49,017 research outputs found
The IBIS view of the galactic centre: INTEGRAL's imager observations simulations
The Imager on Board Integral Satellite (IBIS) is the imaging instrument of
the INTEGRAL satellite, the hard-X/soft-gamma ray ESA mission to be launched in
2001. It provides diagnostic capabilities of fine imaging (12' FWHM), source
identification and spectral sensitivity to both continuum and broad lines over
a broad (15 keV--10 MeV) energy range. It has a continuum sensitivity of
2~10^{-7} ph cm^{-2} s^{-1} at 1 MeV for a 10^6 seconds observation and a
spectral resolution better than 7 % at 100 keV and of 6 % at 1 MeV. The imaging
capabilities of the IBIS are characterized by the coupling of the above quoted
source discrimination capability with a very wide field of view (FOV), namely 9
x 9 degrees fully coded, 29 x 29 degrees partially coded FOV. We present
simulations of IBIS observations of the Galactic Center based on the results of
the SIGMA Galactic Center survey. They show the capabilities of this instrument
in discriminating between different sources while at the same time monitoring a
huge FOV. It will be possible to simultaneously take spectra of all of these
sources over the FOV even if the sensitivity decreases out of the fully coded
area. It is envisaged that a proper exploitation of both the FOV dimension and
the source localization capability of the IBIS will be a key factor in
maximizing its scientific output.Comment: 5 pages, LaTeX, to be published in the 4th Compton Symposium
Conference Proceedings, uses aipproc.cls, aipproc.sty (included
Degenerations of LeBrun twistor spaces
We investigate various limits of the twistor spaces associated to the
self-dual metrics on n CP ^2, the connected sum of the complex projective
planes, constructed by C. LeBrun. In particular, we explicitly present the
following 3 kinds of degenerations whose limits of the metrics are: (a) LeBrun
metrics on (n-1) CP ^2$, (b) (Another) LeBrun metrics on the total space of the
line bundle O(-n) over CP ^1 (c) The hyper-Kaehler metrics on the small
resolution of rational double points of type A_{n-1}, constructed by Gibbons
and Hawking.Comment: 21 pages, 7 figures. V2: A new section added at the end of the
article. V3: Reference slightly update
Monopole metrics and the orbifold Yamabe problem
We consider the self-dual conformal classes on n#CP^2 discovered by LeBrun.
These depend upon a choice of n points in hyperbolic 3-space, called monopole
points. We investigate the limiting behavior of various constant scalar
curvature metrics in these conformal classes as the points approach each other,
or as the points tend to the boundary of hyperbolic space. There is a close
connection to the orbifold Yamabe problem, which we show is not always solvable
(in contrast to the case of compact manifolds). In particular, we show that
there is no constant scalar curvature orbifold metric in the conformal class of
a conformally compactified non-flat hyperkahler ALE space in dimension four.Comment: 34 pages, to appear in Annales de L'Institut Fourie
Toric LeBrun metrics and Joyce metrics
We show that, on the connected sum of complex projective planes, any toric
LeBrun metric can be identified with a Joyce metric admitting a semi-free
circle action through an explicit conformal equivalence. A crucial ingredient
of the proof is an explicit connection form for toric LeBrun metrics.Comment: 10 page
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