T. J. Johnson
A5001069096- Astrophysics and Cosmic Phenomena
- Pulsars and Gravitational Waves Research
- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Radio Astronomy Observations and Technology
- Dark Matter and Cosmic Phenomena
- Geophysics and Gravity Measurements
- Superconducting Materials and Applications
- Particle Accelerators and Free-Electron Lasers
- Astronomical Observations and Instrumentation
- Astronomy and Astrophysical Research
- Particle Detector Development and Performance
- Inertial Sensor and Navigation
- Geophysics and Sensor Technology
- Stellar, planetary, and galactic studies
- Galaxies: Formation, Evolution, Phenomena
- Nuclear Physics and Applications
- GNSS positioning and interference
- Particle physics theoretical and experimental studies
- Solar and Space Plasma Dynamics
- Hydraulic Fracturing and Reservoir Analysis
- Atomic and Subatomic Physics Research
- Reservoir Engineering and Simulation Methods
- Neutrino Physics Research
- Seismic Imaging and Inversion Techniques
George Mason University
2015-2024
United States Naval Research Laboratory
2008-2022
Goddard Space Flight Center
2009-2021
University of Maryland, College Park
2009-2021
Deleted Institution
2010-2021
North-West University
2014-2021
University of Johannesburg
2021
Los Alamos National Laboratory
2021
Universities Space Research Association
2021
Istituto Nazionale di Fisica Nucleare, Roma Tor Vergata
2018
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...
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...
We report on the first Fermi Large Area Telescope (LAT) measurements of so-called "extragalactic" diffuse gamma-ray emission (EGB). This component is generally considered to have an isotropic or nearly distribution sky with diverse contributions discussed in literature. The derivation EGB based detailed modeling bright foreground Galactic emission, detected LAT sources, and solar emission. find spectrum consistent a power law differential spectral index gamma = 2.41 +/- 0.05 intensity I(>100...
The Fermi Large Area Telescope (Fermi-LAT, hereafter LAT), the primary instrument on Gamma-ray Space (Fermi) mission, is an imaging, wide field-of-view, high-energy γ-ray telescope, covering energy range from 20 MeV to more than 300 GeV. During first years of LAT team has gained considerable insight into in-flight performance instrument. Accordingly, we have updated analysis used reduce data for public release as well response functions (IRFs), description provided analysis. In this paper,...
The dramatic increase in the number of known gamma-ray pulsars since launch Fermi Gamma-ray Space Telescope (formerly GLAST) offers first opportunity to study a sizable population these high-energy objects. This catalog summarizes 46 high-confidence pulsed detections using six months data taken by Large Area (LAT), Fermi's main instrument. Sixteen previously unknown were discovered searching for signals at positions bright sources seen with LAT, or objects suspected be neutron stars based on...
ABSTRACT Following its launch in 2008 June, the Fermi Gamma-ray Space Telescope ( ) began a sky survey August. The Large Area (LAT) on three months produced deeper and better resolved map of γ-ray than any previous space mission. We present here initial results for energies above 100 MeV 205 most significant (statistical significance greater ∼10σ) sources these data. These are best characterized localized point-like (i.e., spatially unresolved) early mission
The first three months of sky-survey operation with the Fermi Gamma Ray Space Telescope (Fermi) Large Area (LAT) reveals 132 bright sources at |b|>10 deg test statistic greater than 100 (corresponding to about 10 sigma). Two methods, based on CGRaBS, CRATES and BZCat catalogs, indicate high-confidence associations 106 these known AGNs. This sample is referred as LAT Bright AGN Sample (LBAS). It contains two radio galaxies, namely Centaurus A NGC 1275, 104 blazars consisting 57 flat...
A young and energetic pulsar powers the well-known Crab Nebula. Here, we describe two separate gamma-ray (photon energy greater than 100 mega-electron volts) flares from this source detected by Large Area Telescope on board Fermi Gamma-ray Space Telescope. The first flare occurred in February 2009 lasted approximately 16 days. second was September 2010 4 During these outbursts, flux nebula increased factors of four six, respectively. brevity implies that gamma rays were emitted via...
Pulsars are rapidly-rotating, highly-magnetized neutron stars emitting radiation across the electromagnetic spectrum. Although there more than 1800 known radio pulsars, until recently, only seven were observed to pulse in gamma rays and these all discovered at other wavelengths. The Fermi Large Area Telescope makes it possible pinpoint through their gamma-ray pulsations. We report detection of 16 pulsars blind frequency searches using LAT. Most coincident with previously unidentified...
We present a catalog of gamma-ray sources at energies above 10 GeV based on data from the Large Area Telescope (LAT) accumulated during first three years Fermi Gamma-ray Space mission. The Fermi-LAT >10GeV (1FHL) has 514 sources. For each source we location, spectrum, measure variability, and associations with cataloged other wavelengths. found that 449 (87%) could be associated known sources, which 393 (76% 1FHL sources) are active galactic nuclei. Of 27 pulsars, find 20 (12) to have...
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 report on gamma-ray observations of the Crab Pulsar and Nebula using 8 months survey data with Fermi Large Area Telescope (LAT). The high quality light curve obtained ephemeris provided by Nancay Jodrell Bank radio telescopes shows two main peaks stable in phase energy. first peak leads pulse (281 \pm 12 21) mus, giving new constraints production site non-thermal emission pulsar magnetospheres. improved sensitivity unprecedented statistics afforded LAT enable precise measurement spectral...
Recent observations of supernova remnants (SNRs) hint that they accelerate cosmic rays to energies close ~10(15) electron volts. However, the nature particles produce emission remains ambiguous. We report SNR W44 with Fermi Large Area Telescope at between 2 x 10(8) volts and 3 x10(11) The detection a source morphology corresponding shell implies is produced by accelerated there. gamma-ray spectrum well modeled from protons nuclei. Its steepening above approximately 10(9) provides probe which...
The discovery of bright gamma-ray emission coincident with supernova remnant (SNR) W51C is reported using the Large Area Telescope (LAT) on board Fermi Gamma-ray Space Telescope. a middle-aged (~10^4 yr) intense radio synchrotron in its shell and known to be interacting molecular cloud. spatially extended, broadly consistent X-ray extent SNR W51C. energy spectrum 0.2-50 GeV band exhibits steepening toward high energies. luminosity greater than 1x10^{36} erg/s given distance constraint D>5.5...
Microquasar Spotted Microquasars are binary star systems where a normal sheds matter onto neutron or black hole, generating x-ray radiation and jets of material moving at relativistic speeds. have proved difficult to detect in high-energy gamma rays (> 100 megaelectron volts). Using the Fermi Large Area Telescope, Abdo et al. (p. 1512 , published online 26 November; see Perspective by Bignami ) now report detection variable gamma-ray emission from microquasar Cygnus X-3. The flux is...
The Fermi Gamma-ray Space Telescope has detected the gamma-ray glow emanating from giant radio lobes of galaxy Centaurus A. resolved image shows clearly separated central active source. In contrast to all other galaxies so far in high-energy gamma-rays, lobe flux constitutes a considerable portion (>1/2) total source emission. emission is interpreted as inverse Compton scattered relic radiation cosmic microwave background (CMB), with additional contribution at higher energies...
We report observation of the supernova remnant IC443 (G189.1+3.0) with Fermi Gamma-ray Space Telescope Large Area (LAT) in energy band between 200MeV and 50GeV. is a shell-type mixed morphology located off outer Galactic plane where high-energy emission has been detected X-ray, GeV TeV gamma-ray bands. Past observations suggest interacting surrounding interstellar matter. Proximity dense shocked molecular clouds GeV-TeV regions by EGRET, MAGIC VERITAS suggests an interpretation that...
Gamma-Ray Pulsar Bonanza Most of the pulsars we know about were detected through their radio emission; a few are known to pulse gamma rays but first at other wavelengths (see Perspective by Halpern ). Using Fermi Space Telescope, Abdo et al. (p. 840 , published online 2 July; see cover) report detection 16 previously unknown based on gamma-ray emission alone. Thirteen these coincide with unidentified sources, solving 30-year-old mystery identities. Pulsars fast-rotating neutron stars. With...
Novae are thermonuclear explosions on a white dwarf surface fueled by mass accreted from companion star. Current physical models posit that shocked expanding gas the nova shell can produce X-ray emission but at higher energies has not been widely expected. Here, we report Fermi Large Area Telescope detection of variable gamma-ray (0.1-10 GeV) recently-detected optical symbiotic star V407 Cygni. We propose material interacts with dense ambient medium red giant primary, and particles be...
This is the first of a series papers aimed at characterizing populations detected in high-latitude sky Fermi-LAT survey. In this work, we focus on intrinsic spectral and flux properties source sample. We show that when selection effects are properly taken into account, Fermi sources average steeper than previously found (e.g., bright list) with an photon index 2.40 ± 0.02 over entire 0.1–100 GeV energy band. confirm flat spectrum radio quasars have spectra BL Lacertae objects 2.48 versus...
We report on the discovery of \geq 100 MeV {\gamma} rays from binary system PSR B1259-63/LS 2883 using Large Area Telescope (LAT) board Fermi. The comprises a radio pulsar in orbit around Be star. LAT observations near apastron to ~ 60 days after time periastron, tp, 2010 December 15. No {\gamma}-ray emission was detected this source when it far periastron. Faint appeared as approached At tp + 30d, flux increased over period few peak 20-30 times that seen during pre-periastron period, but...
We report the Fermi Large Area Telescope (LAT) discovery of high-energy (MeV/GeV) γ-ray emission positionally consistent with center radio galaxy M87, at a source significance over 10σ in 10 months all-sky survey data. Following detections Cen A and Per A, this makes M87 third seen LAT. The faint point-like has >100 MeV flux 2.45 (±0.63) × 10−8 photons cm−2 s−1 (photon index = 2.26 ± 0.13) no significant variability detected within LAT observation. This is comparable previous EGRET upper...
We report on the first detection of GeV high-energy gamma-ray emission from a young supernova remnant with Large Area Telescope aboard Fermi Gamma-ray Space Telescope. These observations reveal source no discernible spatial extension detected at significance level 12.2$\sigma$ above 500 MeV location that is consistent position explosion occurred around 1680 in Cassiopeia constellation - A. The flux and spectral shape are scenario which originates relativistic particles accelerated shell this...
The diffuse Galactic gamma-ray emission is produced by cosmic rays (CRs) interacting with the interstellar gas and radiation field. Measurements Energetic Gamma-Ray Experiment Telescope (EGRET) instrument on Compton Observatory indicated excess > 1 GeV relative to models consistent directly measured CR spectra (the so-called ``EGRET excess''). was observed in all directions sky, a variety of explanations have been proposed, including beyond-the-Standard-Model scenarios like annihilating or...
We present γ-ray observations with the Large Area Telescope (LAT) on board Fermi Gamma-Ray Space of nearby radio galaxy Centaurus A (Cen A). The previous EGRET detection is confirmed, and localization improved using data from first 10 months science operation. In work, we presented lobes by LAT; in this concentrate core Cen A. Flux levels as seen LAT are not significantly different that found EGRET, nor extremely soft spectrum (Γ = 2.67 ± 0.10stat 0.08sys where photon flux Φ ∝ E−Γ)....