P. Wilcox

Gamma-Ray Observations of Tycho’s Supernova Remnant with VERITAS and Fermi

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 a particularly good target because it is a young, type Ia SNR that is well-studied over a wide range of energies and located in a relatively clean environment. Since the detection of gamma-ray emission from Tycho’s SNR by VERITAS and Fermi -LAT, there have been several theoretical models proposed to explain its broadband emission and high-energy morphology. We report on an update to the gamma-ray measurements of Tycho’s SNR with 147 hours of VERITAS and 84 months of Fermi -LAT observations, which represents about a factor of two increase in exposure over previously published data. About half of the VERITAS data benefited from a camera upgrade, which has made it possible to extend the TeV measurements toward lower energies. The TeV spectral index measured by VERITAS is consistent with previous results, but the expanded energy range softens a straight power-law fit. At energies higher than 400 GeV, the power-law index is 2.92±0.42stat±0.20sys. It is also softer than the spectral index in the GeV energy range, 2.14±0.09stat ±0.02sys, measured by this study using Fermi–LAT data. The centroid position of the gamma-ray emission is coincident with the center of the remnant, as well as with the centroid measurement of Fermi–LAT above 1 GeV. The results are consistent with an SNR shell origin of the emission, as many models assume. The updated spectrum points to a lower maximum particle energy than has been suggested previously. Subject headings: supernova remnant: general – supernova remnant: individual(Tycho’s SNR) – gamma

Search for Magnetically Broadened Cascade Emission from Blazars with VERITAS

We present a search for magnetically broadened gamma-ray emission around active galactic nuclei (AGN), using VERITAS observations of seven hard-spectrum blazars. A cascade process occurs when multi-TeV gamma rays from AGN interact with extragalactic background light (EBL) photons to produce electron-positron pairs, which then interact with cosmic microwave background (CMB) photons via inverse-Compton scattering to produce gamma rays. Due to the deflection of the electron-positron pairs, a non-zero intergalactic magnetic field (IGMF) would potentially produce detectable effects on the angular distribution of the cascade emission. In particular, an angular broadening compared to the unscattered emission could occur. Through non-detection of angularly broadened emission from 1ES 1218+304, the source with the largest predicted cascade fraction, we exclude a range of IGMF strengths around

Very-high-energy observations of the binaries V 404 Cyg and 4U 0115+634 during giant X-ray outbursts

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A Very High Energy γ-Ray Survey toward the Cygnus Region of the Galaxy

G at the 95% confidence level. The extent of the exclusion range varies with the assumptions made about the intrinsic spectrum of 1ES 1218+304 and the EBL model used in the simulation of the cascade process. All of the sources are used to set limits on the flux due to extended emission.

VERITAS Observations of the BL Lac Object TXS 0506+056

Transient X-ray binaries produce major outbursts in which the X-ray flux can increase over the quiescent level by factors as large as

A strong limit on the very-high-energy emission from GRB 150323A

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Multiwavelength Observations of the Blazar BL Lacertae: A New Fast TeV Gamma-Ray Flare

. The low-mass X-ray binary V 404 Cyg and the high-mass system 4U 0115+634 underwent such major outbursts in June and October 2015, respectively. We present here observations at energies above hundreds of GeV with the VERITAS observatory taken during some of the brightest X-ray activity ever observed from these systems. No gamma-ray emission has been detected by VERITAS in 2.5 hours of observations of the microquasar V 404 Cyg from 2015, June 20-21. The upper flux limits derived from these observations on the gamma-ray flux above 200 GeV of F

Measurement of the Iron Spectrum in Cosmic Rays by VERITAS

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Discovery of very-high-energy emission from RGB J2243+203 and derivation of its redshift upper limit

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Dark matter constraints from a joint analysis of dwarf Spheroidal galaxy observations with VERITAS

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