G. T. Richards
A5005799543- Astrophysics and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Astronomy and Astrophysical Research
- Astronomical Observations and Instrumentation
- Astrophysical Phenomena and Observations
- Radio Astronomy Observations and Technology
- Galaxies: Formation, Evolution, Phenomena
- Dark Matter and Cosmic Phenomena
- Particle Detector Development and Performance
- Stellar, planetary, and galactic studies
- Pulsars and Gravitational Waves Research
- Neutrino Physics Research
- Geophysics and Gravity Measurements
- Scientific Research and Discoveries
- Adaptive optics and wavefront sensing
- Cosmology and Gravitation Theories
- Statistical and numerical algorithms
- Calibration and Measurement Techniques
- Computational Physics and Python Applications
- History and Developments in Astronomy
- Particle Accelerators and Free-Electron Lasers
- Atomic and Subatomic Physics Research
- Solar and Space Plasma Dynamics
- Astrophysics and Star Formation Studies
- Spectroscopy and Chemometric Analyses
University of Delaware
2018-2023
Istituto Nazionale di Fisica Nucleare, Sezione di Perugia
2021
Universidad Veritas
2015-2020
Drexel University
2020
Georgia Institute of Technology
2013-2018
State Street (United States)
2013-2018
Max Planck Society
2016-2018
Max Planck Institute for Radio Astronomy
2016
Behörde für Gesundheit und Verbraucherschutz
2007
Princeton University
2004-2006
We present coordinated multiwavelength observations of the bright, nearby BL Lac object Mrk 421 taken in 2013 January-March, involving GASP-WEBT, Swift, NuSTAR, Fermi-LAT, MAGIC, VERITAS, and other collaborations instruments, providing data from radio to very-high-energy (VHE) gamma-ray bands. NuSTAR yielded previously unattainable sensitivity 3-79 keV range, revealing that spectrum softens when source is dimmer until X-ray spectral shape saturates into a steep power law with photon index...
We present constraints on the annihilation cross section of weakly interacting massive particles dark matter based joint statistical analysis four dwarf galaxies with VERITAS. These results are derived from an optimized photon weighting technique that improves standard imaging atmospheric Cherenkov telescope (IACT) analyses by utilizing spectral and spatial properties individual events. report $\ensuremath{\sim}230$ hours observations five galaxies. find no evidence gamma-ray emission any...
Outbursts from gamma-ray quasars provide insights on the relativistic jets of active galactic nuclei and constraints diffuse radiation fields that fill universe. The detection significant emission above 100 GeV a distant quasar would show some radiated gamma-rays escape pair-production interactions with low-energy photons, be it extragalactic background light (EBL), or near supermassive black hole lying at jet's base. VERITAS detected up to ∼200 PKS 1441+25 (z = 0.939) during 2015 April,...
The high-frequency-peaked BL Lacertae object 1ES 0229+200 is a relatively distant (z = 0.1396), hard-spectrum (Gamma ~ 2.5), very-high-energy-emitting (E > 100 GeV) gamma-ray blazar. Very-high-energy measurements of this active galactic nucleus have been used to place constraints on the intensity extragalactic background light and intergalactic magnetic field. A multi-wavelength study centered around very-high-energy observations by VERITAS presented. This obtained, over period three years,...
High-energy gamma-ray emission from supernova remnants (SNRs) has provided a unique perspective for studies of Galactic cosmic-ray acceleration. Tycho's SNR is particularly good target because it young, type Ia that well-studied over wide range energies and located in relatively clean environment. Since the detection by VERITAS Fermi-LAT, there have been several theoretical models proposed to explain its broadband high-energy morphology. We report on an update measurements with 147 hours 84...
The Galactic Center (GC) region hosts a variety of powerful astronomical sources and rare astrophysical processes that emit large flux non-thermal radiation. inner 375 pc x 600 region, called the Central Molecular Zone, is home to supermassive black hole Sagittarius A*, massive cloud complexes, particle accelerators such as supernova remnants. We present results our improved analysis very-high-energy (VHE) gamma-ray emission above 2 TeV from GC using 125 hours data taken with VERITAS...
TeV J2032+4130 was the first unidentified source discovered at very high energies (VHE; E $>$ 100 GeV), with no obvious counterpart in any other wavelength. It is also extended to be observed VHE gamma rays. Following its discovery, intensive observational campaigns have been carried out all wavelengths order understand nature of object, which met limited success. We report here on a deep observation J2032+4130, based 48.2 hours data taken from 2009 2012 by VERITAS (Very Energetic Radiation...
We report on observations of the pulsar / Be star binary system PSR J2032+4127 MT91 213 in energy range between 100 GeV and 20 TeV with VERITAS MAGIC imaging atmospheric Cherenkov telescope arrays. The orbit has a period approximately 50 years, most recent periastron occurring 2017 November 13. Our span from 18 months prior to one month after. A new, point-like, gamma-ray source is detected, coincident location 213. light curve spectrum are well-characterized over passage. flux variable at...
We present very high energy (VHE) imaging of MGRO J2019+37 obtained with the VERITAS observatory. The bright extended ($\sim2^{\circ}$) unidentified Milagro source is located towards rich star formation region Cygnus-X. resolved into two sources. faint point-like VER J2016+371 overlaps CTB 87, a filled-center remnant (SNR) no evidence supernova shell at time. Its spectrum well fit in $0.65 - 10$ TeV range by power-law model photon index $2.3\pm0.4$. J2019+368 ($\sim1^{\circ}$) source, that...
We present a search for magnetically broadened gamma-ray emission around active galactic nuclei (AGNs), using VERITAS observations of seven hard-spectrum blazars. A cascade process occurs when multi-TeV gamma-rays from an AGN interact with extragalactic background light (EBL) photons to produce electron–positron pairs, which then cosmic microwave via inverse-Compton scattering gamma-rays. Due the deflection non-zero intergalactic magnetic field (IGMF) would potentially detectable effects on...
Cosmic-ray electrons and positrons (CREs) at GeV-TeV energies are a unique probe of our local Galactic neighborhood. CREs lose energy rapidly via synchrotron radiation inverse-Compton scattering processes while propagating within the Galaxy, these losses limit their propagation distance. For with TeV energies, is on order kiloparsec. Within that distance, there only few known astrophysical objects capable accelerating to such high energies. It also possible products annihilation or decay...
We present results from deep observations towards the Cygnus region using 300 hours of very-high-energy (VHE) $\gamma$-ray data taken with VERITAS Cherenkov telescope array and over seven years high-energy Fermi satellite at an energy above 1 GeV. As brightest diffuse emission in northern sky, provides a promising area to probe origins cosmic rays. report identification potential Fermi-LAT counterpart VER J2031+415 (TeV J2032+4130), resolve extended VHE source J2019+368 into two candidates...
We present a study of $\gamma$-ray emission from the core-collapse supernova remnant Cas~A in energy range 0.1GeV to 10TeV. used 65 hours VERITAS data cover 200 GeV - 10 TeV, and 10.8 years \textit{Fermi}-LAT 0.1-500 GeV. The spectral analysis shows significant curvature around $1.3 \pm 0.4_{stat}$ that is consistent with expected spectrum pion decay. Above this energy, joint deviates significantly simple power-law, best described by power-law index $2.17\pm 0.02_{stat}$ cut-off $2.3...
We report on multifrequency observations performed during 2012 December-2013 August of the first narrow-line Seyfert 1 galaxy detected in gamma rays, PMN J0948+0022 ($z$ = 0.5846). A gamma-ray flare was observed by Large Area Telescope board Fermi January, reaching a daily peak flux 0.1-100 GeV energy range (155 $\pm$ 31) $\times$10$^{-8}$ ph cm$^{-2}$ s$^{-1}$ 2013 January 1, corresponding to an apparent isotropic luminosity about 1.5$\times$10$^{48}$ erg s$^{-1}$. The flaring period...
HESS J0632+057 is the only gamma-ray binary known so far whose position in sky allows observations with ground-based observatories both northern and southern hemispheres. Here we report on long-term of conducted Very Energetic Radiation Imaging Telescope Array System High Energy Stereoscopic Cherenkov telescopes X-ray satellite Swift, spanning a time range from 2004 to 2012 covering most system's orbit. The very-high-energy (VHE) emission found be variable correlated that at energies. An...
We present deep VERITAS observations of the blazar PKS 1424+240, along with contemporaneous Fermi Large Area Telescope, Swift X-ray Telescope and UV Optical data between 2009 February 19 2013 June 8. This resides at a redshift $z\ge0.6035$, displaying significantly attenuated gamma-ray flux above 100 GeV due to photon absorption via pair-production extragalactic background light. more than hours from three years, multiwavelength light curve spectral energy distributions. The source shows...
Abstract On 2017 September 22, the IceCube Neutrino Observatory reported detection of high-energy neutrino event IC 170922A, potential astrophysical origin. It was soon determined that direction consistent with location gamma-ray blazar TXS 0506+056 (3FGL J0509.4+0541), which in an elevated emission state as measured by Fermi satellite. Very Energetic Radiation Imaging Telescope Array System (VERITAS) observations neutrino/blazar region started on 23 response to alert and continued through...
We report on variability and correlation studies using multiwavelength observations of the blazar Mrk 421 during month February, 2010 when an extraordinary flare reaching a level $\sim$27~Crab Units above 1~TeV was measured in very-high-energy (VHE) $\gamma$-rays with VERITAS observatory. This is highest flux state for ever observed VHE $\gamma$-rays. Data are analyzed from coordinated campaign across multiple instruments including $\gamma$-ray (VERITAS, MAGIC), high-energy (HE) (Fermi-LAT),...
In 2013 March, a flaring episode from the Crab Nebula lasting ∼2 weeks was detected by Fermi-LAT (Large Area Telescope on board Fermi Gamma-ray Space Telescope). The Very Energetic Radiation Imaging Array System (VERITAS) provides simultaneous observations throughout this period. During flare, 20 fold increase in flux above average synchrotron >100 MeV seen Nebula. Simultaneous measurements with VERITAS are consistent non-variable long-term at TeV energies. Assuming linear correlation...
We report the detection of a new TeV gamma-ray source, VER J0521+211, based on observations made with VERITAS imaging atmospheric Cherenkov telescope array. These were motivated by discovery cluster >30GeV photons in first year Fermi-LAT observations. J0521+211 is relatively bright at energies, mean photon flux 1.93 +/- 0.13_stat 0.78_sys 10^-11 cm-2 s-1 above 0.2 during period The source strongly variable daily timescale across all wavebands, from optical to TeV, peak corresponding ~0.3...
We summarize broadband observations of the TeV-emitting blazar 1ES 1959+650, including optical R-band by robotic telescopes Super-LOTIS and iTelescope, UV Swift UVOT, X-ray Telescope (XRT), high-energy gamma-ray with Fermi Large Area (LAT) very-high-energy (VHE) VERITAS above 315 GeV, all taken between 17 April 2012 1 June (MJD 56034 56079). The contemporaneous variability spectral energy distribution is explored in context a simple synchrotron self Compton (SSC) model. In SSC emission...
Between the beginning of its full-scale scientific operations in 2007 and 2012, VERITAS Cherenkov telescope array observed more than 130 blazars; these, 26 were detected as very-high-energy (VHE; E>100 GeV) {\gamma}-ray sources. In this work, we present analysis results a sample 114 undetected objects. The observations constitute total live-time ~570 hours. includes several unidentified Fermi-Large Area Telescope (LAT) sources (located at high Galactic latitude) well all from second...