A5025627634- Astrophysics and Cosmic Phenomena
- Gamma-ray bursts and supernovae
- Astrophysical Phenomena and Observations
- Radio Astronomy Observations and Technology
- Pulsars and Gravitational Waves Research
- Dark Matter and Cosmic Phenomena
- Stellar, planetary, and galactic studies
- High-pressure geophysics and materials
- Mechanics and Biomechanics Studies
- Astronomical Observations and Instrumentation
- Neutrino Physics Research
- Particle Detector Development and Performance
- Astronomy and Astrophysical Research
- Scientific Measurement and Uncertainty Evaluation
- Adaptive optics and wavefront sensing
- Atmospheric Ozone and Climate
- Radiation Detection and Scintillator Technologies
- Photocathodes and Microchannel Plates
- Superconducting Materials and Applications
- Astrophysics and Star Formation Studies
- Particle Accelerators and Free-Electron Lasers
- Solar and Space Plasma Dynamics
- Cosmology and Gravitation Theories
- Mediterranean and Iberian flora and fauna
- Nuclear Physics and Applications
Grand Valley State University
2012-2023
University of Delaware
2008-2019
University of Iowa
2008-2011
University College Dublin
2010
Iowa State University
2009
University of California, Santa Barbara
2000-2005
University of Wisconsin–Madison
1997
The XMM-OM instrument extends the spectral coverage of XMM-Newton observatory into ultraviolet and optical range. It provides imaging time-resolved data on targets simultaneously with observations in EPIC RGS. also has ability to track stars its field view, thus providing an improved post-facto aspect solution for spacecraft. An overview operation is given, together current information performance instrument.
The accretion of matter onto a massive black hole is believed to feed the relativistic plasma jets found in many active galactic nuclei (AGN). Although some AGN accelerate particles energies exceeding 10^12 electron Volts (eV) and are bright sources very-high-energy (VHE) gamma-ray emission, it not yet known where VHE emission originates. Here we report on radio observations galaxy M87, revealing period extremely strong flares accompanied by increase flux from its nucleus. These results...
We report the discovery of TeV gamma-ray emission from Type Ia supernova remnant (SNR) G120.1+1.4, known as Tycho's remnant. Observations performed in period 2008-2010 with VERITAS ground-based observatory reveal weak coming direction remnant, compatible a point source located at $00^{\rm h} \ 25^{\rm m} 27.0^{\rm s},\ +64^{\circ} 10^{\prime} 50^{\prime\prime}$ (J2000). The photon spectrum measured by can be described power-law $dN/dE = C(E/3.42\;\textrm{TeV})^{-\Gamma}$ $\Gamma 1.95 \pm...
LS I +61 303 is one of only a few high-mass X-ray binaries currently detected at high significance in very energy gamma-rays. The system was observed over several orbital cycles (between September 2006 and February 2007) with the VERITAS array imaging air-Cherenkov telescopes. A signal gamma-rays energies above 300 GeV found statistical 8.4 standard deviations. flux measured to be strongly variable; maximum during most apastron. spectrum for period emission can characterized by power law...
We present evidence that the very high energy (VHE, E > 100 GeV) gamma-ray emission coincident with supernova remnant IC 443 is extended. contains one of best studied sites remnant/molecular cloud interaction and pulsar wind nebula CXOU J061705.3+222127, both which are important targets for VHE observations. VERITAS observed 37.9 hr during 2007 detected above 300 GeV an excess 247 events, resulting in a significance 8.3 standard deviations (σ) before trials 7.5σ after point-source search....
We report on TeV γ-ray observations of the blazar Mrk 421 (redshift 0.031) with VERITAS observatory and Whipple 10 m Cherenkov telescope. The excellent sensitivity allowed us to sample fluxes energy spectra unprecedented accuracy where was detected in each pointings. A total 47.3 hr 96 data were acquired between 2006 January 2008 June. present results a study as function time for different flux levels. On May 2 3, bright flares reaching level Crab. complemented radio, optical, X-ray...
The very high energy (VHE; E > 100 GeV) blazar Markarian 501 has a well-studied history of extreme spectral variability and is an excellent laboratory for studying the physical processes within jets active galactic nuclei. However, there are few detailed multiwavelength studies during its quiescent state, due to low luminosity. A short-term study was coordinated in March 2009, focusing around multi-day observation with Suzaku X-ray satellite including {\gamma}-ray data from VERITAS, MAGIC,...
The multiwavelength observation of the nearby radio galaxy M87 provides a unique opportunity to study in detail processes occurring active galactic nuclei from waves TeV γ-rays. Here we report detection γ-ray emission above 250 GeV spring 2007 with VERITAS atmospheric Cerenkov telescope array and discuss its correlation X-ray emission. is measured be pointlike an intrinsic source radius less than 4.5'. differential energy spectrum fitted well by power-law function: dΦ/dE = (7.4 ± 1.3stat...
We report results from an intensive multiwavelength campaign on the intermediate-frequency-peaked BL Lacertae object W Com (z=0.102) during a strong outburst of very high energy gamma-ray emission in June 2008. The signal was detected by VERITAS 2008 7-8 with flux F(>200 GeV) = (5.7+-0.6)x10^-11 cm-2s-1, about three times brighter than discovery March. initial detection this flare at energies above 200 GeV followed observations gamma-rays (AGILE, E>100 MeV), and X-rays (Swift XMM-Newton),...
The intermediate-frequency peaked BL Lacertae (IBL) object 3C 66A is detected during 2007 - 2008 in VHE (very high energy: E > 100 GeV) gamma-rays with the VERITAS stereoscopic array of imaging atmospheric Cherenkov telescopes. An excess 1791 events detected, corresponding to a significance 21.2 standard deviations (sigma), these observations (32.8 hours live time). observed integral flux above 200 GeV 6% Crab Nebula's and shows evidence for variability on time-scale days. measured energy...
We report on observations of very high energy γ rays from the shell-type supernova remnant (SNR) Cassiopeia A with Very Energetic Radiation Imaging Telescope Array System stereoscopic array four imaging atmospheric Cherenkov telescopes in Arizona. The total exposure time for these is 22 hr, accumulated between September and November 2007. γ-ray source associated SNR was detected above 200 GeV a statistical significance 8.3σ. estimated integral flux this about 3% Crab-Nebula flux. photon...
VERITAS, an Imaging Atmospheric Cherenkov Telescope (IACT) system for gammma‐ray astronomy in the GeV‐TeV range, has recently completed its first season of observations with a full array four telescopes. A number astrophysical gamma‐ray sources have been detected, both galactic and extragalactic, including previously unknown at TeV energies. We describe status some highlight results, assess technical performance, sensitivity shower reconstruction capabilities.
The high-frequency-peaked BL Lacertae object RGB J0710+591 was observed in the very high-energy (VHE; E > 100 GeV) wave band by VERITAS array of atmospheric Cherenkov telescopes. observations, taken between 2008 December and 2009 March totaling 22.1 hr, yield discovery VHE gamma rays from source. is detected at a statistical significance 5.5 standard deviations (5.5σ) above background, corresponding to an integral flux (3.9 +/- 0.8) x 10-12 cm-2 s-1 (3% Crab Nebula's flux) 300 GeV....
We report the detection of very high energy γ-ray emission from intermediate-frequency-peaked BL Lacertae object W Comae (z = 0.102) by VERITAS. The source was observed between 2008 January and April. A strong outburst measured in middle March, lasting for only 4 days. spectrum during two highest flare nights is fit a power law found to be steep, with differential photon spectral index Γ 3.81 ± 0.35stat± 0.34syst. integral flux above 200 GeV those corresponds roughly 9% Crab Nebula....
We report the detection of very-high-energy (VHE) gamma-ray emission from supernova remnant (SNR) G106.3+2.7. Observations performed in 2008 with VERITAS atmospheric Cherenkov telescope resolve extended overlapping elongated radio SNR. The 7.3 sigma (pre-trials) has a full angular extent roughly 0.6deg by 0.4deg. Most notably, centroid VHE is centered near peak coincident 12CO (J = 1-0) emission, 0.4deg away pulsar PSR J2229+6114, situated at northern end Evidently current-epoch particles...
We report the first detection of very-high-energy (VHE) gamma-ray emission above 140 GeV from PKS 1424+240, a BL Lac object with an unknown redshift. The photon spectrum measured by VERITAS is well described power law index 3.8 +- 0.5_stat 0.3_syst and flux normalization at 200 (5.1 0.9_stat 0.5_syst) x 10^{-11} TeV^-1 cm^-2 s^-1, where stat syst denote statistical systematical uncertainty, respectively. VHE steady over observation period between MJD 54881 55003 (2009 February 19 to June...
Indirect dark matter searches with ground-based gamma-ray observatories provide an alternative for identifying the particle nature of that is complementary to direct search or accelerator production experiments. We present results observations dwarf spheroidal galaxies Draco, Ursa Minor, Boötes 1, and Willman 1 conducted by Very Energetic Radiation Imaging Telescope Array System (VERITAS). These are nearby dominated objects located at a typical distance several tens kiloparsecs which there...
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 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 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 spectral analysis of XMM-Newton data ten dwarf novae, nine which were observed during quiescent state. The X-ray spectra indicate the presence hot, optically thin plasma with temperature distribution consistent simple, isobaric cooling flow. likely origin emission is in boundary layer settling onto white dwarf. Using flow model, we derive temperatures, accretion rates, rotational velocities, and elemental abundances emitting gas. discuss implications our findings for structure...
The VERITAS collaboration reports the detection of very-high-energy gamma-ray emission from high-frequency-peaked BL Lac object 1ES 1218+304 located at a redshift z = 0.182. A signal was detected with statistical significance 10.4 standard deviations (10.4σ) for observations taken during first three months 2007, confirming discovery this made by MAGIC collaboration. photon spectrum between ∼160 GeV and ∼1.8 TeV is well described power law an index Γ 3.08 ± 0.34stat 0.2sys. integral flux...
We present results from an intensive VERITAS monitoring campaign of the high-frequency peaked BL Lac object 1ES 1218+304 in 2008/2009. Although was detected previously by MAGIC and at a persistent level ~6% Crab Nebula flux, new data reveal prominent flare reaching ~20% Crab. While very high energy (VHE) flares are quite common many nearby blazars, case (redshift z = 0.182) is particularly interesting since it belongs to group blazars that exhibit unusually hard VHE spectra considering their...
We report on the results of two coordinated multiwavelength campaigns that focused blazar Markarian 421 during its 2006 and 2008 outbursts. These obtained UV X-ray data using XMM-Newton satellite, while gamma-ray were utilizing three imaging atmospheric Cerenkov telescopes, Whipple 10 m telescope VERITAS, both based in Arizona, as well MAGIC telescope, La Palma Canary Islands. The effort between groups allowed for truly simultaneous UV/X-ray/gamma-ray wavelengths a significant portion...