  Flares in Sagittarius A* are produced by hot plasmas within a few
Schwarzschild radii of the supermassive black hole at the Galactic center. The
recent detection of a correlation between the spectral index and flux during a
near infrared (NIR) flare provides a means to conduct detailed investigations
of the plasma heating and radiation processes. We study the evolution of the
electron distribution function under the influence of a turbulent magnetic
field in a hot collisionless plasma. The magnetic field, presumably generated
through instabilities in the accretion flow, can both heat the plasma via
resonant wave-particle coupling and cool the electrons via radiation. The
electron distribution can generally be approximated as relativistic Maxwellian.
To account for the observed correlation, we find that the magnetic field needs
to be anti-correlated with the electron ''temperature''. NIR and X-ray light
curves are produced for a cooling and a heating phase. The model predicts
simultaneous flare activity in the NIR and X-ray bands, which can be compared
with observations. These results can be applied to MHD simulations to study the
radiative characteristics of collisionless plasmas, especially accretion flows
in low-luminosity AGNs.
