4 arc min. Distance estimates place it between 3 and more than 7 kiloparsecs (10,000 to 23,000 lightyears), with the current consensus being a distance of , as of 2021. The available evidence supports a type Ia supernova as the source of this remnant, which is the result of a carbon-oxygen white dwarf interacting with a companion star. The integrated X-ray spectrum resembles that of Tycho's supernova remnant, a type Ia supernova. The abundance of oxygen relative to iron in the remnant of SN 1604 is roughly solar, whereas a core-collapse scenario should produce a much higher abundance of oxygen. No surviving central source has been identified, which is consistent with a type Ia event. Finally, the historical records for the brightness of this event are consistent with type Ia supernovae. There is evidence for interaction of the supernova ejecta with circumstellar matter from the progenitor star, which is unexpected for type Ia but has been observed in some cases. A bow shock located to the north of this system is believed to have been created by mass loss prior to the explosion. Observations of the remnant are consistent with the interaction of a supernova with a bipolar planetary nebula that belonged to one or both of the progenitor stars. The remnant is not spherically symmetric, which is likely due to the progenitor being a runaway star system. The bow shock is caused by the interaction of the advancing stellar wind with the interstellar medium. A remnant rich in nitrogen and silica indicate the system consisted of a white dwarf with an evolved companion that had likely already passed through the asymptotic giant branch stage. See also List of supernova remnants List of supernovae Supernova Early Warning System References Further reading External links Light curves on the Open Supernova Catalog Ophiuchus (constellation) Supernova remnants Supernova 1604 in science 1604 16041009 Historical supernovae