Low-angular-momentum accretion shocks can power weak-to-moderate X-ray flares from SgrA*

Abstract

X-ray flares from Sgr~A* span broad ranges in duration, fluence, and luminosity, but their origin remains unsettled. We test whether standing shocks in low-angular-momentum magnetized accretion flows can provide a viable energy reservoir to account for these events. Using semi-analytic trans-magnetosonic shock solutions, we estimate the kinetic energy available in the downstream post-shock flow and compare it with the 25-year \textit{Chandra} X-ray flare catalog. For each theoretical solution, we compute the required efficiency $\epsilon =E_{\mathrm{data}}/E_{\mathrm{sh}}$, where $E_{\mathrm{data}}$ is the observed radiated energy for each flare and $E_{\mathrm{sh}}$ is the available energy in the shocked flow. Notably, the weak flares require $\epsilon \sim 10^{-3}$--$10^{-2}$, while moderate flares require a few percent. We perform the analyses for weakly and highly spinning cases, and the resulting weak-to-moderate flare energy budget remains unchanged. For the fiducial accretion rate and bolometric correction, the kinetic energy reservoir in standing shock is sufficient for the observed weak-to-moderate flare population, whereas the strongest events likely require higher efficiency which can be mediated via additional magnetic energy dissipation channel.

12 pages, 4 figures. Accepted for publication in The Astrophysical Journal