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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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The birth of multi-messenger astrophysics
Oct 16, 2017

On August 17, 2017, the gravitational wave interferometers Advanced Ligo and Advanced Virgo recorded a signal from the merger of a binary neutron star system, a type of signal that had never been seen before. Complementing this exciting discovery, a large variety of electromagnetic observations were able to record signals from the same event. They range from the detection of a gamma-ray burst about 2 seconds after the gravitational wave event, over near-infrared, optical and UV emission from decay of radioactive nuclei created in the resulting kilonova to X-ray and radio emissions detected several days and weeks after the event. This first and extremely successful observation campaign is marking the beginning of truly multi-messenger astrophysics.

The gravitational wave event was localized within a 3 by 10 degree region, well beyond the H.E.S.S. field of view and requiring multiple pointings to cover the area. The H.E.S.S. target selection identified regions of high probability to find a counterpart of the gravitational wave event. These regions already contained the counterpart SSS17a that has later been identified in the optical domain, several hours after our observations. As a result, H.E.S.S. was the first ground-based pointing instrument to obtain data on this object. A subsequent monitoring campaign with the H.E.S.S. telescopes extended over several days, covering timescales from 0.22 to 5.2 days and energy ranges between 270 GeV to 8.55 TeV. No significant gamma-ray emission has been found within this time interval. The derived upper limits on the very-high-energy gamma-ray flux for the first time constrain non-thermal, high-energy emission following the merger of a confirmed binary neutron star system, and further observations of this source will allow to check whether TeV energies are reached on a larger time scale.

For more information, see the H.E.S.S. paper

Patrick Fleury left us on 14th September 2017.
Sep 17, 2017

Patrick Fleury left us on 14th September 2017.

He acted as director of the PNHE laboratory of Ecole Polytechnique from 1973 to 1984, and oversaw its establishment at Palaiseau.

Throughout his career, Patrick Fleury played a major, and often pioneering rĂ´le in several domains of the research in physics at the CNRS/IN2P3, but also for the massive data processing and very large scale integration (VLSI).

In particle physics, after having been a key person in the bubble chamber era, he steered his laboratory towards electronic detectors and pushed their use at CERN, already from the end of the '60s.

He made fundamental contributions to the emergence of ground-based gamma-ray astronomy and its establishment as a scientific discipline in France and abroad, with the ARTEMIS, CAT, CELESTE, and HESS projects, as well as building-up the participation of the CNRS/IN2P3 in NASA's Fermi gamma-ray satellite.

As president of the scientific evaluation committee of VIRGO, he was an important player in the IN2P3's engagement in the gravitational wave domain.

Patrick was an exceptional scientist. He was a visionary, passionate and clear-thinking, a builder of projects, with great intellectual and moral force, and profound humanity.

H.E.S.S. measures the extension of the Crab nebula in TeV gamma rays
Jul 28, 2017

Resolving source extensions that are smaller than the angular resolution requires a good understanding of the instrument point spread function. Using a novel, more realistic approach to simulate the instrument response, H.E.S.S. has now pushed the point-source resolvability in very-high-energy gamma-ray astronomy to a new level. These so-called run-wise simulations reduce the systematic uncertainties on the gamma-ray direction reconstruction, and allow us to resolve, for the first time, the extension of the Crab Nebula in TeV gamma rays. More information can be found in M. Holler et al., Proc. ICRC 2017 (Busan), arXiv:1707.04196.
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
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