GLOBAL ENERGY-CONSERVATION IN GRAVITATIONAL LENSING

Global properties of energy conservation in gravitational microlensing are discussed. We consider the influence of a gravitating body on the observations done at different locations on a sphere surrounding the source. We show that a mass located outside this sphere only redistrib utes the photons, so some observers register a larger energy flux, pho ton count rate etc. at the cost of other observers, but there is no ne t effect on the whole sphere. A lensing mass located inside the observ ers' sphere reduces its surface area, and also redshifts photons on av erage. The redistribution of photons is accompanied by a net decrease of averaged energy flux because of the redshift. However, the total ph oton count from a bursting source is increased on average as the area of the observers' sphere is reduced.