178 research outputs found
Very-high-energy γ -Ray Emission from Young Massive Star Clusters in the Large Magellanic Cloud
The Tarantula Nebula in the Large Magellanic Cloud is known for its high star formation activity. At its center lies the young massive star cluster R136, providing a significant amount of the energy that makes the nebula shine so brightly at many wavelengths. Recently, young massive star clusters have been suggested to also efficiently produce very high-energy cosmic rays, potentially beyond PeV energies. Here, we report the detection of very-high-energy γ-ray emission from the direction of R136 with the High Energy Stereoscopic System, achieved through a multicomponent, likelihood-based modeling of the data. This supports the hypothesis that R136 is indeed a very powerful cosmic-ray accelerator. Moreover, from the same analysis, we provide an updated measurement of the γ-ray emission from 30 Dor C, the only superbubble detected at TeV energies presently. The γ-ray luminosity above 0.5 TeV of both sources is (2–3) × 1035 erg s−1. This exceeds by more than a factor of 2 the luminosity of HESS J1646−458, which is associated with the most massive young star cluster in the Milky Way, Westerlund 1. Furthermore, the γ-ray emission from each source is extended with a significance of >3σ and a Gaussian width of about 30 pc. For 30 Dor C, a connection between the γ-ray emission and the nonthermal X-ray emission appears likely. Different interpretations of the γ-ray signal from R136 are discussed
The Vanishing of the Primary Emission Region in PKS 1510-089
In 2021 July, PKS 1510-089 exhibited a significant flux drop in the high-energy γ-ray (by a factor 10) and optical (by a factor 5) bands and remained in this low state throughout 2022. Similarly, the optical polarization in the source vanished, resulting in the optical spectrum being fully explained through the steady flux of the accretion disk and the broad-line region. Unlike the aforementioned bands, the very-high-energy γ-ray and X-ray fluxes did not exhibit a significant flux drop from year to year. This suggests that the steady-state very-high-energy γ-ray and X-ray fluxes originate from a different emission region than the vanished parts of the high-energy γ-ray and optical jet fluxes. The latter component has disappeared through either a swing of the jet away from the line of sight or a significant drop in the photon production efficiency of the jet close to the black hole. Either change could become visible in high-resolution radio images
Evidence for γ-ray emission from the remnant of Kepleras supernova based on deep H.E.S.S. observations
Observations with imaging atmospheric Cherenkov telescopes (IACTs) have enhanced our knowledge of nearby supernova (SN) remnants with ages younger than 500 yr by establishing Cassiopeia A and the remnant of Tycho’s SN as very-high-energy (VHE) γ-ray sources. The remnant of Kepler’s SN, which is the product of the most recent naked-eye SN in our Galaxy, is comparable in age to the other two, but is significantly more distant. If the γ-ray luminosities of the remnants of Tycho’s and Kepler’s SNe are similar, then the latter is expected to be one of the faintest γ-ray sources within reach of the current generation IACT arrays. Here we report evidence at a statistical level of 4.6σ for a VHE signal from the remnant of Kepler’s SN based on deep observations by the High Energy Stereoscopic System (H.E.S.S.) with an exposure of 152 h. The measured integral flux above an energy of 226 GeV is ∼0.3% of the flux of the Crab Nebula. The spectral energy distribution (SED) reveals a γ-ray emitting component connecting the VHE emission observed with H.E.S.S. to the emission observed at GeV energies with Fermi-LAT. The overall SED is similar to that of the remnant of Tycho’s SN, possibly indicating the same nonthermal emission processes acting in both these young remnants of thermonuclear SNe.H.E.S.S. Collaboration ... F. Aharonian ... S. Einecke ..., G. Rowell ... et al
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 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} cm^{3} s^{-1} for 1.5 TeV DM mass in the W^{+}W^{-} annihilation channel, and 1.2×10^{-26} cm^{3} 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
The Vanishing of the Primary Emission Region in PKS 1510–089
Published 2023 August 1In 2021 July, PKS 1510−089 exhibited a significant flux drop in the high-energy γ-ray (by a factor 10) and optical (by a factor 5) bands and remained in this low state throughout 2022. Similarly, the optical polarization in the source vanished, resulting in the optical spectrum being fully explained through the steady flux of the accretion disk and the broad-line region. Unlike the aforementioned bands, the very-high-energy γ-ray and X-ray fluxes did not exhibit a significant flux drop from year to year. This suggests that the steady-state very-high-energy γ-ray and X-ray fluxes originate from a different emission region than the vanished parts of the high-energy γ-ray and optical jet fluxes. The latter component has disappeared through either a swing of the jet away from the line of sight or a significant drop in the photon production efficiency of the jet close to the black hole. Either change could become visible in high-resolution radio images.F. Aharonian ... S. Einecke ... G. Rowell ... et al. (H.E.S.S. Collaboration
H.E.S.S. Follow-up Observations of GRB 221009A
GRB 221009A is the brightest gamma-ray burst (GRB) ever detected. To probe the very-high-energy (VHE; >100 GeV) emission, the High Energy Stereoscopic System (H.E.S.S.) began observations 53 hr after the triggering event, when the brightness of the moonlight no longer precluded observations. We derive differential and integral upper limits using H.E.S.S. data from the third, fourth, and ninth nights after the initial GRB detection, after applying atmospheric corrections. The combined observations yield an integral energy flux upper limit of FUL = 9.7 ´ 10- erg cm- s- 95% 12 2 1 above Ethr = 650 GeV. The constraints derived from the H.E.S.S. observations complement the available multiwavelength data. The radio to X-ray data are consistent with synchrotron emission from a single electron population, with the peak in the spectral energy distribution occurring above the X-ray band. Compared to the VHE-bright GRB 190829A, the upper limits for GRB 221009A imply a smaller gamma-ray to X-ray flux ratio in the afterglow. Even in the absence of a detection, the H.E.S.S. upper limits thus contribute to the multiwavelength picture of GRB 221009A, effectively ruling out an IC-dominated scenario.F. Aharonian ... S. Einecke ... G. Rowell ... et al. (H.E.S.S. Collaboration
Constraints on the intergalactic magnetic field using Fermi-LAT and H.E.S.S. blazar observations
Magnetic fields in galaxies and galaxy clusters are believed to be the result
of the amplification of intergalactic seed fields during the formation of
large-scale structures in the universe. However, the origin, strength, and
morphology of this intergalactic magnetic field (IGMF) remain unknown. Lower
limits on (or indirect detection of) the IGMF can be obtained from observations
of high-energy gamma rays from distant blazars. Gamma rays interact with the
extragalactic background light to produce electron-positron pairs, which can
subsequently initiate electromagnetic cascades. The -ray signature of
the cascade depends on the IGMF since it deflects the pairs. Here we report on
a new search for this cascade emission using a combined data set from the Fermi
Large Area Telescope and the High Energy Stereoscopic System. Using
state-of-the-art Monte Carlo predictions for the cascade signal, our results
place a lower limit on the IGMF of G for a coherence
length of 1 Mpc even when blazar duty cycles as short as 10 yr are assumed.
This improves on previous lower limits by a factor of 2. For longer duty cycles
of () yr, IGMF strengths below G
( G) are excluded, which rules out specific models for IGMF
generation in the early universe.Comment: 20 pages, 7 figures, 4 tables. Accepted for publication in ApJ
Letters. Auxiliary data is provided in electronic format at
https://zenodo.org/record/801431
H.E.S.S. follow-up observations of GRB221009A
GRB221009A is the brightest gamma-ray burst ever detected. To probe the
very-high-energy (VHE, \!100 GeV) emission, the High Energy Stereoscopic
System (H.E.S.S.) began observations 53 hours after the triggering event, when
the brightness of the moonlight no longer precluded observations. We derive
differential and integral upper limits using H.E.S.S. data from the third,
fourth, and ninth nights after the initial GRB detection, after applying
atmospheric corrections. The combined observations yield an integral energy
flux upper limit of above GeV. The
constraints derived from the H.E.S.S. observations complement the available
multiwavelength data. The radio to X-ray data are consistent with synchrotron
emission from a single electron population, with the peak in the SED occurring
above the X-ray band. Compared to the VHE-bright GRB190829A, the upper limits
for GRB221009A imply a smaller gamma-ray to X-ray flux ratio in the afterglow.
Even in the absence of a detection, the H.E.S.S. upper limits thus contribute
to the multiwavelength picture of GRB221009A, effectively ruling out an IC
dominated scenario.Comment: 10 pages, 4 figures. Accepted for publication in APJL. Corresponding
authors: J. Damascene Mbarubucyeye, H. Ashkar, S. J. Zhu, B. Reville, F.
Sch\"ussle
A MeerKAT, e-MERLIN, H.E.S.S. and Swift search for persistent and transient emission associated with three localised FRBs
HESS J1809193: a halo of escaped electrons around a pulsar wind nebula?
Context. 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)Comment: 14 pages, 10 figures. Accepted for publication in A&A. Corresponding
authors: Vikas Joshi, Lars Mohrman
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