Search

Massive stellar clusters have recently been hypothesised as candidates for the acceleration of hadronic cosmic rays up to PeV energies. Previously, the H.E.S.S. Collaboration has reported about very extended $��$-ray emission around Westerlund 1, a massive young stellar cluster in the Milky Way. In this contribution we present an updated analysis that employs a new analysis technique and is based on a much larger data set, allowing us to constrain better the morphology and the energy spectrum of the emission. The analysis technique used is a three-dimensional likelihood analysis, which is especially well suited for largely extended sources. The origin of the $��$-ray emission will be discussed in light of multi-wavelength observations., 10 pages, 6 figures, ICRC 2021 conference proceedings

36th International Cosmic Ray Conference, Madison, USA, 24 Jul 2019 - 1 Aug 2019; PoS(ICRC2019)756 (2019)., The detection of the first electromagnetic counterpart to the binaryneutron star merger remnant GW170817 established the connectionbetween short gamma-ray bursts and binary neutron star mergers aswell as it confirmed the forging of heavy elements in the ejecta (a socalledkilonova) via the r process. The brightening of non-thermal radioand X-ray emission, however, came with some surprise and lastedmore than 100 days. Current theoretical models attempt to explain thelight curve as either originating from a relativistic off-axis jet, or akilonova-like outflow. Combining the VLA and Chandra measurementswith observations in the GeV - TeV domain, can help to break theambiguity between energy in non-thermal electrons and magnetic fieldof the emission region, almost independent of the assumed origin ofthe emission. Here we report for the first time on deep H.E.S.S.observations of EM170817 between 120 and 270 days after the binaryneutron star merger with the full H.E.S.S. array of telescopes as wellas on updated prompt (

Stellar flares have been extensively studied in soft X-rays (SXR) by basically every X-ray mission. Hard X-ray (HXR) emission from stellar superflares, however, have only been detected from a handful of objects over the past years. One very extreme event was the superflare from the young M-dwarf DG CVn binary star system, which triggered Swift/BAT as if it was a $��$-ray burst (GRB). In this work, we estimate the expected $��$-ray emission from DG CVn and the most extreme stellar flares by extrapolating from solar flares based on measured solar energetic particles (SEPs), as well as thermal and non-thermal emission properties. We find that ions are plausibly accelerated in stellar superflares to 100 GeV energies, and possibly up to TeV energies in the associated coronal mass ejections. The corresponding $��^0$-decay $��$-ray emission could be detectable from stellar superflares with ground-based $��$-ray telescopes. On the other hand, the detection of $��$-ray emission implies particle densities high enough that ions suffer significant losses due to inelastic proton-proton scattering. The next-generation Cherenkov Telescope Array (CTA) should be able to probe superflares from M-dwarfs in the solar neighbourhood and constrain the energy in interacting cosmic rays and/or their maximum energy. The detection of $��$-ray emission from stellar flares would open a new window for the study of stellar physics, the underlying physical processes in flares and their impact on habitability of planetary systems., 8 pages, 3 figures, 2 tables

In this paper the current status of ��-ray observations of starburst galaxies from hundreds of MeV up to TeV energies with space-based instruments and ground-based Imaging Atmospheric Cherenkov Telescopes (IACTs) is summarised. The properties of the high-energy (HE; 100 MeV < E < 100 GeV) and very-high-energy (VHE; E > 100 GeV) emission of the archetypical starburst galaxies M 82 and NGC 253 are discussed and put into context with the HE ��-ray emission detected from other galaxies that show enhanced star-formation activity such as NGC 4945 and NGC 1068. Finally, prospects to study the star-formation - ��-ray emission connection from Galactic systems to entire galaxies with the forthcoming Cherenkov Telescope Array (CTA) are outlined., 8 pages, 2 figures, solicited talk, to be published in High Energy Gamma-Ray Astronomy (eds. F. Aharonian, W. Hofmann, F. Rieger) the proceedings of the 5th Heidelberg international symposium on high energy gamma-ray astronomy

The nature of the first unidentified VHE gamma-ray source with significant angular offset from the Galactic plane of 3.5 degrees, HESS J1507-622, is explored. Fermi-LAT data in the high-energy (HE, 100 MeV < E < 100 GeV) gamma-ray range collected over 34 month are used to describe the spectral energy distribution (SED) of the source. HESS J1507-622 is detected in the Fermi energy range and its spectrum is best described by a power law in energy with Gamma=1.7 +/- 0.1 stat +/- 0.2_sys and integral flux between (0.3-300) GeV of F = (2.0 +/-0.5_stat +/- 1.0_sys) x 10^-9 cm^-2 s^-1. With the available data it is not possible to discriminate between a hadronic and a leptonic scenario for HESS J1507-622. The location and compactness of the source indicate a considerable physical offset from the Galactic plane for this object. In case of a multiple-kpc distance, this challenges a pulsar wind nebula (PWN) origin for HESS J1507-622 since the time of travel for a pulsar born in the Galactic disk to reach such a location would exceed the inverse Compton (IC) cooling time of electrons that are energetic enough to produce VHE gamma-rays. However, an origin of this gamma-ray source connected to a pulsar that was born off the Galactic plane in the explosion of a hypervelocity star cannot be excluded. The nature of HESS J1507-622 is still unknown to date, and a PWN scenario cannot be ruled out in general. On the contrary HESS J1507-622 could be the first discovered representative of a population of spatially extended VHE gamma-ray emitters with HE gamma-ray counterpart that are located at considerable offsets from the Galactic plane. Future surveys in the VHE gamma-ray range are necessary to probe the presence or absence of such a source population.(abridged), accepted for publication in A&A, 7 pages, 3 figures

The detection of an astrophysical flux of high-energy neutrinos by IceCube is a major step forward in the search for the origin of cosmic rays, as this emission is expected to originate in hadronic interactions taking place in or near cosmic-ray accelerators. No neutrino point sources, or significant correlation with known astrophysical objects, have been identified in the IceCube data so far. The hadronic interactions responsible for the neutrino emission should also lead to the production of high-energy gamma rays. The search for neutrino sources can then be performed by studying the spatial and temporal correlations between neutrino events and very high energy (VHE, E > 100 GeV) gamma rays. We report here on the search for VHE gamma-ray emission with the H.E.S.S. imaging air Cherenkov telescopes (IACTs) at the reconstructed position of muon neutrino events detected by IceCube. We will provide an up-to-date summary of the extensive program to perform prompt IACT observations of realtime IceCube neutrino event positions. A recent highlight of this program are the H.E.S.S. observations during the broad multi-wavelength campaign that followed the detection of the neutrino event IceCube-170922A arriving from a direction consistent with the location of a flaring gamma-ray blazar TXS 0506+056 in September 2017. We'll present the H.E.S.S. observations obtained within ~4h hours of the neutrino detection as well as a complementary search for gamma-ray emission at longer timescales and put them into the multi-wavelength and multi-messenger context., Proceedings of the 36th International Cosmic Ray Conference, 2019, Madison, WI, USA