Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Gravitational Microlensing and the Structure of the Inner Milky Way   We analyze the first-year MACHO collaboration observations of microlensing
towards the Galactic center using a new direct likelihood technique that is
sensitive to the distribution of the events on the sky. We consider the full
set of 41 events, and calculate the direct likelihood against a
simply-parameterized Galactic model consisting of either a gaussian or
exponential bar and a double exponential disk. Optical depth maps are
calculated taking into account the contribution of both disk lenses and
sources. We show that based on the presently available data, a slope in the
optical depth has been clearly detected ($3\sigma$) in Galactic latitude and
that there are indications of a small slope in Galactic longitude. We discuss
limits that can be set on the mass, angle and axis ratio of the Galactic bulge.
We show that based on microlensing considerations alone, $M_{Bulge}>1.5\times
10^{10}\Msol$ at the 90\% confidence level and that the bulge inclination angle
is less than $30 \deg$ also at the 90\% confidence level. The mostly likely bar
mass is $M_{Bulge}=3.5\times10^{10}\Msol$. Such a high mass would imply a low
MACHO fraction for the halo. We consider disk parameters and show that there
are two degeneracies between the effects of a disk and those of a bar on the
optical depths. Finally, we discuss how to break these degeneracies and
consider various strategies for future microlensing observations.

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The categories of this paper are: cond-mat
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The categories of this paper are: bayes-an
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The categories of this paper are: hep-th
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The categories of this paper are: nucl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: math
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The categories of this paper are: eess
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The categories of this paper are: stat
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The categories of this paper are: comp-gas
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The categories of this paper are: dg-ga
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The categories of this paper are: adap-org
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The categories of this paper are: hep-lat
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The categories of this paper are: chao-dyn
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The categories of this paper are: quant-ph
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The categories of this paper are: chem-ph
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The categories of this paper are: ao-sci