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Using 7 years of MACHO survey data, we present a new determination of theoptical depth to microlensing towards the Galactic bulge. We select the sampleof 62 microlensing events (60 unique) on clump giant sources and perform adetailed efficiency analysis. We use only the clump giant sources because theseare bright bulge stars and are not as strongly affected by blending as otherevents. Using a subsample of 42 clump events concentrated in just 4.5 squaredegrees, we find tau = 2.17^{+0.47}_{-0.38} x 10^{-6} at (l,b) = (1.50, -2.68),somewhat smaller than found in most previous MACHO studies, but in excellentagreement with recent theoretical predictions. We also present the opticaldepth in each of the 19 fields in which we detected events, and find limits onoptical depth for fields with no events. The errors in optical depth inindividual fields are dominated by Poisson noise. We measure optical depthgradients (1.06 +/- 0.71) x 10^{-6} deg^{-1} and (0.29 +/- 0.43) x 10^{-6}deg^{-1} in the galactic latitude b and longitude l directions, respectively.Finally, we discuss the possibility of anomalous duration distribution ofevents in the field 104 centered on (l,b) = (3.11, -3.01) as well asinvestigate spatial clustering of events in all fields.Comment: 42 pages, 15 figures (6 of them in color), 12 tables; results  unchanged, discussion of blending strengthened including addition of new  appendix; to be published in ApJ, Vol. 630, Sept. 10, 2005 issu

Microlensing Optical Depth toward the Galactic Bulge Using Clump Giants from the MACHO Survey