@article{DavidsenKwiatekCharalampidouetal.2017, author = {Davidsen, Joern and Kwiatek, Grzegorz and Charalampidou, Elli-Maria and Goebel, Thomas H. W. and Stanchits, Sergei and Rueck, Marc and Dresen, Georg}, title = {Triggering Processes in Rock Fracture}, series = {Physical review letters}, volume = {119}, journal = {Physical review letters}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.119.068501}, pages = {8}, year = {2017}, abstract = {We study triggering processes in triaxial compression experiments under a constant displacement rate on sandstone and granite samples using spatially located acoustic emission events and their focal mechanisms. We present strong evidence that event-event triggering plays an important role in the presence of large-scale or macrocopic imperfections, while such triggering is basically absent if no significant imperfections are present. In the former case, we recover all established empirical relations of aftershock seismicity including the Gutenberg-Richter relation, a modified version of the Omori-Utsu relation and the productivity relation-despite the fact that the activity is dominated by compaction-type events and triggering cascades have a swarmlike topology. For the Gutenberg-Richter relations, we find that the b value is smaller for triggered events compared to background events. Moreover, we show that triggered acoustic emission events have a focal mechanism much more similar to their associated trigger than expected by chance.}, language = {en} } @article{LechleitnerBreitenbachRehfeldetal.2017, author = {Lechleitner, Franziska A. and Breitenbach, Sebastian Franz Martin and Rehfeld, Kira and Ridley, Harriet E. and Asmerom, Yemane and Prufer, Keith M. and Marwan, Norbert and Goswami, Bedartha and Kennett, Douglas J. and Aquino, Valorie V. and Polyak, Victor and Haug, Gerald H. and Eglinton, Timothy I. and Baldini, James U. L.}, title = {Tropical rainfall over the last two millennia: evidence for a low-latitude hydrologic seesaw}, series = {Scientific reports}, volume = {7}, journal = {Scientific reports}, publisher = {Nature Publ. Group}, address = {London}, issn = {2045-2322}, doi = {10.1038/srep45809}, pages = {9}, year = {2017}, abstract = {The presence of a low-to mid-latitude interhemispheric hydrologic seesaw is apparent over orbital and glacial-interglacial timescales, but its existence over the most recent past remains unclear. Here we investigate, based on climate proxy reconstructions from both hemispheres, the inter-hemispherical phasing of the Intertropical Convergence Zone (ITCZ) and the low-to mid-latitude teleconnections in the Northern Hemisphere over the past 2000 years. A clear feature is a persistent southward shift of the ITCZ during the Little Ice Age until the beginning of the 19th Century. Strong covariation between our new composite ITCZ-stack and North Atlantic Oscillation (NAO) records reveals a tight coupling between these two synoptic weather and climate phenomena over decadal-to-centennial timescales. This relationship becomes most apparent when comparing two precisely dated, high-resolution paleorainfall records from Belize and Scotland, indicating that the low-to mid-latitude teleconnection was also active over annual-decadal timescales. It is likely a combination of external forcing, i.e., solar and volcanic, and internal feedbacks, that drives the synchronous ITCZ and NAO shifts via energy flux perturbations in the tropics.}, language = {en} } @article{SchubertFrischAllardetal.2017, author = {Schubert, Marcel and Frisch, Johannes and Allard, Sybille and Preis, Eduard and Scherf, Ullrich and Koch, Norbert and Neher, Dieter}, title = {Tuning side chain and main chain order in a prototypical donor-acceptor copolymer}, series = {Elementary Processes in Organic Photovoltaics}, volume = {272}, journal = {Elementary Processes in Organic Photovoltaics}, publisher = {Springer}, address = {Berlin}, isbn = {978-3-319-28338-8}, issn = {0065-3195}, doi = {10.1007/978-3-319-28338-8_10}, pages = {243 -- 265}, year = {2017}, abstract = {The recent development of donor-acceptor copolymers has led to an enormous improvement in the performance of organic solar cells and organic field-effect transistors. Here we describe the synthesis, detailed characterisation, and application of a series of structurally modified copolymers to investigate fundamental structure-property relationships in this class of conjugated polymers. The interplay between chemical structure and optoelectronic properties is investigated. These are further correlated to the charge transport and solar cell performance, which allows us to link their chemical structure to the observed physical properties.}, language = {en} } @article{ThielemannKuehnSchickPontiusetal.2017, author = {Thielemann-K{\"u}hn, Nele and Schick, Daniel and Pontius, Niko and Trabant, Christoph and Mitzner, Rolf and Holldack, Karsten and Zabel, Hartmut and F{\"o}hlisch, Alexander and Schuessler-Langeheine, Christian}, title = {Ultrafast and Energy-Efficient Quenching of Spin Order: Antiferromagnetism Beats Ferromagnetism}, series = {Physical review letters}, volume = {119}, journal = {Physical review letters}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.119.197202}, pages = {6}, year = {2017}, abstract = {By comparing femtosecond laser pulse induced ferro- and antiferromagnetic dynamics in one and the same material-metallic dysprosium-we show both to behave fundamentally different. Antiferromagnetic order is considerably faster and much more efficiently reduced by optical excitation than its ferromagnetic counterpart. We assign the fast and extremely efficient process in the antiferromagnet to an interatomic transfer of angular momentum within the spin system. Our findings imply that this angular momentum transfer channel is effective in other magnetic metals with nonparallel spin alignment. They also point out a possible route towards energy-efficient spin manipulation for magnetic devices.}, language = {en} } @article{MorHerzogGolezetal.2017, author = {Mor, Selene and Herzog, Marc and Golez, Denis and Werner, Philipp and Eckstein, Martin and Katayama, Naoyuki and Nohara, Minoru and Takagi, Hide and Mizokawa, Takashi and Monney, Claude and Staehler, Julia}, title = {Ultrafast Electronic Band Gap Control in an Excitonic Insulator}, series = {Physical review letters}, volume = {119}, journal = {Physical review letters}, publisher = {American Physical Society}, address = {College Park}, issn = {0031-9007}, doi = {10.1103/PhysRevLett.119.086401}, pages = {11559 -- 11567}, year = {2017}, abstract = {We report on the nonequilibrium dynamics of the electronic structure of the layered semiconductor Ta2NiSe5 investigated by time-and angle-resolved photoelectron spectroscopy. We show that below the critical excitation density of F-C = 0.2 mJ cm(-2), the band gap narrows transiently, while it is enhanced above FC. Hartree-Fock calculations reveal that this effect can be explained by the presence of the low-temperature excitonic insulator phase of Ta2NiSe5, whose order parameter is connected to the gap size. This work demonstrates the ability to manipulate the band gap of Ta2NiSe5 with light on the femtosecond time scale.}, language = {en} } @article{EckertNorellMiedemaetal.2017, author = {Eckert, Sebastian and Norell, Jesper and Miedema, Piter S. and Beye, Martin and Fondell, Mattis and Quevedo, Wilson and Kennedy, Brian and Hantschmann, Markus and Pietzsch, Annette and Van Kuiken, Benjamin E. and Ross, Matthew and Minitti, Michael P. and Moeller, Stefan P. and Schlotter, William F. and Khalil, Munira and Odelius, Michael and F{\"o}hlisch, Alexander}, title = {Ultrafast Independent N-H and N-C Bond Deformation Investigated with Resonant Inelastic X-Ray Scattering}, series = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition}, volume = {56}, journal = {Angewandte Chemie : a journal of the Gesellschaft Deutscher Chemiker ; International edition}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1433-7851}, doi = {10.1002/anie.201700239}, pages = {6088 -- 6092}, year = {2017}, abstract = {The femtosecond excited-state dynamics following resonant photoexcitation enable the selective deformation of N-H and N-C chemical bonds in 2-thiopyridone in aqueous solution with optical or X-ray pulses. In combination with multiconfigurational quantum-chemical calculations, the orbital-specific electronic structure and its ultrafast dynamics accessed with resonant inelastic X-ray scattering at the N 1s level using synchrotron radiation and the soft X-ray free-electron laser LCLS provide direct evidence for this controlled photoinduced molecular deformation and its ultrashort time-scale.}, language = {en} } @article{KocReinhardtReppertetal.2017, author = {Koc, Azize and Reinhardt, M. and Reppert, Alexander von and Roessle, Matthias and Leitenberger, Wolfram and Dumesnil, K. and Gaal, Peter and Zamponi, Flavio and Bargheer, Matias}, title = {Ultrafast x-ray diffraction thermometry measures the influence of spin excitations on the heat transport through nanolayers}, series = {Physical review : B, Condensed matter and materials physics}, volume = {96}, journal = {Physical review : B, Condensed matter and materials physics}, publisher = {American Physical Society}, address = {College Park}, issn = {2469-9950}, doi = {10.1103/PhysRevB.96.014306}, pages = {7}, year = {2017}, abstract = {We investigate the heat transport through a rare earth multilayer system composed of yttrium (Y), dysprosium (Dy), and niobium (Nb) by ultrafast x-ray diffraction. This is an example of a complex heat flow problem on the nanoscale, where several different quasiparticles carry the heat and conserve a nonequilibrium for more than 10 ns. The Bragg peak positions of each layer represent layer-specific thermometers that measure the energy flow through the sample after excitation of the Y top layer with fs-laser pulses. In an experiment-based analytic solution to the nonequilibrium heat transport problem, we derive the individual contributions of the spins and the coupled electron-lattice system to the heat conduction. The full characterization of the spatiotemporal energy flow at different starting temperatures reveals that the spin excitations of antiferromagnetic Dy speed up the heat transport into the Dy layer at low temperatures, whereas the heat transport through this layer and further into the Y and Nb layers underneath is slowed down. The experimental findings are compared to the solution of the heat equation using macroscopic temperature-dependent material parameters without separation of spin and phonon contributions to the heat. We explain why the simulated energy density matches our experiment-based derivation of the heat transport, although the simulated thermoelastic strain in this simulation is not even in qualitative agreement.}, language = {en} } @article{EckertNiskanenJayetal.2017, author = {Eckert, Sebastian and Niskanen, Johannes and Jay, Raphael Martin and Miedema, Piter S. and Fondell, Mattis and Kennedy, Brian and Quevedo, Wilson and Iannuzzi, Marcella and F{\"o}hlisch, Alexander}, title = {Valence orbitals and local bond dynamics around N atoms of histidine under X-ray irradiation}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {19}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c7cp05713j}, pages = {32091 -- 32098}, year = {2017}, abstract = {The valence orbitals of aqueous histidine under basic, neutral and acidic conditions and their X-ray induced transformations have been monitored through N 1s resonant inelastic X-ray scattering. Using density functional ab initio molecular dynamics simulations in the core-hole state within the Z + 1 approximation, core-excitation-induced molecular transformations are quantified. Spectroscopic evidence for a highly directional X-ray-induced local N-H dissociation within the scattering duration is presented for acidic histidine. Our report demonstrates a protonation-state and chemical-environment dependent propensity for a molecular dissociation, which is induced by the absorption of high energy photons. This case study indicates that structural deformations in biomolecules under exposure to ionizing radiation, yielding possible alteration or loss of function, is highly dependent on the physiological state of the molecule upon irradiation.}, language = {en} } @article{KayserMaturilliGrahametal.2017, author = {Kayser, Markus and Maturilli, Marion and Graham, Robert M. and Hudson, Stephen R. and Rinke, Annette and Cohen, Lana and Kim, Joo-Hong and Park, Sang-Jong and Moon, Woosok and Granskog, Mats A.}, title = {Vertical thermodynamic structure of the troposphere during the Norwegian young sea ICE expedition (N-ICE2015)}, series = {Journal of geophysical research-atmosheres}, volume = {122}, journal = {Journal of geophysical research-atmosheres}, number = {20}, publisher = {American Geophysical Union}, address = {Washington}, issn = {2169-897X}, doi = {10.1002/2016JD026089}, pages = {10855 -- 10872}, year = {2017}, abstract = {The Norwegian young sea ICE (N-ICE2015) expedition was designed to investigate the atmosphere-snow-ice-ocean interactions in the young and thin sea ice regime north of Svalbard. Radiosondes were launched twice daily during the expedition from January to June 2015. Here we use these upper air measurements to study the multiple cyclonic events observed during N-ICE2015 with respect to changes in the vertical thermodynamic structure, moisture content, and boundary layer characteristics. We provide statistics of temperature inversion characteristics, static stability, and boundary layer extent. During winter, when radiative cooling is most effective, we find the strongest impact of synoptic cyclones. Changes to thermodynamic characteristics of the boundary layer are associated with transitions between the radiatively "clear" and "opaque" atmospheric states. In spring, radiative fluxes warm the surface leading to lifted temperature inversions and a statically unstable boundary layer. Further, we compare the N-ICE2015 static stability distributions to corresponding profiles from ERA-Interim reanalysis, from the closest land station in the Arctic North Atlantic sector, Ny-Alesund, and to soundings from the SHEBA expedition (1997/1998). We find similar stability characteristics for N-ICE2015 and SHEBA throughout the troposphere, despite differences in location, sea ice thickness, and snow cover. For Ny-Alesund, we observe similar characteristics above 1000 m, while the topography and ice-free fjord surrounding Ny-Alesund generate great differences below. The long-term radiosonde record (1993-2014) from Ny-Alesund indicates that during the N-ICE2015 spring period, temperatures were close to the climatological mean, while the lowest 3000 m were 1-3 degrees C warmer than the climatology during winter. Plain Language Summary The Norwegian young sea ICE (N-ICE2015) expedition was designed to investigate the atmosphere-snow-ice-ocean interactions in the young and thin sea ice regime north of Svalbard. Radiosondes were launched twice daily during the expedition from January to June 2015. Here we use these upper air measurements to study the multiple cyclonic events observed during N-ICE2015 with respect to changes in the vertical thermodynamic structure, moisture content, and the atmospheric boundary layer characteristics. During winter, we find the strongest impact of synoptic cyclones, which transport warm and moist air into the cold and dry Arctic atmosphere. In spring, incoming solar radiation warms the surface. This leads to very different thermodynamic conditions and higher moisture content, which reduces the contrast between stormy and calm periods. Further, we compare the N-ICE2015 measurements to corresponding profiles from ERA-Interim reanalysis, from the closest land station in the Arctic North Atlantic sector, Ny-Alesund, and to soundings from the SHEBA expedition (1997/1998). We find similar stability characteristics for N-ICE2015 and SHEBA throughout the troposphere, despite differences in location, sea ice thickness, and snow cover. The comparisons highlight the value of the N-ICE2015 observation and show the importance of winter time observations in the Arctic North Atlantic sector.}, language = {en} } @article{AllenArchambaultArcheretal.2017, author = {Allen, C. and Archambault, S. and Archer, A. and Benbow, W. and Bird, R. and Bourbeau, E. and Brose, Robert and Buchovecky, M. and Buckley, J. H. and Bugaev, V. and Cardenzana, J. V. and Cerruti, M. and Chen, Xuhui and Christiansen, J. L. and Connolly, M. P. and Cui, W. and Daniel, M. K. and Eisch, J. D. and Falcone, Abe and Feng, Q. and Fernandez-Alonso, M. and Finley, J. P. and Fleischhack, H. and Flinders, A. and Fortson, L. and Furniss, A. and Gillanders, G. H. and Griffin, S. and Grube, J. and Huetten, M. and Hakansson, N. and Hanna, D. and Hervet, O. and Holder, J. and Hughes, G. and Humensky, T. B. and Johnson, C. A. and Kaaret, P. and Kar, P. and Kelley-Hoskins, N. and Kertzman, M. and Kieda, D. and Krause, M. and Krennrich, F. and Kumar, S. and Lang, M. J. and Maier, G. and McArthur, S. and McCann, A. and Meagher, K. and Moriarty, P. and Mukherjee, R. and Nguyen, T. and Nieto, D. and Ong, R. A. and Otte, A. N. and Park, N. and Petrashyk, A. and Pichel, A. and Pohl, Martin and Popkow, A. and Pueschel, Elisa and Quinn, J. and Ragan, K. and Reynolds, P. T. and Richards, G. T. and Roache, E. and Rovero, A. C. and Rulten, C. and Sadeh, I. and Santander, Marcos and Sembroski, G. H. and Shahinyan, K. and Telezhinsky, Igor O. and Tucci, J. V. and Tyler, J. and Wakely, S. P. and Weinstein, A. and Wilhelm, Alina and Williams, D. A.}, title = {Very-High-Energy gamma-Ray Observations of the Blazar 1ES 2344+514 with VERITAS}, series = {Monthly notices of the Royal Astronomical Society}, volume = {471}, journal = {Monthly notices of the Royal Astronomical Society}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1093/mnras/stx1756}, pages = {2117 -- 2123}, year = {2017}, abstract = {We present very-high-energy gamma-ray observations of the BL Lac object 1ES 2344+514 taken by the Very Energetic Radiation Imaging Telescope Array System between 2007 and 2015. 1ES 2344+514 is detected with a statistical significance above the background of 20.8 sigma in 47.2 h (livetime) of observations, making this the most comprehensive very-high-energy study of 1ES 2344+514 to date. Using these observations, the temporal properties of 1ES 2344+514 are studied on short and long times-scales. We fit a constant-flux model to nightly and seasonally binned light curves and apply a fractional variability test to determine the stability of the source on different time-scales. We reject the constant-flux model for the 2007-2008 and 2014-2015 nightly binned light curves and for the long-term seasonally binned light curve at the > 3 sigma level. The spectra of the time-averaged emission before and after correction for attenuation by the extragalactic background light are obtained. The observed time-averaged spectrum above 200 GeV is satisfactorily fitted (x(2)/NDF = 7.89/6) by a power-law function with an index Gamma = 2.46 +/- 0.06(stat) +/- 0.20(sys) and extends to at least 8 TeV. The extragalactic-backgroundlight-deabsorbed spectrum is adequately fit (x(2)/NDF = 6.73/6) by a power-law function with an index Gamma = 2.15 +/- 0.06(stat) +/- 0.20(sys) while an F-test indicates that the power law with an exponential cut-off function provides a marginally better fit (x(2)/NDF = 2.56/5) at the 2.1 sigma level. The source location is found to be consistent with the published radio location and its spatial extent is consistent with a point source.}, language = {en} } @article{LeussuUsoskinValliappanetal.2017, author = {Leussu, R. and Usoskin, IIlya G. and Valliappan, Senthamizh Pavai and Diercke, Andrea and Arlt, Rainer and Denker, Carsten and Mursula, K.}, title = {Wings of the butterfly}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {599}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201629533}, pages = {8}, year = {2017}, abstract = {The spatio-temporal evolution of sunspot activity, the so-called Maunder butterfly diagram, has been continously available since 1874 using data from the Royal Greenwich Observatory, extended by SOON network data after 1976. Here we present a new extended butterfly diagram of sunspot group occurrence since 1826, using the recently digitized data from Schwabe (1826-1867) and Sporer (1866-1880). The wings of the diagram are separated using a recently developed method based on an analysis of long gaps in sunspot group occurrence in different latitude bands. We define characteristic latitudes, corresponding to the start, end, and the largest extent of the wings (the F, L, and H latitudes). The H latitudes (30 degrees-45 degrees) are highly significantly correlated with the strength of the wings (quantified by the total sum of the monthly numbers of sunspot groups). The F latitudes (20 degrees-30 degrees) depict a weak tendency, especially in the southern hemisphere, to follow the wing strength. The L latitudes (2 degrees-10 degrees) show no clear relation to the wing strength. Overall, stronger cycle wings tend to start at higher latitudes and have a greater wing extent. A strong (5-6)-cycle periodic oscillation is found in the start and end times of the wings and in the overlap and gaps between successive wings of one hemisphere. While the average wing overlap is zero in the southern hemisphere, it is two to three months in the north. A marginally significant oscillation of about ten solar cycles is found in the asymmetry of the L latitudes. The new long database of butterfly wings provides new observational constraints to solar dynamo models that discuss the spatio-temporal distribution of sunspot occurrence over the solar cycle and longer.}, language = {en} } @article{MunozMoffatHilletal.2017, author = {Munoz, Melissa and Moffat, Anthony F. J. and Hill, Grant M. and Shenar, Tomer and Richardson, Noel D. and Pablo, Herbert and St-Louis, Nicole and Ramiaramanantsoa, Tahina}, title = {WR 148: identifying the companion of an extreme runaway massive binary}, series = {Monthly notices of the Royal Astronomical Society}, volume = {467}, journal = {Monthly notices of the Royal Astronomical Society}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1093/mnras/stw2283}, pages = {3105 -- 3121}, year = {2017}, abstract = {WR 148 (HD 197406) is an extreme runaway system considered to be a potential candidate for a short-period (4.3173 d) rare WR + compact object binary. Provided with new high-resolution, high signal-to-noise spectra from the Keck observatory, we determine the orbital parameters for both the primary WR and the secondary, yielding respective projected orbital velocity amplitudes of 88.1 ± 3.8\&\#8201;km\&\#8201;s\&\#8722;1 and 79.2 ± 3.1\&\#8201;km\&\#8201;s\&\#8722;1 and implying a mass ratio of 1.1 ± 0.1. We then apply the shift-and-add technique to disentangle the spectra and obtain spectra compatible with a WN7ha and an O4-6 star. Considering an orbital inclination of \&\#8764;67°, derived from previous polarimetry observations, the system's total mass would be a mere 2-3M\&\#8857;\&\#8288;, an unprecedented result for a putative massive binary system. However, a system comprising a 37M\&\#8857; secondary (typical mass of an O5V star) and a 33M\&\#8857; primary (given the mass ratio) would infer an inclination of \&\#8764;18°. We therefore reconsider the previous methods of deriving the orbital inclination based on time-dependent polarimetry and photometry. While the polarimetric results are inconclusive requiring better data, the photometric results favour low inclinations. Finally, we compute WR 148's space velocity and retrace the runaway's trajectory back to the Galactic plane (GP). With an ejection velocity of 198 ± 27\&\#8201;km\&\#8201;s\&\#8722;1 and a travel time of 4.7 ± 0.8 Myr to reach its current location, WR 148 was most likely ejected via dynamical interactions in a young cluster.}, language = {en} } @article{DeBeckerdelValleRomeroetal.2017, author = {De Becker, M. and del Valle, Maria Victoria and Romero, G. E. and Peri, C. S. and Benaglia, P.}, title = {X- ray study of bow shocks in runaway stars}, series = {Monthly notices of the Royal Astronomical Society}, volume = {471}, journal = {Monthly notices of the Royal Astronomical Society}, publisher = {Oxford Univ. Press}, address = {Oxford}, issn = {0035-8711}, doi = {10.1093/mnras/stx1826}, pages = {4452 -- 4464}, year = {2017}, abstract = {Massive runaway stars produce bow shocks through the interaction of their winds with the interstellar medium, with the prospect for particle acceleration by the shocks. These objects are consequently candidates for non-thermal emission. Our aim is to investigate the X-ray emission from these sources. We observed with XMM-Newton a sample of five bow shock runaways, which constitutes a significant improvement of the sample of bow shock runaways studied in X-rays so far. A careful analysis of the data did not reveal any X-ray emission related to the bow shocks. However, X-ray emission from the stars is detected, in agreement with the expected thermal emission from stellar winds. On the basis of background measurements we derive conservative upper limits between 0.3 and 10 keV on the bow shocks emission. Using a simple radiation model, these limits together with radio upper limits allow us to constrain some of the main physical quantities involved in the non-thermal emission processes, such as the magnetic field strength and the amount of incident infrared photons. The reasons likely responsible for the non-detection of non-thermal radiation are discussed. Finally, using energy budget arguments, we investigate the detectability of inverse Compton X-rays in a more extended sample of catalogued runaway star bow shocks. From our analysis we conclude that a clear identification of non-thermal X-rays from massive runaway bow shocks requires one order of magnitude (or higher) sensitivity improvement with respect to present observatories.}, language = {en} } @article{MiedemaMitznerGanschowetal.2017, author = {Miedema, P. S. and Mitzner, Rolf and Ganschow, S. and F{\"o}hlisch, Alexander and Beye, Martin}, title = {X-ray spectroscopy on the active ion in laser crystals}, series = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, volume = {19}, journal = {Physical chemistry, chemical physics : a journal of European Chemical Societies}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {1463-9076}, doi = {10.1039/c7cp03026f}, pages = {21800 -- 21806}, year = {2017}, abstract = {The active ions in typical laser crystals were studied with Resonant Inelastic X-ray Scattering (RIXS) and Partial Fluorescence Yield X-ray Absorption (PFY-XAS) spectroscopies as solid state model systems for dilute active centers. We analyzed Ti3+ and Cr3+ in alpha-Al2O3:Ti3+ and LiCaAlF6:Cr3+, respectively. The comparison of experimental data with semi-empirical multiplet calculations provides insights into the electronic structure and shows how measured crystal field energies are related across different spectroscopies.}, language = {en} } @article{SanjurjoFerrrinTorrejonPostnovetal.2017, author = {Sanjurjo-Ferrrin, G. and Torrejon, J. M. and Postnov, K. and Oskinova, Lida and Rodes-Roca, J. J. and Bernabeu, Guillermo}, title = {XMM-Newton spectroscopy of the accreting magnetar candidate 4U0114+65}, series = {Astronomy and astrophysics : an international weekly journal}, volume = {606}, journal = {Astronomy and astrophysics : an international weekly journal}, publisher = {EDP Sciences}, address = {Les Ulis}, issn = {1432-0746}, doi = {10.1051/0004-6361/201630119}, pages = {4039 -- 4042}, year = {2017}, abstract = {Methods. We analysed the energy-resolved light curve and the time-resolved X-ray spectra provided by the EPIC cameras on board XMM-Newton. We also analysed the first high-resolution spectrum of this source provided by the Reflection Grating Spectrometer. Results. An X-ray pulse of 9350 +/- 160 s was measured. Comparison with previous measurements confirms the secular spin up of this source. We successfully fit the pulse-phase-resolved spectra with Comptonisation models. These models imply a very small (r similar to 3 km) and hot (kT similar to 2-3 keV) emitting region and therefore point to a hot spot over the neutron star (NS) surface as the most reliable explanation for the X-ray pulse. The long NS spin period, the spin-up rate, and persistent X-ray emission can be explained within the theory of quasi-spherical settling accretion, which may indicate that the magnetic field is in the magnetar range. Thus, 4U0114+65 could be a wind-accreting magnetar. We also observed two episodes of low luminosity. The first was only observed in the low-energy light curve and can be explained as an absorption by a large over-dense structure in the wind of the B1 supergiant donor. The second episode, which was deeper and affected all energies, may be due to temporal cessation of accretion onto one magnetic pole caused by non-spherical matter capture from the structured stellar wind. The light curve displays two types of dips that are clearly seen during the high-flux intervals. The short dips, with durations of tens of seconds, are produced through absorption by wind clumps. The long dips, in turn, seem to be associated with the rarefied interclump medium. From the analysis of the X-ray spectra, we found evidence of emission lines in the X-ray photoionised wind of the B1Ia donor. The Fe K alpha line was found to be highly variable and much weaker than in other X-ray binaries with supergiant donors. The degree of wind clumping, measured through the covering fraction, was found to be much lower than in supergiant donor stars with earlier spectral types. Conclusions. The XMM-Newton spectroscopy provided further support for the magnetar nature of the neutron star in 4U0114+65. The light curve presents dips that can be associated with clumps and the interclump medium in the stellar wind of the mass donor.}, language = {en} }