J. W. Hewitt
A5077512726- Astrophysics and Cosmic Phenomena
- Dark Matter and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Astronomy and Astrophysical Research
- Astronomical Observations and Instrumentation
- Radio Astronomy Observations and Technology
- Neutrino Physics Research
- Astro and Planetary Science
- Astrophysical Phenomena and Observations
- Particle Detector Development and Performance
- Solar and Space Plasma Dynamics
- Particle Accelerators and Free-Electron Lasers
- Mercury impact and mitigation studies
- Particle physics theoretical and experimental studies
- Galaxies: Formation, Evolution, Phenomena
- Toxic Organic Pollutants Impact
- Astrophysics and Star Formation Studies
- Ionosphere and magnetosphere dynamics
- Geophysics and Gravity Measurements
- Pulsars and Gravitational Waves Research
- Simulation Techniques and Applications
- SAS software applications and methods
- GNSS positioning and interference
- Adaptive optics and wavefront sensing
- Spacecraft and Cryogenic Technologies
University of North Florida
2011-2023
Uppsala University
2022
Max Planck Society
2018
Goddard Space Flight Center
2014-2016
University of Maryland, Baltimore County
2014-2016
We present the fourth Fermi Large Area Telescope catalog (4FGL) of gamma-ray sources. Based on first eight years science data from Gamma-ray Space mission in energy range 50 MeV to 1 TeV, it is deepest yet this range. Relative 3FGL catalog, 4FGL has twice as much exposure well a number analysis improvements, including an updated model for Galactic diffuse emission, and two sets light curves (1-year 2-month intervals). The includes 5064 sources above 4 sigma significance, which we provide...
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.,...
The dwarf spheroidal satellite galaxies of the Milky Way are some most dark-matter-dominated objects known. Due to their proximity, high dark matter content, and lack astrophysical backgrounds, widely considered be among promising targets for indirect detection via $\ensuremath{\gamma}$ rays. Here we report on $\ensuremath{\gamma}$-ray observations 25 based 4 years Fermi Large Area Telescope (LAT) data. None significantly detected in rays, present flux upper limits between 500 MeV GeV. We...
The Fermi bubbles are two large structures in the gamma-ray sky extending to 55° above and below Galactic center. We analyze 50 months of Large Area Telescope data between 100 MeV 500 GeV 10° latitude derive spectrum morphology bubbles. thoroughly explore systematic uncertainties that arise when modeling diffuse emission through separate approaches. is well described by either a log parabola or power law with an exponential cutoff. exclude simple more than 7σ significance. cutoff has index...
We present a catalog of sources detected above 50 GeV by the {\it Fermi}-Large Area Telescope (LAT) in 80 months data. The newly delivered Pass 8 event-level analysis allows detection and characterization GeV--2 TeV energy range. In this band, Fermi}-LAT has 360 sources, which constitute second hard (2FHL). improved angular resolution enables precise localization point ($\sim$1.7$'$ radius at 68 % C.~L.) spatially extended sources. find that 86 can be associated with counterparts other...
Abstract We report the discovery of GRB 221009A, highest flux gamma-ray burst (GRB) ever observed by Fermi Gamma-ray Burst Monitor (Fermi-GBM). This has continuous prompt emission lasting more than 600 s, which smoothly transitions to afterglow visible in Fermi-GBM energy range (8 keV–40 MeV), and total energetics higher any other sample. By using a variety new existing analysis techniques we probe spectral temporal evolution 221009A. find no prior trigger time ( t 0 ; 2022 October 9 at...
Abstract We present 294 pulsars found in GeV data from the Large Area Telescope (LAT) on Fermi Gamma-ray Space Telescope. Another 33 millisecond (MSPs) discovered deep radio searches of LAT sources will likely reveal pulsations once phase-connected rotation ephemerides are achieved. A further dozen optical and/or X-ray binary systems colocated with also harbor gamma-ray MSPs. This catalog thus reports roughly 340 and candidates, 10% all known pulsars, compared to ≤11 before Fermi. Half...
We present the fourth Fermi Large Area Telescope catalog (4FGL) of gamma-ray sources. Based on first eight years science data from Gamma-ray Space mission in energy range 50 MeV to 1 TeV, it is deepest yet this range. Relative 3FGL catalog, 4FGL has twice as much exposure well a number analysis improvements, including an updated model for Galactic diffuse emission, and two sets light curves (1-year 2-month intervals). The includes 5064 sources above 4 sigma significance, which we provide...
Current theories predict relativistic hadronic particle populations in clusters of galaxies addition to the already observed leptons. In these scenarios interactions give rise neutral pions which decay into γ rays that are potentially observable with Large Area Telescope (LAT) on board Fermi space telescope. We present a joint likelihood analysis searching for spatially extended γ-ray emission at locations 50 galaxy four years Fermi-LAT data under assumption universal cosmic-ray (CR) model...
ABSTRACT We present results from γ -ray observations of the Coma cluster incorporating six years Fermi -LAT data and newly released “Pass 8” event-level analysis. Our analysis region reveals low-significance residual structures within virial radius that are too faint for a detailed investigation with current data. Using likelihood approach is free assumptions on spectral shape we derive upper limits flux expected energetic particle interactions in cluster. also consider benchmark spatial...
The All-sky Medium Energy Gamma-ray Observatory (AMEGO) is a probe class mission concept that will provide essential contributions to multimessenger astrophysics in the late 2020s and beyond. AMEGO combines high sensitivity 200 keV 10 GeV energy range with wide field of view, good spectral resolution, polarization sensitivity. Therefore, key study astrophysical objects have unique signatures gamma-ray regime, such as neutron star mergers, supernovae, flaring active galactic nuclei....
ABSTRACT We report the Fermi Large Area Telescope detection of extended γ -ray emission from lobes radio galaxy Fornax A using 6.1 years Pass 8 data. After Centaurus A, this is now second example an source attributed to a galaxy. Both flat disk morphology and following were preferred over point-source description, core contribution was constrained be <?CDATA $\lt 14$?> % total flux. alignment elongation with demonstrated by rotating template. found no significant evidence for variability on...
We present a complete analysis of Fermi Large Area Telescope (LAT) data GRB 221009A, the brightest Gamma-Ray Burst (GRB) ever detected. The burst emission above 30 MeV detected by LAT preceded 1 s low-energy (< 10 MeV) pulse that triggered Monitor (GBM), as has been observed in other GRBs. prompt phase 221009A lasted few hundred seconds. It was so bright we identify Bad Time Interval (BTI) 64 seconds caused extremely high flux hard X-rays and soft gamma rays, during which event...
The discovery of rapidly variable Very High Energy (VHE; E > 100 GeV) gamma-ray emission from 4C +21.35 (PKS 1222+216) by MAGIC on 2010 June 17, triggered the high activity detected Fermi Large Area Telescope (LAT) in energy (HE; MeV) gamma-rays, poses intriguing questions location emitting region this flat spectrum radio quasar. We present multifrequency data collected centimeter to VHE during investigate properties source and discuss a possible model. first hint detection at was observed...
We present a detailed investigation of the $\gamma$-ray emission in vicinity supernova remnant (SNR) W28 (G6.4$-$0.1) observed by Large Area Telescope (LAT) onboard Fermi Gamma-ray Space Telescope. detected significant spatially coincident with TeV sources HESS J1800$-$240A, B, and C, located outside radio boundary SNR. Their spectra 2-100 GeV band are consistent extrapolation power-law sources. also identified new source emission, dubbed Source W, which lies coincides from western part W28....
Supernovae (SNe) exploding in a dense circumstellar medium (CSM) are hypothesized to accelerate cosmic rays collisionless shocks and emit GeV γ-rays TeV neutrinos on timescale of several months. We perform the first systematic search for γ-ray emission Fermi Large Area Telescope data energy range from ensemble 147 SNe Type IIn CSM. excess at each location one-year time window. In order enhance possible weak signal, we simultaneously study closest optically brightest sources our sample...
We have measured the gamma-ray emission spectrum of Moon using data collected by Large Area Telescope onboard Fermi satellite during its first seven years operation, in energy range from 30 MeV up to a few GeV. also studied time evolution flux, finding correlation with solar activity. developed full Monte Carlo simulation describing interactions cosmic rays lunar surface. The results present analysis can be explained framework this model, where production gamma is due cosmic-ray proton and...
We present an analysis of the gamma-ray measurements by Large Area Telescope onboard \textit{Fermi Gamma-ray Space Telescope} in region supernova remnant~(SNR) Monoceros Loop~(G205.5$+$0.5). The brightest peak is spatially correlated with Rosette Nebula, which a molecular cloud complex adjacent to southeast edge SNR. After subtraction this emission spatial modeling, from SNR emerges, extended and fit Gaussian template. spectra are significantly better reproduced curved shape than simple...
We report the discovery of extended gamma-ray emission measured by Large Area Telescope (LAT) onboard Fermi Gamma-ray Space in region supernova remnant (SNR) HB3 (G132.7+1.3) and W3 HII complex adjacent to southeast remnant. is spatially associated with bright 12CO (J=1-0) emission. The correlated this gas SNR. discuss possibility that gamma rays originate interactions between particles accelerated SNR interstellar or radiation fields. decay neutral pions produced nucleon-nucleon hadrons...
Galactic cosmic ray (CRs) sources, classically proposed to be Supernova Remnants (SNRs), must meet the energetic particle content required by direct measurements of high energy CRs. Indirect gamma-ray SNRs with Fermi Large Area Telescope (LAT) have now shown directly that at least three accelerate protons. With first LAT SNR Catalog, we systematically characterized GeV gamma-rays emitted 279 known primarily from radio surveys. We present these sources in a multiwavelength context, including...
We perform a comprehensive stacking analysis of data collected by the Fermi Large Area Telescope (LAT) gamma-ray bursts (GRB) localized Swift spacecraft, which were not detected LAT but fell within instrument's field view at time trigger. examine total 79 GRBs comparing observed counts over range intervals to that expected from designated background orbits, as well using joint likelihood technique model distribution stacked counts. find strong evidence for subthreshold emission MeV GeV...
We performed Herschel HIFI, PACS and SPIRE observations towards the molecular cloud interacting supernova remnant G349.7+0.2. An extremely broad emission line was detected at 557 GHz from ground state transition 1_{10}-1_{01} of ortho-water. This water can be separated into three velocity components with widths 144, 27 4 km/s. The 144 km/s component is broadest to date in literature. width shows importance probing shock dynamics. revealed 3 additional ortho-water lines, as well numerous...