1,721,513 research outputs found
The H.E.S.S. Standard Analysis Technique
No full textThe High Energy Stereoscopic System (H.E.S.S.) is an array of four imaging atmospheric Cherenkov telescopes located in Namibia. With the ability to detect a 1 % Crab Nebula flux source in ~25 hours of observation, H.E.S.S. is currently the most sensitive detector of astrophysical VHE (>100GeV) photons. The H.E.S.S. collaboration has published the detection of more than 30 sources of VHE γ-rays, rejecting the large cosmic-ray background, and determining the spectrum and flux of the detected sources is presented
Search for TeV emission from the Fermi Bubbles at low Galactic latitudes with H.E.S.S. inner Galaxy survey
Full text linkThe Fermi Bubbles were discovered about a decade ago in the Fermi-LAT data as a double-lobe structure extending up to 55° in Galactic latitudes above and below the Galactic Center. At the moment their origin is still unknown. The H.E.S.S. collaboration is currently performing the first ever survey in TeV gamma rays of the Milky Way inner region: the Inner Galaxy Survey. This survey is intended to achieve the best sensitivity to faint and diffuse emissions in a region of several degrees around the Galactic Centre. It provides an unprecedented sensitivity to dark matter signals, new diffuse emissions, and TeV outflows from the Galactic Centre. Understanding the properties of the Fermi Bubbles at low Galactic latitudes will provide key insights into their origin. We search for TeV emission at the base of the Fermi Bubbles using low-latitude spatial templates. The first results obtained with the 2014-2020 H.E.S.S. observations will be reported
The young massive stellar cluster Westerlund 1 in gamma rays as seen with H.E.S.S.
No full textMassive 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
The exceptionally powerful tev γ-ray emitters in the large magellanic cloud
No full textThe Large Magellanic Cloud, a satellite galaxy of the Milky Way, has been observed with the High Energy Stereoscopic System (H.E.S.S.) above an energy of 100 billion electron volts for a deep exposure of 210 hours. Three sources of different types were detected: the pulsar wind nebula of the most energetic pulsar known, N 157B; the radio-loud supernova remnant N 132D; and the largest nonthermal x-ray shell, the superbubble 30 Dor C. The unique object SN 1987A is, unexpectedly, not detected, which constrains the theoretical framework of particle acceleration in very young supernova remnants. These detections reveal the most energetic tip of a γ-ray source population in an external galaxy and provide via 30 Dor C the unambiguous detection of γ-ray emission from a superbubble.M. Actis … G. Rowell … et al. (for the H.E.S.S. Collaboration
V.H.E. Gamma Rays From Microquasars
Full text linkThis thesis is concerned with the detection of very high energy (VHE) 7-rays from microquasars, a recently discovered subclass of x-ray binaries that display jets of relativistic particles. A general introduction to ground based 7-ray astronomy is presented, which discusses the production of Cherenkov radiation and how VHE 7-rays are detected via extended air showers in the atmosphere. The important processes involved in the production and absorption of 7-rays are detailed, before the design of The High Energy Stereoscopic System (H.E.S.S.) Phase I telescope array, based in Namibia, is briefly described. There follows a general section on microquasars, describing x-ray binaries and the morphological analogy between microquasars and active galactic nuclei (AGN). Some important properties of jets are detailed before the spectral states of x-ray binaries and their importance in relation to jets are discussed. A synchrotron self-Compton (SSC) model designed for AGN is reviewed in some detail and is applied to the blazar 3C 279, showing a good fit to data. This SSC model is then applied to the microquasars GRS 1915+105, V4641 Sgr and GX 339-4 using a scale-invariant method to investigate if the jets from microquasars can be considered simply as scaled down AGN jets. Conclusions are drawn from the results. Data taken with H.E.S.S. on four microquasars are presented. The techniques used to take and analyse this data are described in some detail using data taken on the Crab nebula as an example of a VHE 7-ray emitter, before the analysis results for observations of GRS 1915+105, Circinus X-1, GX 339-4 and V4641 Sgr are presented. A novel method for manufacturing aluminum mirrors suitable for use on ground based 7-ray telescopes is described in detail along with the testing techniques used. The next generation telescope, H.E.S.S. Phase II is then described briefly. The thesis concludes with a brief outline of future work to be conducted, based on the SSC model, as applied to microquasars. A proposal for observations of IGR J19140+0951, which was tentatively detected in the field of GRS 1915+105, is outlined
VHE observations of pulsar wind nebulae with H.E.S.S.
No full textThe H.E.S.S. detector is an array of atmospheric-Cherenkov telescopes dedicated to the observation of very high energy (VHE)γ-rays. Situated in Namibia, the full four-telescope array is operational since December 2003. Among many types of targets, the H.E.S.S. collaboration is studying pulsar wind nebulae (PWN) in the VHE γ-ray domain. These objects can produce VHE emission by the inverse Compton process, whereby relativistic electrons and positrons in the shocked pulsar wind interact with lower-energy ambient photons. The PWN inside MSH15-52, G0.9+0.1 and near the Vela pulsar have been observed by H.E.S.S. since 2004. The results of these observations are reported here
Search for dark matter annihilation towards the inner Milky Way halo with the H.E.S.S. Inner Galaxy Survey
No full textThe presence of dark matter (DM) is suggested by a wealth of astrophysical and cosmological measurements. However, its underlying nature is yet unknown. Among the most promising candidates are weakly interacting massive particles (WIMPs): particles with mass and coupling strength at the electroweak scale and thermally produced in the early universe have a present relic density consistent with that observed today. WIMP self annihilation would produce Standard Model particles including gamma-rays, which have been long-time recognized as a prime messenger to indirectly detect dark matter signals. The centre of the Milky Way is predicted as the brightest source of DM annihilations. The H.E.S.S. collaboration is currently performing a survey of the inner region of the Milky Way, the Inner Galaxy Survey (IGS), intended to achieve the best sensitivity to faint and diffuse emissions in a region of several degrees around the Galactic Centre. We analyzed 2014-2020 observations taken with the five-telescope array to search for a DM annihilation signal. With the current dataset of about 550 hours, we found no significant excess and therefore derived strong constraints on the velocity-weighted annihilation cross-section. TeV thermal WIMPs can be probed in different annihilation channels
PKS2005-489 at VHE: four years of monitoring with HESS and simultaneous multi-wavelength observations
Full text linkVHE observations of PKS 2005-489 were made with HESS from 2004 through 2007, together with three simultaneous multi-wavelength campaigns performed with XMM-Newton and RXTE in 2004 and 2005. A strong VHE signal, ~17sigma total, is detected during the four years of HESS observations (90.3 hrs live time). The integral flux above the average analysis threshold of 400 GeV is ~3% of the Crab and varies weakly on time-scales from days to years. At X-ray energies the flux is observed to vary by more than an order of magnitude between 2004 and 2005. Strong changes in the X-ray spectrum (DeltaGamma~0.7) are also observed, which appear to be mirrored in the VHE band. The SED of PKS 2005-489, constructed for the first time with contemporaneous data on both humps, shows significant evolution. The large flux variations in the X-ray band, coupled with weak or no variations in the VHE band and a similar spectral behavior, suggest the emergence of a new, separate, harder emission component in September 2005.F. Acero, B. Nicholas, G. Rowell,...and et al, and H.E.S.S. Collaboration
The effects of atmosphere conditions on gamma-ray astronomy
Full text linkThe High Energetic Stereoscopic System (H.E.S.S.) experiment is an array of imaging atmospheric Cherenkov (IAC) telescopes of the next generation, with enlarged mirrors and advanced detector electronics compared to its predecessors. As a member of the international H.E.S.S. collaboration, the Durham 7-rау astronomy group took over the responsibility for design, construction and commissioning of calibration systems for the H.E.S.S. telescopes and atmospheric monitoring devices. The atmosphere is an essential part of the detector system for the IAC technique, monitoring of the atmosphere's parameter is therefore important for energy calibration of the detector and variability studies of 7-ray sources to distinguish between detector and source fluctuations. A weather station, several infrared radiometers and an infrared LIDAR system have been installed to provide constant monitoring of all relevant parameters. This thesis reports about the work performed for the design and commissioning of the calibration module. Furthermore, the technicalities of the LIDAR system and the IR radiometer, their use in terms of 7-ray astronomy, especially studies about the variability of zenith angle dependencies and the correlation with other atmospheric parameters and telescope trigger rates are discussed
The optical system of the H.E.S.S. II telescope
No full textThe stereoscopic system of four large imaging atmospheric Cherenkov telescopes operated by the H.E.S.S. collaboration in the Khomas Highland of Namibia is planned to be extended by a central very large telescope. The new telescope with its 30m type reflector, called H.E.S.S. II, is designed to provide a total mirror area of 600m² for the imaging of extensive air showers onto the Cherenkov camera consisting of 2048 photomultiplier tubes of about 0.07⁰ size. In order to guarantee for a stable and reliable imaging of excellent quality for the whole field of view of 3.2⁰ , intense technical studies as well as detailed Monte Carlo simulations of the optical system have been performed
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