Publication archive

Publication archive

Field-aligned beams are known to originate from the quasi-perpendicular side of the Earth's bow shock, while the diffuse ion population consists of accelerated ions at the quasi-parallel side of the bow shock. The two distinct ion populations show typical characteristics in their velocity space distributions. By using particle and magnetic field measurements from one Cluster spacecraft we present a case study when the two ion populations are observed simultaneously in the foreshock region during a high Mach number, high solar wind velocity event. We present the spatial-temporal evolution of the field-aligned beam ion distribution in front of the Earth's bow shock, focusing on the processes in the deep foreshock region, i.e. on the quasi-parallel side. Our analysis demonstrates that the scattering of field-aligned beam (FAB) ions combined with convection by the solar wind results in the presence of lower-energy, toroidal gyrating ions at positions deeper in the foreshock region which are magnetically connected to the quasi-parallel bow shock. The gyrating ions are superposed onto a higher energy diffuse ion population. It is suggested that the toroidal gyrating ion population observed deep in the foreshock region has its origins in the FAB and that its characteristics are correlated with its distance from the FAB, but is independent on distance to the bow shock along the magnetic field.
Published: 30 March 2007
Non-thermal continuum (NTC) radiation is, with auroral kilometric radiation (AKR), one of the two electromagnetic emissions generated within the Earth's magnetosphere and radiated into space. The location of the source of NTC has been sought for several decades, with only limited success. The constellation formed by the four CLUSTER spacecraft provides the possibility of triangulation in the vicinity of the source, thus allowing progress in source localisation, while simultaneously revealing the beaming properties of NTC radio sources. We present a case event showing two beams localised on opposite sides of the magnetic equator. At any selected frequency, triangulation points to a single region source of small size. Its position is compatible with the range of possible loci of sources predicted by the radio window theory of Jones (1982) in a frame of constraints relaxed from the simple sketch proposed in early works. The analysis of similar observations from the Dynamics Explorer 1 by Jones et al. (1987) enabled the authors to claim validation of the radio window theory. CLUSTER observations, however, reveal a large beaming cone angle projected onto the ecliptic plane, a feature unobservable by Dynamics Explorer which had a different spin axis orientation. According to the radio window theory, such a large observed cone angle can only be formed by a series of point sources, each beaming in a narrow cone angle. This study demonstrates the difficulty of validating NTC linear generation mechanisms using global beaming properties alone.
Published: 30 March 2007
Addressing the origin of the energetic particle injections into the inner magnetosphere, we investigate the 23 February 2004 substorm using a favorable constellation of four Cluster (near perigee), LANL and Geotail spacecraft. Both an energy-dispersed and a dispersionless injection were observed by Cluster crossing the plasma sheet horn, which mapped to 9-12 RE in the equatorial plane close to the midnight meridian. Two associated narrow equatorward auroral tongues/streamers propagating from the oval poleward boundary could be discerned in the global images obtained by IMAGE/WIC. As compared to the energy-dispersed event, the dispersionless injection front has important distinctions consequently repeated at 4 spacecraft: a simultaneous increase in electron fluxes at energies ~1..300 keV, ~25 nT increase in BZ and a local increase by a factor 1.5-1.7 in plasma pressure. The injected plasma was primarily of solar wind origin. We evaluated the change in the injected flux tube configuration during the dipolarization by fitting flux increases observed by the PEACE and RAPID instruments, assuming adiabatic heating and the Liouville theorem. Mapping the locations of the injection front detected by the four spacecraft to the equatorial plane, we estimated the injection front thickness to be ~1 RE and the earthward propagation speed to be ~200-400 km/s (at 9-12 RE). Based on observed injection properties, we suggest that it is the underpopulated flux tubes (bubbles with enhanced magnetic field and sharp inner front propagating earthward), which accelerate and transport particles into the strong-field dipolar region.
Published: 30 March 2007
Magnetic reconnection is a universal process leading to energy conversion in plasmas. It occurs in the Solar System, in laboratory plasmas and is important in astrophysics. Reconnection has been observed so far only at large-scale boundaries between different plasma environments. It is not known whether reconnection occurs and is important in turbulent plasmas where many small-scale boundaries can form. Solar and laboratory measurements as well as numerical simulations indicate such possibility. Here we report, for the first time, in situ evidence of reconnection in a turbulent plasma. The turbulent environment is the solar wind downstream of the Earth's bow shock. We show that reconnection is fast and electromagnetic energy is converted into heating and acceleration of particles. This has significant implications for laboratory and astrophysical plasmas where both turbulence and reconnection should be common.
Published: 25 March 2007
The ice-rich south polar layered deposits of Mars were probed with the Mars Advanced Radar for Subsurface and Ionospheric Sounding on the Mars Express orbiter. The radar signals penetrate deep into the deposits (more than 3.7 kilometers). For most of the area, a reflection is detected at a time delay that is consistent with an interface between the deposits and the substrate. The reflected power from this interface indicates minimal attenuation of the signal, suggesting a composition of nearly pure water ice. Maps were generated of the topography of the basal interface and the thickness of the layered deposits. A set of buried depressions is seen within 300 kilometers of the pole. The thickness map shows an asymmetric distribution of the deposits and regions of anomalous thickness. The total volume is estimated to be 1.6 × 106 cubic kilometers, which is equivalent to a global water layer approximately 11 meters thick.
Published: 15 March 2007
Contents
  • Foreword
  • 5th Announcement of Opportunity (AO-5)
  • Key Programmes in AO-5
  • Science Highlights
  • Science Operations - Highlights
  • The Fastest INTEGRAL TOO
  • ISOC Science Data Archive Version 2.7
  • INTEGRAL Visualisation Tool & Explorer
  • INTEGRAL Publication Status
  • Changes in ISOC
Published: 15 March 2007
A set of experimental data is presented for a high-Mach-number (Mf = 5) quasiperpendicular (thetaBn = 81 degrees) bow shock layer crossed by Cluster spacecraft on 24 January 2001 at 07:05-07:09 UT. The measurements of magnetic field, spectra of electric field fluctuations, and ion distributions reveal that the shock is highly nonstationary. In particular, the magnetic field profiles measured aboard different spacecraft differ considerably from each other. The mean frequency of downshifted waves observed upstream of the shock ramp oscillates with a characteristic time comparable with the proton gyroperiod. In addition, the reflection of ions from the shock is bursty and a characteristic time for this process is also comparable with the ion gyroperiod. All of these features in conjunction are the first convincing experimental evidence in favor of the shock front reformation.
Published: 09 March 2007
The shock arrival of an Interplanetary Coronal Mass Ejection (ICME) at ~09:50 UT on 22 November 1997 resulted in the development of an intense (Dst<-100 nT) geomagnetic storm at Earth. In the early, quiet phase of the storm, in the sheath region of the ICME, an unusual large spiral structure (diameter of ~1000 km) was observed at very high latitudes by the Polar UVI instrument. The evolution of this structure started as a polewardly displaced auroral bulge which further developed into the spiral structure spreading across a large part of the polar cap. This study attempts to examine the cause of the chain of events that resulted in the giant auroral spiral. During this period the interplanetary magnetic field (IMF) was dominantly northward (Bz>25 nT) with a strong duskward component (By>15 nT) resulting in a highly twisted tail plasma sheet. Geotail was located at the equatorial dawnside magnetotail flank and observed accelerated plasma flows exceeding the solar wind bulk velocity by almost 60%. These flows are observed on the magnetosheath side of the magnetopause and the acceleration mechanism is proposed to be typical for strongly northward IMF. Identified candidates to the cause of the spiral structure include a By induced twisted magnetotail configuration, the development of magnetopause surface waves due to the enhanced pressure related to the accelerated magnetosheath flows aswell as the formation of additional magnetopause deformations due to external solar wind pressure changes. The uniqeness of the event indicate that most probably a combination of the above effects resulted in a very extreme tail topology. However, the data coverage is insufficient to fully investigate the physical mechanism behind the observations.
Published: 08 March 2007
The science requirements for an X-ray Observatory to be deployed in the post-XMM-Newton and Chandra era have been widely debated. Future spectroscopic investigations will require an enormous increase in collecting area to enable the use of the next generation of advanced spectrometers that will provide the necessary plasma diagnostics capability. The key breakthrough needed is to combine a lightweight material which exhibits excellent X-ray reflecting properties, whilst achieving a self-supporting construction that avoids the distortions inherent in fixation of the optics elements. The progress towards such a breakthrough is reported in this Technical Note, describing a successful proof of concept demonstration of many disparate technology advances across a broad development front. More detailed aspects of some of the development activities are provided in the comprehensive suite of papers presented at the 2006 SPIE Annual Symposium. Links to those papers are provided at:

http://www.rssd.esa.int/index.php?project=XEUS&page=SPIE_Documents

This note provides a brief overview of critical issues and some recent updates since the publication of the above papers.
Published: 02 March 2007
Published: 02 March 2007
The Cross-scale TRS is one of ESA's Technology Reference Studies. The purpose of the TRSs is to provide a focus for the development of strategically important technologies that are of likely relevance for future scientific missions. This is accomplished through the study of several technologically demanding and scientifically interesting missions, which are not part of the ESA science programme. The TRSs subsequently act as a reference for possible future technology development activities. The TRSs will not interfere with (or replace) the standard ESA mission selection process.

The purpose of this preliminary payload resources document is to translate the typical science requirements into a payload resource budget, which is required for the first part of the system design of the Cross-scale TRS.

The document is (currently) an open document and regular updates, primarily refinements, are expected. Particularly, iterative steps with industrial study partners and the ESA TRS study manager are foreseen. Revisions will be published, as required, at the start of as well as during the system design. This document will be evolved into a straw man Payload Definition Document.

Published: 28 February 2007
The Cross-scale TRS is one of ESA's Technology Reference Studies. The purpose of the TRSs is to provide a focus for the development of strategically important technologies that are of likely relevance for future scientific missions. This is accomplished through the study of several technologically demanding and scientifically interesting missions, which are not part of the ESA science programme. The TRSs subsequently act as a reference for possible future technology development activities. The TRSs will not interfere with (or replace) the standard ESA mission selection process.

The purpose of the mission requirements document is to provide level 1 (mission) requirements for the Cross-scale TRS system design study.

Published: 28 February 2007
The ESA Concurrent Design Facility (CDF) was requested and financed by ESA/ESTEC/SCIAM to carry out the assessment study of a Far-InfraRed Interferometer Technology Reference Study (FIRI). The main science objective is to perform measurements at significantly improved angular resolution obtainable with today's IR telescopes (i.e. sub-arcsec resolution) by using space Interferometry. The overall mission goals were to study the following:
  • Formation and evolution of stars
  • Formation of planetary systems and planet detection
  • Formation and evolution of galaxies
The objectives of the study were to assess the feasibility of a Far-InfraRed Michelson Interferometer mission and the identification of the critical technology in order to define a Technology Development Plan with particular emphasis on the following:
  • To assess the feasibility of a far-infrared Michelson interferometer based on a single spacecraft
  • To design the mission
  • To identify the critical technologies and define their development plan
  • To make cost, risk and programmatics analysis for the mission and for the technology development plan
Published: 16 June 2006
We describe two peculiar galaxies falling into the massive galaxy clusters Abell 1689 (z ~ 0.18) and Abell 2667 (z ~ 0.23), respectively. Hubble Space Telescope (HST) images show extraordinary trails composed of bright blue knots (-16.5 < M < -11.5 mag) and stellar streams associated with each of these systems. Combining optical, near- and mid-infrared and radio observations we prove that while both galaxies show similar extended trails of star-forming knots, their recent star formation histories are different. One (~L*) is experiencing a strong burst of star formation, appearing as a rare example of a luminous infrared cluster galaxy. In comparison, the other (~0.1L*) has recently ceased its star formation activity. Our model suggests that the morphologies and star formation in these galaxies have been influenced by the combined action of tidal interaction (likely with the cluster potential) and of ram pressure with the intracluster medium (ICM). These results can be used to gain more insights to the origin of S0s, dwarf and ultracompact dwarf (UCD) cluster galaxies.
Published: 22 February 2007
This report is the summary of the work done in the DARWIN System Assessment Study and presents its main results: selected concept and architecture, preliminary design, main performance at functional and interface levels. This study has spanned around 12 months, featuring:
  • a Phase 1 devoted to requirements review and architecture trade-of: it has led to the selection of the non planar arrangement
  • a Phase 2 devoted to preliminary design: together with the consolidation of the selected arrangement, it has produced the payload and spacecraft preliminary design, including performance budgets
Published: 15 February 2007
In December 2002, when France's Stentor satellite was all set to use electric propulsion for stationkeeping, ESA's SMART-1 was just completing its first end-to-end spacecraft test. Then Stentor was lost in the Ariane-5 launch failure, making SMART-1 the first and only technology demonstration mission with Hall-effect plasma propulsion. As a result, there was a great deal of interest in the electric propulsion community in SMART-1's flight.
Published: 15 February 2007
ESA's fleet of four Cluster satellites was launched in 2000 to investigate the magnetic interaction between the Sun and Earth. Designed to last 3 years, the mission has now been extended to the end of 2009. But the batteries of the satellites are well beyond their design lives and are starting to fail - the power situation first became critical during the long eclipses in September 2006. The battery aboard one could not power the heaters or computer, so new options had to be developed to avoid dangerous low temperatures and to regain control after each eclipse.
Published: 15 February 2007
The Cross-scale TRS is one of ESA's Technology Reference Studies. The purpose of the TRSs is to provide a focus for the development of strategically important technologies that are of likely relevance for future scientific missions. This is accomplished through the study of several technologically demanding and scientifically interesting missions, which are not part of the ESA science programme. The TRSs subsequently act as a reference for possible future technology development activities. The TRSs will not interfere with (or replace) the standard ESA mission selection process.
Published: 22 April 2006
Observations of a Flux Transfer Event (FTE) signature at the dayside magnetopause are reported, which was consecutively observed on 4 January 2005 by both the Double Star/TC1 spacecraft and the Cluster quartet, while the spacecraft were traversing through the northern-dusk magnetopause. The event occurred as a magnetosheath FTE first at the Cluster spacecraft at about 07:13 UT on 4 January 2005 and crossed each of the others within 2 minutes. The spatial separations between the Cluster spacecraft were of the order of 200 km. The TC1 signature occurred about 108s after Cluster. All findings including magnetic fluxes, orientations and hot ion velocity distributions strongly suggest that Cluster and TC1 encountered the magnetosheath branch of the same flux tube at two different positions along its length and this is borne out by computation of the expected time delay. Four-spacecraft timing is used to obtain the velocity of FTE.
Published: 08 February 2007
Context. In recent years, giant amplitude X-ray flares have been observed from a handful of non-active galaxies. The most plausible scenario of these unusual phenomena is tidal disruption of a star by a quiescent supermassive black hole at the centre of the galaxy.
Aims. Only a small number of these type of events have been observed and confirmed to date. The discovery of more cases would allow a number of fundamental conclusions to be drawn about properties such as the frequency of tidal disruption events, the distribution of quiescent black hole masses and their influence in the context of galaxy/AGN formation and evolution among others.
Methods. Comparing the XMM-Newton Slew Survey Source Catalogue with the ROSAT PSPC All-Sky Survey five galaxies have been detected a factor of up to 88 brighter in XMM-Newton with respect to ROSAT PSPC upper limits and presenting a soft X-ray colour. X-ray luminosities of these sources derived from slew observations have been found in the range 1041-1044 erg s-1, fully consistent with the tidal disruption model. This model predicts that during the peak of the outburst, flares reach X-ray luminosities up to 1045 erg s-1, which is close to the Eddington luminosity of the black hole, and afterwards a decay of the flux on a time scale of months to years is expected. Multi-wavelength follow-up observations have been performed on these highly variable objects in order to disentangle their nature and to investigate their dynamical evolution.
Results. Here we present sources coming from the XMM-Newton Slew Survey that could fit in the paradigm of tidal disruption events. X-ray and optical observations revealed that two of these objects are in full agreement with that scenario and three other sources that, showing signs of optical activity, need further investigation within the transient galactic nuclei phenomena.
Published: 08 February 2007
5-Dec-2020 00:27 UT

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