Halim Ashkar
A5061901775- Astrophysics and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Dark Matter and Cosmic Phenomena
- Pulsars and Gravitational Waves Research
- Radiomics and Machine Learning in Medical Imaging
- Particle Detector Development and Performance
- Neutrino Physics Research
- Radio Astronomy Observations and Technology
- Cosmology and Gravitation Theories
- Particle physics theoretical and experimental studies
- Radiation Detection and Scintillator Technologies
- Galaxies: Formation, Evolution, Phenomena
- Nuclear Physics and Applications
- Astronomical Observations and Instrumentation
- Particle Accelerators and Free-Electron Lasers
- Astro and Planetary Science
- Astronomy and Astrophysical Research
- Atomic and Subatomic Physics Research
- Superconducting and THz Device Technology
- Astrophysics and Star Formation Studies
- Ionosphere and magnetosphere dynamics
- Scientific Research and Discoveries
- Scientific Computing and Data Management
- Advanced X-ray and CT Imaging
École Polytechnique
2022-2025
Centre National de la Recherche Scientifique
2022-2025
Laboratoire Leprince-Ringuet
2022-2025
Commissariat à l'Énergie Atomique et aux Énergies Alternatives
2019-2023
Institut de Recherche sur les Lois Fondamentales de l'Univers
2019-2023
CEA Paris-Saclay
2019-2023
Université Paris-Saclay
2019-2023
Campbell Collaboration
2019-2023
TU Dortmund University
2023
University of Łódź
2023
Gamma-ray bursts (GRBs), which are bright flashes of gamma rays from extragalactic sources followed by fading afterglow emission, associated with stellar core collapse events. We report the detection very-high-energy (VHE) GRB 190829A, between 4 and 56 hours after trigger, using High Energy Stereoscopic System (H.E.S.S.). The low luminosity redshift 190829A reduce both internal external absorption, allowing determination its intrinsic energy spectrum. Between energies 0.18 3.3 tera-electron...
SS 433 is a microquasar, stellar binary system that launches collimated relativistic jets. We observed in gamma rays using the High Energy Stereoscopic System (H.E.S.S.) and found an energy-dependent shift apparent position of gamma-ray emission from parsec-scale These observations trace energetic electron population indicate inverse Compton scattering mechanism rays. Our modeling morphology constrains location particle acceleration requires abrupt deceleration jet flow. infer presence...
The central region of the Milky Way is one foremost locations to look for dark matter (DM) signatures. We report first results on a search DM particle annihilation signals using new observations from an unprecedented gamma-ray survey Galactic Center (GC) region, ${\it i.e.}$, Inner Galaxy Survey, at very high energies ($\gtrsim$ 100 GeV) performed with H.E.S.S. array five ground-based Cherenkov telescopes. No significant excess found in 2014-2020 dataset and profile likelihood ratio analysis...
Recurrent Novae are repeating thermonuclear explosions in the outer layers of white dwarfs, due to accretion fresh material from a binary companion. The shock generated by ejected slamming into companion star's wind, accelerates particles very-high-energies. We report very-high-energy (VHE, $\gtrsim100$\,GeV) gamma rays recurrent nova RS\,Ophiuchi up month after its 2021 outburst, using High Energy Stereoscopic System. VHE emission has similar temporal profile lower-energy GeV emission,...
GRB221009A is the brightest gamma-ray burst ever detected. To probe very-high-energy (VHE, $>$\!100 GeV) emission, High Energy Stereoscopic System (H.E.S.S.) began observations 53 hours after triggering event, when brightness of moonlight no longer precluded observations. We derive differential and integral upper limits using H.E.S.S. data from third, fourth, ninth nights initial GRB detection, applying atmospheric corrections. The combined yield an energy flux limit $\Phi_\mathrm{UL}^{95\%}...
Dwarf spheroidal galaxy satellites of the Milky Way are prime targets for indirect detection dark matter with gamma rays due to their proximity, high content, and absence nonthermal emission processes. Recently, Dark Energy Survey (DES) revealed existence new ultrafaint dwarf galaxies in southern-hemisphere sky, therefore ideally located ground-based observations imaging atmospheric Cherenkov telescope array H.E.S.S. We present a search very-high-energy ($E\ensuremath{\gtrsim}100\text{...
Young massive stellar clusters are extreme environments and potentially provide the means for efficient particle acceleration. Indeed, they increasingly considered as being responsible a significant fraction of cosmic rays (CRs) accelerated within Milky Way. Westerlund 1, most known young cluster in our Galaxy is prime candidate studying this hypothesis. While very-high-energy $\gamma$-ray source HESS J1646-458 has been detected vicinity 1 past, its association could not be firmly...
The radio galaxy M87 is a variable very-high energy (VHE) gamma-ray source, exhibiting three major flares reported in 2005, 2008, and 2010. Despite extensive studies, the origin of VHE emission yet to be understood. In this study, we investigate spectrum during states high activity, utilizing 20.2$\,$ hours H.E.S.S. observations. Our findings indicate preference for curved spectrum, characterized by log-parabola model with extra-galactic background light (EBL) above 0.3$\,$TeV at 4$\sigma$...
The identification of PeVatrons, hadronic particle accelerators reaching the knee cosmic ray spectrum (few $10^{15}$ eV), is crucial to understand origin rays in Galaxy. We provide an update on unidentified source HESS J1702-420, a promising PeVatron candidate. present new observations J1702-420 made with High Energy Stereoscopic System (H.E.S.S.), and processed using improved analysis techniques. configuration was optimized enhance collection area at highest energies. applied...
Geminga is an enigmatic radio-quiet gamma-ray pulsar located at a mere 250 pc distance from Earth. Extended very-high-energy emission around the was discovered by Milagro and later confirmed HAWC, which are both water Cherenkov detector-based experiments. However, evidence for wind nebula in gamma rays has long evaded detection imaging atmospheric telescopes (IACTs) despite targeted observations. The of on angular scales > 2 deg poses considerable challenge background estimation IACT data...
In July 2021, PKS 1510-089 exhibited a significant flux drop in the high-energy gamma-ray (by factor 10) and optical 5) bands remained this low state throughout 2022. Similarly, polarization source vanished, resulting spectrum being fully explained through steady of accretion disk broad-line region. Unlike aforementioned bands, very-high-energy X-ray fluxes did not exhibit from year to year. This suggests that steady-state originate different emission region than vanished parts jet fluxes....
Context. HESS J1809$-$193 is an unassociated very-high-energy $\gamma$-ray source located on the Galactic plane. While it has been connected to nebula of energetic pulsar PSR J1809$-$1917, supernova remnants and molecular clouds present in vicinity also constitute possible associations. Recently, detection emission up energies $\sim$100 TeV with HAWC observatory led renewed interest J1809$-$193. Aims. We aim understand origin Methods. analysed 93.2 h data taken above 0.27 High Energy...
Monochromatic gamma-ray signals constitute a potential smoking gun signature for annihilating or decaying dark matter particles that could relatively easily be distinguished from astrophysical instrumental backgrounds. We provide an updated assessment of the sensitivity Cherenkov Telescope Array (CTA) to such signals, based on observations Galactic centre region as well selected dwarf spheroidal galaxies. find current limits and detection prospects masses above 300 GeV will significantly...
Aims. Colliding wind binary systems have long been suspected to be high-energy (HE; 100 MeV < E GeV) {\gamma}-ray emitters. {\eta} Car is the most prominent member of this object class and confirmed emit phase-locked HE {\gamma} rays from hundreds ~100 GeV energies. This work aims search for characterise very-high-energy (VHE; >100 emission around last periastron passage in 2014 with ground-based High Energy Stereoscopic System (H.E.S.S.). Methods. The region was observed H.E.S.S. between...
The flat spectrum radio quasar (FSRQ) PKS 1510−089 is known for its complex multiwavelength behaviour and it one of only a few FSRQs detected in very-high-energy (VHE, E > 100 GeV) γ rays. VHE -ray observations with H.E.S.S. MAGIC late May early June 2016 resulted the detection an unprecedented flare, which revealed, first time, intranight variability this source. While common timescale 1.5 h has been found, there significant deviation near end ∼20 min marking cessation event. peak flux...
The High Altitude Water Cherenkov (HAWC) observatory and the Energy Stereoscopic System (H.E.S.S.) are two leading instruments in ground-based very-high-energy gamma-ray domain. HAWC employs water detection (WCD) technique, while H.E.S.S. is an array of Imaging Atmospheric Telescopes (IACTs). facilities therefore differ multiple aspects, including their observation strategy, size field view angular resolution, to different analysis approaches. Until now, it has been unclear if results...
The colliding-wind binary system $\eta$ Carinae has been identified as a source of high-energy (HE, below $\sim$100\,GeV) and very-high-energy (VHE, above gamma rays in the last decade, making it unique among these systems. With its eccentric 5.5-year-long orbit, periastron passage, during which stars are separated by only $1-2$\,au, is an intriguing time interval to probe particle acceleration processes within system. In this work, we report on extensive VHE observation campaign that for...
The colliding-wind binary system η Carinae has been identified as a source of high-energy (HE, below ∼100,GeV) and very (VHE, above gamma rays in the last decade, making it unique among these systems. With its eccentric 5.5-year-long orbit, periastron passage, during which stars are separated by only $1-2$,au, is an intriguing time interval to probe particle acceleration processes within system. In this work, we report on extensive VHE observation campaign that for first covers full passage...
The results of the first extragalactic gamma-ray survey by High Energy Stereoscopic System (H.E.S.S.) are presented. comprises 2720 hours very high-energy observations sky, recorded with H.E.S.S. from 2004 up to end 2012. These data have been re-analysed using a common consistent set up-to-date calibration and analysis tools. From this analysis, list 23 detected objects, predominantly blazars, was obtained. This catalogue assessed in terms source class populations that it contains. level...
Abstract A wide variety of Galactic sources show transient emission at soft and hard X-ray energies: low-mass high-mass binaries containing compact objects, isolated neutron stars exhibiting extreme variability as magnetars well pulsar wind nebulae. Although most them can up to MeV and/or GeV energies, many have not yet been detected in the TeV domain by Imaging Atmospheric Cherenkov Telescopes. In this paper, we explore feasibility detecting new transients with Telescope Array Observatory...
ABSTRACT A deep survey of the Large Magellanic Cloud at ∼0.1–100 TeV photon energies with Cherenkov Telescope Array is planned. We assess detection prospects based on a model for emission galaxy, comprising four known emitters, mock populations sources, and interstellar galactic scales. also detectability 30 Doradus SN 1987A, constraints that can be derived nature dark matter. The will allow fine spectral studies N 157B, 132D, LMC P3, C, half dozen other sources should revealed, mainly...
PSR B1259-63/LS 2883 is a gamma-ray binary system consisting of pulsar in an eccentric orbit around bright Oe stellar-type companion star that features dense circumstellar disc. The high- and very-high-energy (HE, VHE) emission from the times its periastron passage are characterised, particular, at time HE flares reported to have occurred 2011, 2014, 2017. Spectra light curves were derived observations conducted with H.E.S.S.-II array 2014 A local double-peak profile asymmetric peaks VHE...