Hydrodynamic evolution of Sgr A East: the imprint of a supernova remnant in the Galactic Centre

Abstract

We perform three-dimensional numerical simulations to study the hydrodynamic evolution of Sgr A East, the only known supernova remnant (SNR) in the center of our Galaxy, to infer its debated progenitor SN type and its potential impact on the Galactic center environment. Three sets of simulations are performed, each of which represents a represent a certain type of SN explosion (SN Iax, SN Ia or core-collapse SN) expanding against a nuclear outflow of hot gas driven by massive stars, whose thermodynamical properties have been well established by previous work and fixed in the simulations. All three simulations can simultaneously roughly reproduce the extent of Sgr A East and the position and morphology of an arc-shaped thermal X-ray feature, known as the “ridge”. Confirming previous work, our simulations show that the ridge is the manifestation of a strong collision between the expanding SN ejecta and the nuclear outflow. The simulation of the core-collapse SN, with an assumed explosion energy of 5 × 1050 erg and an ejecta mass of 10 M⊙, can well match the X-ray flux of the ridge, whereas the simulations of the SN Iax and SN Ia explosions underpredict its X-ray emission, due to a smaller ejecta mass. All three simulations constrain the age of Sgr A East to be ≲1500 yr and predict that the ridge should fade out over the next few hundred years. We address the implications of these results for our understanding of the Galactic center environment.

Does Diffuse Circumnuclear Gas around Sgr A* Achieve Collisional Ionization Equilibrium or Remain Non-equilibrium Ionization?

“…Motions by these streamers may introduce collisions with surrounding gas. Moreover, the possible X-ray ridge feature located in the outer region of this work (Rockefeller et al 2005) suggest that there undergoes a supernovae explosion within past 2000 yr (see Zhang et al 2023, not taken into account in this work). Consequently, gases in this region are promising to remain in an NEI state.…”

“…Consequently, the asymmetry of the gas within ∼0.01 pc can then be safely neglected (Ressler et al 2018). Besides, as shown in the middle and right panels of Figure 1, the diffuse X-ray emission between 1″ and 20″ are fairly smooth and symmetric, suggesting that there are no strong stellar activities recently (either X-ray binaries or supernovae, but see, e.g., Zhang et al 2023 for shocks driven by supernovae in the outer region). Second, the 1D model can reach a dynamical range in a radius of 6-7 orders of magnitude, while numerical simulations can only reach a factor of ∼10 3−4 .…”

“…First, we extend to include a larger region of up to ∼20″ (i.e., up to sub-pc scale), which now has sufficient signal-to-noise thanks to the continuous efforts of Chandra. As we will show in Section 3.2.1, such extension is necessary for our investigation of non-equilibrium ionization process (NEI, see Section 3.2 below, and Ji et al 2006;Zhang et al 2023). Second, also the motivation of this work is to probe the possible observational evidence of NEI in Sgr A * .…”

“…Indeed, the diffuse soft X-rays at scales larger than ∼1′ are quite asymmetric and show filamentary features in soft X-rays, compared to the more uniform distribution in hard X-rays (Muno et al 2004). They may be created by collisions of stellar winds and/or the expanding supernova remnants (e.g., Zhang et al 2023, see Genzel et al 2010 for a review). Quataert (2004, see also Xu et al 2006) is pioneered in understanding the gas properties between ∼0 2 and 10″.…”