J. Niemiec
A5058226131- Astrophysics and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Dark Matter and Cosmic Phenomena
- Astrophysical Phenomena and Observations
- Solar and Space Plasma Dynamics
- Pulsars and Gravitational Waves Research
- Particle Detector Development and Performance
- Radio Astronomy Observations and Technology
- Ionosphere and magnetosphere dynamics
- Neutrino Physics Research
- Cosmology and Gravitation Theories
- Radiation Detection and Scintillator Technologies
- Laser-Plasma Interactions and Diagnostics
- Astronomical Observations and Instrumentation
- Particle physics theoretical and experimental studies
- Particle Accelerators and Free-Electron Lasers
- Galaxies: Formation, Evolution, Phenomena
- Astro and Planetary Science
- Magnetic confinement fusion research
- Astronomy and Astrophysical Research
- CCD and CMOS Imaging Sensors
- Planetary Science and Exploration
- Adaptive optics and wavefront sensing
- High-Energy Particle Collisions Research
- Astrophysics and Star Formation Studies
Institute of Nuclear Physics, Polish Academy of Sciences
2016-2025
Polish Academy of Sciences
1966-2024
Cracow University of Technology
2021-2024
ETH Zurich
2019-2023
University of Warsaw
2019-2023
University of Turku
2023
Durham University
2023
Czech Academy of Sciences, Institute of Physics
2019-2023
Jagiellonian University
2016-2023
Deutsches Elektronen-Synchrotron DESY
2023
The very large collection area of ground-based gamma-ray telescopes gives them a substantial advantage over balloon or satellite based instruments in the detection very-high-energy (>600 GeV) cosmic-ray electrons. Here we present electron spectrum derived from data taken with High Energy Stereoscopic System (H.E.S.S.) imaging atmospheric Cherenkov telescopes. In this measurement, first type, are able to extend measurement beyond range accessible direct measurements. We find evidence for...
We report on the first simultaneous observations that cover optical, X-ray, and high-energy gamma-ray bands of BL Lac object PKS 2155−304. The were observed for 11 days, between 2008 August 25 September 6 (MJD 54704−54715), jointly with Fermi Gamma-ray Space Telescope HESS atmospheric Cherenkov array, providing MeV–TeV spectral energy distribution (SED) new generation γ-ray telescopes. ATOM telescope RXTE Swift observatories provided optical X-ray coverage low-energy component over same time...
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,...
Magnetic fields in galaxies and galaxy clusters are believed to be the result of amplification intergalactic seed during formation large-scale structures universe. However, origin, strength, morphology this magnetic field (IGMF) remain unknown. Lower limits on (or indirect detection of) IGMF can obtained from observations high-energy gamma rays distant blazars. Gamma interact with extragalactic background light produce electron-positron pairs, which subsequently initiate electromagnetic...
Abstract Collisionless shock waves in supernova remnants and the solar wind heat electrons less effectively than they ions, as is predicted by kinetic simulations. However, values of T e / p inferred from H α profiles remnant shocks behave differently a function Mach number or Alfvén what measured Here we determine for using profiles, speeds proper motions, electron temperatures X-ray spectra. We also improve estimates sound speed used to numbers. find that determinations are robust...
Abstract The SST-1M (webpage: https://sst-1m.space ) is a Small-Sized Telescope (SST) designed to provide cost-effective and high-performance solution for gamma-ray astrophysics, particularly energies beyond few TeV. goal integrate this telescope into an array of similar instruments, leveraging its lightweight design, earthquake resistance, established Davies-Cotton configuration. Additionally, optical system function without protective dome, allowing it withstand the harsh atmospheric...
We present results of 2D and 3D PIC simulations magnetic turbulence production by isotropic cosmic-ray ions drifting upstream SNR shocks. The studies aim at testing recent predictions a strong amplification short wavelength field studying the evolution its backreaction on cosmic rays. observe that an oblique filamentary mode grows more rapidly than non-resonant parallel modes found in analytical theory, growth rate perturbations is much slower estimated for plane-wave mode, possibly because...
<i>Aims. <i/>A detailed study of the spectrum and variability source HESS J1745-290 in Galactic Center (GC) region using new data from H.E.S.S. array Cherenkov telescopes is presented. Flaring activity quasi periodic oscillations (QPO) are investigated.<i>Methods. <i/>The image analysis performed with a combination semi-analytical shower model statistical moment-based Hillas technique. The lightcurves derived likelihood method based on spectral shape hypothesis. Rayleigh tests Fourier GC...
In the past few decades, several models have predicted an energy dependence of speed light in context quantum gravity. For cosmological sources such as active galaxies, this minuscule effect can add up to measurable photon-energy dependent time lags. Letter a search for lags during High Energy Stereoscopic System observations exceptional very high flare galaxy PKS 2155-304 on 28 July 2006 is presented. Since no significant lag found, lower limits scale modifications are derived.
The shell-type supernova remnant (SNR) RCW 86, possibly associated with the historical SN 185, its relatively large size (about 40' in diameter) and presence of nonthermal X-rays is a promising target for γ-ray observations. high sensitivity, good angular resolution few arcminutes field view High Energy Stereoscopic System (HESS) make it ideally suited study morphology such extended sources. HESS observations have indeed led to discovery SNR 86 very energy (VHE; E > 100 GeV) γ-rays. With 31...
Plasma instabilities (e.g., Buneman, Weibel and other two-stream instabilities) excited in collisionless shocks are responsible for particle (electron, positron, ion) acceleration. Using a new 3-D relativistic particle-in-cell code, we have investigated the acceleration shock structure associated with an unmagnetized electron-positron jet propagating into plasma. The simulation has been performed using long system order to study nonlinear stages of instability, mechanism, structure. Cold...
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$\sigma$...
VERITAS, an Imaging Atmospheric Cherenkov Telescope (IACT) system for gammma‐ray astronomy in the GeV‐TeV range, has recently completed its first season of observations with a full array four telescopes. A number astrophysical gamma‐ray sources have been detected, both galactic and extragalactic, including previously unknown at TeV energies. We describe status some highlight results, assess technical performance, sensitivity shower reconstruction capabilities.
Since September 2005, the Whipple 10m Gamma-ray Telescope has been operated primarily as a blazar monitor. The five Northern Hemisphere blazars that have already detected at Observatory, Markarian 421, H1426+428, 501, 1ES 1959+650 and 2344+514, are monitored routinely each night they visible. We report on 421 observations taken from November 2005 to June 2006 in gamma-ray, X-ray, optical radio bands. During this time, was found be variable all wavelengths probed. Both variability...
We report the detection of very high energy γ-ray emission from intermediate-frequency-peaked BL Lacertae object W Comae (z = 0.102) by VERITAS. The source was observed between 2008 January and April. A strong outburst measured in middle March, lasting for only 4 days. spectrum during two highest flare nights is fit a power law found to be steep, with differential photon spectral index Γ 3.81 ± 0.35stat± 0.34syst. integral flux above 200 GeV those corresponds roughly 9% Crab Nebula....
We have investigated via two-dimensional relativistic MHD simulations the long-term evolution of turbulence created by a shock propagating through an inhomogeneous medium. In postshock region, magnetic field is strongly amplified turbulent motions triggered preshock density inhomogeneities. Using long-simulation box we followed magnetic-field amplification until it fully developed and saturated. The velocity sub-relativistic even for strong shock. Magnetic-field controled motion saturation...
The single-mirror small-size telescope (SST-1M) is one of the three proposed designs for telescopes (SSTs) Cherenkov Telescope Array (CTA) project. SST-1M will be equipped with a 4 m-diameter segmented reflector dish and an innovative fully digital camera based on silicon photo-multipliers. Since SST sub-array consist up to 70 telescopes, challenge not only build excellent performance, but also design them so that their components can commissioned, assembled tested by industry. In this paper...
Collisionless shocks are ubiquitous in the Universe and often associated with strong magnetic field. Here we use large-scale particle-in-cell simulations of non-relativistic perpendicular high-Mach-number regime to study amplification field within shocks. The is amplified at shock transition due ion-ion two-stream Weibel instability. normalized magnetic-field strength strongly correlates Alfv\'enic Mach number. Mock spacecraft measurements derived from PIC fully consistent those taken...
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....
The process of cosmic ray first-order Fermi acceleration at relativistic shock waves is studied with the method Monte Carlo simulations. simulations are based on numerical integration particle equations motion in a turbulent magnetic field near shock. In comparison to earlier studies, few "realistic" features structure included. upstream consists mean component inclined some angle normal finite-amplitude sinusoidal perturbations imposed upon it. assumed be static local plasma rest frame....
<i>Aims. <i/>Detection of a <i>γ<i/>-ray source above 300 GeV is reported, confirming the unidentified MGRO J1908+06, discovered by Milagro collaboration at median energy 20 TeV.<i>Methods. <i/>The was observed during 27 h as part extension HESS Galactic plane survey to longitudes >30°. <i>Results. <i/>HESS J1908+063 detected significance level 10.9<i>σ<i/> with an integral flux 1 TeV (3.76 <i>±<i/> )10<sup>-12<sup/> ph cm<sup>-2<sup/> s<sup>-1<sup/>, and spectral photon index <i>Γ<i/> =...
The VERITAS collaboration reports the detection of very-high-energy gamma-ray emission from high-frequency-peaked BL Lac object 1ES 1218+304 located at a redshift z = 0.182. A signal was detected with statistical significance 10.4 standard deviations (10.4σ) for observations taken during first three months 2007, confirming discovery this made by MAGIC collaboration. photon spectrum between ∼160 GeV and ∼1.8 TeV is well described power law an index Γ 3.08 ± 0.34stat 0.2sys. integral flux...