A5018964309- Astrophysics and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Dark Matter and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Galaxies: Formation, Evolution, Phenomena
- Astrophysical Phenomena and Observations
- Astronomy and Astrophysical Research
- Particle Detector Development and Performance
- Neutrino Physics Research
- Astronomical Observations and Instrumentation
- Pulsars and Gravitational Waves Research
- Particle physics theoretical and experimental studies
- Cosmology and Gravitation Theories
- Radiation Detection and Scintillator Technologies
- Astrophysics and Star Formation Studies
- Stellar, planetary, and galactic studies
- Particle Accelerators and Free-Electron Lasers
- Solar and Space Plasma Dynamics
- Astro and Planetary Science
- Computational Physics and Python Applications
- CCD and CMOS Imaging Sensors
- Space exploration and regulation
- Impact of Light on Environment and Health
- Nuclear Physics and Applications
- Ionosphere and magnetosphere dynamics
University of Oxford
2015-2024
North-West University
2021-2024
Max Planck Institute for Nuclear Physics
2023
Friedrich-Alexander-Universität Erlangen-Nürnberg
2021-2023
Deutsches Elektronen-Synchrotron DESY
2021-2023
University of Copenhagen
2023
Nagoya University
2022
Brera Astronomical Observatory
2022
CEA Paris-Saclay
2021
Max Planck Institute for Astronomy
2021
The Large Area Telescope (LAT) aboard the Fermi Gamma-ray Space provides an unprecedented opportunity to study gamma-ray blazars. To capitalize on this opportunity, beginning in late 2007, about a year before start of LAT science operations, we began large-scale, fast-cadence 15 GHz radio monitoring program with 40-m telescope at Owens Valley Radio Observatory (OVRO). This 1158 northern (declination>-20 deg) sources from Candidate Blazar Survey (CGRaBS) and now encompasses over 1500 sources,...
We present the first catalog of active galactic nuclei (AGNs) detected by Large Area Telescope (LAT), corresponding to 11 months data collected in scientific operation mode. The First LAT AGN Catalog (1LAC) includes 671 γ-ray sources located at high Galactic latitudes (|b|>10°) that are with a test statistic greater than 25 and associated statistically AGNs. Some multiple AGNs, consequently, 709 comprising 300 BL Lacertae objects, 296 flat-spectrum radio quasars, 41 AGNs other types, 72...
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...
We provide an updated assessment of the power Cherenkov Telescope Array (CTA) to search for thermally produced dark matter at TeV scale, via associated gamma-ray signal from pair-annihilating particles in region around Galactic centre. find that CTA will open a new window discovery potential, significantly extending range robustly testable models given standard cuspy profile density distribution. Importantly, even cored profile, projected sensitivity be sufficient probe various...
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...
We report on optical spectroscopy of 165 flat spectrum radio quasars (FSRQs) in the Fermi 1LAC sample, which have helped allow a nearly complete study this population. FSRQs show significant evidence for non-thermal emission even optical; degree depends γ-ray hardness. They also smaller virial estimates hole mass than quasar sample. This appears to be largely due preferred (axial) view FSRQ and non-isotropic (H/R ∼ 0.4) distribution broad-line velocities. Even after correction bias, higher...
We describe a uniform all-sky survey of bright blazars, selected primarily by their flat radio spectra, that is designed to provide large catalog likely gamma-ray AGN. The defined sample has 1625 targets with and X-ray properties similar those the EGRET spread uniformly across |b| > 10 deg sky. also report progress toward optical characterization sample; objects known R < 23, 85% have been classified 81% measured redshifts. One goal this program focus attention on most interesting...
We present the first results of VLBA Imaging and Polarimetry Survey (VIPS), a 5 GHz VLBI survey 1127 sources with flat radio spectra. Through automated data reduction imaging routines, we have produced publicly available I, Q, U images detected polarized flux density from 37% sources. also developed an algorithm to use each source's I image automatically classify it as pointlike source, core jet, compact symmetric object (CSO) candidate, or complex source. Using Sloan Digital Sky (SDSS),...
Fermi has provided the largest sample of γ-ray-selected blazars to date. In this work we use a uniformly selected set 211 BL Lacertae (BL Lac) objects detected by during its first year operation. We obtained redshift constraints for 206 out Lac in our sample, making it and most complete available literature. determine luminosity function evolution with cosmic time. find that classes is positive, space density peaking at modest (z ≈ 1.2). Low-luminosity, high-synchrotron–peaked (HSP) are an...
We report on spectroscopic observations covering most of the 475 BL Lacs in 2nd Fermi LAT catalog AGN. Including archival measurements (correcting several erroneous literature values) we now have redshifts for 44% Lacs. establish firm lower redshift limits via intervening absorption systems and statistical searches host galaxies an additional 51% sample leaving only 5% unconstrained. The new raise median z from 0.23 to 0.33 include as large z=2.471. Spectroscopic minima absorbers ~ z= 0.70,...
We present results from the first twelve months of operation Radio Galaxy Zoo, which upon completion will enable visual inspection over 170,000 radio sources to determine host galaxy emission and morphology. Zoo uses $1.4\,$GHz images both Faint Images Sky at Twenty Centimeters (FIRST) Australia Telescope Large Area Survey (ATLAS) in combination with mid-infrared $3.4\,\mu$m {\it Wide-field Infrared Explorer} (WISE) $3.6\,\mu$m Spitzer Space Telescope}. early analysis WISE colours galaxies....
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...
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{...
Area of sky No.
In the first of a series papers investigating emission from blazar jets radio to high-energy γ-rays, we revisit class models where jet has uniform conical ballistic structure. We argue that by using simple developments these models, in context new multifrequency data extending γ-ray energies, valuable insights may be obtained into properties fully realistic must ultimately have. this paper consider synchrotron and synchrotron-self-Compton jet, modelling recent simultaneous multiwavelength...
Cosmological and astrophysical observations suggest that 85% of the total matter Universe is made Dark Matter (DM). However, its nature remains one most challenging fundamental open questions particle physics. Assuming DM, this exotic form cannot consist Standard Model (SM) particles. Many models have been developed to attempt unraveling DM such as Weakly Interacting Massive Particles (WIMPs), favored candidates. WIMP annihilations decay could produce SM particles which in turn hadronize...
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 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...
Radio galaxies at redshift z > 4 have proved to be very elusive. By searching for objects with unusual radio spectra between 38 and 4850 MHz, following up blind spectroscopy, we discovered the first galaxy known 4, 8C1435 + 635. In this paper present our observations, discuss evidence redshift, compare properties of 8Cl435 635 those other 3 galaxies. We also try assess likelihood significant gravitational amplification by a foreground group or cluster = 0.23.
In this paper we develop the jet model of Potter & Cotter to include a magnetically dominated accelerating parabolic base transitioning slowly decelerating conical with geometry set by recent radio observations M87. We conserve relativistic energy-momentum and particle number along calculate observed synchrotron emission from calculating integrated line-of-sight opacity through in rest frame each section plasma. inverse-Compton synchrotron, cosmic microwave background (CMB), accretion disc,...
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...