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E. Aliu, S. Archambault,
T. Arlen,
T. Aune,
M. Beilicke,
W. Benbow,
A. Bouvier,
J. H. Buckley,
V. Bugaev,
A. Cesarini, [......],
A. Varlotta,
V. V. Vassiliev,
S. Vincent,
M. Vivier,
S. P. Wakely,
T. C. Weekes,
A. Weinstein,
R. Welsing,
D. A. Williams,
B. Zitzer
[show abstract]
[hide abstract]
ABSTRACT: We report the discovery of TeV gamma-ray emission coincident with the
shell-type radio supernova remnant (SNR) CTA 1 using the VERITAS gamma-ray
observatory. The source, VER J0006+729, was detected as a 6.5 standard
deviation excess over background and shows an extended morphology, approximated
by a two-dimensional Gaussian of semi-major (semi-minor) axis 0.30 degree (0.24
degree) and a centroid 5' from the Fermi gamma-ray pulsar PSR J0007+7303 and
its X-ray pulsar wind nebula (PWN). The photon spectrum is well described by a
power-law dN/dE = N_0 (E/3 TeV)^(-\Gamma), with a differential spectral index
of \Gamma = 2.2 +- 0.2_stat +- 0.3_sys, and normalization N_0 = (9.1 +-
1.3_stat +- 1.7_sys) x 10^(-14) cm^(-2) s^(-1) TeV^(-1). The integral flux,
F_\gamma = 4.0 x 10^(-12) erg cm^(-2) s^(-1) above 1 TeV, corresponds to 0.2%
of the pulsar spin-down power at 1.4 kpc. The energetics, co-location with the
SNR, and the relatively small extent of the TeV emission strongly argue for the
PWN origin of the TeV photons. We consider the origin of the TeV emission in
CTA 1.
The Astrophysical Journal 12/2012; 764(1):38. · 6.02 Impact Factor
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E. Aliu, S. Archambault,
T. Arlen,
T. Aune,
M. Beilicke,
W. Benbow,
M. Bottcher,
A. Bouvier,
J. H. Buckley,
V. Bugaev, [......],
T. C. Weekes,
A. Weinstein,
R. Welsing,
D. A. Williams,
B. Zitzer,
P. Fortin,
D. Horan,
M. Fumagalli,
K. Kaplan,
J. X. Prochaska
[show abstract]
[hide abstract]
ABSTRACT: We report on VERITAS very-high-energy (VHE; E>100 GeV) observations of six
blazars selected from the Fermi Large Area Telescope First Source Catalog
(1FGL). The gamma-ray emission from 1FGL sources was extrapolated up to the VHE
band, taking gamma-ray absorption by the extragalactic background light into
account. This allowed the selection of six bright, hard-spectrum blazars that
were good candidate TeV emitters. Spectroscopic redshift measurements were
attempted with the Keck Telescope for the targets without Sloan Digital Sky
Survey (SDSS) spectroscopic data. No VHE emission is detected during the
observations of the six sources described here. Corresponding TeV upper limits
are presented, along with contemporaneous Fermi observations and non-concurrent
Swift UVOT and XRT data. The blazar broadband spectral energy distributions
(SEDs) are assembled and modeled with a single-zone synchrotron self-Compton
model. The SED built for each of the six blazars show a synchrotron peak
bordering between the intermediate- and high-spectrum-peak classifications,
with four of the six resulting in particle-dominated emission regions.
The Astrophysical Journal 10/2012; 759(2):102. · 6.02 Impact Factor
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E. Aliu, S. Archambault,
T. Arlen,
T. Aune,
M. Beilicke,
W. Benbow,
A. Bouvier,
J. H. Buckley,
V. Bugaev,
K. Byrum, [......],
S. Vincent,
M. Vivier,
R. G. Wagner,
S. P. Wakely,
T. C. Weekes,
A. Weinstein,
R. Welsing,
D. A. Williams,
B. Zitzer,
V. Kondratiev
[show abstract]
[hide abstract]
ABSTRACT: We present the results of a joint observational campaign between the Green
Bank radio telescope and the VERITAS gamma-ray telescope, which searched for a
correlation between the emission of very-high-energy (VHE) gamma rays
($E_{\gamma} >$ 150 GeV) and Giant Radio Pulses (GRPs) from the Crab pulsar at
8.9 GHz. A total of 15366 GRPs were recorded during 11.6 hours of simultaneous
observations, which were made across four nights in December 2008 and in
November and December 2009. We searched for an enhancement of the pulsed
gamma-ray emission within time windows placed around the arrival time of the
GRP events. In total, 8 different time windows with durations ranging from
0.033 ms to 72 s were positioned at three different locations relative to the
GRP to search for enhanced gamma-ray emission which lagged, led, or was
concurrent with, the GRP event. Further, we performed separate searches on main
pulse GRPs and interpulse GRPs and on the most energetic GRPs in our data
sample. No significant enhancement of pulsed VHE emission was found in any of
the preformed searches. We set upper limits of 5-10 times the average VHE flux
of the Crab pulsar on the flux simultaneous with interpulse GRPs on
single-rotation-period time scales. On $\sim$8-second time scales around
interpulse GRPs, we set an upper limit of 2-3 times the average VHE flux.
Within the framework of recent models for pulsed VHE emission from the Crab
pulsar, the expected VHE-GRP emission correlations are below the derived
limits.
The Astrophysical Journal 10/2012; 760(2):136. · 6.02 Impact Factor
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E. Aliu, S. Archambault,
T. Arlen,
T. Aune,
M. Beilicke,
W. Benbow,
M. Bottcher,
A. Bouvier,
V. Bugaev,
A. Cannon, [......],
K. Tsurusaki,
A. Varlotta,
V. V. Vassiliev,
M. Vivier,
S. P. Wakely,
J. E. Ward,
A. Weinstein,
R. Welsing,
D. A. Williams,
B. Zitzer
[show abstract]
[hide abstract]
ABSTRACT: We present observations of the BL Lac object 1ES 0414+009 in the >200 GeV
gamma-ray band by the VERITAS array of Cherenkov telescopes. 1ES 0414+009 was
observed by VERITAS between January 2008 and February 2011, resulting in 56.2
hours of good quality pointed observations. These observations resulted in a
detection of 822 events from the source corresponding to a statistical
significance of 6.4 standard deviations (6.4 sigma) above the background. The
source flux, showing no evidence for variability, is measured as 5.2 +/-
1.1_stat +/- 2.6_sys * 10^-12 photons cm^-2 s^-1 above 200 GeV, equivalent to
approximately 2% of the Crab Nebula flux above this energy. The differential
photon spectrum from 230 GeV to 850 GeV is well fit by a power law with an
photon index of Gamma 3.4 +/- 0.5_stat +/- 0.3_sys and a flux normalization of
1.6 +/- 0.3_stat +/- 0.8_sys * 10^-11 photons cm^-2 s^-1 at 300 GeV. We also
present multiwavelength results taken in the optical (MDM), X-ray (Swift-XRT),
and GeV (Fermi-LAT) bands and use these results to construct a broadband
spectral energy distribution (SED). Modeling of this SED indicates that
homogenous one-zone leptonic scenarios are not adequate to describe emission
from the system, with a lepto-hadronic model providing a better fit to the
data.
The Astrophysical Journal 06/2012; 755(2):118. · 6.02 Impact Factor
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E. Aliu, S. Archambault,
T. Arlen,
T. Aune,
M. Beilicke,
W. Benbow,
A. Bouvier,
S. M. Bradbury,
J. H. Buckley,
V. Bugaev, [......],
S. Vincent,
M. Vivier,
S. P. Wakely,
J. E. Ward,
T. C. Weekes,
A. Weinstein,
T. Weisgarber,
R. Welsing,
D. A. Williams,
B. Zitzer
[show abstract]
[hide abstract]
ABSTRACT: We report on very high energy (E > 100 GeV) gamma-ray observations of V407
Cygni, a symbiotic binary that underwent a nova outburst producing 0.1-10 GeV
gamma rays during 2010 March 10-26. Observations were made with the Very
Energetic Radiation Imaging Telescope Array System during 2010 March 19-26 at
relatively large zenith angles, due to the position of V407 Cyg. An improved
reconstruction technique for large zenith angle observations is presented and
used to analyze the data. We do not detect V407 Cygni and place a differential
upper limit on the flux at 1.6 TeV of 2.3 \times 10^(-12) erg cm^(-2) s^(-1)
(at the 95% confidence level). When considered jointly with data from
Fermi-LAT, this result places limits on the acceleration of very high energy
particles in the nova.
05/2012;
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E. Aliu, S. Archambault,
T. Arlen,
T. Aune,
M. Beilicke,
W. Benbow,
M. Böttcher,
A. Bouvier,
S. M. Bradbury,
J. H. Buckley, [......],
M. Vivier,
S. P. Wakely,
J. E. Ward,
T. C. Weekes,
A. Weinstein,
T. Weisgarber,
D. A. Williams,
B. Zitzer,
P. Fortin,
and D. Horan
[show abstract]
[hide abstract]
ABSTRACT: We report on the discovery of high-energy (HE; E > 0.1 GeV) and very high energy (VHE; E > 100 GeV) γ-ray emission from the high-frequency-peaked BL Lac object RBS 0413. VERITAS, a ground-based γ-ray observatory, detected VHE γ rays from RBS 0413 with a statistical significance of 5.5 standard deviations (σ) and a γ-ray flux of (1.5 ± 0.6stat ± 0.7syst) × 10–8 photons m–2 s–1 (~1% of the Crab Nebula flux) above 250 GeV. The observed spectrum can be described by a power law with a photon index of 3.18 ± 0.68stat ± 0.30syst. Contemporaneous observations with the Large Area Telescope (LAT) on the Fermi Gamma-ray Space Telescope detected HE γ rays from RBS 0413 with a statistical significance of more than 9σ, a power-law photon index of 1.57 ± 0.12stat +0.11 – 0.12sys, and a γ-ray flux between 300 MeV and 300 GeV of (1.64 ± 0.43stat +0.31 – 0.22sys) × 10–5 photons m–2 s–1. We present the results from Fermi-LAT and VERITAS, including a spectral energy distribution modeling of the γ-ray, quasi-simultaneous X-ray (Swift-XRT), ultraviolet (Swift-UVOT), and R-band optical (MDM) data. We find that, if conditions close to equipartition are required, both the combined synchrotron self-Compton/external-Compton and the lepto-hadronic models are preferred over a pure synchrotron self-Compton model.
The Astrophysical Journal 04/2012; 750(2):94. · 6.02 Impact Factor
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VERITAS Collaboration,
E. Aliu, S. Archambault,
T. Arlen,
T. Aune,
M. Beilicke,
W. Benbow,
M. Boettcher,
A. Bouvier,
S. M. Bradbury, [......],
M. Vivier,
S. P. Wakely,
J. E. Ward,
T. C. Weekes,
A. Weinstein,
T. Weisgarber,
D. A. Williams,
B. Zitzer,
P. Fortin,
D. Horan
[show abstract]
[hide abstract]
ABSTRACT: We report on the discovery of high-energy (HE; E > 0.1 GeV) and very
high-energy (VHE; E > 100 GeV) gamma-ray emission from the
high-frequency-peaked BL Lac object RBS 0413. VERITAS, a ground-based gamma-ray
observatory, detected VHE gamma rays from RBS 0413 with a statistical
significance of 5.5 standard deviations (sigma) and a gamma-ray flux of (1.5
\pm 0.6stat \pm 0.7syst) \times 10^(-8) photons m^(-2) s^(-1) (\sim 1% of the
Crab Nebula flux) above 250 GeV. The observed spectrum can be described by a
power law with a photon index of 3.18 \pm 0.68stat \pm 0.30syst.
Contemporaneous observations with the Large Area Telescope (LAT) on the Fermi
Gamma-ray Space Telescope detected HE gamma rays from RBS 0413 with a
statistical significance of more than 9 sigma, a power-law photon index of 1.57
\pm 0.12stat +0.11sys -0.12sys and a gamma-ray flux between 300 MeV and 300 GeV
of (1.64 \pm 0.43stat +0.31sys -0.22sys) \times 10^(-5) photons m^(-2) s^(-1).
We present the results from Fermi-LAT and VERITAS, including a spectral energy
distribution modeling of the gamma-ray, quasi-simultaneous X-ray (Swift-XRT),
ultraviolet (Swift-UVOT) and R-band optical (MDM) data. We find that, if
conditions close to equipartition are required, both the combined synchrotron
self-Compton/external-Compton and the lepto-hadronic models are preferred over
a pure synchrotron self-Compton model.
04/2012;
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E. Aliu, S. Archambault,
T. Arlen,
T. Aune,
M. Beilicke,
W. Benbow,
A. Bouvier,
S. M. Bradbury,
J. H. Buckley,
V. Bugaev, [......],
M. Vivier,
R. G. Wagner,
S. P. Wakely,
J. E. Ward,
T. C. Weekes,
A. Weinstein,
T. Weisgarber,
D. A. Williams,
B. Zitzer,
for the VERITAS Collaboration
[show abstract]
[hide abstract]
ABSTRACT: The VERITAS array of Cherenkov telescopes has carried out a deep
observational program on the nearby dwarf spheroidal galaxy Segue 1. We report
on the results of nearly 48 hours of good quality selected data, taken between
January 2010 and May 2011. No significant $\gamma$-ray emission is detected at
the nominal position of Segue 1, and upper limits on the integrated flux are
derived. According to recent studies, Segue 1 is the most dark matter-dominated
dwarf spheroidal galaxy currently known. We derive stringent bounds on various
annihilating and decaying dark matter particle models. The upper limits on the
velocity-weighted annihilation cross-section are $\mathrm{<\sigma v >^{95% CL}
\lesssim 10^{-23} cm^{3} s^{-1}}$, improving our limits from previous
observations of dwarf spheroidal galaxies by at least a factor of two for dark
matter particle masses $\mathrm{m_{\chi}\gtrsim 300 GeV}$. The lower limits on
the decay lifetime are at the level of $\mathrm{\tau^{95% CL} \gtrsim 10^{24}
s}$. Finally, we address the interpretation of the cosmic ray lepton anomalies
measured by ATIC and PAMELA in terms of dark matter annihilation, and show that
the VERITAS observations of Segue 1 disfavor such a scenario.
02/2012;
