Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: The Hubble Constant from the Gravitational Lens B1608+656   We present a refined gravitational lens model of the four-image lens system
B1608+656 based on new and improved observational constraints: (i) the three
independent time-delays and flux-ratios from VLA observations, (ii) the
radio-image positions from VLBA observations, (iii) the shape of the
deconvolved Einstein Ring from optical and infrared HST images, (iv) the
extinction-corrected lens-galaxy centroids and structural parameters, and (v) a
stellar velocity dispersion, sigma_ap=247+-35 km/s, of the primary lens galaxy
(G1), obtained from an echelle spectrum taken with the Keck--II telescope. The
lens mass model consists of two elliptical mass distributions with power-law
density profiles and an external shear, totaling 22 free parameters, including
the density slopes which are the key parameters to determine the value of H_0
from lens time delays. This has required the development of a new lens code
that is highly optimized for speed. The minimum-chi^2 model reproduces all
observations very well, including the stellar velocity dispersion and the shape
of the Einstein Ring. A combined gravitational-lens and stellar dynamical
analysis leads to a value of the Hubble Constant of H_0=75(+7/-6) km/s/Mpc (68
percent CL; Omega_m=0.3, Omega_Lambda=0.7. The non-linear error analysis
includes correlations between all free parameters, in particular the density
slopes of G1 and G2, yielding an accurate determination of the random error on
H_0. The lens galaxy G1 is ~5 times more massive than the secondary lens galaxy
(G2), and has a mass density slope of gamma_G1=2.03(+0.14/-0.14) +- 0.03 (68
percent CL) for rho~r^-gamma', very close to isothermal (gamma'=2). (Abridged)

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The categories of this paper are: cond-mat
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The categories of this paper are: hep-ph
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The categories of this paper are: funct-an
30
The categories of this paper are: q-alg
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The categories of this paper are: atom-ph
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The categories of this paper are: cmp-lg
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The categories of this paper are: econ
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The categories of this paper are: comp-gas
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The categories of this paper are: math-ph
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The categories of this paper are: cs
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The categories of this paper are: acc-phys
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The categories of this paper are: supr-con
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The categories of this paper are: math
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The categories of this paper are: mtrl-th
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The categories of this paper are: alg-geom
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The categories of this paper are: adap-org