We present a study of γ-ray emission from the core-collapse supernova remnant Cas A in the energy range from 0.1 GeV to 10 TeV. We used 65 hr of the Very Energetic Radiation Imaging Telescope Array ...System (VERITAS) data to cover 200 GeV-10 TeV, and 10.8 yr of Fermi-Large Area Telescope (LAT) data to cover 0.1-500 GeV. The spectral analysis of Fermi-LAT data shows a significant spectral curvature around 1.3 0.4stat GeV that is consistent with the expected spectrum from pion decay. Above this energy, the joint spectrum from Fermi-LAT and VERITAS deviates significantly from a simple power law, and it is best described by a power law with a spectral index of 2.17 0.02stat and a cutoff energy of 2.3 0.5stat TeV. These results, along with radio, X-ray, and γ-ray data, are interpreted in the context of leptonic and hadronic models. Assuming a one-zone model, we exclude a purely leptonic scenario and conclude that proton acceleration up to at least 6 TeV is required to explain the observed γ-ray spectrum. From modeling of the entire multiwavelength spectrum, a minimum magnetic field inside the remnant of Bmin 150 G is deduced.
The extragalactic background light (EBL), a diffuse photon field in the optical and infrared range, is a record of radiative processes over the universe's history. Spectral measurements of blazars at ...very high energies (>100 GeV) enable the reconstruction of the spectral energy distribution (SED) of the EBL, as the blazar spectra are modified by redshift- and energy-dependent interactions of the gamma-ray photons with the EBL. The spectra of 14 VERITAS-detected blazars are included in a new measurement of the EBL SED that is independent of EBL SED models. The resulting SED covers an EBL wavelength range of 0.56-56 m, and is in good agreement with lower limits obtained by assuming that the EBL is entirely due to radiation from cataloged galaxies.
Blazars are known for their variability on a wide range of timescales at all wavelengths. Most studies of TeV gamma-ray blazars focus on short timescales, especially during flares. With a decade of ...observations from the Fermi-LAT and VERITAS, we present an extensive study of the long-term multiwavelength radio-to-gamma-ray flux-density variability, with the addition of a couple of short-time radio-structure and optical polarization observations of the blazar 1ES 1215+303 (z = 0.130), with a focus on its gamma-ray emission from 100 MeV to 30 TeV. Multiple strong GeV gamma-ray flares, a long-term increase in the gamma-ray and optical flux baseline, and a linear correlation between these two bands are observed over the ten-year period. Typical HBL behaviors are identified in the radio morphology and broadband spectrum of the source. Three stationary features in the innermost jet are resolved by Very Long Baseline Array at 43.1, 22.2, and 15.3 GHz. We employ a two-component synchrotron self-Compton model to describe different flux states of the source, including the epoch during which an extreme shift in energy of the synchrotron peak frequency from infrared to soft X-rays is observed.
The radio source 3C 264, hosted by the giant elliptical galaxy NGC 3862, was observed with the Very Energetic Radiation Imaging Telescope Array System (VERITAS) between 2017 February and 2019 May. ...These deep observations resulted in the discovery of very high energy (VHE; E > 100 GeV) γ-ray emission from this active galaxy. An analysis of ∼57 hr of quality-selected live time yields a detection at the position of the source, corresponding to a statistical significance of 7.8 standard deviations above background. The observed VHE flux is variable on monthly timescales, with an elevated flux seen in 2018 observations. The VHE emission during this elevated state is well characterized by a power-law spectrum with a photon index Γ = 2.20 0.27 and flux F(>315 GeV) = ( cm−2 s−1, or approximately 0.7% of the Crab Nebula flux above the same threshold. 3C 264 (z = 0.0217) is the most distant radio galaxy detected at VHE, and the elevated state is thought to be similar to that of the famously outbursting jet in M87. Consequently, extensive contemporaneous multiwavelength data were acquired in 2018 at the time of the VHE high state. An analysis of these data, including Very Long Baseline Array, Very Large Array, Hubble Space Telescope, Chandra, and Swift observations in addition to the VERITAS data, is presented, along with a discussion of the resulting spectral energy distribution.
We conduct a search for periodic emission in the very high-energy (VHE) gamma-ray band (E > 100 GeV) from a total of 13 pulsars in an archival VERITAS data set with a total exposure of over 450 hr. ...The set of pulsars includes many of the brightest young gamma-ray pulsars visible in the Northern Hemisphere. The data analysis resulted in nondetections of pulsed VHE gamma-rays from each pulsar. Upper limits on a potential VHE gamma-ray flux are derived at the 95% confidence level above three energy thresholds using two methods. These are the first such searches for pulsed VHE emission from each of the pulsars, and the obtained limits constrain a possible flux component manifesting at VHEs as is seen for the Crab pulsar.
HESS J0632+057 is a gamma-ray binary composed of a compact object orbiting a Be star with a period of about 315 days. Extensive X-ray and TeV gamma-ray observations have revealed a peculiar light ...curve containing two peaks, separated by a dip. We present the results of simultaneous observations in hard X-rays with NuSTAR and in TeV gamma-rays with VERITAS, performed in 2017 November and December. These observations correspond to the orbital phases φ 0.22 and 0.3, where the fluxes are rising toward the first light-curve peak. A significant variation of the spectral index from 1.77 0.05 to 1.56 0.05 is observed in the X-ray data. The multiwavelength spectral energy distributions (SED) derived from the observations are interpreted in terms of a leptonic model, in which the compact object is assumed to be a pulsar and nonthermal radiation is emitted by high-energy electrons accelerated at the shock formed by the collision between the stellar and pulsar wind. The results of the SED fitting show that our data can be consistently described within this scenario, and allow us to estimate the magnetization of the pulsar wind at the location of the shock formation. The constraints on the pulsar wind magnetization provided by our results are shown to be consistent with those obtained from other systems.
Production of exclusive dijets in diffractive deep inelastic
e
±
p
scattering has been measured with the ZEUS detector at HERA using an integrated luminosity of 372 pb
-
1
. The measurement was ...performed for
γ
∗
–
p
centre-of-mass energies in the range
90
<
W
<
250
GeV
and for photon virtualities
Q
2
>
25
GeV
2
. Energy flows around the jet axis are presented. The cross section is presented as a function of
β
and
ϕ
, where
β
=
x
/
x
I
P
,
x
is the Bjorken variable and
x
I
P
is the proton fractional longitudinal momentum loss. The angle
ϕ
is defined by the
γ
∗
–dijet plane and the
γ
∗
–
e
±
plane in the rest frame of the diffractive final state. The
ϕ
cross section is measured in bins of
β
. The results are compared to predictions from models based on different assumptions about the nature of the diffractive exchange.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Abstract
The ground-based gamma-ray observatory Very Energetic Radiation Imaging Telescope Array System (VERITAS,
https://veritas.sao.arizona.edu/
) is sensitive to photons of astrophysical origin ...with energies in the range between ≈85 GeV and ≈30 TeV. The instrument consists of four 12 m diameter imaging Cherenkov telescopes operating at the Fred Lawrence Whipple Observatory in southern Arizona. VERITAS started four-telescope operations in 2007 and collects about 1100 hr of good-weather data per year. The VERITAS collaboration has published over 100 journal articles since 2008 reporting on gamma-ray observations of a large variety of objects: Galactic sources like supernova remnants, pulsar wind nebulae, and binary systems; extragalactic sources like star-forming galaxies, dwarf-spheroidal galaxies, and highly variable active galactic nuclei. This note presents VTSCat: the catalog of high-level data products from all VERITAS publications.
PDF
