Abstract
Dark matter is a key piece of the current cosmological scenario, with weakly interacting massive particles (WIMPs) a leading dark matter candidate. WIMPs have not been detected in their ...conventional parameter space (100 GeV ≲
M
χ
≲ 100 TeV), a mass range accessible with current Imaging Atmospheric Cherenkov Telescopes. As ultraheavy dark matter (UHDM;
M
χ
≳ 100 TeV) has been suggested as an underexplored alternative to the WIMP paradigm, we search for an indirect dark matter annihilation signal in a higher mass range (up to 30 PeV) with the VERITAS
γ
-ray observatory. With 216 hr of observations of four dwarf spheroidal galaxies, we perform an unbinned likelihood analysis. We find no evidence of a
γ
-ray signal from UHDM annihilation above the background fluctuation for any individual dwarf galaxy nor for a joint-fit analysis, and consequently constrain the velocity-weighted annihilation cross section of UHDM for dark matter particle masses between 1 TeV and 30 PeV. We additionally set constraints on the allowed radius of a composite UHDM particle.
Abstract We use the Very Energetic Radiation Imaging telescope Array System (VERITAS) imaging air Cherenkov telescope array to obtain the first measured angular diameter of β UMa at visual ...wavelengths using stellar intensity interferometry (SII) and independently constrain the limb-darkened angular diameter. The age of the Ursa Major moving group has been assessed from the ages of its members, including nuclear member Merak ( β UMa), an A1-type subgiant, by comparing effective temperature and luminosity constraints to model stellar evolution tracks. Previous interferometric limb-darkened angular-diameter measurements of β UMa in the near-infrared (Center for High Angular Resolution Astronomy (CHARA) Array, 1.149 ± 0.014 mas) and mid-infrared (Keck Nuller, 1.08 ± 0.07 mas), together with the measured parallax and bolometric flux, have constrained the effective temperature. This paper presents current VERITAS-SII observation and analysis procedures to derive squared visibilities from correlation functions. We fit the resulting squared visibilities to find a limb-darkened angular diameter of 1.07 ± 0.04 (stat) ± 0.05 (sys) mas, using synthetic visibilities from a stellar atmosphere model that provides a good match to the spectrum of β UMa in the optical wave band. The VERITAS-SII limb-darkened angular diameter yields an effective temperature of 9700 ± 200 ± 200 K, consistent with ultraviolet spectrophotometry, and an age of 390 ± 29 ± 32 Myr, using MESA Isochrones and Stellar Tracks. This age is consistent with 408 ± 6 Myr from the CHARA Array angular diameter.
Abstract
We report on multiwavelength target-of-opportunity observations of the blazar PKS 0735+178, located 2.°2 away from the best-fit position of the IceCube neutrino event IceCube-211208A ...detected on 2021 December 8. The source was in a high-flux state in the optical, ultraviolet, X-ray, and GeV
γ
-ray bands around the time of the neutrino event, exhibiting daily variability in the soft X-ray flux. The X-ray data from Swift-XRT and NuSTAR characterize the transition between the low-energy and high-energy components of the broadband spectral energy distribution (SED), and the
γ
-ray data from Fermi-LAT, VERITAS, and H.E.S.S. require a spectral cutoff near 100 GeV. Both the X-ray and
γ
-ray measurements provide strong constraints on the leptonic and hadronic models. We analytically explore a synchrotron self-Compton model, an external Compton model, and a lepto-hadronic model. Models that are entirely based on internal photon fields face serious difficulties in matching the observed SED. The existence of an external photon field in the source would instead explain the observed
γ
-ray spectral cutoff in both the leptonic and lepto-hadronic models and allow a proton jet power that marginally agrees with the Eddington limit in the lepto-hadronic model. We show a numerical lepto-hadronic model with external target photons that reproduces the observed SED and is reasonably consistent with the neutrino event despite requiring a high jet power.
Abstract
We report the detection of very high energy gamma-ray emission from the blazar S3 1227+25 (VER J1230+253) with the Very Energetic Radiation Imaging Telescope Array System (VERITAS). VERITAS ...observations of the source were triggered by the detection of a hard-spectrum GeV flare on 2015 May 15 with the Fermi-Large Area Telescope (LAT). A combined 5 hr VERITAS exposure on May 16 and 18 resulted in a strong 13
σ
detection with a differential photon spectral index, Γ = 3.8 ± 0.4, and a flux level at 9% of the Crab Nebula above 120 GeV. This also triggered target-of-opportunity observations with Swift, optical photometry, polarimetry, and radio measurements, also presented in this work, in addition to the VERITAS and Fermi-LAT data. A temporal analysis of the gamma-ray flux during this period finds evidence of a shortest variability timescale of
τ
obs
= 6.2 ± 0.9 hr, indicating emission from compact regions within the jet, and the combined gamma-ray spectrum shows no strong evidence of a spectral cutoff. An investigation into correlations between the multiwavelength observations found evidence of optical and gamma-ray correlations, suggesting a single-zone model of emission. Finally, the multiwavelength spectral energy distribution is well described by a simple one-zone leptonic synchrotron self-Compton radiation model.
Abstract
The Breakthrough Listen Initiative is conducting a program using multiple telescopes around the world to search for “technosignatures”: artificial transmitters of extraterrestrial origin ...from beyond our solar system. The Very Energetic Radiation Imaging Telescope Array System (VERITAS) Collaboration joined this program in 2018 and provides the capability to search for one particular technosignature: optical pulses of a few nanoseconds in duration detectable over interstellar distances. We report here on the analysis and results of dedicated VERITAS observations of Breakthrough Listen targets conducted in 2019 and 2020 and of archival VERITAS data collected since 2012. Thirty hours of dedicated observations of 136 targets and 249 archival observations of 140 targets were analyzed and did not reveal any signals consistent with a technosignature. The results are used to place limits on the fraction of stars hosting transmitting civilizations. We also discuss the minimum pulse sensitivity of our observations and present VERITAS observations of CALIOP: a space-based pulsed laser on board the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations. The detection of these pulses with VERITAS, using the analysis techniques developed for our technosignature search, allows a test of our analysis efficiency and serves as an important proof of principle.
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.
We use the VERITAS imaging air Cherenkov Telescope (IACT) array to obtain the
first measured angular diameter of $\beta$ UMa at visual wavelengths using
stellar intensity interferometry (SII) and ...independently constrain the
limb-darkened angular diameter. The age of the Ursa Major moving group has been
assessed from the ages of its members, including nuclear member Merak ($\beta$
UMa), an A1-type subgiant, by comparing effective temperature and luminosity
constraints to model stellar evolution tracks. Previous interferometric
limb-darkened angular-diameter measurements of $\beta$ UMa in the near-infrared
(CHARA Array, $1.149 \pm 0.014$ mas) and mid-infrared (Keck Nuller, $1.08 \pm
0.07$ mas), together with the measured parallax and bolometric flux, have
constrained the effective temperature. This paper presents current VERITAS-SII
observation and analysis procedures to derive squared visibilities from
correlation functions. We fit the resulting squared visibilities to find a
limb-darkened angular diameter of $1.07 \pm 0.04 {\rm (stat)} \pm 0.05$ (sys)
mas, using synthetic visibilities from a stellar atmosphere model that provides
a good match to the spectrum of $\beta$ UMa in the optical wave band. The
VERITAS-SII limb-darkened angular diameter yields an effective temperature of
$9700\pm200\pm 200$ K, consistent with ultraviolet spectrophotometry, and an
age of $390\pm 29 \pm 32 $ Myr, using MESA Isochrones and Stellar Tracks
(MIST). This age is consistent with $408 \pm 6$ Myr from the CHARA Array
angular diameter.
G106.3$+$2.7, commonly considered a composite supernova remnant (SNR), is
characterized by a boomerang-shaped pulsar wind nebula (PWN) and two distinct
("head" & "tail") regions in the radio band. A ...discovery of very-high-energy
(VHE) gamma-ray emission ($E_\gamma > 100$ GeV) followed by the recent
detection of ultra-high-energy (UHE) gamma-ray emission ($E_\gamma > 100$ TeV)
from the tail region suggests that G106.3$+$2.7 is a PeVatron candidate. We
present a comprehensive multi-wavelength study of the Boomerang PWN (100"
around PSR J2229+6114) using archival radio and Chandra data obtained from two
decades ago, a new NuSTAR X-ray observation from 2020, and upper limits on
gamma-ray fluxes obtained by Fermi and VERITAS observatories. The NuSTAR
observation allowed us to detect a 51.67 ms spin period from the pulsar PSR
J2229+6114 and the PWN emission characterized by a power-law model with $\Gamma
= 1.52\pm0.06$ up to 20 keV. Contrary to the previous radio study by Kothes et
al. 2006, we prefer a much lower PWN B-field ($B\sim3$ $\mu$G) and larger
distance ($d \sim 8$ kpc) based on (1) the non-varying X-ray flux over the last
two decades, (2) the energy-dependent X-ray PWN size resulting from synchrotron
burn-off and (3) the multi-wavelength spectral energy distribution (SED) data.
Our SED model suggests that the PWN is currently re-expanding after being
compressed by the SNR reverse shock $\sim 1000$ years ago. In this case, the
head region should be formed by GeV--TeV electrons injected earlier by the
pulsar propagating into the low density environment.
Compilation of papers presented by the VERITAS Collaboration at the 38th International Cosmic Ray Conference (ICRC), held July 26 through August 3, 2023 in Nagoya, Japan.
Dark matter is a key piece of the current cosmological scenario, with weakly interacting massive particles (WIMPs) a leading dark matter candidate. WIMPs have not been detected in their conventional ...parameter space (100 GeV \(\lesssim M_{\chi} \lesssim\) 100 TeV), a mass range accessible with current Imaging Atmospheric Cherenkov Telescopes. As ultraheavy dark matter (UHDM; \(M_{\chi} \gtrsim\) 100 TeV) has been suggested as an under-explored alternative to the WIMP paradigm, we search for an indirect dark matter annihilation signal in a higher mass range (up to 30 PeV) with the VERITAS gamma-ray observatory. With 216 hours of observations of four dwarf spheroidal galaxies, we perform an unbinned likelihood analysis. We find no evidence of a \(\gamma\)-ray signal from UHDM annihilation above the background fluctuation for any individual dwarf galaxy nor for a joint-fit analysis, and consequently constrain the velocity-weighted annihilation cross section of UHDM for dark matter particle masses between 1 TeV and 30 PeV. We additionally set constraints on the allowed radius of a composite UHDM particle.
