| 1. |
- Beth, A., et al.
(författare)
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First in situ detection of the cometary ammonium ion NH4+ (protonated ammonia NH3) in the coma of 67P/C-G near perihelion
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : OXFORD UNIV PRESS. - 0035-8711 .- 1365-2966. ; 462, s. S562-S572
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Tidskriftsartikel (refereegranskat)abstract
- In this paper, we report the first in situ detection of the ammonium ion NH4+ at 67P/Churyumov-Gerasimenko (67P/C-G) in a cometary coma, using the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis (ROSINA)/Double Focusing Mass Spectrometer (DFMS). Unlike neutral and ion spectrometers onboard previous cometary missions, the ROSINA/DFMS spectrometer, when operated in ion mode, offers the capability to distinguish NH4+ from H2O+ in a cometary coma. We present here the ion data analysis of mass-to-charge ratios 18 and 19 at high spectral resolution and compare the results with an ionospheric model to put these results into context. The model confirms that the ammonium ion NH4+ is one of the most abundant ion species, as predicted, in the coma near perihelion.
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| 2. |
- Edberg, Niklas J. T., et al.
(författare)
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CME impact on comet 67P/Churyumov-Gerasimenko
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 462, s. S45-S56
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Tidskriftsartikel (refereegranskat)abstract
- We present Rosetta observations from comet 67P/Churyumov-Gerasimenko during the impact of a coronal mass ejection (CME). The CME impacted on 2015 Oct 5-6, when Rosetta was about 800 km from the comet nucleus, and 1.4 au from the Sun. Upon impact, the plasma environment is compressed to the level that solar wind ions, not seen a few days earlier when at 1500 km, now reach Rosetta. In response to the compression, the flux of suprathermal electrons increases by a factor of 5-10 and the background magnetic field strength increases by a factor of similar to 2.5. The plasma density increases by a factor of 10 and reaches 600 cm(-3), due to increased particle impact ionization, charge exchange and the adiabatic compression of the plasma environment. We also observe unprecedentedly large magnetic field spikes at 800 km, reaching above 200 nT, which are interpreted as magnetic flux ropes. We suggest that these could possibly be formed by magnetic reconnection processes in the coma as the magnetic field across the CME changes polarity, or as a consequence of strong shears causing Kelvin-Helmholtz instabilities in the plasma flow. Due to the limited orbit of Rosetta, we are not able to observe if a tail disconnection occurs during the CME impact, which could be expected based on previous remote observations of other CME-comet interactions.
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| 3. |
- Galand, M., et al.
(författare)
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Ionospheric plasma of comet 67P probed by Rosetta at 3 au from the Sun
- 2016
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 462, s. S331-S351
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Tidskriftsartikel (refereegranskat)abstract
- We propose to identify the main sources of ionization of the plasma in the coma of comet 67P/Churyumov-Gerasimenko at different locations in the coma and to quantify their relative importance, for the first time, for close cometocentric distances (< 20 km) and large heliocentric distances (> 3 au). The ionospheric model proposed is used as an organizing element of a multi-instrument data set from the Rosetta Plasma Consortium (RPC) plasma and particle sensors, from the Rosetta Orbiter Spectrometer for Ion and Neutral Analysis and from the Microwave Instrument on the Rosetta Orbiter, all on board the ESA/Rosetta spacecraft. The calculated ionospheric density driven by Rosetta observations is compared to the RPC-Langmuir Probe and RPC-Mutual Impedance Probe electron density. The main cometary plasma sources identified are photoionization of solar extreme ultraviolet (EUV) radiation and energetic electron-impact ionization. Over the northern, summer hemisphere, the solar EUV radiation is found to drive the electron density - with occasional periods when energetic electrons are also significant. Over the southern, winter hemisphere, photoionization alone cannot explain the observed electron density, which reaches sometimes higher values than over the summer hemisphere; electron-impact ionization has to be taken into account. The bulk of the electron population is warm with temperature of the order of 7-10 eV. For increased neutral densities, we show evidence of partial energy degradation of the hot electron energy tail and cooling of the full electron population.
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| 4. |
- Heritier, K. L., et al.
(författare)
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Vertical structure of the near-surface expanding ionosphere of comet 67P probed by Rosetta
- 2017
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 469, s. S118-S129
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Tidskriftsartikel (refereegranskat)abstract
- The plasma environment has been measured for the first time near the surface of a comet. This unique data set has been acquired at 67P/Churyumov-Gerasimenko during ESA/Rosetta spacecraft's final descent on 2016 September 30. The heliocentric distance was 3.8 au and the comet was weakly outgassing. Electron density was continuously measured with Rosetta Plasma Consortium (RPC)-Mutual Impedance Probe (MIP) and RPC-LAngmuir Probe (LAP) during the descent from a cometocentric distance of 20 km down to the surface. Data set from both instruments have been cross-calibrated for redundancy and accuracy. To analyse this data set, we have developed a model driven by Rosetta Orbiter Spectrometer for Ion and Neutral Analysis-COmetary Pressure Sensor total neutral density. The two ionization sources considered are solar extreme ultraviolet radiation and energetic electrons. The latter are estimated from the RPC-Ion and Electron Sensor (IES) and corrected for the spacecraft potential probed by RPC-LAP. We have compared the results of the model to the electron densities measured by RPC-MIP and RPC-LAP at the location of the spacecraft. We find good agreement between observed and modelled electron densities. The energetic electrons have access to the surface of the nucleus and contribute as the main ionization source. As predicted, the measurements exhibit a peak in the ionospheric density close to the surface. The location and magnitude of the peak are estimated analytically. The measured ionospheric densities cannot be explained with a constant outflow velocity model. The use of a neutral model with an expanding outflow is critical to explain the plasma observations.
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| 5. |
- Shebanits, Oleg, et al.
(författare)
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Ion and aerosol precursor densities in Titan's ionosphere : A multi-instrument case study
- 2016
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 121:10, s. 10075-10090
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Tidskriftsartikel (refereegranskat)abstract
- The importance of the heavy ions and dust grains for the chemistry and aerosol formation in Titan's ionosphere has been well established in the recent years of the Cassini mission. In this study we combine independent in situ plasma (Radio Plasma and Wave Science Langmuir Probe (RPWS/LP)) and particle (Cassini Plasma Science Electron Spectrometer, Cassini Plasma Science Ion Beam Spectrometer, and Ion and Neutral Mass Spectrometer) measurements of Titan's ionosphere for selected flybys (T16, T29, T40, and T56) to produce altitude profiles of mean ion masses including heavy ions and develop a Titan-specific method for detailed analysis of the RPWS/LP measurements (applicable to all flybys) to further constrain ion charge densities and produce the first empirical estimate of the average charge of negative ions and/or dust grains. Our results reveal the presence of an ion-ion (dusty) plasma below similar to 1100 km altitude, with charge densities exceeding the primary ionization peak densities by a factor >= 2 in the terminator and nightside ionosphere (n(e)/n(i) <= 0.1). We suggest that ion-ion (dusty) plasma may also be present in the dayside ionosphere below 900 km (n(e)/n(i) < 0.5 at 1000 km altitude). The average charge of the dust grains (>= 1000 amu) is estimated to be between -2.5 and -1.5 elementary charges, increasing toward lower altitudes.
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| 6. |
- Edberg, Niklas J. T., et al.
(författare)
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Solar wind interaction with comet 67P : Impacts of corotating interaction regions
- 2016
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Ingår i: Journal of Geophysical Research - Space Physics. - 2169-9380 .- 2169-9402. ; 121:2, s. 949-965
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Tidskriftsartikel (refereegranskat)abstract
- We present observations from the Rosetta Plasma Consortium of the effects of stormy solar wind on comet 67P/Churyumov-Gerasimenko. Four corotating interaction regions (CIRs), where the first event has possibly merged with a coronal mass ejection, are traced from Earth via Mars (using Mars Express and Mars Atmosphere and Volatile EvolutioN mission) to comet 67P from October to December 2014. When the comet is 3.1-2.7AU from the Sun and the neutral outgassing rate approximate to 10(25)-10(26)s(-1), the CIRs significantly influence the cometary plasma environment at altitudes down to 10-30km. The ionospheric low-energy (approximate to 5eV) plasma density increases significantly in all events, by a factor of >2 in events 1 and 2 but less in events 3 and 4. The spacecraft potential drops below -20V upon impact when the flux of electrons increases. The increased density is likely caused by compression of the plasma environment, increased particle impact ionization, and possibly charge exchange processes and acceleration of mass-loaded plasma back to the comet ionosphere. During all events, the fluxes of suprathermal (approximate to 10-100eV) electrons increase significantly, suggesting that the heating mechanism of these electrons is coupled to the solar wind energy input. At impact the magnetic field strength in the coma increases by a factor of 2-5 as more interplanetary magnetic field piles up around the comet. During two CIR impact events, we observe possible plasma boundaries forming, or moving past Rosetta, as the strong solar wind compresses the cometary plasma environment. We also discuss the possibility of seeing some signatures of the ionospheric response to tail disconnection events.
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| 7. |
- Edberg, Niklas J. T., et al.
(författare)
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Spatial distribution of low-energy plasma around comet 67P/CG from Rosetta measurements
- 2015
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Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 42:11, s. 4263-4269
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Tidskriftsartikel (refereegranskat)abstract
- We use measurements from the Rosetta plasma consortium Langmuir probe and mutual impedance probe to study the spatial distribution of low-energy plasma in the near-nucleus coma of comet 67P/Churyumov-Gerasimenko. The spatial distribution is highly structured with the highest density in the summer hemisphere and above the region connecting the two main lobes of the comet, i.e., the neck region. There is a clear correlation with the neutral density and the plasma to neutral density ratio is found to be approximate to 1-210(-6), at a cometocentric distance of 10km and at 3.1AU from the Sun. A clear 6.2h modulation of the plasma is seen as the neck is exposed twice per rotation. The electron density of the collisionless plasma within 260km from the nucleus falls off with radial distance as approximate to 1/r. The spatial structure indicates that local ionization of neutral gas is the dominant source of low-energy plasma around the comet.
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| 8. |
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| 9. |
- Eriksson, C., et al.
(författare)
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Golimumab är effektivt vid ulcerös kolit under svenska förhållanden. Interimsanalys av en svensk prospektiv multi-centerstudie, GO-SWIBREG
- 2018
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Konferensbidrag (refereegranskat)abstract
- Bakgrund: Randomiserade kontrollerade prövningar har visat effekt av golimumab vid ulcerös kolit men studiedeltagare och förhållanden i kliniska prövningar motsvarar inte alltid svensk klinisk vardag. Syftet med denna studie var att utvärdera säkerhet och effekt av behandling med golimumab vid ulcerös kolit under svenska förhållanden.Metod: Detta är en prospektiv kohortstudie med inklusion av patienter från svenska sjukhus. Patienter med måttlig till svår aktiv ulcerös kolit, definierad som endoskopiskt Mayo score ≥2 och som påbörjade golimumab fr.o.m. 1/6-2014 inkluderades efter att informerat samtycke inhämtats. Kliniska karakteristika, behandling, klinisk-, biokemisk- och endoskopisk aktivitet liksom skattning av livskvalité samlades in vid inklusion samt prospektivt med hjälp av ett elektroniskt studieformulär, integrerat i svenska kvalitetsregistret för IBD (SWIBREG). Primärt effektmått var klinisk effekt vid 3 samt 12 månader (definierat som minskat Mayo score med ≥3 poäng eller 30 % från inklusion), samt klinisk remission (definierad som Mayo score ≤ 2 utan några enskilda poäng >1). Kontinuerliga data presenteras som median och kvartilavstånd. För statistisk jämförelse mellan inklusion och uppföljning användes Wilcoxon-signed rank test. Data från induktionsbehandling samt 3-månadersuppföljning presenteras här.Resultat: 50 patienter inkluderades t.o.m. 15/9-2017. Vid studiestart var 24/50 (48 %) samtidigt behandlade med immunmodulerare, 16/50 (32 %) med perorala kortikosteroider samt 27/50 (54 %) med 5-ASA. Totalt hade 35/50 (70 %) tidigare fått behandling med minst en TNF-hämmare (tabell 1). Efter 12 veckor hade 37/50 (74 %), fortfarande behandling med golimumab. Av de patienter som fortsatte med golimumab till vecka 12 var 8 (22 %) i klinisk remission och 13 (35 %) uppvisade klinisk respons. Totalt Mayo score minskade i median från 7 (6-10) vid inklusion till 5 (1-8) vid 12 veckor (p<0.01). Fekalt calprotektin minskade från 710 (275-1850) µg/g till 390 (45-870) µg/g (p=0.02). Livskvalitet hos golimumab-behandlade patienter förbättrades, uppmätt som en signifikant minskning av poäng på short health scale (p=0.04).Slutsats: Golimumab-behandlade patienter i Sverige utgör en svårbehandlad grupp. Trots det kan förbättring av kliniska parametrar, inflammatorisk aktivitet och upplevd livskvalité uppnås redan efter 12 veckors golimumab-behandling.
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| 10. |
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