53709598
Multiwavelength Observations of the TeV Binary LS I +61° 303 with VERITAS, Fermi-LAT, and Swift/XRT during a TeV Outburst
We present the results of a multiwavelength observational campaign on the TeV binary system LS I +61° 303 with the VERITAS telescope array (>200 GeV), Fermi-LAT (0.3-300 GeV), and Swift/XRT (2-10 keV). The data were taken from 2011 December through 2012 January and show a strong detection in all three wavebands. During this period VERITAS obtained 24.9 hr of quality selected livetime data in which LS I +61° 303 was detected at a statistical significance of 11.9σ. These TeV observations show evidence for nightly variability in the TeV regime at a post-trial significance of 3.6σ. The combination of the simultaneously obtained TeV and X-ray fluxes do not demonstrate any evidence for a correlation between emission in the two bands. For the first time since the launch of the Fermi satellite in 2008, this TeV detection allows the construction of a detailed MeV-TeV spectral energy distribution from LS I +61° 303. This spectrum shows a distinct cutoff in emission near 4 GeV, with emission seen by the VERITAS observations following a simple power-law above 200 GeV. This feature in the spectrum of LS I +61° 303, obtained from overlapping observations with Fermi-LAT and VERITAS, may indicate that there are two distinct populations of accelerated particles producing the GeV and TeV emission.
121713887
The detection at high and very high energies of the blazar 1ES 1312-423
The deep observation campaign led on Centaurus A with the High Energy Stereoscopic System (H.E.S.S.) has revealed a significant very high energy (VHE, E ≥ 100 GeV) excess coincident with the blazar 1ES 1312-423, 2° away from the radio galaxy. The source is also detected at high energy (HE, 20 MeV-300 GeV) with the Fermi Large Area Telescope (Fermi-LAT) after 3.5 years of all-sky monitoring. The high and very high energy spectra, together with Swift-XRT and ATOM observations are used to draw the first broad band spectral energy distribution (SED) of 1ES 1312-423. The non-thermal emission of this faint HBL is reproduced with a synchrotron self-Compton (SSC) model combined with a black-body spectrum for the host galaxy.
58887396
A search for enhanced very high energy GAMMA-RAY emission from the 2013 march crab nebula flare
In 2013 March, a flaring episode from the Crab Nebula lasting similar to 2 weeks was detected by Fermi-LAT (Large Area Telescope on board the Fermi Gamma-ray Space Telescope). The Very Energetic Radiation Imaging Telescope Array System (VERITAS) provides simultaneous observations throughout this period. During the flare, Fermi-LAT detected a 20 fold increase in flux above the average synchrotron flux >100 MeV seen from the Crab Nebula. Simultaneous measurements with VERITAS are consistent with the non-variable long-term average Crab Nebula flux at TeV energies. Assuming a linear correlation between the very high energy flux change >1 TeV and the flux change seen in the Fermi-LAT band >100 MeV during the period of simultaneous observations, the linear correlation factor can be constrained to be at most 8.6 x 10(-3) with 95% confidence.
53531034
Discovery of a new tev Gamma-Ray source - VER J0521+211
We report the detection of a new TeV gamma-ray source, VER J0521+211, based on observations made with the VERITAS imaging atmospheric Cherenkov Telescope Array. These observations were motivated by the discovery of a cluster of >30 GeV photons in the first year of Fermi Large Area Telescope observations. VER J0521+211 is relatively bright at TeV energies, with a mean photon flux of (1.93 ± 0.13stat ± 0.78sys) × 10–11 cm–2 s–1 above 0.2 TeV during the period of the VERITAS observations. The source is strongly variable on a daily timescale across all wavebands, from optical to TeV, with a peak flux corresponding to ~0.3 times the steady Crab Nebula flux at TeV energies. Follow-up observations in the optical and X-ray bands classify the newly discovered TeV source as a BL Lac-type blazar with uncertain redshift, although recent measurements suggest z = 0.108. VER J0521+211 exhibits all the defining properties of blazars in radio, optical, X-ray, and gamma-ray wavelengths.
1747404
Thick pixelated CZT detectors with isolated steering grids
We explore the possibility to improve the performance of 0.5 cm thick cadmium zinc telluride (CZT) detectors with the help of steering grids on the anode side of the detectors. Steering grids can improve the energy resolution of CZT detectors by enhancing the small pixel effect; furthermore, they can increase their detection efficiency by steering electrons to the anode pixels which otherwise would drift to the area between pixels. Previously, the benefit of steering grids had been compromised by additional noise associated with currents between the steering grids and the anode pixels. We use thin film deposition techniques to isolate the steering grid from the CZT substrate by a 150 nm thick layer of the isolator Al2O3. While the thin layer does not affect the beneficial effect of the steering grid on the weighting potentials and the electric field inside the detector, it suppresses the currents between the steering grid and the anode pixels. In this contribution, we present first results from a 2times2times0.5 cm3 CZT detector with 8times8 pixels that we tested before and after deposition of an isolated steering grid. The steering grid improves the 662 keV energy resolution of the detector by a factor of 1.3 (from about 2% to about 1.5%), while not reducing the detection efficiency. To gain further insights into the detector response in the region between pixels, we measured energy spectra with a collimated 137Cs source. The collimator measurements can be used to enhance our understanding of energy spectra measured under flood illumination of the detectors
118220245
Cherenkov and Jansky: Our Understanding of AGN at the Highest Energies
Misaligned blazars have been the subject of some of the most successful radio and gamma-ray multiwavelength campaigns. These campaigns have included many of the major ground and space based gamma-ray telescopes and span decades of energy. Even though misaligned blazars account for only a small number of the total AGN detected at VHE, they provide a unique view on the AGN population. By viewing blazars at larger angles to our line of sight, they become a unique laboratory for the study of AGN jet substructure and the morphology of non-thermal emission processes. This contribution will discuss our understanding of three VHE misaligned blazars.
92351247
Probing color singlet exchange in proton anti-proton collisions at 630-GeV and 1800-GeV
118390823
Rapidity gaps in hard processes at D0
Latest results on jet production with rapidity gaps at the Fermilab Tevatron Collider are presented. Jet production via color-singlet exchange at high momenta transfer is observed as a class of events with low particle multiplicity (or rapidity gaps) between the two highest transverse energy jets. The particle multiplicity in various regions, and the dependencies on jet pseudorapidity separation and jet transverse energy are studied for these events. Results from two classes of dijet events with one or two forward rapidity gaps are also presented. The topology of these events is consistent with expectations for hard single diffraction and hard double pomeron exchange processes, respectively.