358 research outputs found
AX J1749.1-2733 and AX J1749.2-2725 - the close pair of X-ray pulsars behind the Galactic Center: an optical identification
Two faint X-ray pulsars, AX J1749.2-2725 and AX J1749.1-2733, located in the
direction to the Galactic Center, were studied in detail using data of
INTEGRAL, XMM-Newton and Chandra observatories in X-rays, the SOFI/NTT
instrument in infrared and the RTT150 telescope in optics. X-ray positions of
both sources were determined with the uncertainty better than ~1 arcsec, that
allowed us to identify their infrared counterparts. From the subsequent
analysis of infrared and optical data we conclude that counterparts of both
pulsars are likely massive stars of B0-B3 classes located behind the Galactic
Center at distances of 12-20 kpc, depending on the type, probably in further
parts of galactic spiral arms. In addition, we investigated the extinction law
towards the galactic bulge and found that it is significantly different from
standard one.Comment: 6 pages, 7 figures, will be published in MNRA
Accurate Localization and Identification of Six Hard X-ray Sources from Chandra and XMM-Newton data
We present the results of Chandra and XMM-Newton observations for six hard
X-ray sources (IGR J12134-6015, IGR J18293-1213, IGR J18219-1347, IGR
J17350-2045, IGR J18048-1455, XTE J1901+014) from the INTEGRAL all-sky survey.
Based on these observations, we have improved significantly the localization
accuracy of the objects and, therefore, have managed to identify their optical
counterparts. Using data from the publicly available 2MASS and UKIDSS infrared
sky surveys as well as data from the SOFI/NTT telescope (European Southern
Observatory), we have determined the magnitudes of the optical counterparts,
estimated their types and (in some cases) the distances to the program objects.
A triplet of iron lines with energies of 6.4, 6.7, and 6.9 keV has been
detected in the X-ray spectrum of IGR J18048-1455; together with the detection
of pulsations with a period of ~1440 s from this source, this has allowed it to
be classified as a cataclysmic variable, most likely an intermediate polar. In
addition, broadband X-ray spectra of IGR J12134-6015 and IGR J17350-2045 in
combination with infrared and radio observations suggest an extragalactic
nature of these objects. The source IGR J18219-1347 presumably belongs to the
class of high-mass X-ray binaries.Comment: 15 pages, 9 figures. Will be published in Astronomy Letters, 2012,
Vol. 38, No. 10, pp. 629-63
Analogues of the central point theorem for families with -intersection property in
In this paper we consider families of compact convex sets in
such that any subfamily of size at most has a nonempty intersection. We
prove some analogues of the central point theorem and Tverberg's theorem for
such families
Notes about the Caratheodory number
In this paper we give sufficient conditions for a compactum in
to have Carath\'{e}odory number less than , generalizing an old result of
Fenchel. Then we prove the corresponding versions of the colorful
Carath\'{e}odory theorem and give a Tverberg type theorem for families of
convex compacta
Tverberg-type theorems for intersecting by rays
In this paper we consider some results on intersection between rays and a
given family of convex, compact sets. These results are similar to the center
point theorem, and Tverberg's theorem on partitions of a point set
Graphene as a quantum surface with curvature-strain preserving dynamics
We discuss how the curvature and the strain density of the atomic lattice
generate the quantization of graphene sheets as well as the dynamics of
geometric quasiparticles propagating along the constant curvature/strain
levels. The internal kinetic momentum of Riemannian oriented surface (a vector
field preserving the Gaussian curvature and the area) is determined.Comment: 13p, minor correction
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