| 1. |
- Aharonian, F., et al.
(författare)
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SIMULTANEOUS OBSERVATIONS OF PKS 2155-304 WITH HESS, FERMI, RXTE, AND ATOM : SPECTRAL ENERGY DISTRIBUTIONS AND VARIABILITY IN A LOW STATE
- 2009
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Ingår i: Astrophysical Journal Letters. - 2041-8205 .- 0004-637X .- 1538-4357. ; 696:2, s. L150-L155
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Tidskriftsartikel (refereegranskat)abstract
- We report on the first simultaneous observations that cover the optical, X-ray, and high-energy gamma-ray bands of the BL Lac object PKS 2155-304. The gamma-ray bands were observed for 11 days, between 2008 August 25 and 2008 September 6 (MJD 54704-54715), jointly with the Fermi Gamma-ray Space Telescope and the HESS atmospheric Cherenkov array, providing the first simultaneous MeV-TeV spectral energy distribution (SED) with the new generation of gamma-ray telescopes. The ATOM telescope and the RXTE and Swift observatories provided optical and X-ray coverage of the low-energy component over the same time period. The object was close to the lowest archival X-ray and very high energy (VHE; > 100 GeV) state, whereas the optical flux was much higher. The light curves show relatively little (similar to 30%) variability overall when compared to past flaring episodes, but we find a clear optical/VHE correlation and evidence for a correlation of the X-rays with the high-energy spectral index. Contrary to previous observations in the flaring state, we do not find any correlation between the X-ray and VHE components. Although synchrotron self-Compton models are often invoked to explain the SEDs of BL Lac objects, the most common versions of these models are at odds with the correlated variability we find in the various bands for PKS 2155-304.
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| 2. |
- De Angelis, A., et al.
(författare)
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Science with e-ASTROGAM A space mission for MeV-GeV gamma-ray astrophysics
- 2018
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Ingår i: Journal of High Energy Astrophysics. - : Elsevier. - 2214-4048 .- 2214-4056. ; 19, s. 1-106
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Tidskriftsartikel (refereegranskat)abstract
- e-ASTROGAM ('enhanced ASTROGAM') is a breakthrough Observatory space mission, with a detector composed by a Silicon tracker, a calorimeter, and an anticoincidence system, dedicated to the study of the non-thermal Universe in the photon energy range from 0.3 MeV to 3 GeV - the lower energy limit can be pushed to energies as low as 150 keV for the tracker, and to 30 keV for calorimetric detection. The mission is based on an advanced space-proven detector technology, with unprecedented sensitivity, angular and energy resolution, combined with polarimetric capability. Thanks to its performance in the MeV-GeV domain, substantially improving its predecessors, e-ASTROGAM will open a new window on the non-thermal Universe, making pioneering observations of the most powerful Galactic and extragalactic sources, elucidating the nature of their relativistic outflows and their effects on the surroundings. With a line sensitivity in the MeV energy range one to two orders of magnitude better than previous generation instruments, e-ASTROGAM will determine the origin of key isotopes fundamental for the understanding of supernova explosion and the chemical evolution of our Galaxy. The mission will provide unique data of significant interest to a broad astronomical community, complementary to powerful observatories such as LIGO-Virgo-GEO600-KAGRA, SKA, ALMA, E-ELT, TMT, LSST, JWST, Athena, CTA, IceCube, KM3NeT, and LISA.
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| 3. |
- Pelssers, Bart Eduard Jan, 1991-
(författare)
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Enhancing Direct Searches for Dark Matter : Spatial-Temporal Modeling and Explicit Likelihoods
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Astronomical and cosmological observations on different scales point to the existence of dark matter. In the current cosmological paradigm this dark matter accounts for about 26% of the energy-density of the universe, yet has not been directly observed. Weakly Interacting Massive Particles (WIMPs) and axions are two candidates among the many theories and particles proposed to explain dark matter. Direct detection experiments aim to detect the scattering or coupling of dark matter to the detector medium. The event rate in such experiments is expected to exhibit an annual modulation due to the motion of the Earth through the Galactic dark matter halo. The XENON collaboration built several experiments that have searched for WIMP dark matter by looking for WIMPs scattering on xenon nuclei. The heart of these detectors consists of a Time Projection Chamber (TPC) which records the scintillation light (S1) and ionization charge (S2) signal following a recoiling xenon nucleus as well as its position and time. Using these ultra-low background detectors, the XENON collaboration has set world-leading exclusion limits on the WIMP-nucleon scattering cross-section. In this thesis several different ways of enhancing direct detection experiments are presented, involving time dependent signal models, event reconstruction and a method enhancing statistical inference. First, during a search for event rate modulation, spanning almost 4 years of XENON100 data, no oscillation was found to be compatible with the expected signature. This thesis presents a verification of the correctness of the test statistic distribution used in this analysis using dedicated simulations. Second, the positions of interactions in XENON detectors are used for detector volume fiducialization as well as for modeling the position dependent detector response. This thesis presents the position reconstruction methods used during the first XENON1T science analysis. Third, a new algorithm for position and energy reconstruction using the likelihood-free paradigm is presented. This simulator-based method increases the accuracy of the previous method by up to 15% and can simultaneously infer the transverse position and size of the charge signal. Fourth, to enhance the physics reach of future dark matter searches using xenon TPCs, a new method for computing differential rates is developed. This method replaces the calculation usually performed by Monte-Carlo simulations with an equivalent analytic expression. This enables the use of higher dimensional explicit (profile) likelihood functions, resulting in better signal-background discrimination. The new method uses time dependent signal models (encoding annual modulation) as well as spatially non-uniform sources such as a radiogenic neutron background and fully accounts for the non-uniform detector response. This method can significantly reduce the exposure needed for a potential dark matter discovery in future detectors such as XENONnT. Lastly, the amplitude of the axion dark matter field is expected to exhibit stochastic behavior. Experiments whose measurements are shorter than the coherence time of the field need to include this effect in their data analysis and inference. This thesis presents an analysis of a simulated axion signal in a CASPEr-ZULF-like detector, showing that exclusion limits on the axion amplitude are too strong by a factor ~4 when not including the axion amplitude fluctuation.
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| 4. |
- Aalbers, J., et al.
(författare)
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A next-generation liquid xenon observatory for dark matter and neutrino physics
- 2023
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Ingår i: Journal of Physics G: Nuclear and Particle Physics. - : IOP Publishing. - 0954-3899 .- 1361-6471. ; 50:1
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Forskningsöversikt (refereegranskat)abstract
- The nature of dark matter and properties of neutrinos are among the most pressing issues in contemporary particle physics. The dual-phase xenon time-projection chamber is the leading technology to cover the available parameter space for weakly interacting massive particles, while featuring extensive sensitivity to many alternative dark matter candidates. These detectors can also study neutrinos through neutrinoless double-beta decay and through a variety of astrophysical sources. A next-generation xenon-based detector will therefore be a true multi-purpose observatory to significantly advance particle physics, nuclear physics, astrophysics, solar physics, and cosmology. This review article presents the science cases for such a detector.
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| 5. |
- Aalbers, J., et al.
(författare)
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DARWIN : towards the ultimate dark matter detector
- 2016
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Ingår i: Journal of Cosmology and Astroparticle Physics. - : IOP Publishing. - 1475-7516. ; :11
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Tidskriftsartikel (refereegranskat)abstract
- DARk matter WImp search with liquid xenoN (DARWIN(2)) will be an experiment for the direct detection of dark matter using a multi-ton liquid xenon time projection chamber at its core. Its primary goal will be to explore the experimentally accessible parameter space for Weakly Interacting Massive Particles (WIMPs) in a wide mass-range, until neutrino interactions with the target become an irreducible background. The prompt scintillation light and the charge signals induced by particle interactions in the xenon will be observed by VUV sensitive, ultra-low background photosensors. Besides its excellent sensitivity to WIMPs above a mass of 5 GeV/c(2), such a detector with its large mass, low-energy threshold and ultra-low background level will also be sensitive to other rare interactions. It will search for solar axions,galactic axion-like particles and the neutrinoless double-beta decay of Xe-136, as well as measure the low-energy solar neutrino flux with <1% precision, observe coherent neutrino-nucleus interactions, and detect galactic supernovae. We present the concept of the DARWIN detector and discuss its physics reach, the main sources of backgrounds and the ongoing detector design and R&D efforts.
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| 6. |
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| 7. |
- Aalbers, Jelle, et al.
(författare)
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Finding dark matter faster with explicit profile likelihoods
- 2020
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Ingår i: Physical Review D. - 2470-0010 .- 2470-0029. ; 102:7
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Tidskriftsartikel (refereegranskat)abstract
- Liquid xenon time-projection chambers are the world's most sensitive detectors for a wide range of dark matter candidates. We show that the statistical analysis of their data can be improved by replacing detector response Monte Carlo simulations with an equivalent deterministic calculation. This allows the use of high-dimensional undiscretized models, yielding up to similar to 2 times better discrimination of the dominant backgrounds. In turn, this could significantly extend the physics reach of upcoming experiments such as XENONnT and LZ, and bring forward a potential 5 sigma dark matter discovery by over a year.
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| 8. |
- Aalbers, Jelle, et al.
(författare)
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Solar neutrino detection sensitivity in DARWIN via electron scattering
- 2020
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 80:12
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Tidskriftsartikel (refereegranskat)abstract
- We detail the sensitivity of the proposed liquid xenon DARWIN observatory to solar neutrinos via elastic electron scattering. We find that DARWIN will have the potential to measure the fluxes of five solar neutrino components: pp, 7Be, 13N, 15O and pep. The precision of the 13N, 15O and pep components is hindered by the double-beta decay of 136Xe and, thus, would benefit from a depleted target. A high-statistics observation of pp neutrinos would allow us to infer the values of the electroweak mixing angle, sin2 theta w, and the electron-type neutrino survival probability, Pee, in the electron recoil energy region from a few keV up to 200 keV for the first time, with relative precision of 5% and 4%, respectively, with 10 live years of data and a 30 tonne fiducial volume. An observation of pp and 7Be neutrinos would constrain the neutrino-inferred solar luminosity down to 0.2%. A combination of all flux measurements would distinguish between the high- (GS98) and low-metallicity (AGS09) solar models with 2.1-2.5 sigma significance, independent of external measurements from other experiments or a measurement of 8B neutrinos through coherent elastic neutrino-nucleus scattering in DARWIN. Finally, we demonstrate that with a depleted target DARWIN may be sensitive to the neutrino capture process of 131Xe.
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| 9. |
- Aalbers, Jelle, et al.
(författare)
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The triggerless data acquisition system of the XENONnT experiment
- 2023
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Ingår i: Journal of Instrumentation. - 1748-0221. ; 18:7
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Tidskriftsartikel (refereegranskat)abstract
- The XENONnT detector uses the latest and largest liquid xenon-based time projection chamber (TPC) operated by the XENON Collaboration, aimed at detecting Weakly Interacting Massive Particles and conducting other rare event searches. The XENONnT data acquisition (DAQ) system constitutes an upgraded and expanded version of the XENON1T DAQ system. For its operation, it relies predominantly on commercially available hardware accompanied by open-source and custom-developed software. The three constituent subsystems of the XENONnT detector, the TPC (main detector), muon veto, and the newly introduced neutron veto, are integrated into a single DAQ, and can be operated both independently and as a unified system. In total, the DAQ digitizes the signals of 698 photomultiplier tubes (PMTs), of which 253 from the top PMT array of the TPC are digitized twice, at ×10 and ×0.5 gain. The DAQ for the most part is a triggerless system, reading out and storing every signal that exceeds the digitization thresholds. Custom-developed software is used to process the acquired data, making it available within ∼30 s for live data quality monitoring and online analyses. The entire system with all the three subsystems was successfully commissioned and has been operating continuously, comfortably withstanding readout rates that exceed ∼500 MB/s during calibration. Livetime during normal operation exceeds 99% and is ∼90% during most high-rate calibrations. The combined DAQ system has collected more than 2 PB of both calibration and science data during the commissioning of XENONnT and the first science run.
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| 10. |
- Abdalla, H., et al.
(författare)
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A search for new supernova remnant shells in the Galactic plane with HESS
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 612
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Tidskriftsartikel (refereegranskat)abstract
- A search for new supernova remnants (SNRs) has been conducted using TeV gamma-ray data from the H.E.S.S. Galactic plane survey. As an identification criterion, shell morphologies that are characteristic for known resolved TeV SNRs have been used. Three new SNR candidates were identified in the H.E.S.S. data set with this method. Extensive multiwavelength searches for counterparts were conducted. A radio SNR candidate has been identified to be a counterpart to HESS J1534-571. The TeV source is therefore classified as a SNR. For the other two sources, HESS J1614-518 and HESS J1912 + 101, no identifying counterparts have been found, thus they remain SNR candidates for the time being. TeV-emitting SNRs are key objects in the context of identifying the accelerators of Galactic cosmic rays. The TeV emission of the relativistic particles in the new sources is examined in view of possible leptonic and hadronic emission scenarios, taking the current multiwavelength knowledge into account.
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