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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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First gamma-ray images from the upgraded H.E.S.S. cameras
Mar 1, 2017

The newly refurbished H.E.S.S. cameras in Namibia have detected its first gamma-ray signals: Markarian 421, a well-known blazar in the constellation of Ursa Major, has been observed during an active state and was detected at high significance. After four years of development, testing, production and deployment, this is the last big milestone of the H.E.S.S. I camera upgrade project. See our Source of the Month 03/2017 for details.
The Population of TeV Pulsar Wind Nebulae in the H.E.S.S. Galactic Plane Survey
February 28, 2017

The sky maps and source catalogue of the H.E.S.S. Galactic Plane Survey allow for a detailed study of TeV pulsar wind nebulae found throughout the last decade with H.E.S.S. Besides a correlation between the TeV surface brightness and the pulsar spin-down power, the study hints at a correlation between the offset between pulsar and nebula and the apparent TeV efficiency of the object. The paper can be downloaded from the preprint server: arXiv:1702.08280
H.E.S.S. Contributions to the 34th International Cosmic Ray Conference (ICRC2015), The Hague, The Netherlands
October 8, 2015

A wide of range of H.E.S.S. contributions to the ICRC 2015 addresses first results using the H.E.S.S. II telescope, results from the four-telescope system, techniques for data analysis as well as hardware aspects. See list of conference contributions.

Discovery of variable VHE gamma-ray emission from the binary system 1FGL J1018.6-5856
March 12, 2015

Re-observations of the very-high-energy source HESS J1018-589 A -- coincident with the Fermi-LAT gamma-ray binary 1FGL J1018.6-5856 -- have resulted in a source detection significance of more than 9σ. Variability is clearly detected in the night-by-night lightcurve. When folded on the orbital period of 16.58 days, the rebinned lightcurve peaks in phase with the observed X-ray and high-energy phaseograms. The paper can be found on the preprint server: arXiv:1503.02711.

Constraints on an annihilation signal from a core of constant Dark Matter density around the Milky Way center
February 16, 2015

An annihilation signal of dark matter is searched for from the central region of the Milky Way, based on 9 h of dedicated ON/OFF observations of the Galactic center region with H.E.S.S. Upper limits on the velocity-averaged annihilation cross section are derived for the 300 GeV to 10 TeV mass range. These represent the strongest limits on annihilating TeV mass dark matter without the assumption of a centrally cusped dark matter density distribution in the search region. The paper can be found on the preprint server: arXiv:1502.03244.

An exceptionally powerful trio in the Large Magellanic Cloud H.E.S.S. - discovers three extremely luminous gamma-ray sources in Milky Way’s satellite galaxy
January 22, 2015

In the Large Magellanic Cloud, H.E.S.S. discovered most luminous very high-energy gamma-ray sources: three objects of different type, namely the most powerful pulsar wind nebula, the most powerful supernova remnant, and a shell of 270 light years in diameter blown by multiple stars, and supernovae – a so-called superbubble. This is the first time that stellar-type gamma-ray sources are detected in an external galaxy, at these gamma-ray energies. The superbubble represents a new source class in very high-energy gamma rays. See press release for details. The results are published in Science 347 (2015) 406-412.

The 2012 flare of PG 1553+113 seen with H.E.S.S. and Fermi-LAT
January 21, 2015

Very high energy gamma-ray flaring activity of the BL Lac object PG 1553+113 has been detected by the H.E.S.S. telescopes. The flux of the source increased by a factor of 3 during the nights of 2012 April 26 and 27 with respect to the archival measurements with hint of intra-night variability. No counterpart of this event has been detected in the Fermi-LAT data. This pattern is consistent with VHE gamma ray flaring being caused by the injection of ultrarelativistic particles, emitting gamma rays at the highest energies. The paper can be found on the preprint server: arXiv:1501.05087.

H.E.S.S. reveals a lack of TeV emission from the supernova remnant Puppis A
December 27, 2014

Puppis A is an interesting 4 kyr-old supernova remnant (SNR) that shows strong evidence of interaction between the forward shock and a molecular cloud, and is emitting gamma rays in the Fermi energy range. Very-high-energy gamma-ray emission from Puppis A is for the first time searched for with H.E.S.S.. The analysis of the H.E.S.S. data does not reveal any significant emission towards Puppis A, implying that its broadband gamma-ray spectrum must exhibit a spectral break or cutoff. The paper can be found on the preprint server: arXiv:1412.6997.

Detection of TeV emission from the interaction region between the supernova remnant G349.7+0.2 and a molecular cloud
December 12, 2014

G349.7+0.2 is a young Galactic supernova remnant (SNR) located at the distance of 11.5 kpc and observed across the entire electromagnetic spectrum from radio to high energy (HE; 0.1 GeV < E < 100 GeV) gamma-rays. Radio and infrared observations indicate that the remnant is interacting with a molecular cloud. In this paper, the detection of very high energy (VHE, E > 100 GeV) gamma-ray emission coincident with this SNR with the High Energy Stereoscopic System (H.E.S.S.) is reported. This makes it one of the farthest Galactic SNR ever detected in this domain. The paper can be found on the preprint server: arXiv:1412.2251.

Diffuse Galactic gamma-ray emission with H.E.S.S
December 3, 2014

After completion of the systematic survey of the inner Galaxy, the H.E.S.S. experiment is in a prime position to observe large-scale diffuse emission at TeV energies. Data of the H.E.S.S. Galactic Plane Survey are investigated in regions off known gamma-ray sources. For the first time large-scale gamma-ray emission along the Galactic Plane using imaging atmospheric Cherenkov telescopes has been observed. The paper can be found on the preprint server: arXiv:1411.7568.

Discovery of the VHE gamma-ray source HESS J1832-093 in the vicinity of SNR G22.7-0.2
November 30, 2014

The region around the supernova remnant (SNR) W41 contains several TeV sources and has prompted the H.E.S.S. Collaboration to perform deep observations of this field of view. This resulted in the discovery of the new very high energy (VHE) source HESS J1832-093, spatially coincident with a part of the radio shell of the neighboring remnant G22.7-0.2. Dedicated XMM-Newton observations led to the discovery of a new X-ray point source spatially coincident with the TeV excess. The paper can be found on the preprint server: arXiv:1411.0572.

The high-energy gamma-ray emission of AP Librae
October 31, 2014

The gamma-ray spectrum of the low-frequency-peaked BL Lac (LBL) object AP Librae is studied, following the discovery of very-high-energy (VHE) gamma-ray emission up to TeV energies by H.E.S.S.; AP Librae is one of the few VHE emitters of the LBL type. This study also makes use of Fermi-LAT observations in the high energy range, providing the longest continuous light curve (5 years) ever published on this source. The source underwent a flaring event on MJD 56306-56376 in the HE range. While the H.E.S.S. and Fermi-LAT fluxes are in good agreement where they overlap, a spectral curvature between the steep VHE spectrum and the Fermi-LAT spectrum is observed. The paper - authored by the H.E.S.S. and Fermi-LAT Collaborations – can be found on the preprint server: arXiv:1410.5897.

Search for dark matter annihilation signatures in H.E.S.S. observations of Dwarf Spheroidal Galaxies
October 31, 2014

Dwarf spheroidal galaxies are characterized by a large mass-to-light ratio.They are amongst the most promising candidates for indirect dark matter searches. During the last years the H.E.S.S. telescopes observed five of these dwarf galaxies for more than 140 hours in total, searching for TeV gamma-ray emission from annihilation of dark matter particles. In the absence of a significant signal new constraints on the annihilation cross-section applicable to Weakly Interacting Massive Particles (WIMPs) are derived by combining the observations of the five dwarf galaxies. The paper can be found on the preprint server: arXiv:1410.2589.

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.

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