The Underluminous Nature of Sgr A*
  In the last several years, a number of observing campaigns of the massive
black hole Sgr A* has been carried out in order to address two important
issues: one concerns the underluminous nature of Sgr A* with its bolometric
luminosity being several orders of magnitude less than those of its more
massive counterparts. It turns out that the angular momentum of the ionized
stellar winds from orbiting stars in one or two disks orbiting Sgr A* could be
a critical factor in estimating accurately the accretion rate unto Sgr A*. A
net angular momentum of ionized gas feeding Sgr A* could lower the Bondi rate.
Furthermore, the recent time delay picture of the peak flare emission can be
understood in the context of adiabatic expansion of hot plasma. The expansion
speed of the plasma is estimated to be sub-relativistic. However, relativistic
bulk motion of the plasma could lead to outflow from Sgr A*. Significant
outflow from Sgr A* could then act as a feedback which could then reduce Bondi
accretion rate. These uncertain factors can in part explain the underluminous
nature of Sgr A*. The other issue is related to the emission mechanism and the
cause of flare activity in different wavelength bands. Modeling of X-ray and
near-IR flares suggests that inverse Compton scattering (ICS) of IR flare
photons by the energetic electrons responsible for the submm emission can
account for the X-ray flares. A time delay of minutes to tens of minutes is
predicted between the peak flaring in the near-IR and X-rays, NOT due to
adiabatic expansion of optically thick hot plasma, but to the time taken for IR
flare photons to cross the accretion flow before being upscattered.
