SN 393 is the modern designation for a probable supernova that was reported by the Chinese in the year 393 CE. An extracted record of this astronomical event was translated into English as follows: The second lunar month mentioned in the record corresponds to the period 27 February to 28 March 393 CE, while the ninth lunar month ran from 22 October to 19 November 393 CE. The bowl-shaped asterism named Wěi is formed by the tail of the modern constellationScorpius. This asterism consists of the stars in Scorpius designated ε, μ, ζ, η, θ, ι, κ, λ and ν. The guest star reached an estimated apparent magnitude of −1 and was visible for about eight months before fading from sight, whose lengthy duration suggests the source was a supernova.
Modern observations
Before 1975, the observation made by the Chinese between February and March 393 CE was considered to be likely a bright nova with a secondary maximum. At the time, there were only seven possible candidate supernova remnants near where SN 393 was observed. Assuming maximum –1 magnitude occurred close to away, this immediately ruled out four possible candidates. Another discounted remnant was G350.0-1.8, as the expectant expansion rate indicated the supernova occurred around 8,000 years ago. Of the two remaining sources, G348.5+0.1 and G348.7+0.3, were both at the required 10,000 pc. distance and also each had estimated ages of 1,500 years. If true, it seems unlikely such supernovae would be visible to the naked eye over eight months, especially because they occurred close to a particularly dusty part of the galactic plane.
Confirmation of SN 393
During 1996, the ROSATAll Sky Survey discovered another nearby supernova remnant, RX J1713.7-3946, which two years later, was suggested as a better match for SN 393. Observations in 1999 suggested that this remnant was associated with H II region, G347.611 +0.204, whose distance was about, but in 2003, examining interactions between a nearby molecular cloud and the expanding remnant found the closer distance of around. In 2004, measures of the degree of X-ray and neutral hydrogen absorption by intervening matter between the remnant and Earth, confirmed this closer distance, making the true physical remnant diameter as, assuming the apparent angular diameter of about 1.2° or 70 arcminutes. Supernova remnant RX J1713.7-3946 is consistent with type II or type Ib supernovae. SN 393's progenitor had a mass of at least 15 solar masses, whose destruction generated energies of about, with three solar masses of material ejected into the surrounding interstellar medium.
