L. A. Kelley
A5079645113- Astrophysics and Cosmic Phenomena
- Dark Matter and Cosmic Phenomena
- Particle Detector Development and Performance
- Gamma-ray bursts and supernovae
- Neutrino Physics Research
- Radio Astronomy Observations and Technology
- Radiation Detection and Scintillator Technologies
- Particle Accelerators and Free-Electron Lasers
- Crystallography and Radiation Phenomena
- Particle physics theoretical and experimental studies
- Laser-Matter Interactions and Applications
- Particle accelerators and beam dynamics
- Electron and X-Ray Spectroscopy Techniques
- Graphite, nuclear technology, radiation studies
- Solar and Space Plasma Dynamics
- Laser-Plasma Interactions and Diagnostics
- X-ray Spectroscopy and Fluorescence Analysis
- Astronomy and Astrophysical Research
- Ion-surface interactions and analysis
- Radiation Therapy and Dosimetry
- Astro and Planetary Science
- Nuclear Physics and Applications
- Radio, Podcasts, and Digital Media
- Pulsars and Gravitational Waves Research
- Underwater Vehicles and Communication Systems
University of Delaware
2021
University of California, Santa Cruz
1996-2012
George Mason University
2000
University of Hawaii System
1988-1992
The diffuse gamma radiation arising from the interaction of cosmic-ray particles with matter and in Galaxy is one few probes available to study origin cosmic rays. Data Milagro gamma-ray observatory—a water Cerenkov detector that continuously views ~2 sr overhead sky—shows brightest extended region entire northern sky Cygnus Galactic plane. TeV image contains at least new source, MGRO J2019+37, which 10.9 σ above isotropic background, as well correlations density region. However, flux (after...
The recent advances in TeV gamma-ray astronomy are largely the result of ability to differentiate between extensive air showers generated by gamma rays and hadronic cosmic rays. Air Cherenkov telescopes have developed perfected "imaging" technique over past several decades. However until now no background rejection method has been successfully used an shower array detect a source We report on from electromagnetic Milagro ray observatory, based energetic particles shower. is emission Crab...
Milagrito, a detector sensitive to very high energy gamma rays, monitored the northern sky from 1997 February through 1998 May. With large field of view and duty cycle, this instrument was well suited perform search for TeV gamma-ray bursts (GRBs). We report on made counterparts GRBs observed by BATSE. BATSE detected 54 within Milagrito during period. An excess events coincident in time space with one these bursts, GRB 970417a, Milagrito. The has chance probability 2.8x10-5 being fluctuation...
In the 1950s, Landau, Pomeranchuk, and Migdal (LPM) predicted that cross section for bremsstrahlung from highly relativistic particles in dense media would be suppressed due to interference between amplitudes of nearby interactions. We have measured production rates 5 500 MeV photons 8 25 GeV electrons traversing thin gold carbon targets. observe, within 5% accuracy, suppression at level by Migdal. For extremely targets, we observe ``edge effects'' where LPM is reduced near edges also point...
Milagro is a water Cerenkov extensive air shower array that continuously monitors the entire overhead sky in TeV energy band. The results from an analysis of ~3 yr data (2000 December-2003 November) are presented. have been searched for steady point sources gamma rays between declinations 11 and 80°. Two detected, Crab Nebula active galaxy Mrk 421. For remainder northern hemisphere, we set 95% confidence level (CL) upper limits 275 600 mcrab (4.8 × 10-12 to 10.5 cm-2 s-1) above 1 source 5°...
In 1953, Ter-Mikaelian predicted that low energy bremsstrahlung from relativistic electrons moving through a medium is suppressed, because of interactions between the emitted photon and in medium. This suppression occurs emission takes place on long distance scale, allowing for destructive interference different instantaneous amplitudes. We present measurements cross sections 200 keV to 20 MeV photons produced by 8 25 GeV carbon gold targets. Our data show dielectric at level, reducing...
Gamma-ray emission from a narrow band at the galactic equator has previously been detected up to 30 GeV. We report evidence for TeV gamma-ray signal region of plane by Milagro, large-field-of-view water Cherenkov detector extensive air showers. An excess with significance 4.5 standard deviations observed longitude l E (40 degrees, 100 degrees) and latitude /b/ < 5 degrees. Under assumption simple power law spectrum, no cutoff in EGRET-Milagro energy range, measured integral flux is phi...
The cross section for bremsstrahlung from highly relativistic particles is suppressed due to interference caused by multiple scattering in dense media, and photon interactions with the electrons all materials. We present here a detailed study of production 200 keV 500 MeV photons 8 25 GeV traversing variety target For most targets, we observe expected suppressions good accuracy. that finite thickness effects are important thin targets.
The Crab Nebula was detected with the Milagro experiment at a statistical significance of 17 standard deviations over lifetime experiment. sensitive to approximately 100 GeV - TeV gamma ray air showers by observing particle footprint reaching ground. fraction detectors recording signals from photons ground is suitable proxy for energy primary and has been used measure photon spectrum between ~1 ~100 TeV. emission believed be caused inverse-Compton up-scattering scattering ambient an...
Data taken with the CYGNUS detector between 1989 September and 1993 January have been used to search for 1 s bursts of ultrahigh-energy gamma rays from point sources at arbitrary locations in northern sky. We find no evidence such bursts. set a theory-dependent upper limit on rate-density evaporating black holes 8.5×105 pc−3 yr−1 99% C.L. When same emission spectrum is recalculate previous limits based direct searches, this most restrictive by nearly 2 orders magnitude.Received 12 July...
Evidence of TeV emission from GRB 970417a has been previously reported using data the Milagrito detector. Constraints on fluence and energy spectrum are now derived additional a scaler system that recorded rate signals photomultipliers. This analysis shows if observed, it must contain photons with energies above 650 GeV. Some consequences this observation discussed.
The Milagro gamma-ray observatory employs a water Cherenkov detector to observe extensive air showers produced by high energy particles interacting in the Earth's atmosphere. has wide field of view and duty cycle, monitoring northern sky almost continuously 100 GeV TeV range. is, thus, uniquely capable searching for very high-energy emission from bursts (GRBs) during prompt phase. Detection >100 counterparts would place powerful constraints on GRB mechanisms. Twenty-five...
The Milagro telescope monitors the northern sky for 100 GeV-100 TeV transient emission through continuous very high energy (VHE) wide-field observations. large effective area and ~100 GeV threshold of allow it to detect VHE gamma-ray burst (GRB) with much higher sensitivity than previous instruments a fluence at energies comparable that dedicated GRB satellites keV-MeV energies. Even in absence positive detection, observations can place important constraints on progenitor models. We present...
Milagrito was an extensive air-shower observatory that served as a prototype for the larger Milagro instrument. operated from 1997 February to 1998 May. Although it designed very high energy (few hundred GeV threshold) water-Cerenkov gamma-ray observatory, could also be used study solar energetic particles (SEPs). By recording scaler data, which correspond photomultiplier tube singles rates, sensitive muons and small showers hadronic primary with rigidities above ~4 GV. simultaneously...
The neutralino, the lightest stable supersymmetric particle, is a strong theoretical candidate for missing astronomical ``dark matter''. A profusion of such neutralinos can accumulate near Sun when they lose energy upon scattering and are gravitationally captured. Pair-annihilations those may produce very high (VHE, above $100 GeV$) gamma-rays. Milagro an air shower array which uses water Cherenkov technique to detect extensive showers capable observing VHE gamma-rays from direction with...
view Abstract Citations (18) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Daily Search for Emission of Ultra--High-Energy Radiation from Point Sources Alexandreas, D. E. ; Allen, G. Berley, Biller, S. Burman, R. L. Cady, Cavalli-Sforza, M. Chang, C. Y. Coyne, Dion, Dorfan, Ellsworth, W. Freedman, J. Fujikawa, B. K. Goodman, A. Haines, T. Hoffman, Kelley, Klein, Krakauer, Kwok, P. Lu, X. -Q. Nagle, Potter, Sandberg, V. Sinnis, Shoup, Stark,...
The Milagrito water Cerenkov detector near Los Alamos, New Mexico, was operated as a sky monitor at energies of few TeV between 1997 February and 1998 May, including the period strong, long-lasting flare Markarian 501. served test run for full Milagro detector. An event excess with significance 3.7 sigma from 501 observed, in agreement expectations.
view Abstract Citations (18) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Search for Emission of Ultra--High-Energy Radiation from Active Galactic Nuclei Alexandreas, D. E. ; Allen, G. Berley, Biller, S. Burman, R. L. Cavalli-Sforza, M. Chang, C. Y. Chen, Chumney, P. Coyne, Dion, Dorfan, Ellsworth, W. Goodman, J. A. Haines, T. Hoffman, Kelley, Klein, Nagle, Schaller, Schnee, Shoup, Sinnis, Stark, Weeks, Williams, Wu, -P. Yang, Yodh, B....
A search for steady TeV point sources anywhere in the northern sky has been made with data from Milagrito air-shower particle detector. Over 3 × 109 events, collected 1997 February to 1998 May, have used this study. No statistically significant excess above background isotropic flux of cosmic rays was found any direction declination between -5° and 717. Upper limits are derived photon 1 source sky.
We address the challenge of finding optimal laser intensity and wavelength to drive high-energy, strong field rescattering report maximum yields K-shell <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"> <mml:mrow class="MJX-TeXAtom-ORD"> <mml:msub> <mml:mi mathvariant="normal">L</mml:mi> </mml:mrow> mathvariant="normal">I</mml:mi> </mml:msub> </mml:math> -shell hole creation. Surprisingly, our results show laser-driven is able create inner shell holes in all atoms...
We have performed an experiment to measure accurately the Landau‐Pomeranchuk‐Migdal (LPM) effect in production of 5 500 MeV photons due bremsstrahlung 8 and 25 Gev electron beams traversing thin (2 6% X0) targets varying densities. Our measurements confirm that LPM exists Migdal calculations are accurate. see that, for targets, suppression disappears leaving a Bethe‐Heitler spectrum, as predicted by theory. For intermediate target thicknesses, we lack acceptable theory, but measured energy...
We have developed a technique that allows SLAC to provide parasitic low-intensity secondary e/sup +/ and -/ beams up 25 GeV End Stations A B the FFTB during SLC operation. This beam was successfully used for one-month-long experimental run in Station by E146 collaboration. The experiment 400 MeV electron at intensities averaging one per pulse 120 pulses second. method producing such without need dedicated time operate parasitically from SLC: photons produced scrapers linac sectors 28, 29 30...
The Milagro Gamma Ray Observatory is the world's first large-area water Cherenkov detector capable of continuously monitoring sky at TeV energies. Located in northern New Mexico, will perform an all survey Northern Hemisphere energies between ~250 GeV and 50 TeV. With a high duty cycle, large area (~5000 square meters), wide field-of-view (~1 sr), uniquely searching for transient DC sources high-energy gamma-ray emission. has been operating since February, 1999. current status initial...