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

Magnetic Fourier Integral Operators

In some previous papers we have defined and studied a 'magnetic' pseudodifferential calculus as a gauge covariant generalization of the Weyl calculus when a magnetic field is present. In this paper we extend the standard Fourier Integral Operators Theory to the case with a magnetic field, proving composition theorems, continuity theorems in 'magnetic' Sobolev spaces and Egorov type theorems. The main application is the representation of the evolution group generated by a 1-st order 'magnetic' pseudodifferential operator (in particular the relativistic Schr\"{o}dinger operator with magnetic field) as such a 'magnetic' Fourier Integral Operator. As a consequence of this representation we obtain some estimations for the distribution kernel of this evolution group and a result on the propagation of singularities

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

XMM-Newton discovery of transient X-ray pulsar in NGC 1313

We report on the discovery and analysis of the transient X-ray pulsar XMMU J031747.5-663010 detected in the 2004 November 23 XMM-Newton observation of the spiral galaxy NGC 1313. The X-ray source exhibits pulsations with a period P~765.6 s and a nearly sinusoidal pulse shape and pulsed fraction ~38% in the 0.3-7 keV energy range. The X-ray spectrum of XMMU J031747.5-663010 is hard and is well fitted with an absorbed simple power law of photon index ~1.5 in the 0.3-7 keV energy band. The X-ray properties of the source and the absence of an optical/UV counterpart brighter than 20 mag allow us to identify XMMU J031747.5-663010 as an accreting X-ray pulsar located in NGC 1313. The estimated absorbed 0.3-7 keV luminosity of the source L~1.6\times 10^{39} ergs/s, makes it one of the brightest X-ray pulsars known. Based on the relatively long pulse period and transient behaviour of the source, we classify it as a Be binary X-ray pulsar candidate. XMMU J031747.5-663010 is the second X-ray pulsar detected outside the Local Group, after transient 18 s pulsating source CXOU J073709.1+653544 discovered in the nearby spiral galaxy NGC 2403.Comment: 6 pages, 4 figures. Accepted for publication in MNRAS. Updated to match the accepted versio

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

Interstellar extinction and the distribution of stellar populations in the direction of the ultra-deep Chandra Galactic field

We studied the stellar population in the central 6.6x6.6arcmin,region of the ultra-deep (1Msec) Chandra Galactic field - the "Chandra bulge field" (CBF) approximately 1.5 degrees away from the Galactic Center - using the Hubble Space Telescope ACS/WFC blue (F435W) and red (F625W) images. We mainly focus on the behavior of red clump giants - a distinct stellar population, which is known to have an essentially constant intrinsic luminosity and color. By studying the variation in the position of the red clump giants on a spatially resolved color-magnitude diagram, we confirm the anomalous total-to-selective extinction ratio, as reported in previous work for other Galactic bulge fields. We show that the interstellar extinction in this area is = 4 on average, but varies significantly between ~3-5 on angular scales as small as 1 arcminute. Using the distribution of red clump giants in an extinction-corrected color-magnitude diagram, we constrain the shape of a stellar-mass distribution model in the direction of this ultra-deep Chandra field, which will be used in a future analysis of the population of X-ray sources. We also show that the adopted model for the stellar density distribution predicts an infrared surface brightness in the direction of the "Chandra bulge field" in good agreement (i.e. within ~15%) with the actual measurements derived from the Spitzer/IRAC observations.Comment: 9 pages, 9 figures. Accepted for publication in A&