R. P. Johnson
A5103136566- Astrophysics and Cosmic Phenomena
- Dark Matter and Cosmic Phenomena
- Particle Detector Development and Performance
- Radiation Therapy and Dosimetry
- Gamma-ray bursts and supernovae
- Nuclear Physics and Applications
- Radiation Detection and Scintillator Technologies
- Pulsars and Gravitational Waves Research
- Medical Imaging Techniques and Applications
- Particle physics theoretical and experimental studies
- Radio Astronomy Observations and Technology
- Astrophysical Phenomena and Observations
- CCD and CMOS Imaging Sensors
- Advanced X-ray and CT Imaging
- X-ray Diffraction in Crystallography
- Crystallization and Solubility Studies
- Quantum Chromodynamics and Particle Interactions
- Cosmology and Gravitation Theories
- Atomic and Subatomic Physics Research
- High-Energy Particle Collisions Research
- Astronomical Observations and Instrumentation
- Astronomy and Astrophysical Research
- Neutrino Physics Research
- Crystallography and molecular interactions
- Space Science and Extraterrestrial Life
University of California, Santa Cruz
2015-2024
Loma Linda University
2017
Santa Cruz County Office of Education
2017
University of Maryland, College Park
2010
United States Naval Research Laboratory
2008-2009
Istituto Nazionale di Fisica Nucleare, Sezione di Pisa
2008
Kavli Institute for Particle Astrophysics and Cosmology
2008
Stanford University
1984-2008
SLAC National Accelerator Laboratory
1984-2008
Istituto Nazionale di Fisica Nucleare, Sezione di Bari
2007
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...
Designed as a high-sensitivity gamma-ray observatory, the Fermi Large Area Telescope is also an electron detector with large acceptance exceeding 2 m;{2} sr at 300 GeV. Building on analysis, we have developed efficient detection strategy which provides sufficient background rejection for measurement of steeply falling spectrum up to 1 TeV. Our high precision data show that falls energy E-3.0 and does not exhibit prominent spectral features. Interpretations in terms conventional diffusive...
This catalog summarizes 117 high-confidence ⩾0.1 GeV gamma-ray pulsar detections using three years of data acquired by the Large Area Telescope (LAT) on Fermi satellite. Half are neutron stars discovered LAT through periodicity searches in and radio around unassociated source positions. The pulsars evenly divided into groups: millisecond pulsars, young radio-loud radio-quiet pulsars. We characterize pulse profiles energy spectra derive luminosities when distance information exists. Spectral...
The gamma-ray sky >100 MeV is dominated by the diffuse emissions from interactions of cosmic rays with interstellar gas and radiation fields Milky Way. Observations these provide a tool to study cosmic-ray origin propagation, medium. We present measurements first 21 months Fermi-LAT mission compare models emission generated using GALPROP code. are fitted data incorporate astrophysical input for distribution sources, fields. To assess uncertainties associated input, grid created varying...
Satellite galaxies of the Milky Way are among most promising targets for dark matter searches in gamma rays. We present a search consisting weakly interacting massive particles, applying joint likelihood analysis to 10 satellite with 24 months data Fermi Large Area Telescope. No signal is detected. Including uncertainty distribution, robust upper limits placed on annihilation cross sections. The 95% confidence level range from about 10(-26) cm3 s(-1) at 5 GeV 5×10(-23) 1 TeV, depending final...
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,...
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...
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
We report on the observation of bright, long gamma-ray burst, GRB 090902B, by Gamma-ray Burst Monitor (GBM) and Large Area Telescope (LAT) instruments on-board Fermi observatory. This was one brightest GRBs to have been observed LAT, which detected several hundred photons during prompt phase. With a redshift z = 1.822, this burst is among most luminous Fermi. Time-resolved spectral analysis reveals significant power-law component in LAT data that distinct from usual Band model emission seen...
We present the results of our analysis cosmic-ray electrons using about $8\ifmmode\times\else\texttimes\fi{}{10}^{6}$ electron candidates detected in first 12 months on-orbit by Fermi Large Area Telescope. This work extends previously published spectrum down to 7 GeV, giving a spectral range approximately 2.5 decades up 1 TeV. describe detail and its validation beam-test data. In addition, we measured via subset events selected for best energy resolution as cross-check on measurement full...
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...
Dark matter in the Milky Way may annihilate directly into gamma rays, producing a monoenergetic spectral line. Therefore, detecting such signature would be strong evidence for dark annihilation or decay. We search lines Fermi Large Area Telescope observations of halo energy range 200 MeV to 500 GeV using analysis methods from our most recent line searches. The main improvements relative previous works are use 5.8 years data reprocessed with Pass 8 event-level and additional resulting...
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...
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...
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...
We report on the observations of 14 dwarf spheroidal galaxies with Fermi Gamma-Ray Space Telescope taken during first 11 months survey mode operations. The telescope provides a new opportunity to test particle dark matter models through expected gamma-ray emission produced by pair annihilation weakly interacting massive particles (WIMPs). Local Group galaxies, largest galactic substructures predicted cold scenario, are attractive targets for such indirect searches because they nearby and...
We report the detection of high-energy gamma-ray emission from two starburst galaxies using data obtained with Large Area Telescope on board Fermi Gamma-ray Space Telescope. Steady point-like above 200 MeV has been detected at significance levels 6.8 sigma and 4.8 respectively, sources positionally coincident locations M82 NGC 253. The total fluxes are consistent originating interaction cosmic rays local interstellar gas radiation fields constitute evidence for a link between massive star...
Dark matter (DM) particle annihilation or decay can produce monochromatic γ rays readily distinguishable from astrophysical sources. γ-ray line limits 30 to 200 GeV obtained 11 months of Fermi Large Area Space Telescope data 20–300 are presented using a selection based on requirements for analysis, and integrated over most the sky. We obtain flux upper in range 0.6–4.5×10−9 cm−2 s−1, give corresponding DM cross-section lifetime limits. Theoretical implications briefly discussed.Received 19...
We report the discovery by Large Area Telescope (LAT) onboard Fermi Gamma-ray Space of high-energy gamma-ray emission from peculiar quasar PMN J0948+0022 (z=0.5846). The optical spectrum this object exhibits rather narrow Hbeta (FWHM(Hbeta) ~ 1500 km s^-1), weak forbidden lines and is therefore classified as a narrow-line type I quasar. This class objects thought to have relatively small black hole mass accrete at high Eddington ratio. radio loudness variability compact core indicates...
We report the discovery of high-energy (E>100 MeV) gamma-ray emission from NGC 1275, a giant elliptical galaxy lying at center Perseus cluster galaxies, based on observations made with Large Area Telescope (LAT) Fermi Gamma ray Space Telescope. The positional source is only ~3' away 1275 nucleus, well within 95% LAT error circle ~5'.The spatial distribution photons consistent point source. average flux and power-law photon index measured 2008 August 4 to December 5 are F_gamma =...
This is the first report of Fermi Gamma-Ray Space Telescope observations quasar 3C 454.3, which has been undergoing pronounced long-term outbursts since 2000. The data from Large Area Telescope, covering 2008 July 7–October 6, indicate strong, highly variable γ-ray emission with an average flux ∼3 × 10−6 photons cm−2 s−1, for energies >100 MeV. variable, distinct, symmetrically shaped flares increases by a factor several on timescale about 3 days. variability indicates compact region, and...