HESS - in Africa

The HESS collaboration was formed as a European-African partnership. Germany, France and South Africa participate with the largest groups.

The HESS array is set up in Namibia, which is thus home to the largest optical telescope and the largest gamma-ray observatory in the world. The HESS telescopes have been constructed and errected in Namibia by local companies. They are maintained and operated by Namibian staff. HESS operations are carried out by Namibian staff. Namibia's UNAM is the host partner of HESS. The facility is set up on a local Namibian farm, and provides job to farm workers as well.

HESS science was the basis of more than 100 degrees awarded to African students.

HESS - the Collaboration

The HESS collaboration consists of 240 scientists in 39 institutions working in 13 countries from four continents.

The collaborating institutions jointly fund the operations of the array. They provide the resources, develop the science program, conduct the observations (on site or remotely) ensure the proper functionality of all hardware components, maintain the calibration and analysis chains and carry out analysis and interpretation of the data obtained.

About 1/3 each of the collaboration are students, postdoctoral and senior researchers.

The collaborations meets twice annually in person (since 2020 in hybrid mode) with many virtual meetings in different working groups and projects.

HESS - the Science

HESS has detected a wide range of sources, source-classes and phenomena in the VHE energy band (Quasars, Radio Galaxies, BL Lac objects. Starburst galaxies, GRB, SNR, PWN, Novae, Stellar Clusters, Starforming regions, Molecular Clouds, Gamma-ray binaries, Microquasars, the Galactic Centre, Diffuse ISM, and more.)

Observations have been used to measure or constrain the level of the extragalactic background light, cosmic magentic fields, violation of Lorentz invariance, Dark Matter in different environments, the spectra and distribution of Galactic Cosmic Rays.

HESS conducted the first surveys of the VHE Gamma-ray sky and currently employs surveys of the Galactic plane, the LMC and several extragalactic fields.

HESS - the Observatory

The HESS project started as an experiment to develop and validate the technique of stereoscopic imaging with atmospheric Cerenkov telescopes and to explore the universe in the VHE band (< 100 GeV photon energies). The experiment thus finally opened the third window for routine ground-based astronomical research.

The facility is used by the collaboration to conduct a coherent observing program for astronomical studies as a first priority. It continues to be used to develop and advance new experimental and instrumental techniques.

HESS is open for external proposals, and ToO projects and collaborates with many partners in joint astronomial and astro-particle physics projects.

It operates auxiliary instruments for optical monitoring and conducts observations as intensity interferometer.

HESS - the Telescopes

HESS is comprised of 5 telescopes:

Four Davis-Cotton telescopes of 12 m diameter, one giant IACT of 28 m.

All telescopes have been designed in Germany and manufactured in Namibia.

HESS - the Array

The five telescopes are set up in a quadratic configuration (120 m side length) with the giant telescope placed in the centre of the array. This enables stereoscopic observation of the gamma-ray showers with high multiplicity for reconstruction of shower images and identification of gamma-rays.

Once any of the cameras of either telescope is triggered by a shower, data from all five telescopes are read out (figure). The combined images of the shower allow an accurate reconstruction of the direction and energy of the incoming gamma-ray photon.

Using telescopes of different sizes allows to reconstruct photons over a wide range of energies (<100 GeV to 100 TeV for HESS). HESS is the only hybrid array using this technique.

Apply for HESS observations

Any scientist can apply for HESS observations in annual calls for proposals in september each year.

Up to 10% of HESS observing time is available for external proposals. The proposals are evaluated by the HESS observing program committee on scientific merrit only. Any data obtained through external programs will be calibrated and made available for proposers as fits files to be analysed using public analysis software.

Priviledged access is granted for one year.

Alternatively, external proposers may chose to collaborate with the HESS team analysing their data.

Become a HESS member

The HESS collaboration is a cooperative endeavour of scientific institutions, laboratories and university groups. Each member institution may appoint individual scientists and doctoral student as HESS members. Member institutions provide an access fee and an annual contribution scaled to the number of individual members.

All individual members are entitled to propose for HESS observations, join any ongoing HESS project and become a coauthor, use the entire HESS archive, grant access to any student under their supervision.

Members are expected to contribute to the operation and scientific mission of the collaboration.

Trigger HESS ToO observations

HESS runs dedicated ToO programs on GRB, Neutrino alerts, GW alerts, Blazars, Novae, FRBs, and individual sources with predefined selection cuts.

HESS collaborates with individual teams on dedicated trigger schemes.

HESS is also open to individual requests for ToO observations in DDT mode. Any such trigger requests that are not covered by the standard HESS ToO programs within their selection cuts is Assessed. Once granted, proposers are informed and invited to cooperate in joint scientific analysis of the HESS data obtained.

Use HESS public data

A growing fraction of HESS data is made available for open use. The entire archive of HESS data comprises more than 20000 h of high quality data taken with the full HESS array or subsets of the array.

While the original and intermediate data are stored in propriatory data formats, data made publically available are offered in FITS. Public data are available through the virtual observatory, through the HESS webpage or in dedicated subsets that relate to HESS surveys. Data published in tabular form is available as auxiliary data set of the corresponding publications.

Watch the HESS GRB program

HESS routinely observes GRB communicated via the GCN network subject to visibility constraints at the HESS site and a source-specific latency constraint (flux, redshift, MWL properties). Any GRB that triggers HESS observations is publically available via the HESS GRB link to provide information for potential MWL followup.

Further information about the HESS observations and preliminary Information of quicklook analysis is shared with MWL partners.

Employ HESS public tools

Starting out as an experiment, the original tools, procedures and data formats were proprietary to allow for quick and versatile adaption of new ideas and strategies.

As calibration and analysis strategies matured, and HESS results were used alongside other astronomical data, the collaboration adapted the widely used FITS format for calibrated data and launched the development of public tools.

In particular, the library Gammapy was developed. Gammapy is an open-source Python package for gamma-ray astronomy. It is recommended to analyze HESS data and shall be used as core library for the science analysis tools of the CTA.

Be a HESS MWL collaborator

The HESS collaboration entertains a broad MWL progam to enhance the science exploitation of the observing program.

The HESS collaboration is interested and open to partner with corresponding scientific interests.

HESS is keen to exploit trigger opportunities for observations in TOO studies, MWL observations of monitoring campaigns and follow.up studies of ToO observations.

HESS also routinely seeks to use dedicated MWL data obtained in lower frequency observations (radio through Xray) through imaging, interferometry, spectroscopy and polarimetry.

Browse HESS publications

The collaboration has published more than 300 research papers.

While most results have been published in the main research journals of astrophysics and particle physics, selected results, in particular on methods, extensions of previous work, and upper limits have been published in conference proceedings.

The full list of publications is available on the HESS web pages . For many of the publications links to auxilliary data in Tabular form of fits files are available in the individual links.