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- Thomas, HS, et al.
(author)
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- 2019
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swepub:Mat__t
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- Aharonian, F., et al.
(author)
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Constraining the cosmic-ray pressure in the inner Virgo Cluster using HESS observations of M 87
- 2023
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 675
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Journal article (peer-reviewed)abstract
- The origin of the gamma-ray emission from M 87 is currently a matter of debate. This work aims to localize the very high-energy (VHE; 100 GeV - 100 TeV) gamma-ray emission from M 87 and probe a potential extended hadronic emission component in the inner Virgo Cluster. The search for a steady and extended gamma-ray signal around M 87 can constrain the cosmic-ray energy density and the pressure exerted by the cosmic rays onto the intracluster medium and allow us to investigate the role of cosmic rays in the active galactic nucleus feedback as a heating mechanism in the Virgo Cluster. The High Energy Stereoscopic System (H.E.S.S.) telescopes are sensitive to VHE gamma rays and have been used to observe M 87 since 2004. We utilized a Bayesian block analysis to identify M 87 emission states with H.E.S.S. observations from 2004 to 2021, dividing them into low, intermediate, and high states. Because of the causality argument, an extended (≳1 kpc) signal is allowed only in steady emission states. Hence, we fitted the morphology of the 120 h low-state data and find no significant gamma-ray extension. Therefore, we derive for the low state an upper limit of 58″(corresponding to ≈4.6 kpc) in the extension of a single-component morphological model described by a rotationally symmetric 2D Gaussian model at the 99.7% confidence level. Our results exclude the radio lobes (≈30 kpc) as the principal component of the VHE gamma-ray emission from the low state of M 87. The gamma-ray emission is compatible with a single emission region at the radio core of M 87. These results, with the help of two multiple-component models, constrain the maximum cosmic-ray to thermal pressure ratio to XCR, max. ≲ 0.32 and the total energy in cosmic-ray protons to UCR ≲ 5 × 1058 erg in the inner 20 kpc of the Virgo Cluster for an assumed cosmic-ray proton power-law distribution in momentum with spectral index αp = 2.1
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- Aharonian, F., et al.
(author)
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Discovery of a radiation component from the Vela pulsar reaching 20 teraelectronvolts
- 2023
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In: Nature Astronomy. - : Nature Publishing Group. - 2397-3366. ; 7:11, s. 1341-1350
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Journal article (peer-reviewed)abstract
- Gamma-ray observations have established energetic isolated pulsars as outstanding particle accelerators and antimatter factories. However, many questions are still open regarding the acceleration and radiation processes involved, as well as the locations where they occur. The radiation spectra of all gamma-ray pulsars observed to date show strong cutoffs or a break above energies of a few gigaelectronvolts. Using the High Energy Stereoscopic System's Cherenkov telescopes, we discovered a radiation component from the Vela pulsar which emerges beyond this generic cutoff and extends up to energies of at least 20 teraelectronvolts. This is an order of magnitude larger than in the case of the Crab pulsar, the only other pulsar detected in the teraelectronvolt energy range. Our results challenge the state-of-the-art models for the high-energy emission of pulsars. Furthermore, they pave the way for investigating other pulsars through their multiteraelectronvolt emission, thereby imposing additional constraints on the acceleration and emission processes in their extreme energy limit. The H.E.S.S. gamma-ray observatory has observed gamma rays with energies of at least 20 TeV from a pulsar, an energy regime that is hard to reconcile with the existing theories of gamma-ray production for such objects.
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- Aharonian, F., et al.
(author)
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Search for the evaporation of primordial black holes with HESS
- 2023
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In: Journal of Cosmology and Astroparticle Physics. - : Institute of Physics Publishing (IOPP). - 1475-7516. ; :4
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Journal article (peer-reviewed)abstract
- Primordial Black Holes (PBHs) are hypothetical black holes predicted to have been formed from density fluctuations in the early Universe. PBHs with an initial mass around 1014-1015 g are expected to end their evaporation at present times in a burst of particles and very-high-energy (VHE) gamma rays. Those gamma rays may be detectable by the High Energy Stereoscopic System (H.E.S.S.), an array of imaging atmospheric Cherenkov telescopes. This paper reports on the search for evaporation bursts of VHE gamma rays with H.E.S.S., ranging from 10 to 120 seconds, as expected from the final stage of PBH evaporation and using a total of 4816 hours of observations. The most constraining upper limit on the burst rate of local PBHs is 2000 pc-3 yr-1 for a burst interval of 120 seconds, at the 95% confidence level. The implication of these measurements for PBH dark matter are also discussed.
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6. |
- Aharonian, F., et al.
(author)
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HESS J1809-193 : A halo of escaped electrons around a pulsar wind nebula?
- 2023
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 672
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Journal article (peer-reviewed)abstract
- Context. HESS J1809-193 is an unassociated very-high-energy gamma-ray source located on the Galactic plane. While it has been connected to the nebula of the energetic pulsar PSR J1809-1917, supernova remnants and molecular clouds present in the vicinity also constitute possible associations. Recently, the detection of gamma-ray emission up to energies of similar to 100 TeV with the HAWC observatory has led to renewed interest in HESS J1809-193.Aims. We aim to understand the origin of the gamma-ray emission of HESS J1809-193.Methods. We analysed 93.2 h of data taken on HESS J1809-193 above 0.27 TeV with the High Energy Stereoscopic System (H.E.S.S.), using a multi-component, three-dimensional likelihood analysis. In addition, we provide a new analysis of 12.5 yr of Fermi-LAT data above 1 GeV within the region of HESS J1809-193. The obtained results are interpreted in a time-dependent modelling framework.Results. For the first time, we were able to resolve the emission detected with H.E.S.S. into two components: an extended component (modelled as an elongated Gaussian with a 1-sigma semi-major and semi-minor axis of similar to 0.62 degrees and similar to 0.35 degrees, respectively) that exhibits a spectral cutoff at similar to 13 TeV, and a compact component (modelled as a symmetric Gaussian with a 1-sigma radius of similar to 0.1 degrees) that is located close to PSR J1809-1917 and shows no clear spectral cutoff. The Fermi-LAT analysis also revealed extended gamma-ray emission, on scales similar to that of the extended H.E.S.S. component.Conclusions. Our modelling indicates that based on its spectrum and spatial extent, the extended H.E.S.S. component is likely caused by inverse Compton emission from old electrons that form a halo around the pulsar wind nebula. The compact component could be connected to either the pulsar wind nebula or the supernova remnant and molecular clouds. Due to its comparatively steep spectrum, modelling the Fermi-LAT emission together with the H.E.S.S. components is not straightforward.
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- Aharonian, F., et al.
(author)
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Unveiling extended gamma-ray emission around HESS J1813-178
- 2024
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 686
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Journal article (peer-reviewed)abstract
- Context. HESS J1813-178 is a very-high-energy gamma-ray source spatially coincident with the young and energetic pulsar PSR J1813-1749 and thought to be associated with its pulsar wind nebula (PWN). Recently, evidence for extended high-energy emission in the vicinity of the pulsar has been revealed in the Fermi Large Area Telescope (LAT) data. This motivates revisiting the HESS J1813-178 region, taking advantage of improved analysis methods and an extended dataset. Aims. Using data taken by the High Energy Stereoscopic System (H.E.S.S.) experiment and the Fermi-LAT, we aim to describe the gamma-ray emission in the region with a consistent model, to provide insights into its origin. Methods. We performed a likelihood-based analysis on 32 hours of H.E.S.S. data and 12 yr of Fermi-LAT data and we fitted a spectromorphological model to the combined datasets. These results allowed us to develop a physical model for the origin of the observed.-ray emission in the region. Results. In addition to the compact very-high-energy gamma-ray emission centred on the pulsar, we find a significant yet previously undetected component along the Galactic plane. With Fermi-LAT data, we confirm extended high-energy emission consistent with the position and elongation of the extended emission observed with H.E.S.S. These results establish a consistent description of the emission in the region from GeV energies to several tens of TeV. Conclusions. This study suggests that HESS J1813-178 is associated with a gamma-ray PWN powered by PSR J1813-1749. A possible origin of the extended emission component is inverse Compton emission from electrons and positrons that have escaped the confines of the pulsar and form a halo around the PWN.
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9. |
- Aharonian, F., et al.
(author)
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Detection of extended gamma-ray emission around the Geminga pulsar with HESS
- 2023
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In: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 673
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Journal article (peer-reviewed)abstract
- Geminga is an enigmatic radio-quiet gamma-ray pulsar located at a mere 250 pc distance from Earth. Extended very-high-energy gamma-ray emission around the pulsar was discovered by Milagro and later confirmed by HAWC, which are both water Cherenkov detector-based experiments. However, evidence for the Geminga pulsar wind nebula in gamma rays has long evaded detection by imaging atmospheric Cherenkov telescopes (IACTs) despite targeted observations. The detection of gamma-ray emission on angular scales greater than or similar to 2 degrees poses a considerable challenge for the background estimation in IACT data analysis. With recent developments in understanding the complementary background estimation techniques of water Cherenkov and atmospheric Cherenkov instruments, the H.E.S.S. IACT array can now confirm the detection of highly extended gamma-ray emission around the Geminga pulsar with a radius of at least 3 degrees in the energy range 0.5-40 TeV. We find no indications for statistically significant asymmetries or energy-dependent morphology. A flux normalisation of (2.8 +/- 0.7) x 10-12 cm-2 s-1 TeV-1 at 1 TeV is obtained within a 1 degrees radius region around the pulsar. To investigate the particle transport within the halo of energetic leptons around the pulsar, we fitted an electron diffusion model to the data. The normalisation of the diffusion coefficient obtained of D-0 = 7.6-1.2+1.5 x 1027 cm2 s-1, at an electron energy of 100 TeV, is compatible with values previously reported for the pulsar halo around Geminga, which is considerably below the Galactic average.
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10. |
- Gurholt, Tiril P., et al.
(author)
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Intracranial and subcortical volumes in adolescents with early‐onset psychosis : A multisite mega‐analysis from the ENIGMA consortium
- 2020
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In: Human Brain Mapping. - Stockholm : Wiley. - 1065-9471 .- 1097-0193. ; 43:1, s. 373-384
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Journal article (peer-reviewed)abstract
- Early-onset psychosis disorders are serious mental disorders arising before the age of 18 years. Here, we investigate the largest neuroimaging dataset, to date, of patients with early-onset psychosis and healthy controls for differences in intracranial and subcortical brain volumes. The sample included 263 patients with early-onset psychosis (mean age: 16.4 ± 1.4 years, mean illness duration: 1.5 ± 1.4 years, 39.2% female) and 359 healthy controls (mean age: 15.9 ± 1.7 years, 45.4% female) with magnetic resonance imaging data, pooled from 11 clinical cohorts. Patients were diagnosed with early-onset schizophrenia (n = 183), affective psychosis (n = 39), or other psychotic disorders (n = 41). We used linear mixed-effects models to investigate differences in intracranial and subcortical volumes across the patient sample, diagnostic subgroup and antipsychotic medication, relative to controls. We observed significantly lower intracranial (Cohen's d = −0.39) and hippocampal (d = −0.25) volumes, and higher caudate (d = 0.25) and pallidum (d = 0.24) volumes in patients relative to controls. Intracranial volume was lower in both early-onset schizophrenia (d = −0.34) and affective psychosis (d = −0.42), and early-onset schizophrenia showed lower hippocampal (d = −0.24) and higher pallidum (d = 0.29) volumes. Patients who were currently treated with antipsychotic medication (n = 193) had significantly lower intracranial volume (d = −0.42). The findings demonstrate a similar pattern of brain alterations in early-onset psychosis as previously reported in adult psychosis, but with notably low intracranial volume. The low intracranial volume suggests disrupted neurodevelopment in adolescent early-onset psychosis.
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11. |
- Hinrichsen, F., et al.
(author)
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Microbial regulation of hexokinase 2 links mitochondrial metabolism and cell death in colitis
- 2021
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In: Cell Metabolism. - : Elsevier BV. - 1550-4131. ; 33:12
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Journal article (peer-reviewed)abstract
- Hexokinases (HK) catalyze the first step of glycolysis limiting its pace. HK2 is highly expressed in gut epithelium, contributes to immune responses, and is upregulated during inflammation. We examined the microbial regulation of HK2 and its impact on inflammation using mice lacking HK2 in intestinal epithelial cells (Hk2(Delta IEC)). Hk2(Delta IEC) mice were less susceptible to acute colitis. Analyzing the epithelial transcriptome from Hk2(Delta IEC) mice during colitis and using HK2-deficient intestinal organoids and Caco-2 cells revealed reduced mitochondrial respiration and epithelial cell death in the absence of HK2. The microbiota strongly regulated HK2 expression and activity. The microbially derived short-chain fatty acid (SCFA) butyrate repressed HK2 expression via histone deacetylase 8 (HDAC8) and reduced mitochondrial respiration in wild-type but not in HK2-deficient Caco-2 cells. Butyrate supplementation protected wild-type but not Hk2(Delta IEC) mice from colitis. Our findings define a mechanism how butyrate promotes intestinal homeostasis and suggest targeted HK2-inhibition as therapeutic avenue for inflammation.
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