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Register a new userSgr A* Observations with H.E.S.S. II
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The Galactic Centre has been studied with the High Energy Stereoscopic System (H.E.S.S.) for over 10 years, revealing a bright, complex gamma-ray morphology. Besides a strong point-like very-high-energy gamma-ray source coincident with the supermassive black hole Sgr A*, pre- vious analyses also revealed a diffuse ridge of gamma-ray emission, indicative of a powerful cosmic-ray accelerator in this region. The addition of a fifth telescope with 600 m 2 mirror area to the centre of the H.E.S.S. array has increased the energy range accessible, allowing observations to take place down to 100 GeV and potentially below. This wider energy range allows an important overlap in observations with satellite instruments such as the Fermi-LAT gamma-ray telescope. We will present the results of new H.E.S.S observations of the Galactic Centre region and show a detailed analysis of the central source, including comparisons to results at other wavelengths.
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The High Energy Stereoscopic System (H.E.S.S.) has been searching for counterparts of Gamma Ray Bursts (GRBs) for many years. In 2012 the system was upgraded with a fifth $28$ m diameter telescope (CT5) which is equipped with faster motors for rapid repointing, marking the start of the second phase of H.E.S.S. operation (H.E.S.S. II). CT5s large light collection area of $600,{rm m}^{2}$ improves the sensitivity to low-energy gamma-rays and even extends the energy range below $100$ GeV. The search for counterparts continues now in the energy range of tens of GeV to tens of TeV. A detection in this energy range would open a new window to the part of the spectrum of these highly energetic explosions which Fermi-LAT has only successfully detected in a reduced subset of events, with rather limited statistics. In the past years, H.E.S.S. has performed followup observations based on GRB detections by Swift-BAT and Fermi-GBM/-LAT. This Target of Opportunity observation program was carried out with a generalised Target of Opportunity Alert system. This contribution will highlight key features of the Target of Opportunity Alert system, present follow-up statistics of GRBs as well as detailed results of promising follow-up observations.
The recent addition of the 28 m Cherenkov telescope (CT5) to the H.E.S.S. array extended the experiments sensitivity towards low energies. The lowest energy threshold is obtained using monoscopic observations with CT5, providing access to gamma-ray energies below 100 GeV. This is particularly beneficial for studies of Active Galactic Nuclei (AGN) with soft spectra and located at redshifts >= 0.5. Stereoscopic measurements with the full array (CT1-5) provide a better background rejection than CT5 Mono, at a cost of a higher threshold. We report on the analysis employing the CT5 data for AGN observations with a < 100 GeV threshold. In particular, the spectra of PKS 2155-304 and PG 1553+113 are presented.
We present a new and deep analysis of the pulsar wind nebula (PWN) HESS,J1825--137 with a comprehensive data set of almost 400 hours taken with the H.E.S.S. array between 2004 and 2016. The large amount of data, and the inclusion of low-threshold H.E.S.S. II data allows us to include a wide energy range of more than 2.5 orders of magnitude, ranging from 150 GeV up to 70 TeV. We exploit this rich data set to study the morphology and the spectral distributions of various subregions of this largely extended source in more detail. We find that HESS,J1825--137 is not only the brightest source in that region above 32 TeV, but is also one of the most luminous of all firmly identified pulsar wind nebulae in the Milky Way.
Keplers supernova remnant (SNR) which is produced by the most recent naked-eye supernova in our Galaxy is one of the best studied SNRs, but its gamma-ray detection has eluded us so far. Observations with modern imaging atmospheric Cherenkov telescopes (IACT) have enlarged the knowledge about nearby SNRs with ages younger than 500 years by establishing Cassiopeia A and Tychos SNRs as very high energy (VHE) gamma-ray sources and setting a lower limit on the distance to Keplers SNR. This SNR is significantly more distant than the other two and expected to be one of the faintest gamma-ray sources within reach of the IACT arrays of this generation. We report strong evidence for a VHE signal from Keplers SNR based on deep observations of the High Energy Stereoscopic System (H.E.S.S.) with an exposure of 152 hours, including 122 hours accumulated in 2017-2020. We further discuss implications of this result for cosmic-ray acceleration in young SNRs.
Observations of binary systems obtained recently with the High Energy Stereoscopic System (H.E.S.S) of Cherenkov telescopes are reported. The outcomes of a detailed observation campaign on PSR B1259-63 during its periastron passage in 2014 will be presented. This system was observed for the first time with H.E.S.S. II, providing spectra and light curves down to 200 GeV, which will be compared with observations conducted during previous periastron passages and with results from an analysis of contemporaneously taken Fermi-LAT data. Also long-term observations of LS 5039 with H.E.S.S in phase I and phase II are reported. This source was monitored at very high energies (VHEs) in a period of time spanning more than ten years. Its spectral energy distribution measured with H.E.S.S. II extends down to 120 GeV. Spectral results from the Fermi-LAT observations are shown as well, and the compatibility with H.E.S.S. results in the overlapping energy range is discussed. The identification of the new gamma-ray binary candidate HESS J1832-093 will also be presented. Furthermore, the search for VHE emission from the microquasars GRS 1915+105, Circinus X-1 and V4641 Sgr based on data from H.E.S.S. observations conducted contemporaneously with the RXTE satellite experiment will be reported. These data provide constraints on the integral gamma-ray flux at different X-ray states of the three sources.
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