1,029 research outputs found

    Isotopic and hydrogeochemical characterization of high-altitude karst aquifers in complex geological settings. The Ordesa and Monte Perdido National Park (Northern Spain) case study.

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    The Ordesa and Monte Perdido National Park, located in the Southern Pyrenees, constitutes the highest karst system in Western Europe. No previous studies regarding its geochemical and isotopic groundwater characterization are available in this area. This work presents the results of field and sampling campaigns carried out between July 2007 and September 2013. The groundwater presents high calcium bicarbonate contents due to the occurrence of upper Cretaceous and lower Paleocene-Eocene carbonate materials in the studied area. Other relevant processes include dissolution of anhydrite and/or gypsum and incongruent dissolution of Mg-limestone and dolomite. The water stable isotopes (δ18O, δ2H) showthat the oceanic fronts from the Atlantic Ocean are responsible for the high levels of precipitation. In autumn, winter, and spring, a deuterium excess is found in the rechargewater,which could be related to local atmospheric transport of low-altitude snow sublimation vapour and its later condensation on the snowsurface at higher altitude,where recharge ismostly produced. The recharge zones are mainly between 2500mand 3200ma.s.l. The tritiumcontent of the water suggests short groundwater transit times. The isotopic composition of dissolved sulphate points to the existence of regional fluxes mixed with local discharge in some of the springs. This work highlights the major role played by the altitude difference between the recharge and discharge zones in controlling the chemistry and the vertical variability of the isotopic composition in high-altitude karst aquifers

    The heritability and patterns of DNA methylation in normal human colorectum

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    DNA methylation (DNAm) has been linked to changes in chromatin structure, gene expression and disease. The DNAm level can be affected by genetic variation; although, how this differs by CpG dinucleotide density and genic location of the DNAm site is not well understood. Moreover, the effect of disease causing variants on the DNAm level in a tissue relevant to disease has yet to be fully elucidated. To this end, we investigated the phenotypic profiles, genetic effects and regional genomic heritability for 196080 DNAm sites in healthy colorectum tissue from 132 unrelated Colombian individuals. DNAm sites in regions of low-CpG density were more variable, on average more methylated and were more likely to be significantly heritable when compared with DNAm sites in regions of high-CpG density. DNAm sites located in intergenic regions had a higher mean DNAm level and were more likely to be heritable when compared with DNAm sites in the transcription start site (TSS) of a gene expressed in colon tissue. Within CpG-dense regions, the propensity of the DNAm level to be heritable was lower in the TSS of genes expressed in colon tissue than in the TSS of genes not expressed in colon tissue. In addition, regional genetic variation was associated with variation in local DNAm level no more frequently for DNAm sites within colorectal cancer risk regions than it was for DNAm sites outside such regions. Overall, DNAm sites located in different genomic contexts exhibited distinguishable profiles and may have a different biological function

    Measurement of the Crab Nebula Spectrum Past 100 TeV with HAWC

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    We present TeV gamma-ray observations of the Crab Nebula, the standard reference source in ground-based gamma-ray astronomy, using data from the High Altitude Water Cherenkov (HAWC) Gamma-Ray Observatory. In this analysis we use two independent energy-estimation methods that utilize extensive air shower variables such as the core position, shower angle, and shower lateral energy distribution. In contrast, the previously published HAWC energy spectrum roughly estimated the shower energy with only the number of photomultipliers triggered. This new methodology yields a much improved energy resolution over the previous analysis and extends HAWC's ability to accurately measure gamma-ray energies well beyond 100 TeV. The energy spectrum of the Crab Nebula is well fit to a log parabola shape (dNdE=ϕ0(E/7 TeV)αβln(E/7 TeV))\left(\frac{dN}{dE} = \phi_0 \left(E/\textrm{7 TeV}\right)^{-\alpha-\beta\ln\left(E/\textrm{7 TeV}\right)}\right) with emission up to at least 100 TeV. For the first estimator, a ground parameter that utilizes fits to the lateral distribution function to measure the charge density 40 meters from the shower axis, the best-fit values are ϕo\phi_o=(2.35±\pm0.040.21+0.20^{+0.20}_{-0.21})×\times1013^{-13} (TeV cm2^2 s)1^{-1}, α\alpha=2.79±\pm0.020.03+0.01^{+0.01}_{-0.03}, and β\beta=0.10±\pm0.010.03+0.01^{+0.01}_{-0.03}. For the second estimator, a neural network which uses the charge distribution in annuli around the core and other variables, these values are ϕo\phi_o=(2.31±\pm0.020.17+0.32^{+0.32}_{-0.17})×\times1013^{-13} (TeV cm2^2 s)1^{-1}, α\alpha=2.73±\pm0.020.02+0.03^{+0.03}_{-0.02}, and β\beta=0.06±\pm0.01±\pm0.02. The first set of uncertainties are statistical; the second set are systematic. Both methods yield compatible results. These measurements are the highest-energy observation of a gamma-ray source to date.Comment: published in Ap

    Search for Decaying Dark Matter in the Virgo Cluster of Galaxies with HAWC

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    The decay or annihilation of dark matter particles may produce a steady flux of very-high-energy gamma rays detectable above the diffuse background. Nearby clusters of galaxies provide excellent targets to search for the signatures of particle dark matter interactions. In particular, the Virgo cluster spans several degrees across the sky and can be efficiently probed with a wide field-of-view instrument. The High Altitude Water Cherenkov (HAWC) observatory, due to its wide field of view and sensitivity to gamma rays at an energy scale of 300 GeV--100 TeV is well-suited for this search. Using 2141 days of data, we search for gamma-ray emission from the Virgo cluster, assuming well-motivated dark matter sub-structure models. Our results provide some of the strongest constraints on the decay lifetime of dark matter for masses above 10 TeV.Comment: 7 pages, 3 figures. Submitted to PR

    Validation of standardized data formats and tools for ground-level particle-based gamma-ray observatories

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    Ground-based gamma-ray astronomy is still a rather young field of research,with strong historical connections to particle physics. This is why mostobservations are conducted by experiments with proprietary data and analysissoftware, as it is usual in the particle physics field. However in recentyears, this paradigm has been slowly shifting towards the development and useof open-source data formats and tools, driven by upcoming observatories such asthe Cherenkov Telescope Array (CTA). In this context, a community-driven,shared data format (the gamma-astro-data-format or GADF) and analysis toolssuch as Gammapy and ctools have been developed. So far these efforts have beenled by the IACT community, leaving out other types of ground-based gamma-rayinstruments.We aim to show that the data from ground particle arrays, such asthe High-Altitude Water Cherenkov (HAWC) observatory, is also compatible withthe GADF and can thus be fully analysed using the related tools, in this caseGammapy. We reproduce several published HAWC results using Gammapy and dataproducts compliant with GADF standard. We also illustrate the capabilities ofthe shared format and tools by producing a joint fit of the Crab spectrumincluding data from six different gamma-ray experiments. We find excellentagreement with the reference results, a powerful check of both the publishedresults and the tools involved. The data from particle detector arrays such asthe HAWC observatory can be adapted to the GADF and thus analysed with Gammapy.A common data format and shared analysis tools allow multi-instrument jointanalysis and effective data sharing. Given the complementary nature of pointingand wide-field instruments, this synergy will be distinctly beneficial for thejoint scientific exploitation of future observatories such as the SouthernWide-field Gamma-ray Observatory and CTA.<br

    Gamma-ray Emission from Classical Nova V392 Per: Measurements from Fermi and HAWC

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    This paper reports on the γ\gamma-ray properties of the 2018 Galactic novaV392 Per, spanning photon energies \sim0.1 GeV to 100 TeV by combiningobservations from the Fermi Gamma-ray Space Telescope and the HAWC Observatory.In one of the most rapidly evolving γ\gamma-ray signals yet observed for anova, GeV γ\gamma rays with a power law spectrum with index Γ=2.0±0.1\Gamma = 2.0 \pm0.1 were detected over eight days following V392 Per's optical maximum. HAWCobservations constrain the TeV γ\gamma-ray signal during this time and alsobefore and after. We observe no statistically significant evidence of TeVγ\gamma-ray emission from V392 Per, but present flux limits. Tests of theextension of the Fermi/LAT spectrum to energies above 5 TeV are disfavored by 2standard deviations (95\%) or more. We fit V392 Per's GeV γ\gamma rays withhadronic acceleration models, incorporating optical observations, and comparethe calculations with HAWC limits.<br

    HAWC Study of Very-High-Energy γ\gamma-ray Spectrum of HAWC J1844-034

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    Recently, the region surrounding eHWC J1842-035 has been studied extensively by gamma-ray observatories due to its extended emission reaching up to a few hundred TeV and potential as a hadronic accelerator. In this work, we use 1,910 days of cumulative data from the High Altitude Water Cherenkov (HAWC) observatory to carry out a dedicated systematic source search of the eHWC J1842-035 region. During the search we have found three sources in the region, namely, HAWC J1844-034, HAWC J1843-032, and HAWC J1846-025. We have identified HAWC J1844-034 as the extended source that emits photons with energies up to 175 TeV. We compute the spectrum for HAWC J1844-034 and by comparing with the observational results from other experiments, we have identified HESS J1843-033, LHAASO J1843-0338, and TASG J1844-038 as very-high-energy gamma-ray sources with a matching origin. Also, we present and use the multi-wavelength data to fit the hadronic and leptonic particle spectra. We have identified four pulsar candidates in the nearby region from which PSR J1844-0346 is found to be the most likely candidate due to its proximity to HAWC J1844-034 and the computed energy budget. We have also found SNR G28.6-0.1 as a potential counterpart source of HAWC J1844-034 for which both leptonic and hadronic scenarios are feasible.Comment: 13 pages, 9 figures, published in Ap

    Constraints on the very high energy gamma-ray emission from short GRBs with HAWC

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    Many gamma-ray bursts (GRBs) have been observed from radio wavelengths, and afew at very-high energies (VHEs, > 100GeV). The HAWC gamma-ray observatory iswell suited to study transient phenomena at VHEs due to its large field of viewand duty cycle. These features allow for searches of VHE emission and can probedifferent model assumptions of duration and spectra. In this paper, we use datacollected by HAWC between December 2014 and May 2020 to search for emission inthe energy range from 80 to 800 GeV coming from a sample 47 short GRBs thattriggered the Fermi, Swift and Konus satellites during this period. Thisanalysis is optimized to search for delayed and extended VHE emission withinthe first 20 s of each burst. We find no evidence of VHE emission, eithersimultaneous or delayed, with respect to the prompt emission. Upper limits (90%confidence level) derived on the GRB fluence are used to constrain thesynchrotron self-Compton forward-shock model. Constraints for the interstellardensity as low as 10210^{-2} cm3^{-3} are obtained when assuming z=0.3 forbursts with the highest keV-fluences such as GRB 170206A and GRB 181222841.Such a low density makes observing VHE emission mainly from the fast coolingregime challenging.<br
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