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Context. We present a detailed view of the pulsar wind nebula (PWN) HESS J1825-137. We aim to constrain the mechanisms dominating the particle transport within the nebula, accounting for its anomalously large size and spectral characteristics. Aims. The nebula was studied using a deep exposure from over 12 years of H.E.S.S. I operation, together with data from H.E.S.S. II that improve the low-energy sensitivity. Enhanced energy-dependent morphological and spatially resolved spectral analyses probe the very high energy (VHE, E > 0.1 TeV) gamma-ray properties of the nebula. Methods. The nebula emission is revealed to extend out to 1.5 degrees from the pulsar, similar to 1.5 times farther than previously seen, making HESS J1825-137, with an intrinsic diameter of similar to 100 pc, potentially the largest gamma-ray PWN currently known. Characterising the strongly energy-dependent morphology of the nebula enables us to constrain the particle transport mechanisms. A dependence of the nebula extent with energy of R proportional to E alpha with alpha = -0.29 +/- 0.04(stat) +/- 0.05(sys) disfavours a pure diffusion scenario for particle transport within the nebula. The total gamma-ray flux of the nebula above 1 TeV is found to be (1.12 +/- 0.03(stat) +/- 0.25(sys)) +/- 10(-11) cm(-2) s(-1), corresponding to similar to 64% of the flux of the Crab nebula. Results. HESS J1825-137 is a PWN with clearly energy-dependent morphology at VHE gamma-ray energies. This source is used as a laboratory to investigate particle transport within intermediate-age PWNe. Based on deep observations of this highly spatially extended PWN, we produce a spectral map of the region that provides insights into the spectral variation within the nebula.
Context. Pulsar wind nebulae (PWNe) represent the most prominent population of Galactic very-high-energy gamma-ray sources and are thought to be an efficient source of leptonic cosmic rays. Vela X is a nearby middle-aged PWN, which shows bright X-ray and TeV gamma-ray emission towards an elongated structure called the cocoon. Aims. Since TeV emission is likely inverse-Compton emission of electrons, predominantly from interactions with the cosmic microwave background, while X-ray emission is synchrotron radiation of the same electrons, we aim to derive the properties of the relativistic particles and of magnetic fields with minimal modelling. Methods. We used data from the Suzaku XIS to derive the spectra from three compact regions in Vela X covering distances from 0.3 to 4 pc from the pulsar along the cocoon. We obtained gamma-ray spectra of the same regions from H.E.S.S. observations and fitted a radiative model to the multi-wavelength spectra. Results. The TeV electron spectra and magnetic field strengths are consistent within the uncertainties for the three regions, with energy densities of the order 10(-12) erg cm(-3). The data indicate the presence of a cutoff in the electron spectrum at energies of similar to 100 TeV and a magnetic field strength of similar to 6 mu G. Constraints on the presence of turbulent magnetic fields are weak. Conclusions. The pressure of TeV electrons and magnetic fields in the cocoon is dynamically negligible, requiring the presence of another dominant pressure component to balance the pulsar wind at the termination shock. Sub-TeV electrons cannot completely account for the missing pressure, which may be provided either by relativistic ions or from mixing of the ejecta with the pulsar wind. The electron spectra are consistent with expectations from transport scenarios dominated either by advection via the reverse shock or by diffusion, but for the latter the role of radiative losses near the termination shock needs to be further investigated in the light of the measured cutoff energies. Constraints on turbulent magnetic fields and the shape of the electron cutoff can be improved by spectral measurements in the energy range greater than or similar to 10 keV.
The inner region of the Milky Way halo harbors a large amount of dark matter (DM). Given its proximity, it is one of the most promising targets to look for DM. We report on a search for the annihilations of DM particles using gamma-ray observations towards the inner 300 pc of the Milky Way, with the H.E.S.S. array of ground-based Cherenkov telescopes. The analysis is based on a 2D maximum likelihood method using Galactic Center (GC) data accumulated by H.E.S.S. over the last 10 years (2004-2014), and does not show any significant gamma-ray signal above background. Assuming Einasto and Navarro-Frenk-White DM density profiles at the GC, we derive upper limits on the annihilation cross section <sigma nu >. These constraints are the strongest obtained so far in the TeV DM mass range and improve upon previous limits by a factor 5. For the Einasto profile, the constraints reach <sigma nu > values of 6 x 10(-26) cm(3) s(-1) in the W+W- channel for a DM particle mass of 1.5 TeV, and 2 x 10(-26) cm(3) s(-1) in the tau(+)tau(-) channel for a 1 TeV mass. For the first time, ground-based gamma-ray observations have reached sufficient sensitivity to probe <sigma nu > values expected from the thermal relic density for TeV DM particles.
The Olorgesailie Drilling Project and the related Hominin Sites and Paleolakes Drilling Project in East Africa were initiated to test hypotheses and models linking environmental change to hominin evolution by drilling lake basin sediments adjacent to important archeological and paleoanthropological sites. Drill core OL012-1A recovered 139 m of sedimentary and volcaniclastic strata from the Koora paleolake basin, southern Kenya Rift, providing the opportunity to compare paleoenvironmental influences over the past million years with the parallel record exposed at the nearby Olorgesailie archeological site. To refine our ability to link core-to-outcrop paleoenvironmental records, we institute here a methodological framework for deriving a robust age model for the complex lithostratigraphy of OL012-1A. Firstly, chronostratigraphic control points for the core were established based on 4 Ar/39Ar ages from intercalated tephra deposits and a basal trachyte flow, as well as the stratigraphic position of the Brunhes-Matuyama geomagnetic reversal. This dataset was combined with the position and duration of paleosols, and analyzed using a new Bayesian algorithm for high-resolution age-depth modeling of hiatus-bearing stratigraphic sections. This model addresses three important aspects relevant to highly dynamic, nonlinear depositional environments: 1) correcting for variable rates of deposition, 2) accommodating hiatuses, and 3) quantifying realistic age uncertainty with centimetric resolution. Our method is applicable to typical depositional systems in extensional rifts as well as to drill cores from other dynamic terrestrial or aquatic environments. We use the core age model and lithostratigraphy to examine the inter connectivity of the Koora Basin to adjacent areas and sources of volcanism. (C) 2019 Elsevier Ltd. All rights reserved.
The Great Nebula in Carina provides an exceptional view into the violent massive star formation and feedback that typifies giant H II regions and starburst galaxies. We have mapped the Carina star-forming complex in X-rays, using archival Chandra data and a mosaic of 20 new 60 ks pointings using the Chandra X-ray Observatory's Advanced CCD Imaging Spectrometer, as a testbed for understanding recent and ongoing star formation and to probe Carina's regions of bright diffuse X-ray emission. This study has yielded a catalog of properties of > 14,000 X-ray point sources;> 9800 of them have multiwavelength counterparts. Using Chandra's unsurpassed X-ray spatial resolution, we have separated these point sources from the extensive, spatially-complex diffuse emission that pervades the region; X-ray properties of this diffuse emission suggest that it traces feedback from Carina's massive stars. In this introductory paper, we motivate the survey design, describe the Chandra observations, and present some simple results, providing a foundation for the 15 papers that follow in this special issue and that present detailed catalogs, methods, and science results.
The European river lamprey Lampetra fluviatilis and the European brook lamprey Lampetra planeri (Block 1784) are classified as a paired species, characterized by notably different life histories but morphological similarities. Previous work has further shown limited genetic differentiation between these two species at the mitochondrial DNA level. Here, we expand on this previous work, which focused on lamprey species from the Iberian Peninsula in the south and mainland Europe in the north, by sequencing three mitochondrial marker regions of Lampetra individuals from five river systems in Ireland and five in southern Italy. Our results corroborate the previously identified pattern of genetic diversity for the species pair. We also show significant genetic differentiation between Irish and mainland European lamprey populations, suggesting another ichthyogeographic district distinct from those previously defined. Finally, our results stress the importance of southern Italian L. planeri populations, which maintain several private alleles and notable genetic diversity.
The 2.7-2.9 Ma Ertsberg East Skarn System (EESS) is a world-class Cu-Au skarn that formed within and adjacent to an intrusion within a paleodepth of 0.5 km and > 2.5 km. Its economic mineralisation developed by sustained reaction of magmatic fluid with contact metamorphosed siliciclastic and carbonate rocks at the margin of the adjacent Ertsberg quartz monzodiorite intrusion. Based on high-resolution mineral mapping, chemical analysis and thermodynamic calculations, the multistage formation processes of the exoskarn components of the EESS are examined in the context of changing pressure, temperature, fluid composition and fluid phase. We show that contact metamorphism of dolomitic sediments occurred at 51 +/- 5 MPa, between 700 degrees C and 800 degrees C and in the presence of a H2O-CO2-fluid containing similar to 10 to similar to 70 mol% CO2. This prograde metamorphism formed a forsterite + diopside + calcite + phlogopite + spinel assemblage. Such forsterite-dominated skarns account for similar to 55 vol% of the EESS exoskarns. Rare pargasite (previously unrecognized in this deposit) formed locally in the metamorphosed carbonate sequence where the protolith was composed of supratidal evaporites with dolomitic carbonate and interlayered calc-silicate rocks. The subsequent flux of a lower pressure magmatic gas containing SO2(g) caused sulphate metasomatism. This high temperature gas alteration of the metamorphic assemblage also caused skarn Cu-Fe-sulphide mineralisation. The influx of a SO2 gas through fracture permeability occurred at a temperature between similar to 600 and 700 degrees C and caused calcite to be replaced by anhydrite, with the coupled release of H2S(g). This in-situ release of H2S(g) scavenged trace Cu from the gas phase to deposit Cu-Fe-sulphides, which make the economic value of the distinct. We demonstrate that the formation of metal sulphides within forsterite skarns of the Ertsberg East Skarn System required a minimum flux of similar to 1,050 Mt SO2(g) and show that volcanic degassing may have occurred over a time span of similar to 3,900 years. As the system waned, the ambient fluid resulted in partial retrograde serpentinization of olivine and diopside without carbonation, and at temperatures sufficiently high to preserve anhydrite.