HESS Logo News Archive

H.E.S.S. collaboration member Alison Mitchell wins Emmy Noether grant
August 14, 2021

Congratulations to Alison Mitchell for winning an Emmy Noether grant from the Deutsche Forschungsgemeinschaft. Her six-year project "Unveiling the Origin of Galactic Cosmic Rays: Exploring Pulsar Environments at the Highest Energies" will use H.E.S.S. and ultimately CTA to tackle this important question in two steps: After focusing on technical improvements to data analysis and towards detailed and precision studies of individual PWNe systems, the second aim will be to increase the number of known TeV PWNe and halos, conducting multi- wavelength and population studies. The grant will enable Alison to start an Emmy Noether team within the H.E.S.S. group of Erlangen University in October 2021.

The project focus is on the acceleration and transport of Cosmic Rays in Pulsar environments. Within the last year, evidence has emerged that Pulsar Wind Nebulae (PWNe) accelerate electrons and positrons to PeV energies, but the origin of other PeV particles remains unconfirmed. Recent measurements of two nearby pulsars showed surprisingly slow diffusion of Cosmic Rays, causing some tension with current theoretical models.

Alison has started her scientific career as a PhD student in the H.E.S.S. group at MPIK in Heidelberg and subsequently worked for the CTAO, the University of Zurich and ETH. During this time Alison remained a member or an associate member, respectively, of the H.E.S.S. collaboration. For her numerous contributions within the H.E.S.S. collaboration, Alison was awarded the H.E.S.S. Prize in 2020.

New insights into gamma ray burst: H.E.S.S. publishes observations of the third GRB detected at very high photon energies
June 04, 2021

Today, June 04, 2021, the H.E.S.S. collaboration published results of observations of the gamma ray burst GRB190829A. The study appeared in Science Vol. 372, Issue 6546, pp. 1081-1085 (2021) and is available on arXiv 2106.02510 as well. Only the third gamma ray burst to have been detected at very high energies (photon energy > 100 GeV), GRB190829A has a very small distance to Earth compared to most GRBs observed in all energy bands. With a redshift of only z=0.0785, the gamma rays emitted from this explosion suffer only little absorption on their way to Earth and its properties can hence be explored even up to TeV energies, significantly exceeding the range offered by the first two GRBs detected in this energy band.

Unlike GRB180720B, detected with the H.E.S.S. telescopes in 2018 and GRB190114C, observed with the MAGIC telescopes earlier in 2019, GRB190829A has been monitored during three subsequent nights. This extended coverage of the decay in flux, together with high-quality spectral studies offered new insights into the physical processes in these most luminous cosmic explosions. Further information may be obtained in the June 2021 edition of the 'HESS - Source of the Month'

Gammapy selected as open-source software of choice for analysis of H.E.S.S. data
May 10, 2021

Data obtained with the H.E.S.S. telescopes are recorded and stored in "root" format, which is widely used in the particle physics community. From the early phases the collaboration developed several proprietary analysis methods. Processed data are stored in proprietary file structures. In order to facilitate exchange and common treatment of data obtained with other facilities and to allow efficient adaptation of open-source software, the H.E.S.S. collaboration explored data analysis with different open-source tools using the open FITS data format for some time.


Based on extensive tests and development and adaptation, the collaboration now chose Gammapy as its open-source analysis framework. Gammapy v1.0rc Gammapy will be released in the next weeks.

Gammapy-based studies will complement the well-established proprietary analysis methods used by the H.E.S.S. collaboration and facilitate further development of the tools by challenges posed in exploring real observations obtained with H.E.S.S..

H.E.S.S. collaboration member Manuel Meyer wins ERC grant
April 30, 2021

Congratulations to Manuel Meyer for winning a Starting Grant from the European Research Commission on "Searching for axion and axion-like-particle dark matter in the laboratory an d with high-energy astrophysical observations". Manuel and his group will join the H.E.S.S. group at the University of Hamburg starting June 2021.

The grant will enable Manuel to start a dedicated research group which will search for hypothetical axions and axion-like particles. Such particles are predicted in certain theories of particle physics and could explain several unresolved questions in particle physics and cosmology. For example, they are candidates to explain the mysterious dark matter. Manuel Meyer’s team will search for axions by contributing to dedicated laboratory experiments and by searching for their signatures with astrophysical observations — including observations of distant galaxies with the H.E.S.S.

Manuel has started his scientific career as a PhD student in the H.E.S.S. collaboration, has worked as a H.E.S.S. member in several groups of the collaboration thererafter and kept his association wit h the H.E.S.S. collaboration also while working as a Feodor Lynen Research Fellow at Stanford Univer sity.

HESS completes a very successful year 2020.
February 10, 2021

2020 will have its place in history. The Covid-19 pandemic affected the lives of many people all over the world. That is why we are grateful to the continued efforts of our local crew and shifters, and many members of the collaboration, in keeping HESS running during this unprecedented time. Thanks to their hard work, the HESS experiment had an extremely successful year in 2020. We celebrate a record telescope efficiency resulting in the largest annual amount of data taken in the history of the HESS experiment.

2020 has been the first full year in the HESS extension phase that started October 2019 with the installation of a new camera on CT5, the world's largest Imaging Atmospheric Cherenkov Telescope (IACT). For the extension phase of HESS the collaboration had set new goals to increase operational efficiency and agility. While the roll-out and implementation of the upgrades were challenged by global travel restrictions to limit the spread of Covid-19, the high goals that had been set for HESS have been met. Not only did the HESS telescopes continue observations throughout the entire year without interruption - no small feat. The new camera runs flawlessly.

The new camera on the CT5 telescope (shown here after its arrival in Namibia, © C. Föhr, Heidelberg) worked smoothly throughout its first year on site, contributing to the high telescope efficiency.
Many new features in operations increased the on-target time. As a result the number of observing hoeached a new record level. 2020 has been the most successful year in terms of data-taking in the history of HESS. The operational efficiency exceeded 98% for the full 5 telescope array for most of the year, with an average telescope efficiency of 95%. In the entire year about 1180 hours of dark-time observations were taken with each of the 5 telescopes. This record level is unrelated to weather conditions, which caused weather losses that were close to the long-term average.

In addition, the collaboration started taking data under moonlight conditions, reflecting the increasing importance of time-domain astronomy for the HESS science program. This mode is still in its ramp-up phase and is expected to lead to a further increase of observing time in 2021. The collaboration does not take all the work that has gone into making sure the operations were smooth and successful for granted, but aims for another high in 2021 and we is looking forward to again meet in person and celebrate together.

We mourn the passing of our friend and colleague
January 10, 2021

Friends and colleagues were sad and shocked to learn that on January 9, 2021 Albert Jahnke died in his hometown, Windhoek, in Namibia. Albert, who has joined the local crew of the H.E.S.S. experiment on its Farm Göllschau site in 2006, died of an infection with Covid-19.

The H.E.S.S. Collaboration offers its deepest condolences to the family and friends of Albert Jahnke.

Albert Jahnke graduated from Windhoek and subsequently Technikon in South Africa. He had worked in telecommunication with various schools and enterprises before deciding to combine his profession with his long-standing interest in astronomy. In 2006 he joined the team in charge of operating the H.E.S.S. array on Farm Göllschau. First he was responsible for training the monthly shift-crews of H.E.S.S. members, mostly from Europe, for their four-week observing campaigns. Albert introduced them to the safety regulations, instrumentation and operation of the telescopes and observational procedures and worked alongside with them for the first few nights of the monthly shift. He kept his responsibility for this activity throughout his entire engagement in H.E.S.S. and has worked closely with more than a hundred two-to-three-person shift crews.

Over the years Albert took up other duties, contributed to many installations on the H.E.S.S. site, worked tirelessly on maintaining all hardware components, and cooperated closely with the many teams of the collaboration that are in charge of any subsystem of the array to ensure the proper functioning. He contributed to almost all aspects of local operations. His dedication to H.E.S.S. was outstanding and it has frequently been difficult to prevent him from working overtime well past his term of duty. He was always available to help shift-crews with any problem they might face at any time of the day and often provided advice even from home when being off-duty.

Beyond work in the control-building and with the telescopes, Albert's contribution to life on Göllschau will probably be best remembered for his excellent barbecues. These weekly events were known as highlights in the monthly shifts and very much looked forward to by returning visitors.

Albert enjoyed working for H.E.S.S. and was a devoted, reliable and hard-working colleague who contributed much to the success of the experiment. Following a very difficult year he fell victim to the pandemic during a well-deserved Christmas and New Year break.

He has been a good friend to many members of the collaboration. He will be truly missed.

H.E.S.S. data resolve extragalactic jet in Centaurus A
June 18, 2020

Today the H.E.S.S. collaboration published a breakthrough result in the magazine Nature (Volume 582, pages 356–359, 2020), revealing the gamma-ray emission from the famous radio galaxy Centaurus A (also known as NGC 5128) to be spatially extended over thousands of light-years. This is the first time that an extragalactic source has been spatially resolved in the regime of very high energy gamma-ray astronomy and permits a direct determination of the size the region responsible for gamma-ray emission at TeV energies in an active galaxy. The publication, based on advanced data analysis of a large amount of excellent data obtained with the H.E.S.S. array is a technical achievement and an important step in our understanding of relativistic jets in the Universe.

During the last decades the universe beyond our Milky Way has been probed in the light of very high energy (VHE) gamma-rays, identifying many different kinds of distant Quasars and other active galaxies. Curiously, those distant and extremely luminous sources of gamma-ray emission are very often found to vary within weeks or days - sometimes even as fast as hours. It was hence concluded, that the highly energetic emission originates from very compact regions - very likely linked to a massive Black Hole in the center of the host galaxy. The new study of Centaurus A observations reveals that the emitting regions of these very energetic sources are actually extended over many thousands of light-years.

Centaurus A, one of the first radio galaxies to be discovered, is a well-known active galaxy on the Southern Sky that displays prominent jets in highly resolved radio and X-ray images. The H.E.S.S. array detected TeV gamma-ray radiation from this object in 2009 and studies its spectral and temporal characteristics. A new analysis method that now allows mprphological studie source to be spatially extended in the direction of the radio and X-ray jets. While the different angular resolutions that can be achieved in different enrgy ranges prohibit a directs comparison on all angular scales, the figure clearly illustrates that the best-fitting model of the gamma-ray emission lines up with the synchrotron radiation revealed in the radio band.

H.E.S.S. array continues observations during COVID-19 pandemic
May. 10, 2020

While the COVID-19 pandemic has spread around the globe and still imposes severe restrictions in very many countries, the H.E.S.S. array was able to continue operations throughout March and April 2020 and anticipates continuous operations in the forthcoming months. This is very important for scientific investigations within the HESS collaboration and the scientific community at large and is made possible by several favorable circumstances:

The HESS array is located on the Goellschau farm, 120 km south of Windhoek in Namibia, a sparsely populated region in a sparsely populated country. The small local crew and the observers live and work in a very isolated environment already in normal times. Thanks to early and efficient monitoring, Namibia has been able to limit the influx and spread of Corona in the country and suffers very small numbers of infections. The H.E.S.S. site is a very safe place to work and operate. At the same time, Namibian regulations during the pandemic permit the continuation of Scientific Services and thus enabled operations.

The observers that had started their scheduled shift prior to the onset of restrictions have fortunately been able and eager to continue measurements beyond their regular slot, supported by the on-site local H.E.S.S. crew. Advancing further through these difficult times, the H.E.S.S. observing program continues thanks to members of the Namibian H.E.S.S. partner UNAM (University of Namibia), again supported by the local Namibian H.E.S.S. crew. The situation is continuously monitored as the health and safety of everybody involved is of utmost importance.

Continuous observations ensures new scientific discoveries (such as the detections of one of the brightest outbursts yet measured with HESS) in April 2020 and the completion of the test of new instrumentation that has been installed in the end of 2019. The H.E.S.S. collaboration is grateful to all individuals that have made continuous operations and observations possible and continue to do so in the forthcoming times. This includes the local crew in Namibia, shift-teams and many off-site sub-system experts making extra efforts for the operation of the H.E.S.S. array.

First gamma-ray sky map with the new H.E.S.S. CT5 camera, two days after installation
Dec. 9, 2019

The H.E.S.S. collaboration has upgraded its 600 square metre Cherenkov telescope with a new high-performance camera with fully-digital trigger and readout system, and high quantum efficiency photon detectors.

The main goals of the upgrade are a reduction in the energy threshold of the telescope, improved sensitivity, and better stability of operation. The new camera is based on the FlashCam design, which has been developed for the use in the Cherenkov Telescope Array (CTA) by a consortium of the universities from Zürich, Tübingen, Erlangen and Innsnstitute for Nuclear Physics in Heidelberg. After extensive tests of a complete prototype with its hardware, firmware and software, the camera was shipped to Namibia, where it arrived at the beginning of October 2019. After adaption of the mechanical telescope interfaces, the camera was installed on October 20th (Fig. 1).

Fig. 1: The installation and commissioning teams together with the local on-site technical crew in Namibia in front of the H.E.S.S. CT5 telescope with its new camera (October 23rd , 2019).
The telescope was ready to make astrophysical observations just two days after mechanical installation. In its first night of operation, the telescope was pointed at the Crab Nebula, among other targets. Fig. 2 shows the gamma-ray sky map around the Crab Nebula obtained with the standard H.E.S.S. real-time analysis during these first observations with the upgraded telescope. A clear detection is visible at the position of the Crab Nebula.
Fig. 2: Gamma-ray sky map obtained in real time during the first 28 min observation of the Crab Nebula with the H.E.S.S. CT5 telescope, equipped with the new camera.

In the meantime, the telescope with its new camera is participating in routine observations with the complete H.E.S.S. array, confirming the expected performance improvements and stability of operation. With its high-quantum-efficiency light sensors and sophisticated trigger and readout scheme, the new camera will further boost the performance of H.E.S.S.’s world’s largest Cherenkov telescope. With this success the H.E.S.S. collaboration, together with the FlashCam consortium, have also demonstrated a highly efficient mode for the installation and commissioning of cameras, as will be required for the deployment of the around 100 telescopes of the Cherenkov Telescope Array (CTA).

First detection of gamma-ray burst afterglow in very-high-energy gamma light
Nov. 20, 2019

After a decade-long search, scientists have for the first time detected a gamma-ray burst in very-high-energy gamma light. This discovery was made in July 2018 by the H.E.S.S. collaboration using the huge 28-m telescope of the H.E.S.S. array in Namibia. Surprisingly, this Gamma-ray burst, an extremely energetic flash following a cosmological cataclysm, was found to emit very-high-energy gamma-rays long after the initial explosion.

Extremely energetic cosmic explosions generate gamma-ray bursts (GRB), typically lasting for only a few tens of seconds. They are the most luminous explosions in the universe. The burst is followed by a longer lasting afterglow mostly in the optical and X-ray spectral regions whose intensity decreases rapidly. The prompt high energy gamma-ray emission is mostly composed of photons several hundred-thousands to millions of times more energetic than visible light, that can only be observed by satellite-based instruments. Whilst these space-borne observatories have detected a few photons with even higher energies, the question if very-high-energy (VHE) gamma radiation (at least 100 billion times more energetic than visible light and only detectable with ground-based telescopes) is emitted, has remained unanswered until now.

Fig. 1: Gamma-Ray bursts are the most luminous explosions in the universe. Within a few seconds they radiate more energy than the sun in billions of years. Understanding the physical processes at work in these monstrous explosions is an important goal of modern astrophysics. Artist’s view of a GRB and the formation of extremely fast jets (Credit: ESO/A. Roquette)

On 20 July 2018, the Fermi Gamma-Ray Burst Monitor and a few seconds later the Swift Burst Alert Telescope notified the world of a gamma-ray burst, GRB 180720B. Immediately after the alert, several observatories turned to look at this position in the sky. For H.E.S.S., this location became visible only 10 hours later. Nevertheless, the H.E.S.S. team decided to search for a very-high-energy afterglow of the burst. After having looked for a very-high-energy signature of these events for more than a decade, the efforts by the collaboration now bore fruit.

A signature has now been detected with the large H.E.S.S. telescope that is especially suited for such observations. The data collected during two hours from 10 to 12 hours after the gamma-ray burst showed a new point-like gamma-ray source at the position of the burst. While the detection of GRBs at these very-high-energies had long been anticipated, the discovery many hours after the initial event, deep in the afterglow phase, came as a real surprise. The discovery of the first GRB to be detected at such very-high-photon energies is reported in a publication by the H.E.S.S. collaboration et al., in the journal 'Nature' on November 20, 2019.

Fig. 2: The large central H.E.S.S. telescope with 614 m² mirror area that was used for the first detection of a GRB in VHE gamma-ray light and two of the four smaller telescopes, each with 107 m² mirror area. (Credit: MPIK / Christian Föhr, email: christian.foehr@mpi-hd.mpg.de)

GRB 180720B was very strong and lasted for about 50 seconds – a relatively long duration indicating the death of a massive star. In this process, its core collapses to a rapidly rotating black hole. The surrounding gas forms an accretion disk around the black hole, with gas jets ejected perpendicularly to the disk plane creating the gamma-ray flashes. Elementary particles are accelerated in these jets to velocities nearly as high as the speed of light and interact with the surrounding matter and radiation, leading to the copious production of gamma rays.

The very-high-energy gamma radiation which has now been detected not only demonstrates the presence of extremely accelerated particles in GRBs, but also shows that these particles still exist or are created a long time after the explosion. Most probably, the shock wave of the explosion acts here as the cosmic accelerator. Before this H.E.S.S. observation, it had been assumed that such bursts likely are observable only within the first seconds and minutes at these extreme energies, and not many hours after the explosion.

At the time of the H.E.S.S. measurements the X-ray afterglow had already decayed very considerably. Remarkably, the intensities and spectral shapes are similar in the X-ray and gamma-ray regions. There are several theoretical mechanisms for the generation of very-high-energy gamma light by particles accelerated to very-high-energies. The H.E.S.S results strongly constrain the emission to two potential mechanisms. In both cases, however, the observations raise new questions. Although energetically one of these mechanisms is preferred, both the shape of the H.E.S.S. spectrum, and the energy range of the emission at such late times presents a challenge to both emission scenarios.

Fig. 3: GRB 180720B in very-high-energy gamma light, 10 to 12 hours after the burst as seen by the large H.E.S.S. telescope. The red cross indicates the position of GRB 180720B, determined from the optical emission of the GRB. (Credit: H.E.S.S. collaboration)

Detection of VHE gamma-ray emission from GRB190829A
Sep. 24, 2019

Gamma-ray bursts (GRB), known from the 1960's, are burst of gamma rays of extragalactic origin, which appear randomly on the sky at a rate of about one per day, and whose prompt emission is know to last from a few seconds to a few minutes. They are subsequently followed by a afterglow phase, fading progressively during up to a few months. Short GRBs appear to be associated with coalescence of neutron stars, a theory which is now supported by the detection of gravitational waves GW170817 associated with a gamma ray burst on august 17th, 2017. Long GRBs, on the other hand, are most likely produced during the gravitational collapse of giant stars, which can lead to the formation of a black hole or a neutron star. This hypothesis was in particular strongly supported by the observation in 2003 of GRBs in coincidence with supernova (of type Ib/c).

Gamma-ray burst are one of the few types of astrophysical objects that could potentially accelerate particles up to extreme energies (1019 electronvolts), and thus unveil the mystery of Ultra High Energy Cosmic Rays (UHECRs). Until very recently, high energy photons up to about 100 gigaelectronvolts (GeV) from GRBs were deteced by the Fermi-LAT space observatory. In January 2019 the MAGIC ground-based gamma-ray experiment announced the detection of >300 GeV gamma rays from GRB190114C [ATEL #12390] and H.E.S.S. announced the detection of VHE emission from another burst (GRB180720B) at the 1st CTA Symposium in May 2019.

On August 30, 2019 H.E.S.S. reported the detection of very-high energy emission associated with the afterglow phase of the GRB190829A in an Astronomer's Telegram. Gamma-ray emission was detected more than 4 hours after the burst, which will bring new constrains on the models of particle acceleration and radiation, and shed a new light on these extreme objects.

Original announcement: http://www.astronomerstelegram.org/?read=13052

Astronomy and Astrophysics journal highlights HESS results
Feb. 4, 2019

The Astronomy and Astrophysics journal has chosen a HESS paper as an A&A Highlight; selected by A&A Editors as particularly interesting papers.

The pulsar wind nebula HESS J1825-137 was one of the first sources detected by HESS in the Galactic Plane and the first to show strong energy-dependent morphology.

Combining data over more than ten years of HESS observations into a deep exposure on the region enabled detailed spectral and morphological analysis of the nebula. By characterising the extent of the gamma-ray emission in a set of independent energy bands, the changing size was used to test the mechanism of particle transport within the nebula. A spatially resolved spectral analysis into more than 40 regions enabled a spectral map of the nebula to be made.

The A&A Highlight text can be found here: https://www.aanda.org/2019-highlights/1617 The paper can be downloaded from the preprint server: https://arxiv.org/abs/1810.12676

HESS operations to be extended beyond 2019
Jan 30, 2019

Major step for the HESS experiment and ground-based gamma-ray astronomy in general:

In the current context of emerging multi-messenger, multi-wavelength astronomy, the HESS Steering Committee evaluated the possible options for the future of HESS during its meeting on January 28th, 2019. After careful analysis of the proposed strategy for the upcoming years, the Steering Committee unanimously voted in favour of the extension of HESS operations for an initial duration of 3 years. The corresponding extension agreement is currently being finalized between the relevant parties. As part of the strategy towards improved efficiency and faster response to transient phenomena, the camera of the large telescope will be replaced by a brand new, state-of-the-art camera as designed for the upcoming Cherenkov Telescope Array (CTA). This way, HESS will be preparing for the future CTA era while continuing to deliver exciting and excellent science.

The Passing of Professor Sergio Colafrancesco.
Oct 4, 2018

It is with great sadness that the H.E.S.S. Collaboration announces the passing of Professor Sergio Colafrancesco. He passed away on Sunday, 30 September 2018, following a battle with cancer.

The H.E.S.S. Collaboration offers its deepest condolences to the family, friends and colleagues of Prof. Colafrancesco.

He was the DST-NRF Square Kilometre Array (SKA) Research Chair in Radio Astronomy in the School of Physics at the University of the Witwatersrand, Johannesburg, South Africa. His appointment heralded the beginning of distinguished research activity in multiwavelength and multi-messenger astronomy and astrophysics at Wits University, with the establishment of a very active H.E.S.S. group.

Prof. Colafrancesco's SKA Chair is of local and international significance. It was established to contribute to the understanding of the structure, origin and evolution of the Universe and of its sub-structures, from the smallest galaxies to the largest galaxy clusters.

Prof. Colafrancesco was involved in a number of ground-breaking projects that showcased the country's leadership and competitiveness in science. He was a highly cited, internationally recognised expert in cosmology and astrophysics and a leading driver of progress in multi-wavelength and multi-messenger astronmoy and astrophysics in South Africa.

The South African Institute of Physics has conveyed its condolences, adding that Colafrancesco made tremendous contributions to the development of radio and gamma-ray astronomy in South Africa and further afield on the African continent.

Born in Italy, Colafrancesco joined Wits in August 2011 from the University of Rome where he was a professor of astrophysics. Prior to that, he was a senior scientist with the Italian Institute for Astrophysics. He obtained his PhD in Astronomy at the University of Padua, Italy.

Details of his memorial service will be shared once available.

H.E.S.S. Collaboration releases first public test data in open FITS format
Sep 11, 2018

Today, the H.E.S.S. Collaboration has, for the first time, released a small subset of its archival data in Flexible Image Transport System (FITS) format, an open file format widely used in astronomy. The release consists of event lists and instrument response functions for observations of various well-known gamma-ray sources (the Crab nebula, PKS 2155-304, MSH 15-52, RX J1713.7-3946) as well as observations of empty fields for background modeling. It is compliant to the open format specifications developed in view of the upcoming CTA Observatory. The release is meant to support the development of open-source science tools for high-level analysis of gamma-ray data by providing access to "real" gamma-ray data in the appropriate format for the first time.

Links to the data, release notes document, data format specification, tutorials how to analyse the data and more information can be found at https://www.mpi-hd.mpg.de/hfm/HESS/pages/dl3-dr1/

The first multi-messenger hint for a cosmic ray accelerator?
July 11, 2018

On September 19, 2017, a high-energy neutrino of about 290 TeV (IceCube-170922A) was detected by the IceCube neutrino telescope. An alert was distributed to observatories around the globe within 1 minute. The direction of the neutrino (reconstructed to an area of about 1sq deg and consistent with the location of a known gamma-ray blazar TXS 0506+056) became visible at the location of the H.E.S.S. observatory in Namibia around 4 hours later and follow-up observations were started (ATEL #10787). Observations of gamma-rays in the GeV domain obtained with the LAT instrument onboard the Fermi satellite showed the blazar TXS 0506+056 to be in a flaring state since April 2017. The coincidence of the neutrino correlation with a blazar which was undergoing heightened non-thermal emission caught the interest of the wider astronomical community and triggered a comprehensive multi-wavelength follow-up campaign. During this campaign, high-energy gamma rays with energies up to 400 GeV were detected by the MAGIC instrument on La Palma twelve days after the neutrino event detection. The emission in X-rays showed clear evidence for spectral variability, the flux in the optical V band was the highest observed in recent years. A summary of these observations can be found in IceCube Collaboration et al., Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A, Science 361.

There remains a 0.1% probability that the coincidence of the neutrino event with the flare of TXS 0506+056 is purely a random chance coincidence. However, the observed association of a high-energy neutrino event with a blazar during a period of enhanced gamma-ray emission is suggestive that blazars may indeed be one of the long-sought sources of very high-energy cosmic rays, and hence might be responsible for a fraction of the cosmic neutrino flux observed by IceCube.

The image shows an ASAS-SN optical V-band widefield image of the sky centered on the known position (+) of the TXS 0506+056 blazar. Two known objects from catalogues of gamma-ray sources generated Fermi Large Area Telescope are shown as blue circles, one being TXS 0506+056, with diameter representing the 95% position uncertainty. Also shown are the 50% and 90% containment areas (solid-grey and dashed-red contours, respectively) for the best-fit directional reconstruction of a high-energy neutrino detected on 22 September 2017 that indicate positional coincidence with the blazar TXS 0506+056. Subsequent very-high-energy gamma-ray observations from the MAGIC imaging air Cherenkov telescopes also detected this source, with 68% positional uncertainties of those observations shown as the yellow circle. Inset is a zoomed view of the region of interest surrounding TXS 0506+056. From IceCube Collaboration et al., Multimessenger observations of a flaring blazar coincident with high-energy neutrino IceCube-170922A, Science 361.

Galactic science with 15 years of H.E.S.S. data
April 9, 2018

The H.E.S.S. telescopes have surveyed the Milky Way in gamma-ray light for the last 15 years. To celebrate this anniversary, the H.E.S.S. collaboration has published its largest set of science results to date in a series of papers in a special issue of the journal Astronomy & Astrophysics. The more than a dozen publications include the H.E.S.S. Galactic Plane Survey, studies of the populations of pulsar wind nebulae and supernova remnants, as well as the search for new object classes unseen before in very-high-energy gamma rays such as microquasars or shocks around fast-moving stars. These studies are\ complemented by precision measurements of shell-type supernova remnants such as for example RX J1713-3946 and diffuse emission at the centre of our Galaxy. This legacy data set will serve as a benchmark for the community for the coming years and until the next-generation Cherenkov Telescope Array comes online in the 2020s.

For more information, see the press release.

Agnieszka Jacholkowska, our colleague and friend, passed away during the night of March 26th.
Mar 28, 2018

Dr. Agnieszka Jacholkowska, our colleague and friend, passed away during the night of march 26th, 2018, after a battle against cancer.

Agnieszka has been a very enthusiastic scientist, involved first in particle physics and, in a second stage, in gamma-ray astronomy. Her areas of predilection were the QCD physics and standard model and beyond, the search for dark matter or the test of the violation of Lorentz invariance, domains in which she counts an impressive number of contributions.

After a PhD at the Laboratory of Linear Accelerator (LAL), on the search of charmed quark in the BEBC bubbles chamber experiment at CERN, she returned to the Institut of Physics of Warsaw University to study K-proton interaction and then the Compton diffusion in NA14 at CERN. In 1983, at the LAL again, she investigated the deep inelastic diffusions of muons on nucleons in the EMC collaboration. She was hired, in 1986, at CNRS to work on electron-nucleon interaction in the H1 collaboration and later in ALEPH experiment on the Large Electron Position Collider where she studied heavy quarks physics and bosonic coupling. Her last major contribution in particle physique was on CP violation in the b sector before she switched to astroparticle physics at the LUPM laboratory in Montpelier. She started there to investigate cosmic-ray physics with AMS, CELESTE and the H.E.S.S. experiment and finally joined the LPNHE in Paris, in 2008, to pursue her studies in astroparticle physics in the H.E.S.S. experiment and contribute to developments for the CTA project.

We will thoroughly miss her great intellect and kindness, and we would like to express our deepest condolences to her family.

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 rôle 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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