X-ray spectral survey with XMM-Newton of a complete sample of nearby Seyfert galaxies
Results obtained from an X-ray spectral survey of nearby Seyfert galaxies using XMM–Newton are reported. The sample was optically selected, well defined, complete in B  magnitude, and distance limited: it consists of the nearest ($D \la22$ Mpc) 27 Seyfert galaxies (9 of type 1, 18 of type 2) taken from the Ho et al. (1997a, ApJS, 112, 315) sample. This is one of the largest atlases of hard X-ray spectra of low-luminosity active galaxies ever assembled. All nuclear sources except two Seyfert 2s are detected between 2 and 10 keV, half for the first time ever, and average spectra are obtained for all of them. Nuclear luminosities reach values down to 10 38  erg s -1 . The shape of the distribution of X-ray parameters is affected by the presence of Compton-thick objects ($\ga$30% among type 2s). The latter have been identified either directly from their intense FeK line and flat X-ray spectra, or indirectly with flux diagnostic diagrams which use isotropic indicators. After taking into account these highly absorbed sources, we find that (i) the intrinsic X-ray spectral properties (i.e., spectral shapes and luminosities above 2 keV) are consistent between type 1 and type 2 Seyferts, as expected from “unified models”; (ii) Seyfert galaxies as a whole are distributed fairly continuously over the entire range of N H , between 10 20 and 10 25  cm -2 ; and (iii) while Seyfert 1s tend to have lower N H and Seyfert 2s tend to have the highest, we find 30% and 10% exceptions, respectively. Overall the sample is of sufficient quality to well represent the average intrinsic X-ray spectral properties of nearby active galactic nuclei, including a proper estimate of the distribution of their absorbing columns. Finally, we conclude that, with the exception of a few cases, the present study agrees with predictions of unified models of Seyfert galaxies, and extends their validity down to very low luminosities.

title: ASCA view on high-redshift radio-quiet quasars
abstract: We briefly discuss the latest ASCA results on the X-ray spectral properties of high-redshift radio-quiet quasars.

title: MOLECULAR LINES IN BOK GLOBULES AND AROUND HERBIG AE/BE STARS
abstract: We have studied a sample of seven small dark clouds (Bok globules) and eight Herbig Ae/Be stars in the J=1->0 transition of HCO$^{+}$, H$^{13}$CO$^{+}$, HCN and H$^{13}$CN. The choice of these molecules is determined by the simple chemistry and the predicted high abundance of the reactants leading to their formation. The isotopically substituted species (isotopomers), H$^{13}$CO$^{+}$ and H$^{13}$CN, were observed in order to determine, whenever possible, the optical thickness of the main species. The most abundant isotopomers were found in almost all the sources (detection rate 70-90\%). Those sources which exhibited the strongest signals were also searched for the $^{13}$C isotopomers. H$^{13}$CO$^{+}$ was found in one dark cloud and around three Herbig Ae/Be stars, while H$^{13}$CN around only one star. The column densities for each species and the physical conditions of the objects were derived whenever the observational data allowed it.

title: The INTEGRAL mission
abstract: INTEGRAL, the International Gamma-Ray Astrophysics Laboratory, to be launched in 2001, is the second medium-size scientific mission (M2) of the ESA long term programme “Horizon 2000”. INTEGRAL addresses the fine spectroscopy and accurate positioning of celestial gamma-ray sources in the energy range 10 keV to 10 MeV. The observational requirements will be met by a payload utilising coded mask imaging in combination with detector pixel arrays (Imaging) and cooled Germanium detectors (Spectroscopy). INTEGRAL is an ESA led mission in collaboration with Russia and USA. Most of the observing time will be made available to the general scientific community.

title: Probing the Hard X-Ray Properties of High-Redshift Radio-Quiet Quasars with ASCA
abstract: This paper reports the X-ray spectral analysis of five high-redshift (z≥2), radio-quiet quasars observed by ASCA. A simple power-law continuum plus cold Galactic absorption model well fits all the spectra (typically between ~2 and 30 keV in the sources frame). Neither the X-ray spectral hardening, which is attributed to a reflection component and observed in Seyfert galaxies, nor the excess absorption previously detected in high-redshift, radio-loud quasars have been revealed. Only marginal evidence of a neutral or mildly ionized FeKα line is found in one of the quasars. The average spectral slope in the observed 0.7-10 keV energy range, Γ=1.67 ± 0.11 (dispersion σ ~0.07), appears to be flatter than that of low-z, radio-quiet quasars (Γ 1.9-2) and slightly steeper but consistent with Γ=1.61 ± 0.04 (σ ~0.10) of high-z, radio-loud quasars.

title: First Results from a XMM-Newton Survey of a Distance-Limited (D<22 Mpc) Sample of Seyfert Galaxies: I- the Agns
abstract: We report here preliminary results from a survey of nearby Seyfert galaxies using the EPIC CCDs on board XMM-Newton. The total sample consists of 28 Seyfert galaxies, and constitute a well-defined, complete (B 0 deg.) hemisphere. The survey has been initiated in June, 2001, and we report here the results for the 6 objects analyzed so far, namely: NGC3185, NGC3486, NGC3941, NGC4138, NGC4565, and NGC5033. The main goal of this survey is to obtain a better and unbiased understanding of the ``typical'' Seyfert X-ray spectrum (e.g. the distribution of their absorption column density) in the local Universe. This is crucial to verify the predictions and, thus, to validate unified models, and is a fundamental parameter of synthesis models for the X-ray background. A companion poster (paper II: L. Foschini et al., these proceedings) illustrates how this survey will also allow a comprehensive spectral study of the brightest (highest-luminosity) off-nuclear sources in the galaxies.

title: (3+1) -dimensional topological quantum field theory from a tight-binding model of interacting spinless fermions
abstract: Currently, there is much interest in discovering analytically tractable (3+1)-dimensional models that describe interacting fermions with emerging topological properties. Towards that end we present a three-dimensional tight-binding model of spinless interacting fermions that reproduces, in the low-energy limit, a (3+1)-dimensional Abelian topological quantum field theory called the BF model. By employing a mechanism equivalent to Haldane's Chern insulator, we can turn the noninteracting model into a three-dimensional chiral topological insulator. We then isolate energetically one of the two Fermi points of the lattice model. In the presence of suitable fermionic interactions, the system, in the continuum limit, is equivalent to a generalized (3+1)-dimensional Thirring model. The low-energy limit of this model is faithfully described by the BF theory. Our approach directly establishes the presence of (2+1)-dimensional BF theory at the boundary of the lattice and it provides a way to detect the topological order of the model through fermionic density measurements.

title: Induced topological phases at the boundary of 3D topological superconductors.
abstract: We present tight-binding models of 3D topological superconductors in class DIII that support a variety of winding numbers. We show that gapless Majorana surface states emerge at their boundary in agreement with the bulk-boundary correspondence. At the presence of a Zeeman field, the surface states become gapped and the boundary behaves as a 2D superconductor in class D. Importantly, the 2D and 3D winding numbers are in agreement, signifying that the topological phase of the boundary is induced by the phase of the 3D bulk. Hence, the boundary of a 3D topological superconductor in class DIII can be used for the robust realization of localized Majorana zero modes.

title: Skyrmion Superfluidity in Two-Dimensional Interacting Fermionic Systems
abstract: In this article we describe a multi-layered honeycomb lattice model of interacting fermions which supports a new kind of parity-preserving skyrmion superfluidity. We derive the low-energy field theory describing a non-BCS fermionic superfluid phase by means of functional fermionization. Such effective theory is a new kind of non-linear sigma model, which we call double skyrmion model. In the bi-layer case, the quasiparticles of the system (skyrmions) have bosonic statistics and replace the Cooper-pairs role. Moreover, we show that the model is also equivalent to a Maxwell-BF theory, which naturally establishes an effective Meissner effect without requiring a breaking of the gauge symmetry. Finally, we map effective superfluidity effects to identities among fermionic observables for the lattice model. This provides a signature of our theoretical skyrmion superfluidy that can be detected in a possible implementation of the lattice model in a real quantum system.

title: Abelian Chern-Simons-Maxwell theory from a tight-binding model of spinless fermions.
abstract: Abelian Chern-Simons-Maxwell theory can emerge from the bosonization of the (2+1)-dimensional Thirring model that describes interacting Dirac fermions. Here we show how the Thirring model manifests itself in the low energy limit of a two-dimensional tight-binding model of spinless fermions. To establish that, we employ a modification of Haldane's model, where the "doubling" of fermions is rectified by adiabatic elimination. Subsequently, fermionic interactions are introduced that lead to the analytically tractable Thirring model. By local density measurements of the lattice fermions we can establish that for specific values of the couplings the model exhibits the confining (2+1)-dimensional QED phase or a topological ordered phase that corresponds to the Chern-Simons theory. The implementation of the model as well as the measurement protocol are accessible with the current technology of cold atoms in optical lattices.

title: Topological effective field theories for Dirac fermions from index theorem
abstract: Dirac fermions have a central role in high energy physics but it is well known that they emerge also as quasiparticles in several condensed matter systems supporting topological order. We present a general method for deriving the topological effective actions of (3+1) massless Dirac fermions living on general backgrounds and coupled with vector and axial-vector gauge fields. The first step of our strategy is standard (in the Hermitian case) and consists in connecting the determinants of Dirac operators with the corresponding analytical indices through the zeta-function regularization. Then, we introduce a suitable splitting of the heat kernel that naturally selects the purely topological part of the determinant (i.e. the topological effective action). This topological effective action is expressed in terms of gauge fields using the Atiyah-Singer index theorem which computes the analytical index in topological terms. The main new result of this paper is to provide a consistent extension of this method to the non Hermitian case where a well-defined determinant does not exist. Quantum systems supporting relativistic fermions can thus be topologically classified on the basis of their response to the presence of (external or emergent) gauge fields through the corresponding topological effective field theories.