Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Microlensing Optical Depth towards the Galactic Bulge Using Clump Giants
  from the MACHO Survey   Using 7 years of MACHO survey data, we present a new determination of the
optical depth to microlensing towards the Galactic bulge. We select the sample
of 62 microlensing events (60 unique) on clump giant sources and perform a
detailed efficiency analysis. We use only the clump giant sources because these
are bright bulge stars and are not as strongly affected by blending as other
events. Using a subsample of 42 clump events concentrated in just 4.5 square
degrees, 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 excellent
agreement with recent theoretical predictions. We also present the optical
depth in each of the 19 fields in which we detected events, and find limits on
optical depth for fields with no events. The errors in optical depth in
individual fields are dominated by Poisson noise. We measure optical depth
gradients (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 of
events in the field 104 centered on (l,b) = (3.11, -3.01) as well as
investigate spatial clustering of events in all fields.

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The categories of this paper are: gr-qc
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The categories of this paper are: nlin
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The categories of this paper are: hep-th
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The categories of this paper are: patt-sol
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The categories of this paper are: mtrl-th
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The categories of this paper are: bayes-an
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The categories of this paper are: q-bio
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-ph
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The categories of this paper are: funct-an
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The categories of this paper are: chao-dyn
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The categories of this paper are: q-fin
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The categories of this paper are: comp-gas
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The categories of this paper are: cmp-lg
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The categories of this paper are: quant-ph
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The categories of this paper are: physics