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Universal near-horizon conformal structure and black hole entropy
It is shown that a massless scalar probe reveals a universal near-horizon
conformal structure for a wide class of black holes, including the BTZ. The
central charge of the corresponding Virasoro algebra contains information about
the black hole. With a suitable quantization condition on the central charge,
the CFT associated with the black hole in our approach is consistent with the
recent observation of Witten, where the dual theory for the BTZ in the AdS/CFT
framework has been identified with the construction of Frenkel, Lepowsky and
Meurman. This CFT admits the Fischer-Griess monster group as its symmetry. The
logarithm of the dimension of a specific representation of the monster group
has been identified by Witten as the entropy of the BTZ black hole. Our
algebraic approach shows that a wide class of black holes share the same
near-horizon conformal structure as that for the BTZ. With a suitable
quantization condition, the CFT's for all these black holes in our formalism
can be identified with the FLM model, although not through the AdS/CFT
correspondence. The corresponding entropy for the BTZ provides a lower bound
for the entropy of this entire class of black holes.Comment: References updated, text rearrange
An Imaging Polarimeter(IMPOL) for multi-wavelength observations
Taking advantage of the advances in array detector technology, an imaging
polarimeter (IMPOL) has been constructed for measuring linear polarization in
the wavelength band from 400-800 nm. It makes use of a Wollaston prism as the
analyser to measure simultaneously the two orthogonal polarization components
that define a Stoke's parameter. An achromatic half-wave plate is used to
rotate the plane of polarization with respect to the axis of the analyser so
that the second Stoke's parameter also can be determined. With a field of view
correponding to about 30x30 sq. mm for a 1.2 m, f/13 telescope, a sensitive,
liquid-nitrogen cooled CCD camera as the detector and a built-in acquisition
and guidance unit, the instrument can be used for studying stellar fields or
extended objects with an angular resolution close to 2 arcsec. The instrumental
polarization is less than 0.05% and the accuracies of measurement are primarily
limited by photon noise for typical observations.Comment: 10 pages including 5 embedded figures; submitted to Astronomy and
Astrophysics Supplement Series; available on request to A. N. Ramaprakash
([email protected] or [email protected]); quote report n
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