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Welcome to the webpages of H.E.S.S., one of the leading observatories studying very high energy (VHE) gamma-ray astrophysics. To learn more about H.E.S.S. and the high energy universe, or to view pictures from the telescopes and the site in Namibia visit the About H.E.S.S. section.

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Long-term monitoring of PKS 2155−304 with ATOM and H.E.S.S.: investigation of optical/gamma-ray correlations in different spectral states
September 20, 2014

The paper reports the analysis of all the available optical and very high-energy gamma-ray data for the BL Lac object PKS 2155−304, collected simultaneously with the ATOM and H.E.S.S. telescopes from 2007 until 2009. The study also includes X-ray (RXTE, Swift) and high-energy gamma-ray (Fermi-LAT) data. During the period analysed, the source was transitioning from its flaring to quiescent optical states. The paper can be found on the preprint server: arXiv:1409.0253.

Discovery of the hard spectrum VHE gamma-ray source HESS J1641-463
August 31, 2014

H.E.S.S. reports the discovery of a remarkably hard spectrum source, HESS J1641-463. HESS J1641-463 remained unnoticed by the usual analysis techniques due to confusion with the bright nearby source HESS J1640-465. It emerged at a significance level of 8.5 standard deviations after restricting the analysis to events with energies above 4 TeV. It shows a moderate flux level of 1.8% of the Crab Nebula flux above 1 TeV, and a hard spectrum with a photon index of Gamma = 2.07. The paper can be found on the preprint server: arXiv:1408.5280.

Probing the gamma-ray emission from HESS J1834-087 using H.E.S.S. and Fermi LAT observations
July 14, 2014

Previous observations with HESS have revealed the existence of an extended very-high-energy gamma-ray source, HESS J1834-087, coincident with the SNR W41. The origin of the gamma-ray emission has been further investigated with HESS and the Fermi-LAT. The TeV source can be modeled with a sum of two components: one point-like and one significantly extended. Two main scenarios are proposed to explain the emission: a pulsar wind nebula (PWN) or the interaction of SNR W41 with a molecular cloud. The paper can be found on the preprint server: arXiv:1407.0862.

First results from H.E.S.S. II announced: Detection of pulsed gamma-ray emission from Vela in the 30 GeV energy range
June 27, 2014

At the Amsterdam Astroparticle 2014 Conference, H.E.S.S. spokesperson Christian Stegmann presented first results obtained using the 28 m telescope CT5, including the detection of the Crab Nebula, of the AGNs PKS 2155-304 and PG 1553+113, and of the Galactic Center. These (known) VHE sources were observed as part of CT5 commissioning and serve to verify telescope performance. A major highlight is the detection of pulsed emission from the Vela pulsar, in the energy range around 30 GeV, the first detection of pulsed emission using a ground-based gamma-ray instrument in the southern hemisphere, demonstrating the capabilities of the new instrument. The 8-sigma detection of pulsed emission is obtained using an analysis chain optimized to provide lowest energy threshold, with a detection area of 10^4 m^2 at 20 GeV. The presentation is available here.

Search for TeV Gamma-ray Emission from GRB 100621A, an extremely bright GRB in X-rays, with H.E.S.S
May 17, 2014

The long gamma-ray burst (GRB) 100621A, at the time the brightest X-ray transient ever detected by Swift-XRT in the 0.3--10 keV range, has been observed with the four H.E.S.S. 12 m telescopes, starting about 700 s after the satellite trigger. Due to its relatively small redshift of z∼0.5, the favourable position in the southern sky and the relatively short follow-up time of the H.E.S.S. observations, this GRB could be within the sensitivity reach of the H.E.S.S. instrument. However, the analysis of the H.E.S.S. data shows no indication of emission and yields an integral flux upper limit above ∼380 GeV of 4.2×10^−12/cm^2s, assuming a simple Band function extension model. The paper can be found on the preprint server: arXiv:1405.0488.

TeV gamma-ray observations of the young synchrotron-dominated SNRs G1.9+0.3 and G330.2+1.0
April 24, 2014

The non-thermal nature of the X-ray emission from the shell-type supernova remnants (SNRs) G1.9+0.3 and G330.2+1.0 is an indication of intense particle acceleration in the shock fronts of both objects. G1.9+0.3, recently established as the youngest known SNR in the Galaxy, also offers a unique opportunity to study the earliest stages of SNR evolution in the VHE domain. Observations with H.E.S.S. span the period 2004-2010. No significant gamma-ray signal from G1.9+0.3 or G330.2+1.0 is detected. The results are discussed in the framework of both leptonic and hadronic particle acceleration scenarios. The paper can be found on the preprint server: arXiv:1404.1613.

Flux upper limits for 47 AGN observed with H.E.S.S. in 2004-2011
Feb. 22, 2014

About 40% of the observation time of H.E.S.S. is dedicated to studying active galactic nuclei (AGN), with the aim of increasing the sample of known extragalactic very-high-energy sources and constraining the physical processes at play in potential emitters. H.E.S.S. observations of AGN, spanning a period from April 2004 to December 2011, are investigated to constrain AGN gamma-ray fluxes. Only the 47 sources without significant excess detected at the position of the targets are presented. For 41 objects, the flux upper limits are the most constraining reported to date. The paper can be found on the preprint server: arXiv:1402.2332.

HESS J1640-465 - an exceptionally luminous TeV gamma-ray SNR
Jan. 21, 2014

The results of follow-up observations of the TeV gamma-ray source HESSJ 1640-465 are reported. The TeV emission is significantly extended and overlaps with the north-western part of the shell of the SNR G338.3-0.0. The new H.E.S.S. results, a re-analysis of archival XMM-Newton data, and multi-wavelength observations suggest that a significant part of the gamma-ray emission from HESS J1640-465 originates in the SNR shell. In a hadronic scenario, the product of total proton energy and mean target density could be as high as 4x10^52 erg cm^-3, for a distance of 10 kpc. The paper can be found on the preprint server: arXiv:1401.4388.

Search for Extended gamma-ray Emission around AGN with H.E.S.S. and Fermi-LAT
Jan. 15, 2014

Very-high-energy gamma-ray emission from blazars inevitably gives rise to electron-positron pair production through the interaction of these gamma-rays with the Extragalactic Background Light (EBL). Depending on the magnetic fields in the proximity of the source, the cascade initiated from pair production can result in either an isotropic halo around an initially beamed source or a magnetically broadened cascade flux. A search for such halos in H.E.S.S. and Fermi data resulted in upper limits on the extended emission around 1ES 1101-232, 1ES 0229+200 and PKS 2155-304, at a level of few percent of the Crab nebula flux. The paper can be found on the preprint server: arXiv:1401.2915.

Long-term TeV and X-ray Observations of the Gamma-ray Binary HESS J0632+057
Dec. 3, 2013

This joint paper by VERITAS and H.E.S.S. reports on long-term observations of HESS J0632+057 conducted with the Cherenkov telescopes and the X-ray Satellite Swift, spanning a time range from 2004 to 2012 and covering most of the system's orbit. The VHE emission is found to be variable, and is correlated with that at X-ray energies. The VHE light curve shows a distinct maximum at orbital phases close to 0.3, or about 100 days after periastron passage, which coincides with the periodic enhancement of the X-ray emission. The paper can be found on the preprint server: arXiv:1311.6083.

H.E.S.S. Observations of the Crab during its March 2013 GeV Gamma-Ray Flare
Nov. 16, 2013

On March 4, 2013, the Fermi-LAT and AGILE reported a flare from the direction of the Crab Nebula. Observational data taken with the H.E.S.S. instrument on five consecutive days during the flare were analysed concerning the flux and spectral shape of the emission from the Crab Nebula. The observations conducted on 2013 March 6 to March 10 show no significant changes in the flux. The paper can be found on the preprint server: arXiv:1311.3187.

Constraints on axionlike particles with H.E.S.S. from the irregularity of the PKS 2155-304 energy spectrum
Nov. 16, 2013

Axionlike particles (ALPs) are hypothetical light (sub-eV) bosons predicted in some extensions of the Standard Model of particle physics. In astrophysical environments comprising high-energy gamma rays and turbulent magnetic fields, the existence of ALPs can modify the energy spectrum of the gamma rays. Data from the H.E.S.S. observations of the distant BL Lac object PKS 2155-304 are used to derive upper limits on the strength of the ALP coupling to photons. The paper can be found on the preprint server: arXiv:1311.3148.

HESS J1818-154, a new composite supernova remnant discovered in TeV gamma rays and X-rays
Nov. 16, 2013

Composite supernova remnants (SNRs) constitute a class of remnants where non-thermal radiation is observed from both the expanding shell-like shock front and from a pulsar wind nebula (PWN) located inside of the SNR. New H.E.S.S. VHE gamma-ray data and XMM X-ray observations provide strong evidence for the existence of a PWN located inside the shell-type remnant G15.4+0.1 and this SNR can therefore be classified as a composite SNR. The paper can be found on the preprint server: arXiv:1310.6956.

Discovery of very high energy gamma-ray emission from the BL Lac object PKS 0301-243
Oct. 3, 2013

The active galactic nucleus PKS 0301-243 (z=0.266) is a high-synchrotron-peaked BL Lac object that is detected by Fermi/LAT. We report the discovery of PKS 0301-243 at very high energies (E>100 GeV) by the H.E.S.S. from observations between September 2009 and December 2011. The very high energy emission from PKS 0301-243 is used to derive an upper limit on the opacity of the extragalactic background light. The paper can be found on the preprint server: arXiv:1309.6174.

H.E.S.S and Fermi-LAT discovery of gamma rays from the blazar 1ES 1312-423
June 16, 2013

A deep observation campaign carried out by the High Energy Stereoscopic System (H.E.S.S.) on Centaurus A enabled the discovery of gamma rays from the blazar 1ES 1312-423, two degrees away from the radio galaxy. With a flux corresponding to 0.5% of the Crab nebula flux, 1ES 1312-423 is one of the faintest sources ever detected in the very high energy extragalactic sky.Radio, optical, UV, X-ray and Fermi gamma-ray observations complete the spectral energy distribution of this blazar, now covering 16 decades in energy. The paper can be found on the preprint server: arXiv:1306.3186.

Discovery of VHE gamma-rays from the quasar PKS 1510-089
May 7, 2013

The quasar PKS 1510-089 (z=0.361) was detected with H.E.S.S. with high significance, in data from March and April 2009. The GeV and optical light curves show pronounced variability during the period of H.E.S.S. observations. However, there is insufficient evidence to claim statistically significant variability in the VHE data. Unlike typical VHE-detected blazars where the broadband spectrum is dominated by non-thermal radiation at all wavelengths, the quasar PKS 1510-089 has a bright thermal component in the optical to UV frequency band. The paper can be found on the preprint server: arXiv:1304.8071.

Discovery of high and very high-energy emission from the BL Lac object SHBL J001355.9-185406
April 22, 2013

The detection of the high-frequency peaked BL Lac object (HBL) SHBL J001355.9-185406 (z=0.095) at high and very high-energy with the Fermi Large Area Telescope (LAT) and the High Energy Stereoscopic System (H.E.S.S.) is reported. The broadband spectral energy distribution is modelled with a one-zone synchrotron self-Compton (SSC) model. The paper can be found on the preprint server: arXiv:1304.4023.

Time-lapse movies of H.E.S.S. II telescope operation
March 23, 2013

The time-lapse movies by Mathieu de Naurois show the H.E.S.S. telescope under the Namibian night sky, with the Milky Way visible in the 2nd movie (movie 1, movie 2).

Discovery of TeV gamma-ray emission from PKS 0447-439 and derivation of an upper limit on its redshift
March 8, 2013

Very high-energy gamma-ray emission from PKS 0447-439 was detected with the H.E.S.S. Cherenkov telescope array in December 2009. This blazar is one of the brightest extragalactic objects in the Fermi Bright Source List and has a hard spectrum in the MeV to GeV range. The spectrum and light curve measured with H.E.S.S. are presented and compared to the multi-wavelength data at lower energies. The paper can be found on the preprint server: arXiv:1303.1628.

H.E.S.S. observations of the binary system PSR B1259-63/LS 2883 around the 2010/2011 periastron passage
Jan. 21, 2013

The gamma-ray binary system PSR B1259-63/LS 2883 was observed around its 15 Dec. 2010 periastron passage, and gamma ray emission was detected with high significance. The measured integral flux and the spectral shape of the 2011 data are compatible with the results obtained around previous periastron passages. Comparison with Fermi-LAT measurements around periastron indicate that mechanisms of GeV and TeV emission are different. The paper can be found on the preprint server: arXiv:1301.3930.

Search for very high energy gamma ray emission from Galactic globular clusters with H.E.S.S.
Jan. 10, 2013

Globular clusters (GCs) are established emitters of high-energy gamma-rays which could originate from the cumulative emission of the numerous millisecond pulsars; very high energy (VHE) gamma rays were detected from the direction of Terzan 5. This work describes a search for VHE gamma rays from 15 globular clusters covered by H.E.S.S. observations, and uses a stacking analysis to provide a stringent flux limit on this set of objects. The paper can be found on the preprint server: arXiv:1301.1678.

Search for photon line-like signatures from Dark Matter annihilations with H.E.S.S.
Jan. 9, 2013

Gamma-ray line signatures can be expected in the very-high-energy domain due to self-annihilation or decay of dark matter particles in space. Using H.E.S.S. data, upper limits on line-like emission are obtained in the energy range between ~500 GeV and ~25 TeV for the central part of the Milky Way halo and for extragalactic observations, complementing recent limits obtained with the Fermi-LAT instrument at lower energies. The paper can be found on the preprint server: arXiv:1301.1173. See also APS Physics Spotlight.

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