4,243 research outputs found
Low-energy gamma rays from Cygnus X-1
The Cyg X-1 was observed by the balloonborne telescope OPALE, in June 1976. The high energy spectrum of the source, which was in its superlow state, was seen to extend well beyond 1 MeV. The observed low energy gamma ray component of Cyg X-1 is compared with the predictions of recent models involving accretion onto a stellar black hole, and including a possible contribution from the pair annihilation 511 keV gamma ray line
Contact Moishezon threefolds with second Betti number one
We prove that the only contact Moishezon threefold having second Betti number
equal to one is the projective space.Comment: 5 pages. v2: exposition improved as suggested by the referee. To
appear in Archiv der Mat
Compton telescope with coded aperture mask: Imaging with the INTEGRAL/IBIS Compton mode
Compton telescopes provide a good sensitivity over a wide field of view in
the difficult energy range running from a few hundred keV to several MeV. Their
angular resolution is, however, poor and strongly energy dependent. We present
a novel experimental design associating a coded mask and a Compton detection
unit to overcome these pitfalls. It maintains the Compton performance while
improving the angular resolution by at least an order of magnitude in the field
of view subtended by the mask. This improvement is obtained only at the expense
of the efficiency that is reduced by a factor of two. In addition, the
background corrections benefit from the coded mask technique, i.e. a
simultaneous measurement of the source and background. This design is
implemented and tested using the IBIS telescope on board the INTEGRAL satellite
to construct images with a 12' resolution over a 29 degrees x 29 degrees field
of view in the energy range from 200 keV to a few MeV. The details of the
analysis method and the resulting telescope performance, particularly in terms
of sensitivity, are presented
Maximum solutions of normalized Ricci flows on 4-manifolds
We consider maximum solution , , to the normalized
Ricci flow. Among other things, we prove that, if is a smooth
compact symplectic 4-manifold such that and let
, be a solution to (1.3) on whose Ricci curvature
satisfies that and additionally , then there exists an , and a sequence of points
, , satisfying that, by passing to a
subsequence, , in the -pointed
Gromov-Hausdorff sense for any sequence , where
, , are complete complex hyperbolic orbifolds
of complex dimension 2 with at most finitely many isolated orbifold points.
Moreover, the convergence is in the non-singular part of
and
, where
(resp. ) is the Euler characteristic (resp. signature) of
.Comment: 23 page
EGRET Observations of the Diffuse Gamma-Ray Emission in Orion: Analysis Through Cycle 6
We present a study of the high-energy diffuse emission observed toward Orion
by the Energetic Gamma-Ray Experiment Telescope (EGRET) on the Compton
Gamma-Ray Observatory. The total exposure by EGRET in this region has increased
by more than a factor of two since a previous study. A simple model for the
diffuse emission adequately fits the data; no significant point sources are
detected in the region studied ( to and ) in either the composite dataset or in two separate
groups of EGRET viewing periods considered. The gamma-ray emissivity in Orion
is found to be for E > 100 MeV,
and the differential emissivity is well-described as a combination of
contributions from cosmic-ray electrons and protons with approximately the
local density. The molecular mass calibrating ratio is .Comment: 16 pages, including 5 figures. 3 Tables as three separate files.
Latex document, needs AASTEX style files. Accepted for publication in Ap
The final COS-B database: In-flight calibration of instrumental parameters
A method for the determination of temporal variation of sensitivity is designed to find a set of parameters which lead to maximum consistency between the intensities derived from different observation periods. This method is briefly described and the resulting sensitivity and background variations presented
INTEGRAL discovery of a bright highly obscured galactic X-ray binary source IGR J16318-4848
INTEGRAL regularly scans the Galactic plane to search for new objects and in
particular for absorbed sources with the bulk of their emission above 10-20
keV. The first new INTEGRAL source was discovered on 2003 January 29, 0.5
degree from the Galactic plane and was further observed in the X-rays with
XMM-Newton. This source, IGR J16318-4848, is intrinsically strongly absorbed by
cold matter and displays exceptionally strong fluorescence emission lines. The
likely infrared/optical counterpart indicates that IGR J16318-4848 is probably
a High Mass X-Ray Binary neutron star or black hole enshrouded in a Compton
thick environment. Strongly absorbed sources, not detected in previous surveys,
could contribute significantly to the Galactic hard X-ray background between 10
and 200 keV.Comment: 6 pages, 4 figures (fig 1 quality lowered), accepted for publication
in A&A letters (INTEGRAL special issue
Gamma-rays from Type Ia supernova SN2014J
The whole set of INTEGRAL observations of type Ia supernova SN2014J, covering
the period 19-162 days after the explosion has being analyzed. For spectral
fitting the data are split into "early" and "late" periods covering days 19-35
and 50-162, respectively, optimized for Ni and Co lines. As
expected for the early period much of the gamma-ray signal is confined to
energies below 200 keV, while for the late period it is most strong above
400 keV. In particular, in the late period Co lines at 847 and 1248 keV
are detected at 4.7 and 4.3 respectively. The lightcurves in several
representative energy bands are calculated for the entire period. The resulting
spectra and lightcurves are compared with a subset of models. We confirm our
previous finding that the gamma-ray data are broadly consistent with the
expectations for canonical 1D models, such as delayed detonation or
deflagration models for a near-Chandrasekhar mass WD. Late optical spectra (day
136 after the explosion) show rather symmetric Co and Fe lines profiles,
suggesting that unless the viewing angle is special, the distribution of
radioactive elements is symmetric in the ejecta.Comment: 21 pages, 16 figures, accepted by Ap
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