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| Observations and simulations of non-local acceleration of electrons in magnetotail magnetic reconnection events |
| Magnetic reconnection in magnetized plasmas represents a change in magnetic field topology and is associated with a concomitant energization of charged particles that results from a conversion of magnetic energy into particle energy. In Earths magnetosphere this process is associated with the entry of the solar wind into the magnetosphere and with the initiation of auroral substorms. Using data from the THEMIS mission, together with global and test particle simulations, we demonstrate that electrons are energized in two distinct regions: a low-energy population (less than or equal to a few kiloelectronvolts) that arises in a diffusion region where particles are demagnetized and the magnetic topology changes, and a high-energy component (approaching 100 keV) that results from betatron acceleration within dipolarization fronts that sweep towards the inner magnetosphere far from the diffusion region. Thus, the observed particle energization is associated with both magnetic reconnection and with betatron acceleration associated with macroscopic flows. |
| Publication date: 30 Jan 2011 |
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| LISA technical review report |
| Reference: SRE-PA/2011.002/
This technical review report for the LISA candidate mission presents the outcome of an ESA internal review of this L-class candidate mission in the Cosmic Vision 2015-2025 plan. The review was concluded at the end of the mission assessment phase and carried out in frame of the down-selection for L-class missions to proceed to the definition phase. The review focused on the technical and programmatic elements of the mission. |
| Publication date: 29 Jan 2011 |
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| Embedded current sheets in the Earth's magnetotail |
| In this investigation we introduce and discuss quantitative parameters of a thin current sheet embedded in the background plasma sheet. We use Cluster statistics and empirical models, as well as self-consistent simulations, to understand the formation and development of embedded current sheets, in particular in the course of substorms. Data and theory show that the embedded sheet thickness is of the order of a proton larmor radius, a constraint equivalent to magnetic flux conservation. The embedded sheet can be essentially described by two dimensionless parameters B0/Bext and F0/Fext. B0 is the magnetic field at the embedded sheet boundary, Bext is the field at the boundary of the background plasma sheet, and F0 and Fext are magnetic flux values. During the growth phase current density in embedded sheet and B0 increase, while thickness decreases. Sheets with the most intense currents (large B0) are observed after onset. The self-consistent anisotropic sheet model, including both electron and proton currents and combined with the Harris-type background shows that when the proton-scale embedded sheet becomes sufficiently thin, an electron-scale current sheet can appear inside it due to enhanced electron curvature drift. |
| Publication date: 28 Jan 2011 |
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| EJSM-Laplace technical review report |
| Reference: SRE-PA/2011.003/MNCE This technical review report for the EJSM-Laplace candidate mission presents the outcome of an ESA internal review of this L-class candidate mission in the Cosmic Vision 2015-2025 plan. The review was concluded at the end of the mission assessment phase and carried out in frame of the down-selection for L-class missions to proceed to the definition phase. The review focused on the technical and programmatic elements of the mission. |
| Publication date: 27 Jan 2011 |
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| A candidate redshift z≈10 galaxy and rapid changes in that population at an age of 500Myr |
| Searches for very-high-redshift galaxies over the past decade have yielded a large sample of more than 6000 galaxies existing just 900-2000 million years (Myr) after the Big Bang (redshifts 6>z>3). The Hubble Ultra Deep Field (HUDF09) data have yielded the first reliable detections of z~8 galaxies that, together with reports of a gamma-ray burst at z~8.2, constitute the earliest objects reliably reported to date. Observations of z~7-8 galaxies suggest substantial star formation at z>9-10. Here we use the full two-year HUDF09 data to conduct an ultra-deep search for z~10 galaxies in the heart of the reionization epoch, only 500 Myr after the Big Bang. Not only do we find one possible z ~10 galaxy candidate, but we show that, regardless of source detections, the star formation rate density is much smaller (~10%) at this time than it is just ~200 Myr later at z~8. This demonstrates how rapid galaxy build-up was at z~10, as galaxies increased in both luminosity density and volume density from z~10 to z~8. The 100-200 Myr before z~10 is clearly a crucial phase in the assembly of the earliest galaxies. |
| Publication date: 26 Jan 2011 |
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| Bursty bulk flows and dipolarization in MHD simulations of magnetotail reconnection |
| Using three-dimensional MHD simulations of magnetic reconnection in the magnetotail, we investigate the fate of earthward bursty bulk flows (BBFs). The flow bursts are identified as entropy-depleted magnetic flux tubes ("bubbles") generated by the severance of a plasmoid via magnetic reconnection. The onset of fast reconnection coincides closely with a drastic entropy reduction at the onset of lobe reconnection. The fact that, in the simulation, the Alfvén speed does not change significantly at this time suggests that the destabilization of ballooning/interchange modes is important in driving faster reconnection as well as in providing cross-tail structure. In the initial phase, the BBFs are associated with earthward propagating dipolarization fronts. When the flow is stopped nearer to Earth, the region of dipolarization expands both azimuthally and tailward. Tailward flows are found to be associated with a rebound of the earthward flow and with reversed vortices on the outside of the flow. Earthward and tailward flows are also associated with expansion and contraction of the near plasma sheet. All of these features are consistent with recent satellite observations by Cluster and the Time History of Events and their Macroscopic Interactions during Substorms (THEMIS) mission. |
| Publication date: 22 Jan 2011 |
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| An investigation of the SO2 content of the venusian mesosphere using SPICAV-UV in nadir mode |
| Using the SPICAV-UV spectrometer aboard Venus Express in nadir mode, we were able to derive spectral radiance factors in the middle atmosphere of Venus in the 170-320 nm range at a spectral resolution of R ~ 200 during 2006 and 2007 in the northern hemisphere. By comparison with a radiative transfer model of the upper atmosphere of Venus, we could derive column abundance above the visible cloud top for SO2 using its spectral absorption bands near 280 and 220 nm. SO2 column densities show large temporal and spatial variations on a horizontal scale of a few hundred kilometers. Typical SO2 column densities at low latitudes (up to 50°N) were found between 5 and 50 micron-atm, whereas in the northern polar region SO2 content was usually below 5 micron-atm. The observed latitudinal variations follow closely the cloud top altitude derived by SPICAV-IR and are thought to be of dynamical origin. Also, a sudden increase of SO2 column density in the whole northern hemisphere has been observed in early 2007, possibly related to a convective episode advecting some deep SO2 into the upper atmosphere. |
| Publication date: 15 Jan 2011 |
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| IXO technical review report |
| Reference: SRE-PA/2010/104
This technical review report for the IXO candidate mission presents the outcome of an ESA internal review of this L-class candidate mission in the Cosmic Vision 2015-2025 plan. The review was concluded at the end of the mission assessment phase and carried out in frame of the down-selection for L-class missions to proceed to the definition phase. The review focused on the technical and programmatic elements of the mission. |
| Publication date: 14 Jan 2011 |
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| A mature cluster with X-ray emission at z=2.07 |
| We report evidence of a fully established galaxy cluster at z = 2.07, consisting of a ~20 sigma overdensity of red, compact spheroidal galaxies spatially coinciding with extended X-ray emission detected with XMM-Newton. We use VLT VIMOS and FORS2 spectra and deep Subaru, VLT and Spitzer imaging to estimate the redshift of the structure from a prominent z = 2.07 spectroscopic redshift spike of emission-line galaxies, concordant with the accurate 12-band photometric redshifts of the red galaxies. Using NICMOS and Keck AO observations, we find that the red galaxies have elliptical morphologies and compact cores. While they do not form a tight red sequence, their colours are consistent with that of a >1.3 Gyr population observed at z ~ 2.1. From an X-ray luminosity of 7.2×1043 erg/s and the stellar mass content of the red galaxy population, we estimate a halo mass of 5.3-8×1013 solar masses, comparable to the nearby Virgo cluster. These properties imply that this structure could be the most distant, mature cluster known to date and that X-ray luminous, elliptical-dominated clusters are already forming at substantially earlier epochs than previously known. |
| Publication date: 11 Jan 2011 |
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| The role of ULF waves interacting with oxygen ions at the outer ring current during storm times |
| The modulations of the outer ring current O+ ion fluxes by ULF Pc5 waves are investigated by multisatellite observations during storm times. The O+ ions have energies up to tens of keV. We concentrate on the process in terms of drift-bounce resonance of O+ ions with ULF standing waves to understand whether the ring current O+ ions could be accelerated/decelerated by ULF waves. Two case studies are performed, in which the Cluster satellites travel the outer ring current region in the morning sector with radial distances of about 5.5 RE. Distinct O+ ion flux oscillations are observed associated with fundamental mode ULF standing waves. On 25 October 2002, both satellites SC1 and SC4 observe strong poloidal and toroidal standing waves at approximately the same region one by one with a time lag of 45 min. The O+ ion flux oscillations at around 20 keV are dominantly coherent with the poloidal standing wave at 3.4 mHz with cross phases of near 90° with respect to the magnetic field waves. The O+ phase space density spectra at 10 to 25 keV, measured by both satellites, deviate significantly from the typical power law distribution. We suggest that the O+ ions at 10 to 25 keV are accelerated due to drift-bounce resonance with the poloidal standing wave. On 4 November 2002, satellite SC1 observes considerable poloidal and toroidal standing waves. The O+ ion flux oscillation at around 7 keV is well correlated with both of the two wave modes at 3.7 mHz with cross phases of about 90° with respect to the magnetic field waves. The O+ spectra at 4 to 8 keV deviates remarkably from the background power law distribution. When satellite SC4 closely encounters the same region 40 min later, the wave activities at 3.7 mHz are found to be rather weak and the O+ spectra is close to the background power law distribution. We suggest that the spectra variation of SC1 results from the deceleration of O+ ion at 4 to 8 keV via drift-bounce resonances during the strong wave activities. |
| Publication date: 11 Jan 2011 |
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