R. J. Britto
A5040813964- Astrophysics and Cosmic Phenomena
- Radio Astronomy Observations and Technology
- Gamma-ray bursts and supernovae
- Dark Matter and Cosmic Phenomena
- Particle Detector Development and Performance
- Neutrino Physics Research
- Astrophysical Phenomena and Observations
- Astronomical Observations and Instrumentation
- Particle Accelerators and Free-Electron Lasers
- Astronomy and Astrophysical Research
- Pulsars and Gravitational Waves Research
- Galaxies: Formation, Evolution, Phenomena
- Particle physics theoretical and experimental studies
- Solar and Space Plasma Dynamics
- Stellar, planetary, and galactic studies
- Adaptive optics and wavefront sensing
- High-Energy Particle Collisions Research
- Chemistry and Chemical Engineering
- Superconducting and THz Device Technology
- Geophysics and Gravity Measurements
- Nuclear Physics and Applications
- African Botany and Ecology Studies
- Optical Systems and Laser Technology
- Atomic and Subatomic Physics Research
- Terahertz technology and applications
University of the Free State
2016-2024
University of Johannesburg
2015-2022
South African Radio Astronomy Observatory
2017-2021
North-West University
2017-2018
Pennsylvania State University
2018
University of Padua
2016-2017
Istituto di Astrofisica Spaziale e Fisica Cosmica di Milano
2017
University College Dublin
2017
Tata Institute of Fundamental Research
2011-2016
Institut National de Physique Nucléaire et de Physique des Particules
2006-2016
We present the third Fermi Large Area Telescope (LAT) source catalog (3FGL) of sources in 100 MeV–300 GeV range. Based on first 4 yr science data from Gamma-ray Space mission, it is deepest yet this energy Relative to Second LAT catalog, 3FGL incorporates twice as much data, well a number analysis improvements, including improved calibrations at event reconstruction level, an updated model for Galactic diffuse γ-ray emission, refined procedure detection, and methods associating with...
The third catalog of active galactic nuclei (AGNs) detected by the Fermi-LAT (3LAC) is presented. It based on (3FGL) sources between 100 MeV and 300 GeV with a Test Statistic (TS) greater than 25, 2008 August 4 2012 July 31. 3LAC includes 1591 AGNs located at high Galactic latitudes (|b|>10{\deg}), 71% increase over second 2 years data. There are 28 duplicate associations, thus 1563 2192 high-latitude gamma-ray 3FGL AGNs. Most them (98%) blazars. About half newly blazars unknown type, i.e.,...
We present an incremental version (4FGL-DR3, for Data Release 3) of the fourth Fermi-LAT catalog gamma-ray sources. Based on first twelve years science data in energy range from 50 MeV to 1 TeV, it contains 6658 The analysis improves that used 4FGL over eight data: more sources are fit with curved spectra, we introduce a robust spectral parameterization pulsars, and extend points TeV. parameters, distributions, associations updated all Light curves rebuilt yr intervals (not 2 month...
We present a catalog of sources detected above 10 GeV by the Fermi Large Area Telescope (LAT) in first 7 years data using Pass 8 event-level analysis. This is Third Catalog Hard Fermi-LAT Sources (3FHL), containing 1556 objects characterized - 2 TeV energy range. The sensitivity and angular resolution are improved factors 3 relative to previous LAT at same energies (1FHL). vast majority (79%) associated with extragalactic counterparts other wavelengths, including 16 located very high...
The Fermi Large Area Telescope (LAT) Collaboration has recently released a catalog of 360 sources detected above 50 GeV (2FHL). This was obtained using 80 months data re-processed with Pass 8, the newest event-level analysis, which significantly improves acceptance and angular resolution instrument. Most 2FHL at high Galactic latitude are blazars. Using detailed Monte Carlo simulations, we measure, for first time, source count distribution, dN/dS, extragalactic γ-ray E>50 find that it is...
ABSTRACT The Fermi Large Area Telescope (LAT) has an instantaneous field of view (FoV) covering <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>∼</mml:mo> <mml:mn>1</mml:mn> <mml:mrow> <mml:mo stretchy="true">/</mml:mo> </mml:mrow> <mml:mn>5</mml:mn> </mml:math> the sky and it completes a survey entire in high-energy gamma-rays every 3 hr. It enables searches for transient phenomena over timescales from milliseconds to years. Among these could be...
Context:The HAGAR Telescope Array at Hanle, Ladakh has been regularly monitoring the nearby blazar Mkn 421 for past 7yrs. Aims: Blazars show flux variability in all timescales across electromagnetic spectrum. While there is abundant literature characterizing short term flares from different blazars, comparatively little work done to study long variability. We aim temporal and spectral radiation during 2009-2015. Methods: quantify lognormality radio VHE bands, compute correlations between...
As tragédias naturais são eventos devastadores que exigem respostas rápidas e eficazes para minimizar os impactos sociais econômicos nas comunidades afetadas. Este artigo explora o uso de tecnologias construção em madeira, especificamente Cross Laminated Timber (CLT) Light Wood Frame (LWF), como soluções viáveis acelerar processos reconstrução. Com base estudos caso na análise desafios técnicos, culturais regulatórios, propõe estratégias superar as barreiras à ampliação dessas no Brasil, com...
Context: The nearby (z=0.031) TeV blazar Mrk421 was reported to be in a high state of flux activity since November, 2009. Aims: To investigate possible changes the physical parameters during its using multiwavelength data. Methods: We have observed this source bright High Altitude GAmma Ray (HAGAR) telescope array at energies above 250 GeV February 13 - 19, 2010. Optical, X-ray and gamma-ray archival data are also used obtain SEDs light curves. Results: found undergo one brightest flaring...
Since the detection of very high energy (VHE) γ-rays from Mrk 501, its broadband emission radiation was mostly and quite effectively modeled using one zone scenario. However, spectral flux variability studies enabled by multi-wavelength campaigns carried out during recent years have revealed rather complex behavior 501. The observed 501 could be due to a superposition multiple zones. Moreover, new evidence hard intrinsic γ-ray spectra obtained Fermi-LAT observations has challenged theories...
ABSTRACT A prominent outburst of the flat spectrum radio quasar 3C 454.3 was observed in 2014 June with Fermi Large Area Telescope. This characterized by a three-stage light-curve pattern—plateau, flare, and post-flare—that occurred from May to July, similar pattern as during exceptional 2010 November. The highest flux reported this paper 7–29, showing multiple-peak structure light-curves. average these 22 days found be <?CDATA $F[E\gt 100\,\mathrm{MeV}]=(7.2\pm 0.2)\times {10}^{-6}$?> ph cm...
Abstract The optical radiation emitted by blazars contains contributions from synchrotron relativistic electrons in the jets, as well thermal mainly accretion disk (AD), broad-line region (BLR), and host galaxy. unpolarized components AD, BLR, galaxy present themselves decreasing total polarization optical/ultraviolet (UV) spectrum. A combined model for spectral energy distribution (SED) degree of optical/UV is constructed, enabling disentanglement AD components. Our applied to...
ABSTRACT At optical/ultraviolet energies, blazars display an underlying thermal (unpolarized) contribution from the accretion disc, torus, and line-emitting regions, diluting polarized emission jet-component. Optical polarimetry can be used to disentangle non-thermal components, place constraints on particle populations acceleration mechanisms responsible for emission. We present results of a linear optical spectropolarimetric observing campaign 18 (six BL Lac-type objects 12 flat-spectrum...
ABSTRACT We report on results of spectropolarimetry the afterglow long gamma-ray burst GRB 191221B, obtained with SALT/RSS and VLT/FORS2, as well photometry from two telescopes in MASTER Global Robotic Network, at MASTER-SAAO (South Africa) MASTER-OAFA (Argentina) stations. Prompt optical emission was detected by 38 s after alert, which dimmed a magnitude (white-light) ∼10–16.2 mag over period ∼10 ks, followed plateau phase lasting ks then decline to ∼18 80 ks. The light curve shows complex...
Context.If dark matter is made of neutralinos, annihilation such Majorana particles should produce high energy cosmic rays, especially in galaxy halo density regions like centres.Aims.M 31 (Andromeda) our nearest neighbour spiral galaxy, and both its mass low distance make it a source interest for the indirect search through γ-ray detection.Methods.The ground based atmospheric Cherenkov telescope CELESTE observed M from 2001 to 2003, mostly unexplored range 50-500 GeV.Results.These...
Abstract We present the results of an extensive γ -ray data analysis emission from blazar S5 0716+714 with primary motivation to study its temporal and spectral variability behavior. In this work, we extract a 10 days binned light curve 2008 August 4 2016 April 27 in energy range 0.1–300 GeV identify six outburst periods peak flux >4 × −7 ph cm −2 s −1 highly variable source. The brightest flares are identified by zooming these 1 day binning using Bayesian Blocks algorithm. fastest...
We have measured the gamma-ray fluxes of blazars Mrk 421 and 501 in energy range between 50 350 GeV (1.2 to Hz). The detector, called CELESTE, used first 40, then 53 heliostats former solar facility "Thémis" French Pyrénées collect Cherenkov light generated atmospheric particle cascades. signal from is often strong. compare its flux with previously published multi-wavelength studies infer that we are straddling high peak spectral distribution. 2000 was weak (). obtain an upper limit on 1ES...
We report on recent results froma target-of-opportunity program to obtain spectropolarimetry observations with the Southern African Large Telescope (SALT) flaring gamma-ray blazars. SALT and contemporaneous multi-wavelength spectral energy distribution (SED) data are being modelled self-consistently a leptonic single-zone model. Such modeling provides an accurate estimate of degree order magnetic field in emission region thermal contributions (from host galaxy accretion disk) SED, thus...
Flat spectrum radio quasars (FSRQs) are bright active galactic nuclei surrounded by gas clouds within a UV-visible intense radiation field that form the so-called broad line region (BLR). These objects emit relativistic jets from close to central supermassive black hole and through BLR. The Fermi-Large Area Telescope (Fermi-LAT) is sensitive gamma-ray photons $\sim$30 MeV more than 300 GeV. We have performed spectral analysis of FSRQs in 5.5 year (2008-2014) data sample collected Fermi-LAT,...
Blazars represent a subset of AGN with relativistic jets, where the direction jet lies very close to our line sight. The highly Doppler boosted emission from blazar's results in high apparent luminosities, and blazars display variability on periods less than one day up years. At optical wavelengths, observed blazar is superposition polarised non-thermal synchrotron emission, arising jet, unpolarised thermal disc, broad region, torus host galaxy. Polarimetry observations can, therefore, serve...