the ancient Chinese asterism Nan-Dou , which is part of Sagittarius .
The X-ray morphology of G7.7 -3.7 shows an arc-like feature in the SNR south , which is characterized by an under-ionized plasma with sub-solar abundances , a temperature of 0.4 –0.8 keV , and a density of \sim 0.5 ( d / 4 ~ { } { kpc } ) ^ { -0.5 } { cm } ^ { -3 } .
A small shock age of 1.2 \pm 0.6 ( d / 4 ~ { } { kpc } ) ^ { 0.5 } kyr is inferred from the low ionization timescale of 2.4 ^ { +1.1 } _ { -1.3 } \times 10 ^ { 10 } ~ { } { cm } ^ { -3 } { s } of the X-ray arc .
The low foreground absorption ( N _ { H } = 3.5 \pm 0.5 \times 10 ^ { 21 } ~ { } { cm } ^ { -2 } ) of G7.7 - 3.7 made the supernova explosion visible to the naked eyes on the Earth .
The position of G7.7 - 3.7 is consistent with the event of 386 CE , and the X-ray properties suggest that also its age is consistent .
Interestingly , the association between G7.7 - 3.7 and guest star 386 would suggest the supernova to be a low-luminosity supernova , in order to explain the not very long visibility ( 2–4 months ) of the guest star .