Constraining particle acceleration in Sgr A^⋆with simultaneous GRAVITY,<i>Spitzer</i>,<i>NuSTAR</i>, and<i>Chandra</i>observations

We report the time-resolved spectral analysis of a bright near-infrared and moderate X-ray flare Sgr A*. obtained light curves in $M$-, $K$-, $H$-bands mid- $2-8~\mathrm{keV}$ $2-70~\mathrm{keV}$ bands X-ray. The observed slope band is $\nu L_\nu\propto \nu^{0.5\pm0.2}$; L_\nu \propto \nu^{-0.7\pm0.5}$. tested synchrotron self-Compton (SSC) scenarios. brightness faintness, together with slopes, pose challenges for all models explored. rule out scenario which emission SSC. A one-zone model both luminosity are produced by SSC stems from cooled spectrum can explain flare. In order to describe mean SED, require specific values maximum Lorentz factor $\gamma_{max}$, however differ roughly two orders magnitude: suggests that electrons accelerated $\gamma_{max}\sim 500$, while requires acceleration up $\gamma_{max}\sim5\times 10^{4}$. electron densities $10^{10}~\mathrm{cm^{-3}}$ much larger than typical ambient accretion flow, thus an extraordinary event. contrast, assuming source size $1R_s$, be realized magnetic fields comparable flow. For models, temporal evolution regulated through implying sustained particle required at least part