We present preliminary results of the analysis of 5 years of MACHO data on the Galactic bulge microlensing events with clump giants as sources .
This class of events allows one to obtain robust conclusions because relatively bright clump stars are not strongly affected by blending .
We discuss : 1 ) the selection of ‘ giant ’ events , 2 ) the distribution of event durations , 3 ) the anomalous character of event durations and optical depth in the MACHO field 104 centered on ( l,b ) = ( 3 \hbox { $ . ^ { \circ } $ } 1 , -3 \hbox { $ . ^ { \circ } $ } 0 ) .
We report the preliminary average optical depth of \tau = ( 2.0 \pm 0.4 ) \times 10 ^ { -6 } ( internal ) at ( l,b ) = ( 3 \hbox { $ . ^ { \circ } $ } 9 , -3 \hbox { $ . ^ { \circ } $ } 8 ) , and present a map of the spatial distribution of the optical depth .
When field 104 is removed from the sample , the optical depth drops to \tau = ( 1.4 \pm 0.3 ) \times 10 ^ { -6 } , which is in excellent agreement with infrared-based models of the central Galactic region .