The Sgr B2 X-ray Echo of the Galactic Center Supernova Explosion that Produced Sgr A East

Abstract

The possible impact Sgr A East is having on the Galactic center has fueled speculation concerning its age and the energetics of the supernova explosion that produced it. We have carried out the first in-depth analysis of the remnant's evolution and its various interactions: with the stellar winds flowing out from the inner ~2 pc, with the supermassive black hole, Sgr A*, and with the 50 km/s molecular cloud behind and to the East of the nucleus. We have found that a rather "standard" supernova explosion with energy ~1.5e51 ergs is sufficient to create the remnant we see today, and that the latter is probably only ~1,700 years old. The X-ray Ridge between ~9" and 15" to the NE of Sgr A* appears to be the product of the current interaction between the remaining supernova ejecta and the outflowing winds. Perhaps surprisingly, we have also found that the passage of the remnant across the black hole would have enhanced the accretion rate onto the central object by less than a factor 2. Such a small increase cannot explain the current Fe fluorescence observed from the molecular cloud Sgr B2; this fluorescence would have required an increase in Sgr A*'s luminosity by 6 orders of magnitude several hundred years ago. Instead, we have uncovered what appears to be a more plausible scenario for this transient irradiation--the interaction between the expanding remnant and the 50 km/s molecular cloud. The first impact would have occurred about 1,200 years after the explosion, producing a 2-200 keV luminosity of ~1e39 ergs/s. During the intervening 300-400 years, the dissipation of kinetic energy subsided considerably, leading to the much lower luminosity (~1e36 ergs/s at 2-10 keV) we see today.