42 research outputs found
A deep spectromorphological study of the -ray emission surrounding the young massive stellar cluster Westerlund 1
Young massive stellar clusters are extreme environments and potentially
provide the means for efficient particle acceleration. Indeed, they are
increasingly considered as being responsible for a significant fraction of
cosmic rays (CRs) accelerated within the Milky Way. Westerlund 1, the most
massive known young stellar cluster in our Galaxy is a prime candidate for
studying this hypothesis. While the very-high-energy -ray source HESS
J1646-458 has been detected in the vicinity of Westerlund 1 in the past, its
association could not be firmly identified. We aim to identify the physical
processes responsible for the -ray emission around Westerlund 1 and
thus to better understand the role of massive stellar clusters in the
acceleration of Galactic CRs. Using 164 hours of data recorded with the High
Energy Stereoscopic System (H.E.S.S.), we carried out a deep
spectromorphological study of the -ray emission of HESS J1646-458. We
furthermore employed H I and CO observations of the region to infer the
presence of gas that could serve as target material for interactions of
accelerated CRs. We detected large-scale ( diameter) -ray
emission with a complex morphology, exhibiting a shell-like structure and
showing no significant variation with -ray energy. The combined energy
spectrum of the emission extends to several tens of TeV, and is uniform across
the entire source region. We did not find a clear correlation of the
-ray emission with gas clouds as identified through H I and CO
observations. We conclude that, of the known objects within the region, only
Westerlund 1 can explain the bulk of the -ray emission. Several CR
acceleration sites and mechanisms are conceivable, and discussed in detail.
(abridged)Comment: 15 pages, 9 figures. Corresponding authors: L. Mohrmann, S. Ohm, R.
Rauth, A. Specoviu
Search for dark matter annihilation signals in the H.E.S.S. Inner Galaxy Survey
The central region of the Milky Way is one of the foremost locations to look for dark matter (DM) signatures. We report the first results on a search for DM particle annihilation signals using new observations from an unprecedented gamma-ray survey of the Galactic Center (GC) region, , the Inner Galaxy Survey, at very high energies ( 100 GeV) performed with the H.E.S.S. array of five ground-based Cherenkov telescopes. No significant gamma-ray excess is found in the search region of the 2014-2020 dataset and a profile likelihood ratio analysis is carried out to set exclusion limits on the annihilation cross section . Assuming Einasto and Navarro-Frenk-White (NFW) DM density profiles at the GC, these constraints are the strongest obtained so far in the TeV DM mass range. For the Einasto profile, the constraints reach values of for 1.5 TeV DM mass in the annihilation channel, and for 0.7 TeV DM mass in the annihilation channel. With the H.E.S.S. Inner Galaxy Survey, ground-based -ray observations thus probe values expected from thermal-relic annihilating TeV DM particles
Search for dark matter annihilation signals in the H.E.S.S. Inner Galaxy Survey
The central region of the Milky Way is one of the foremost locations to look for dark matter (DM) signatures. We report the first results on a search for DM particle annihilation signals using new observations from an unprecedented gamma-ray survey of the Galactic Center (GC) region, , the Inner Galaxy Survey, at very high energies ( 100 GeV) performed with the H.E.S.S. array of five ground-based Cherenkov telescopes. No significant gamma-ray excess is found in the search region of the 2014-2020 dataset and a profile likelihood ratio analysis is carried out to set exclusion limits on the annihilation cross section . Assuming Einasto and Navarro-Frenk-White (NFW) DM density profiles at the GC, these constraints are the strongest obtained so far in the TeV DM mass range. For the Einasto profile, the constraints reach values of for 1.5 TeV DM mass in the annihilation channel, and for 0.7 TeV DM mass in the annihilation channel. With the H.E.S.S. Inner Galaxy Survey, ground-based -ray observations thus probe values expected from thermal-relic annihilating TeV DM particles
Search for dark matter annihilation signals in the H.E.S.S. Inner Galaxy Survey
The central region of the Milky Way is one of the foremost locations to look for dark matter (DM) signatures. We report the first results on a search for DM particle annihilation signals using new observations from an unprecedented gamma-ray survey of the Galactic Center (GC) region, , the Inner Galaxy Survey, at very high energies ( 100 GeV) performed with the H.E.S.S. array of five ground-based Cherenkov telescopes. No significant gamma-ray excess is found in the search region of the 2014-2020 dataset and a profile likelihood ratio analysis is carried out to set exclusion limits on the annihilation cross section . Assuming Einasto and Navarro-Frenk-White (NFW) DM density profiles at the GC, these constraints are the strongest obtained so far in the TeV DM mass range. For the Einasto profile, the constraints reach values of for 1.5 TeV DM mass in the annihilation channel, and for 0.7 TeV DM mass in the annihilation channel. With the H.E.S.S. Inner Galaxy Survey, ground-based -ray observations thus probe values expected from thermal-relic annihilating TeV DM particles
Search for dark matter annihilation signals in the H.E.S.S. Inner Galaxy Survey
The central region of the Milky Way is one of the foremost locations to look for dark matter (DM) signatures. We report the first results on a search for DM particle annihilation signals using new observations from an unprecedented gamma-ray survey of the Galactic Center (GC) region, , the Inner Galaxy Survey, at very high energies ( 100 GeV) performed with the H.E.S.S. array of five ground-based Cherenkov telescopes. No significant gamma-ray excess is found in the search region of the 2014-2020 dataset and a profile likelihood ratio analysis is carried out to set exclusion limits on the annihilation cross section . Assuming Einasto and Navarro-Frenk-White (NFW) DM density profiles at the GC, these constraints are the strongest obtained so far in the TeV DM mass range. For the Einasto profile, the constraints reach values of for 1.5 TeV DM mass in the annihilation channel, and for 0.7 TeV DM mass in the annihilation channel. With the H.E.S.S. Inner Galaxy Survey, ground-based -ray observations thus probe values expected from thermal-relic annihilating TeV DM particles
Search for dark matter annihilation signals in the H.E.S.S. Inner Galaxy Survey
The central region of the Milky Way is one of the foremost locations to look for dark matter (DM) signatures. We report the first results on a search for DM particle annihilation signals using new observations from an unprecedented gamma-ray survey of the Galactic Center (GC) region, , the Inner Galaxy Survey, at very high energies ( 100 GeV) performed with the H.E.S.S. array of five ground-based Cherenkov telescopes. No significant gamma-ray excess is found in the search region of the 2014-2020 dataset and a profile likelihood ratio analysis is carried out to set exclusion limits on the annihilation cross section . Assuming Einasto and Navarro-Frenk-White (NFW) DM density profiles at the GC, these constraints are the strongest obtained so far in the TeV DM mass range. For the Einasto profile, the constraints reach values of for 1.5 TeV DM mass in the annihilation channel, and for 0.7 TeV DM mass in the annihilation channel. With the H.E.S.S. Inner Galaxy Survey, ground-based -ray observations thus probe values expected from thermal-relic annihilating TeV DM particles
Search for Dark Matter Annihilation Signals in the H.E.S.S. Inner Galaxy Survey
International audienceThe central region of the Milky Way is one of the foremost locations to look for dark matter (DM) signatures. We report the first results on a search for DM particle annihilation signals using new observations from an unprecedented γ-ray survey of the Galactic Center (GC) region, i.e., the Inner Galaxy Survey, at very high energies (≳100 GeV) performed with the H.E.S.S. array of five ground-based Cherenkov telescopes. No significant γ-ray excess is found in the search region of the 2014–2020 dataset and a profile likelihood ratio analysis is carried out to set exclusion limits on the annihilation cross section ⟨σv⟩. Assuming Einasto and Navarro-Frenk-White (NFW) DM density profiles at the GC, these constraints are the strongest obtained so far in the TeV DM mass range. For the Einasto profile, the constraints reach ⟨σv⟩ values of 3.7×10-26 cm3 s-1 for 1.5 TeV DM mass in the W+W- annihilation channel, and 1.2×10-26 cm3 s-1 for 0.7 TeV DM mass in the τ+τ- annihilation channel. With the H.E.S.S. Inner Galaxy Survey, ground-based γ-ray observations thus probe ⟨σv⟩ values expected from thermal-relic annihilating TeV DM particles
HESS J1809193: a halo of escaped electrons around a pulsar wind nebula?
International audienceContext. HESS J1809193 is an unassociated very-high-energy -ray source located on the Galactic plane. While it has been connected to the nebula of the energetic pulsar PSR J18091917, supernova remnants and molecular clouds present in the vicinity also constitute possible associations. Recently, the detection of -ray emission up to energies of 100 TeV with the HAWC observatory has led to renewed interest in HESS J1809193. Aims. We aim to understand the origin of the -ray emission of HESS J1809193. Methods. We analysed 93.2 h of data taken on HESS J1809193 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 J1809193. 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 that exhibits a spectral cut-off at 13 TeV, and a compact component that is located close to PSR J18091917 and shows no clear spectral cut-off. The Fermi-LAT analysis also revealed extended -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. (abridged
Search for Dark Matter Annihilation Signals in the H.E.S.S. Inner Galaxy Survey
The central region of the Milky Way is one of the foremost locations to look for dark matter (DM) signatures. We report the first results on a search for DM particle annihilation signals using new observations from an unprecedented -ray survey of the Galactic Center (GC) region, i.e., the Inner Galaxy Survey, at very high energies (≳100 GeV) performed with the H.E.S.S. array of five ground-based Cherenkov telescopes. No significant -ray excess is found in the search region of the 2014–2020 dataset and a profile likelihood ratio analysis is carried out to set exclusion limits on the annihilation cross section . Assuming Einasto and Navarro-Frenk-White (NFW) DM density profiles at the GC, these constraints are the strongest obtained so far in the TeV DM mass range. For the Einasto profile, the constraints reach values of 3.7×10 cm s for 1.5 TeV DM mass in the WW annihilation channel, and 1.2×10 cm s for 0.7 TeV DM mass in the annihilation channel. With the H.E.S.S. Inner Galaxy Survey, ground-based -ray observations thus probe values expected from thermal-relic annihilating TeV DM particles
HESS J1809193: a halo of escaped electrons around a pulsar wind nebula?
International audienceContext. HESS J1809193 is an unassociated very-high-energy -ray source located on the Galactic plane. While it has been connected to the nebula of the energetic pulsar PSR J18091917, supernova remnants and molecular clouds present in the vicinity also constitute possible associations. Recently, the detection of -ray emission up to energies of 100 TeV with the HAWC observatory has led to renewed interest in HESS J1809193. Aims. We aim to understand the origin of the -ray emission of HESS J1809193. Methods. We analysed 93.2 h of data taken on HESS J1809193 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 J1809193. 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 that exhibits a spectral cut-off at 13 TeV, and a compact component that is located close to PSR J18091917 and shows no clear spectral cut-off. The Fermi-LAT analysis also revealed extended -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. (abridged