Chandra unveils a binary active galactic nucleus in Mrk 463

We analyse Chandra , XMM–Newton and Hubble Space Telescope ( HST ) data of the double-nucleus Ultraluminous Infrared Galaxy (ULIRG), Mrk 463. The Chandra detection of two luminous  ( L _2–10 keV= 1.5 × 10⁴³  and  3.8 × 10⁴² erg cm⁻² s⁻¹)  , unresolved nuclei in Mrk 463 indicates that this galaxy hosts a binary active galactic nucleus (AGN), with a projected separation of ≃3.8 kpc (  3.83 ± 0.01  arcsec). While the East nucleus was already known to be a type 2 Seyfert (and this is further confirmed by our Chandra detection of a neutral iron line), this is the first unambiguous evidence in favour of the AGN nature of the West nucleus. Mrk 463 is therefore the clearest case so far for a binary AGN, after NGC 6240.     

A semi-analytic theory for the motion of a lunar satellite

A semi-analytical solution to the problem of the motion of a satellite of the moon is presented. Perturbative effects which are considered include those due to the attraction of the moon, earth, and sun, the non-sphericity of the moon's gravitational field, coupling of lower-order terms, solar radiation pressure, and physical libration. Short-period terms and intermediate-period terms, terms with the period of the moon's longitude, are produced by means of von Zeipel's method; it is proposed to obtain the secular perturbations, and those depending only on the argument of perilune, by numerical integration of the equations of motions. The short-period terms and intermediate-period terms are developed up to second order, where first order is 10^–2. The secular perturbations and perturbations dependent on the argument of perilune are obtained to third order.     

The Western Mediterranean lamproitic magmatism: origin and geodynamic significance

Ultrapotassic lamproitic rocks in the Western Alps, Tuscany‐Corsica and SE Spain (c. 30 to 1 Ma) show high MgO, Ni and Cr denoting a mantle origin, but also have incompatible element and radiogenic isotope abundances that resemble upper crustal rocks, such as local metapelites and global subducting sediments. The coexistence of mantle and crustal signatures in lamproites indicates a genesis in a lithospheric mantle, which had been contaminated by crustal rocks. The occurrence of lamproitic magmatism along the Alpine collision front suggests that mantle contamination occurred during east‐verging Cretaceous‐Oligocene subduction of the European plate beneath the African margin. We suggest that crustal material originated from the overriding continental margin, which was eroded by the low‐angle subducting European slab. Mantle melting and generation of lamproites took place later, during diachronous opening of Western Mediterranean basins, contemporaneously with a new cycle of magmatism, which was genetically related to the west‐north‐dipping Apennine‐Maghrebian subduction.     

Inconsistent patterns of historical seismicity and earthquake-triggered landsliding in southeastern Sicily: an alarm bell?

In southeastern Sicily, the distribution pattern of earthquake-triggered landslides is inconsistent with historically known seismic activity. In particular, historical seismicity has been stronger in the eastern sector, while earthquake-triggered landsliding is much more developed in the western sector, and this contrasts with expectations. This paper describes the patterns of seismicity and landsliding, and tackles the problem of whether greater landsliding in the western sector may be due (a) to seismicity of the eastern sector or (b) to a high-magnitude, low-recurrence seismicity generated in the western sector itself. It is statistically shown that lithostructural characteristics of rock masses and geometry of hillslopes cannot justify, either singly or jointly, greater landsliding in the western sector if triggering earthquakes are generated in the eastern sector. As a consequence, it is possible that landsliding of the western sector is due to earthquakes generated locally, but having higher magnitude and longer recurrence intervals than historically observed.     

Coseismic rotation changes from the 2004 Sumatra earthquake: the effects of Earth's compressibility versus earthquake induced topography

Polar motion is modelled for the large 2004 Sumatra earthquake via dislocation theory for an incompressible elastic earth model, where inertia perturbations are due to earthquake-triggered topography of density–contrast interfaces, and for a compressible model, where inertia perturbation due to compression-dilatation of Earth's material is included; density and elastic parameters are based on a multilayered reference Earth. Both models are based on analytical Green's functions, propagated from the centre to the Earth's surface. Preliminary and updated seismological solutions are considered in elucidating the effects of improving earthquake parameters on polar motion. The large Sumatra thrust earthquake was particularly efficient in driving polar motion since it was responsible for large material displacements occurring orthogonally to the strike of the earthquake and to the Earth's surface, as imaged by GRACE gravity anomalies over the earthquake area. The effects of earthquake-induced topography are four times larger than the effects of Earth's compressibility, for l = 2 geopotential components. For varying compressional Earth properties and seismic solution, modelled polar motion ranges from 8.6 to 9.4 cm in amplitude and between 117° and 130° east longitude in direction. The close relationship between polar motion direction, earthquake longitude and thrust nature of the event, are established in terms of basic physical concepts.     

Domains of spit evolution in the Goro area, Po Delta, Italy

Goro lagoon was formed during the 19th century in the southern part of the Po Delta. Its origin is related to the growth of a spit system, which progressively occluded the southernmost interdistributary bay from the sea. The development of the spits is due to the morphological prominence of the Po Delta which causes a divergent littoral drift, enhanced by wave refraction over the delta front. During the last century the spit was abandoned, destroyed, and re-constructed several times because of the development of newer spits seawards. Using historical maps and aerial photographs, three different periods are recognised, featuring distinctive spit growth styles: parallel, fan-shaped and branched. The different domains of spit evolution are related to several factors, mainly to the mutual influence of sediment discharge, sand mining along the Po river, wave action over the delta front, human-induced subsidence and direct human interventions along the spits and for flood-control.     

Effects of turbulence development in solar surges

Several authors have claimed for correlations between surges (dark features) and various kinds of solar emissions (radio, microwave, X-ray). In this paper we propose a model to explain such correlations, in particular presenting the properties of the instabilities resulting from the coupling between material flow, connected to the appearance of a surge, and magnetic field topology. As a consequence of such instability a turbulent energy cascade to small characteristic lengths grows up. Depending of the relevant parameters of the surge (dark feature), different regimes can be found, producing different levels of electrons acceleration and mass motion deceleration. We try then to correlate the different developments of the instability with the behavior observed in type I and type III radio bursts related to surges.Proceedings of the Second CERSA Workshop on Particle Acceleration and Trapping in Solar Flares, held at Aubigny-sur-Nère (France), 23–26 June, 1986.     

A kinematic evolutionary model for the Penninic sector of the central Ligurian Alps

The nappe pile presently cropping out in the central sector of the Ligurian Alps, is represented by some principal groups of tectonic units. Starting from the foreland, the outer and lower, weakly metamorphic (up to 0.3 GPa) Briançonnais units support the high-pressure (up to 1.3 GPa) ensemble of inner Briançonnais nappes, in turn overridden by the Prepiedmont units, sourced from the European continental margin. Prepiedmont units form two superposed groups. The lower is composed only of a pre-Namurian basement (Alpine metamorphism up to 0.6 GPa); and the upper is mainly composed of a slightly metamorphic (greenschist facies) post-Namurian cover. At the top lie the high-pressure metamorphosed (up to 0.8 GPa in the sector here considered) ophiolitic units. The group of the non-metamorphic Helminthoid Flysch nappes (original stratigraphic cover of the ophiolitic units) has travelled the greatest distance and is presently mainly set onto the outer part of the chain. Only events up to the stacking of the nappe pile are discussed, disregarding late-stage deformation. As the examined sector is located at a considerable distance from the collisional zone, late processes did not change the overall order of superposition formerly acquired. The model proposes the development of two major, subhorizontal detachment surfaces. The first, shallower one confines at the base a very thin-skinned set of nappes, nearly totally made up of Prepiedmont sedimentary covers that are bounded at their top by the Helminthoid Flysch units. Both these groups underwent a mainly horizontal outwards transport. In contrast, the underlying Prepiedmont crust and the adjoining Briançonnais inner sector (separated by the second, deeper major detachment surface) were progressively dragged into the subduction zone under the ophiolitic units and duplexes were generated. Exhumation of the metamorphic units occurred along the subduction channel, as did stacking of the nappe pile.