The MPE X-ray test facility PANTER: Calibration of hard X-ray (15–50 kev) optics

The Max-Planck-Institut für extraterrestrische Physik (MPE) in Garching, Germany, uses its large X-ray beam line facility PANTER for testing X-ray astronomical instrumentation. A number of telescopes, gratings, filters, and detectors, e.g. for astronomical satellite missions like Exosat, ROSAT, Chandra (LETG), BeppoSAX, SOHO (CDS), XMM-Newton, ABRIXAS, Swift (XRT), have been successfully calibrated in the soft X-ray energy range (< 15keV). Moreover, measurements with mirror test samples for new missions like ROSITA and XEUS have been carried out at PANTER. Here we report on an extension of the energy range, enabling calibrations of hard X-ray optics over the energy range 15–50 keV. Several future X-ray astronomy missions (e.g., Simbol-X, Constellation-X, XEUS) have been proposed, which make use of hard X-ray optics based on multilayer coatings. Such optics are currently being developed by the Osservatorio Astronomico di Brera (OAB), Milano, Italy, and the Harvard-Smithsonian Center for Astrophysics (CfA), Cambridge, MA, USA. These optics have been tested at the PANTER facility with a broad energy band beam (up to 50 keV) using the XMM-Newton EPIC-pn flight spare CCD camera with its good intrinsic energy resolution, and also with monochromatic X-rays between C-K (0.277 keV) and Cu-Kα (8.04 keV). PACS: 95.55.Ka, 95.55.Aq, 41 50.+h, 07.85.Fv     

GIS‐assisted modelling for debris flow hazard assessment based on the events of May 1998 in the area of Sarno,Southern Italy: Part I. Maximum run‐out

Based on the debris flow events that occurred in May 1998 in the area of Sarno, Southern Italy, this paper presents an approach to simulate debris flow maximum run‐out. On the basis of the flow source areas and an average thickness of 1·2 m of the scarps, we estimated debris flow volumes of the order of 10⁴ and 10⁵ m³. Flow mobility ratios (ΔH/L) derived from the x, y, z coordinates of the lower‐most limit of the source areas (i.e. apex of the alluvial fan) and the distal limit of the flows ranged between 0·27 and 0·09. We performed regression analyses that showed a good correlation between the estimated flow volumes and mobility ratios. This paper presents a methodology for predicting maximum run‐out of future debris flow events, based on the developed empirical relationship. We implemented the equation that resulted from the calibration as a set of GIS macros written in Visual Basic for Applications (VBA) and running within ArcGIS. We carried out sensitivity analyses and observed that hazard mapping with this methodology should attempt to delineate hazard zones with a minimum horizontal resolution of 0·4 km. The developed procedure enables the rapid delineation of debris flow maximum extent within reasonable levels of uncertainty, it incorporates sensitivities and it facilitates hazard assessments via graphic user interfaces and with modest computing resources. Copyright © 2007 John Wiley & Sons, Ltd.     

POLARIX: a pathfinder mission of X-ray polarimetry

Since the birth of X-ray astronomy, spectral, spatial and timing observation improved dramatically, procuring a wealth of information on the majority of the classes of the celestial sources. Polarimetry, instead, remained basically unprobed. X-ray polarimetry promises to provide additional information procuring two new observable quantities, the degree and the angle of polarization. Polarization from celestial X-ray sources may derive from emission mechanisms themselves such as cyclotron, synchrotron and non-thermal bremsstrahlung, from scattering in aspheric accreting plasmas, such as disks, blobs and columns and from the presence of extreme magnetic field by means of vacuum polarization and birefringence. Matter in strong gravity fields and Quantum Gravity effects can be studied by X-ray polarimetry, too. POLARIX is a mission dedicated to X-ray polarimetry. It exploits the polarimetric response of a Gas Pixel Detector, combined with position sensitivity, that, at the focus of a telescope, results in a huge increase of sensitivity. The heart of the detector is an Application-Specific Integrated Circuit (ASIC) chip with 105,600 pixels each one containing a full complete electronic chain to image the track produced by the photoelectron. Three Gas Pixel Detectors are coupled with three X-ray optics which are the heritage of JET-X mission. A filter wheel hosting calibration sources unpolarized and polarized is dedicated to each detector for periodic on-ground and in-flight calibration. POLARIX will measure time resolved X-ray polarization with an angular resolution of about 20 arcsec in a field of view of 15 × 15 arcmin and with an energy resolution of 20% at 6 keV. The Minimum Detectable Polarization is 12% for a source having a flux of 1 mCrab and 10⁵ s of observing time. The satellite will be placed in an equatorial orbit of 505 km of altitude by a Vega launcher. The telemetry down-link station will be Malindi. The pointing of POLARIX satellite will be gyroless and it will perform a double pointing during the earth occultation of one source, so maximizing the scientific return. POLARIX data are for 75% open to the community while 25% + SVP (Science Verification Phase, 1 month of operation) is dedicated to a core program activity open to the contribution of associated scientists. The planned duration of the mission is one year plus three months of commissioning and SVP, suitable to perform most of the basic science within the reach of this instrument. A nice to have idea is to use the same existing mandrels to build two additional telescopes of iridium with carbon coating plus two more detectors. The effective area in this case would be almost doubled.     

Lava flow hazard at Nyiragongo Volcano,DRC

Mt. Nyiragongo is one of the most dangerous volcanoes in the world for the risk associated with the propagation of lava flows. In 2002 several vents opened along a huge system of fractures, pouring out lava which reached and destroyed a considerable part of Goma, a town of about 500,000 inhabitants on the shore of Lake Kivu. In a companion paper (Favalli et al. in Bull Volcanol, this issue, 2008) we employed numerical simulations of probable lava flow paths to evaluate the lava flow hazard on the flanks of the volcano, including the neighbouring towns of Goma (DRC) and Gisenyi (Rwanda). In this paper we use numerical simulations to investigate the possibility of significantly reducing the lava flow hazard in the city through the construction of protective barriers. These barriers are added to the DEM of the area as additional morphological elements, and their effect is evaluated by repeating numerical simulations with and without the presence of barriers. A parametric study on barrier location, size, shape and orientation led to the identification of barriers which maximize protection while minimizing their impact. This study shows that the highest hazard area corresponding to eastern Goma, which was largely destroyed by lava flows in 2002, cannot be effectively protected from future lava flows towards Lake Kivu and should be abandoned. On the contrary, the rest of the town can be sheltered from lava flows by means of two barriers that deviate or contain the lava within the East Goma sector. A proposal for the future development of the town is formulated, whereby “new” Goma is completely safe from the arrival of lava flows originating from vents outside its boundaries. The proposal minimizes the risk of further destruction in town due to future lava flows.     

Lava flow hazard at Nyiragongo volcano,D.R.C.

The 2002 eruption of Nyiragongo volcano constitutes the most outstanding case ever of lava flow in a big town. It also represents one of the very rare cases of direct casualties from lava flows, which had high velocities of up to tens of kilometer per hour. As in the 1977 eruption, which is the only other eccentric eruption of the volcano in more than 100 years, lava flows were emitted from several vents along a N–S system of fractures extending for more than 10 km, from which they propagated mostly towards Lake Kivu and Goma, a town of about 500,000 inhabitants. We assessed the lava flow hazard on the entire volcano and in the towns of Goma (D.R.C.) and Gisenyi (Rwanda) through numerical simulations of probable lava flow paths. Lava flow paths are computed based on the steepest descent principle, modified by stochastically perturbing the topography to take into account the capability of lava flows to override topographic obstacles, fill topographic depressions, and spread over the topography. Code calibration and the definition of the expected lava flow length and vent opening probability distributions were done based on the 1977 and 2002 eruptions. The final lava flow hazard map shows that the eastern sector of Goma devastated in 2002 represents the area of highest hazard on the flanks of the volcano. The second highest hazard sector in Goma is the area of propagation of the western lava flow in 2002. The town of Gisenyi is subject to moderate to high hazard due to its proximity to the alignment of fractures active in 1977 and 2002. In a companion paper (Chirico et al., Bull Volcanol, in this issue, 2008) we use numerical simulations to investigate the possibility of reducing lava flow hazard through the construction of protective barriers, and formulate a proposal for the future development of the town of Goma.     

GIS and Volcanic Risk Management

Volcanic catastrophes constitute a majorproblem in many developing and developed countries. Inrecent years population growth and the expansion ofsettlements and basic supply lines (e.g., water, gas,etc.) have greatly increased the impact of volcanicdisasters. Correct land-use planning is fundamental inminimising both loss of life and damage to property.In this contribution Geographical Information Systems(GIS), linked with remote sensing technology andtelecommunications/warning systems, have emerged asone of the most promising tools to support thedecision-making process. Some GIS are presented fortwo volcanic areas in Italy, Mt. Etna and Vesuvius.GIS role in risk management is then discussed, keepingin mind the different volcanic scenarios of effusiveand explosive phenomena. Mt. Etna system covers alarge area (more than 1,000 km²) potentiallyaffected by effusive phenomena (lava flows) whichcause damage to both houses and properties in general.No risk to life is expected. The time-scales of lavaflows allow, at least in principle, modification ofthe lava path by the building of artificial barriers.Vesuvius shows typically an explosive behaviour. Inthe case of a medium size explosive eruption, 600,000people would potentially have to be evacuated from anarea of about 200 km² around the Volcano, sincethey are exposed to ruinous, very fast phenomena likepyroclastic surges and flows, lahars, ash fallout,etc. Ash fallout and floods/lahars are also expectedin distal areas, between Vesuvius and Avellino,downwind of the volcano. GIS include digital elevationmodels, satellite images, volcanic hazard maps andvector data on natural and artificial features (energysupply lines, strategic buildings, roads, railways,etc.). The nature and the level of detail in the twodata bases are different, on the basis of thedifferent expected volcanic phenomena. The GIS havebeen planned: (a) for volcanic risk mitigation (hazard,value, vulnerability and risk map assessing), (b) toprovide suitable tools during an impending crisis, (c)to provide a basis for emergency plans.     

Estimation of lahar and lahar-runout flow hydrograph on natural beds

A numerical model is used to simulate channelized lahars, flowing with a near-constant sediment concentration and volume. Water and debris are usually mobilized in short times and the peak discharge of lahars may reach many thousands of cubic meters per second in a few minutes. A relation for the energy dissipation term must be provided in the model, which in turn depends on debris flow rheology and shape and status of channel bed. A discussion of the form of this term is performed through the simulation of some historical (among the well-documented) lahars and lahar-runout flows with concentrations ranging in a wide spectrum up to 70 percent by volume and irregularly shaped sand and coarser particles dispersed in a fluid matrix of water and fine material. As concentration increases and turbulence decreases, the dissipative term, which, in the first case, is proportional to the square average flow velocity (Manning or Chezy formulation) is well described by a linear dependence on flow velocity, as expected in the laminar case. The numerical reproduction of the examined historical cases suggests that the model can be used for hazard assessment, if some hypotheses are made about lahar hydrograph at the source, its volume, and the shape of the dissipative term.     

Risk from Lahars in the Northern Valleys of Cotopaxi Volcano (Ecuador)

Cotopaxi volcano (Ecuador) is famous for production of large-scale laharsthrough melting of ice and snow on its summit glacier. The lahar hazard inthe northern valleys of the volcano is assessed through numerical simulationof a maximum expected event. Considerations of past activity suggest that anevent like that of the 1877 eruption is the maximum expected lahar event.Review of the historical records reveals that northerly flowing lahars initiallyfollowed the Rio Pita and Rio Salto; at ``La Caldera', owing to a sharp bendin the channel, the lahar partly overflowed into Rio Santa Clara. The laharsalong Rio Pita and Rio Santa Clara were conveyed to the Los Chillos valley.The simulation, using an initial flow volume of 60 × 10<sup>6</sup> m<sup>3</sup>reproduces the maximum heights reached by the 1877 lahar along the northernvalley. The volume of lahar triggered by an eruption similar to that of 1877 isestimated to have a volume about 2/3 of that of 1877. This hypothesized reductionof volume is attributed to shrinkage of the summit glacier over the past century.However, dramatic population growth along valleys exposed to lahar hazard overthe past 100 years makes the present risk from lahars higher than in the past. Thesharp bend of ``La Caldera' represents a crucial site controlling lahar propagation:should a lahar overflow into the Santa Clara valley the risk increases considerablydue to the much higher concentration of human settlements along the valley. Resultsof a lahar simulation in which the entire flow is artificially forced into Rio Pita suggestthat construction of a dyke at ``La Caldera' to prevent overflow would substantiallyreduce the general risk in the area.     

Volcanic geomorphology and tectonics of the Aeolian archipelago (Southern Italy) based on integrated DEM data

The geomorphological and morphometric analysis of the sea floor topography surrounding the Aeolian Islands, South Tyrrhenian Sea, Italy, provides insights into the relationships between the volcanological evolution of the islands and their tectonic features. We constructed geomorphological maps of the submarine portions of the seven large edifices constituting the islands on the basis of a DEM with a 5 m resolution step. These maps include constructional and destructional landforms such as submarine volcanic vents located west of Lipari and north of Alicudi, and hummocky surfaces recognised north of Lipari and Salina. The latter landforms, together with the occurrence of large scars affecting the main edifices on land, suggest that sector collapses affected some islands. Geomorphological data indicate that the location of subaerial and submarine vents is strongly controlled by local tectonic structures striking WNW-ESE (Alicudi-Filicudi sector), NNW-SSE (Salina-Lipari-Vulcano sector) and NE-SW (Panarea-Stromboli sector). The islands can be divided into two groups on the basis of some morphometric parameters: a first group with a pancake-like shape, Dp/D (abrasion platform diameter/basal diameter) higher than 0.40 and H/D (total height/basal diameter) lower than 0.13, and a second group with a conical shape, characterised by Dp/D lower than 0.34 and H/D higher than 0.14. These ratios and other morphometric parameters reflect the different volcanological and structural evolution of the Aeolian Islands. The pancake-like shaped complexes have been created, in addition to their submarine stage, by extrusive and highly explosive activity, whereas the cone-shaped edifices have been characterised by effusive or moderate explosive activity.Editorial responsibility: C Kilburn