Browsing by Author "VERITAS Collaboration"

Now showing 1 - 11 of 11
  • Thumbnail Image
    Item
    Dark matter constraints from a joint analysis of dwarf Spheroidal galaxy observations with VERITAS
    (American Physical Society, 2017-04-05) VERITAS Collaboration; McGill University; Washington University (WUSTL); Harvard University; Smithsonian Institution; University of California System; University of California Los Angeles; Iowa State University; United States Department of Energy (DOE); Argonne National Laboratory; California State University System; California Polytechnic State University San Luis Obispo; Ollscoil na Gaillimhe-University of Galway; Purdue University System; Purdue University; Purdue University West Lafayette Campus; Tsinghua University; Helmholtz Association; Deutsches Elektronen-Synchrotron (DESY); University of Minnesota System; University of Minnesota Twin Cities; California State University East Bay; Brown University; Carnegie Mellon University; Stevens Institute of Technology; University of Potsdam; University of California Santa Cruz; University of Delaware; Columbia University; University of Iowa; Utah System of Higher Education; University of Utah; DePauw University; University College Dublin; University System of Georgia; Georgia Institute of Technology; University of Chicago; Cork Institute of Technology; National Aeronautics & Space Administration (NASA); NASA Goddard Space Flight Center; University System of Maryland; University of Maryland College Park; University of Alabama Tuscaloosa
    We present constraints on the annihilation cross section of weakly interacting massive particles dark matter based on the joint statistical analysis of four dwarf galaxies with VERITAS. These results are derived from an optimized photon weighting statistical technique that improves on standard imaging atmospheric Cherenkov telescope (IACT) analyses by utilizing the spectral and spatial properties of individual photon events. We report on the results of similar to 230 hours of observations of five dwarf galaxies and the joint statistical analysis of four of the dwarf galaxies. We find no evidence of gamma-ray emission from any individual dwarf nor in the joint analysis. The derived upper limit on the dark matter annihilation cross section from the joint analysis is 1.35 x 10(-23) cm(3) s(-1) at 1 TeV for the bottom quark (b (b) over bar) final state, 2.85 x 10(-24) cm(3) s(-1) at 1 TeV for the tau lepton (tau+tau(-)) final state and 1.32 x 10-25 cm(3) s(-1) at 1 TeV for the gauge boson (gamma gamma) final state.
  • Thumbnail Image
    Item
    INVESTIGATING BROADBAND VARIABILITY OF THE TeV BLAZAR 1ES 1959+650
    (IOP Publishing, 2014-12-03) VERITAS Collaboration; Columbia University; McGill University; University of California System; University of California Los Angeles; Harvard University; Smithsonian Astrophysical Observatory; Smithsonian Institution; Washington University (WUSTL); University of Delaware; University College Dublin; University of California Santa Cruz; University of Potsdam; Helmholtz Association; Deutsches Elektronen-Synchrotron (DESY); Ollscoil na Gaillimhe-University of Galway; Purdue University System; Purdue University; Purdue University West Lafayette Campus; University of Minnesota System; University of Minnesota Twin Cities; Iowa State University; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; University of Iowa; Utah System of Higher Education; University of Utah; DePauw University; Saha Institute of Nuclear Physics; University of Chicago; University System of Georgia; Georgia Institute of Technology; Galway Mayo Institute of Technology; National Aeronautics & Space Administration (NASA); NASA Goddard Space Flight Center; California State University System; California Polytechnic State University San Luis Obispo; Cork Institute of Technology; University of Colorado System; University of Colorado Denver; United States Department of Energy (DOE); Argonne National Laboratory; North West University - South Africa; Carnegie Institution for Science; Princeton University; University of Alabama Tuscaloosa
    We summarize broadband observations of the TeV-emitting blazar 1ES 1959+650, including optical R-band observations by the robotic telescopes Super-LOTIS and iTelescope, UV observations by Swift Ultraviolet and Optical Telescope, X-ray observations by the Swift X-ray Telescope, high-energy gamma-ray observations with the Fermi Large Area Telescope, and very-high-energy (VHE) gamma-ray observations by VERITAS above 315 GeV, all taken between 2012 April 17 and 2012 June 1 (MJD 56034 and 56079). The contemporaneous variability of the broadband spectral energy distribution is explored in the context of a simple synchrotron self Compton (SSC) model. In the SSC emission scenario, we find that the parameters required to represent the high state are significantly different than those in the low state. Motivated by possible evidence of gas in the vicinity of the blazar, we also investigate a reflected emission model to describe the observed variability pattern. This model assumes that the non-thermal emission from the jet is reflected by a nearby cloud of gas, allowing the reflected emission to re-enter the blob and produce an elevated gamma-ray state with no simultaneous elevated synchrotron flux. The model applied here, although not required to explain the observed variability pattern, represents one possible scenario which can describe the observations. As applied to an elevated VHE state of 66% of the Crab Nebula flux, observed on a single night during the observation period, the reflected emission scenario does not support a purely leptonic non-thermal emission mechanism. The reflected emission model does, however, predict a reflected photon field with sufficient energy to enable elevated gamma-ray emission via pion production with protons of energies between 10 and 100 TeV.
  • Thumbnail Image
    Item
    A Luminous and Isolated Gamma-Ray Flare from the Blazar B2 1215+30
    (IOP Publishing, 2017-02-21) VERITAS Collaboration; Fermi-LAT Collaboration; Utah System of Higher Education; University of Utah; McGill University; Washington University (WUSTL); Harvard University; Smithsonian Institution; University College Dublin; University of California System; University of California Los Angeles; United States Department of Energy (DOE); Argonne National Laboratory; University of Potsdam; Helmholtz Association; Deutsches Elektronen-Synchrotron (DESY); Purdue University System; Purdue University; Purdue University West Lafayette Campus; Tsinghua University; Iowa State University; Columbia University; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; University of Minnesota System; University of Minnesota Twin Cities; California State University System; California State University East Bay; Ollscoil na Gaillimhe-University of Galway; University of Delaware; University of California Santa Cruz; University of Iowa; DePauw University; University System of Georgia; Georgia Institute of Technology; University of Chicago; Cork Institute of Technology; Centre National de la Recherche Scientifique (CNRS); CNRS - National Institute of Nuclear and Particle Physics (IN2P3); Institut Polytechnique de Paris; UDICE-French Research Universities; Universite Paris Saclay; University of Turku; Linnaeus University; University of Alabama Tuscaloosa
    B2 1215+30 is a BL-Lac-type blazar that was first detected at TeV energies by the MAGIC atmospheric Cherenkov telescopes and subsequently confirmed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS) observatory with data collected between 2009 and 2012. In 2014 February 08, VERITAS detected a large-amplitude flare from B2. 1215+30 during routine monitoring observations of the blazar 1ES. 1218+304, located in the same field of view. The TeV flux reached 2.4 times the Crab Nebula flux with a variability timescale of <3.6 hr. Multiwavelength observations with Fermi-LAT, Swift, and the Tuorla Observatory revealed a correlated high GeV flux state and no significant optical counterpart to the flare, with a spectral energy distribution where the gamma-ray luminosity exceeds the synchrotron luminosity. When interpreted in the framework of a onezone leptonic model, the observed emission implies a high degree of beaming, with Doppler factor delta > 10, and an electron population with spectral index p < 2.3.
  • Thumbnail Image
    Item
    Measurement of cosmic-ray electrons at TeV energies by VERITAS
    (American Physical Society, 2018-09-20) VERITAS Collaboration; Purdue University System; Purdue University; Purdue University West Lafayette Campus; Harvard University; Smithsonian Institution; University of California System; University of California Los Angeles; University of Potsdam; Helmholtz Association; Deutsches Elektronen-Synchrotron (DESY); Washington University (WUSTL); Ollscoil na Gaillimhe-University of Galway; Tsinghua University; McGill University; University of Minnesota System; University of Minnesota Twin Cities; California State University System; California State University East Bay; University of California Santa Cruz; University of Delaware; Columbia University; University of Iowa; Utah System of Higher Education; University of Utah; DePauw University; Iowa State University; University College Dublin; University System of Georgia; Georgia Institute of Technology; Cork Institute of Technology; University of Alabama Tuscaloosa; University of Chicago
    Cosmic-ray electrons and positrons (CREs) at GeV-TeV energies are a unique probe of our local Galactic neighborhood. CREs lose energy rapidly via synchrotron radiation and inverse-Compton scattering processes while propagating within the Galaxy, and these losses limit their propagation distance. For electrons with TeV energies, the limit is on the order of a kiloparsec. Within that distance, there are only a few known astrophysical objects capable of accelerating electrons to such high energies. It is also possible that the CREs are the products of the annihilation or decay of heavy dark matter (DM) particles. VERITAS, an array of imaging air Cherenkov telescopes in southern Arizona, is primarily utilized for gamma-ray astronomy but also simultaneously collects CREs during all observations. We describe our methods of identifying CREs in VERITAS data and present an energy spectrum, extending from 300 GeV to 5 TeV, obtained from approximately 300 hours of observations. A single power-law fit is ruled out in VERITAS data. We find that the spectrum of CREs is consistent with a broken power law, with a break energy at 710 +/- 40(stat) +/- 140(syst) GeV.
  • Thumbnail Image
    Item
    The most powerful flaring activity from the NLSyl PMN J0948+0022
    (Oxford University Press, 2014-11-27) VERITAS Collaboration; University of Bologna; Istituto Nazionale Astrofisica (INAF); United States Department of Defense; United States Navy; Naval Research Laboratory; California Institute of Technology; Royal Institute of Technology; Oskar Klein Centre; National Radio Astronomy Observatory (NRAO); National Aeronautics & Space Administration (NASA); NASA Goddard Space Flight Center; Purdue University System; Purdue University; Purdue University West Lafayette Campus; Washington University (WUSTL); Harvard University; Smithsonian Institution; University of Delaware; University College Dublin; Iowa State University; University of Potsdam; Helmholtz Association; Deutsches Elektronen-Synchrotron (DESY); Columbia University; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; University of Minnesota System; University of Minnesota Twin Cities; University of California System; University of California Santa Cruz; Ollscoil na Gaillimhe-University of Galway; University of Iowa; Utah System of Higher Education; University of Utah; DePauw University; University of Chicago; University System of Georgia; Georgia Institute of Technology; University of California Los Angeles; McGill University; Cork Institute of Technology; United States Department of Energy (DOE); Argonne National Laboratory; University of Alabama Tuscaloosa
    We report on multifrequency observations performed during 2012 December-2013 August of the first narrow-line Seyfert 1 galaxy detected in gamma-rays, PMN J0948+0022 (z = 0.5846). A y -ray flare was observed by the Large Area Telescope on board Fermi during 2012 December-2013 January, reaching a daily peak flux in the 0.1-100 GeV energy range of (155 31) x 10 8 ph cm(-2) S-1 on 2013 January 1, corresponding to an apparent isotropic luminosity of similar to 1.5 x 1048 erg s(-1). The y -ray flaring period triggered Swift and Very Energetic Radiation Imaging Telescope Array System (VERITAS) observations in addition to radio and optical monitoring by Owens Valley Radio Observatory, Monitoring Of Jets in Active galactic nuclei with VLBA Experiments, and Catalina Real-time Transient Survey. A strong flare was observed in optical, UV, and X-rays on 2012 December 30, quasi-simultaneously to the y -ray flare, reaching a record flux for this source from optical to y gamma-rays. VERITAS observations at very high energy (E > 100 GeV) during 2013 January 6-17 resulted in an upper limit of F>0.2 Trev < 4.0 x 10(-12) ph cm(-2) s(-1). We compared the spectral energy distribution (SED) of the flaring state in 2013 January with that of an intermediate state observed in 2011. The two SEDs, modelled as synchrotron emission and an external Compton scattering of seed photons from a dust torus, can be modelled by changing both the electron distribution parameters and the magnetic field.
  • Thumbnail Image
    Item
    Multiwavelength Observations of the Blazar BL Lacertae: A New Fast TeV Gamma-Ray Flare
    (IOP Publishing, 2018-03-28) VERITAS Collaboration; Utah System of Higher Education; University of Utah; Harvard University; Smithsonian Institution; University of California System; University of California Los Angeles; Iowa State University; University of Potsdam; Helmholtz Association; Deutsches Elektronen-Synchrotron (DESY); Washington University (WUSTL); Ollscoil na Gaillimhe-University of Galway; Purdue University System; Purdue University; Purdue University West Lafayette Campus; Tsinghua University; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; McGill University; Columbia University; University of Minnesota System; University of Minnesota Twin Cities; California State University System; California State University East Bay; University of California Santa Cruz; University of Delaware; University of Iowa; DePauw University; University College Dublin; University System of Georgia; Georgia Institute of Technology; University of Chicago; Cork Institute of Technology; University of Alabama Tuscaloosa; Boston University; Saint Petersburg State University; Russian Academy of Sciences; Russian Academy of Science Lebedev Physical Institute; Moscow Institute of Physics & Technology; Max Planck Society; Aalto University; Consejo Superior de Investigaciones Cientificas (CSIC); CSIC - Instituto de Astrofisica de Andalucia (IAA); California Institute of Technology; University of Turku; University of Arizona
    Combined with measurements made by very-long-baseline interferometry, the observations of fast TeV gamma-ray flares probe the structure and emission mechanism of blazar jets. However, only a handful of such flares have been detected to date, and only within the last few years have these flares been observed from lower-frequency-peaked BL. Lac objects and flat-spectrum radio quasars. We report on a fast TeV gamma-ray flare from the blazar BL. Lacertae observed by the Very Energetic Radiation Imaging Telescope Array System (VERITAS). with a rise time of similar to 2.3 hr and a decay time of similar to 36 min. The peak flux above 200 GeV is (4.2 +/- 0.6) x 10(-6) photon m(-2) s(-1) measured with a 4-minute-binned light curve, corresponding to similar to 180% of the flux that is observed from the Crab Nebula above the same energy threshold. Variability contemporaneous with the TeV gamma-ray flare was observed in GeV gamma-ray, X-ray, and optical flux, as well as in optical and radio polarization. Additionally, a possible moving emission feature with superluminal apparent velocity was identified in Very Long Baseline Array observations at 43 GHz, potentially passing the radio core of the jet around the time of the gamma-ray flare. We discuss the constraints on the size, Lorentz factor, and location of the emitting region of the flare, and the interpretations with several theoretical models that invoke relativistic plasma passing stationary shocks.
  • Thumbnail Image
    Item
    Periastron Observations of TeV Gamma-Ray Emission from a Binary System with a 50-year Period
    (IOP Publishing, 2018-10-31) VERITAS Collaboration; MAGIC Collaboration; University of Alabama Tuscaloosa
    We report on observations of the pulsar/Be star binary system PSR J2032+4127/MT91 213 in the energy range between 100 GeV and 20 TeV with the Very Energetic Radiation Imaging Telescope Array and Major Atmospheric Gamma Imaging Cherenkov telescope arrays. The binary orbit has a period of approximately 50 years, with the most recent periastron occurring on 2017 November 13. Our observations span from 18 months prior to periastron to one month after. A new point-like gamma-ray source is detected, coincident with the location of PSR J2032+4127/MT91 213. The gamma-ray light curve and spectrum are well characterized over the periastron passage. The flux is variable over at least an order of magnitude, peaking at periastron, thus providing a firm association of the TeV source with the pulsar/Be star system. Observations prior to periastron show a cutoff in the spectrum at an energy around 0.5 TeV. This result adds a new member to the small population of known TeV binaries, and it identifies only the second source of this class in which the nature and properties of the compact object are firmly established. We compare the gamma-ray results with the light curve measured with the X-ray Telescope on board the Neil Gehrels Swift Observatory and with the predictions of recent theoretical models of the system. We conclude that significant revision of the models is required to explain the details of the emission that we have observed, and we discuss the relationship between the binary system and the overlapping steady extended source, TeV J2032+4130.
  • Thumbnail Image
    Item
    A Strong Limit on the Very-high-energy Emission from GRB 150323A
    (IOP Publishing, 2019-04-10) VERITAS Collaboration; Utah System of Higher Education; University of Utah; Washington University (WUSTL); Harvard University; Smithsonian Institution; University of California System; University of California Los Angeles; University of Potsdam; Helmholtz Association; Deutsches Elektronen-Synchrotron (DESY); Ollscoil na Gaillimhe-University of Galway; Purdue University System; Purdue University; Purdue University West Lafayette Campus; Tsinghua University; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; McGill University; University of Minnesota System; University of Minnesota Twin Cities; California State University System; California State University East Bay; University of California Santa Cruz; University of Delaware; Columbia University; University of Iowa; DePauw University; Iowa State University; University College Dublin; University of Chicago; National Aeronautics & Space Administration (NASA); NASA Goddard Space Flight Center; Cork Institute of Technology; University System of Georgia; Georgia Institute of Technology; University of Alabama Tuscaloosa
    On 2015 March 23, the Very Energetic Radiation Imaging Telescope Array System (VERITAS) responded to a Swift-Burst Alert Telescope (BAT) detection of a gamma-ray burst, with observations beginning 270 s after the onset of BAT emission, and only 135 s after the main BAT emission peak. No statistically significant signal is detected above 140 GeV. The VERITAS upper limit on the fluence in a 40-minute integration corresponds to about 1% of the prompt fluence. Our limit is particularly significant because the very-high-energy (VHE) observation started only similar to 2 minutes after the prompt emission peaked, and Fermi-Large Area Telescope observations of numerous other bursts have revealed that the high-energy emission is typically delayed relative to the prompt radiation and lasts significantly longer. Also, the proximity of GRB 150323A (z = 0.593) limits the attenuation by the extragalactic background light to similar to 50% at 100-200 GeV. We conclude that GRB 150323A had an intrinsically very weak high-energy afterglow, or that the GeV spectrum had a turnover below similar to 100 GeV. If the GRB exploded into the stellar wind of a massive progenitor, the VHE non-detection constrains the wind density parameter to be A greater than or similar to 3 x 10(11) g . cm(-1), consistent with a standard Wolf-Rayet progenitor. Alternatively, the VHE emission from the blast wave would be weak in a very tenuous medium such as the interstellar medium, which therefore cannot be ruled out as the environment of GRB 150323A.
  • Thumbnail Image
    Item
    UPPER LIMITS FROM FIVE YEARS OF BLAZAR OBSERVATIONS WITH THE VERITAS CHERENKOV TELESCOPES
    (IOP Publishing, 2016-05-18) VERITAS Collaboration; McGill University; Washington University (WUSTL); Harvard University; Smithsonian Institution; University College Dublin; University of California System; University of California Santa Cruz; University of California Los Angeles; United States Department of Energy (DOE); Argonne National Laboratory; University of Potsdam; Helmholtz Association; Deutsches Elektronen-Synchrotron (DESY); Ollscoil na Gaillimhe-University of Galway; Purdue University System; Purdue University; Purdue University West Lafayette Campus; Iowa State University; Columbia University; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; University of Minnesota System; University of Minnesota Twin Cities; California State University System; California State University East Bay; University of Delaware; University of Iowa; Utah System of Higher Education; University of Utah; DePauw University; University System of Georgia; Georgia Institute of Technology; University of Chicago; National Aeronautics & Space Administration (NASA); NASA Goddard Space Flight Center; Instituto de Astronomia y Fisica del Espacio (IAFE); Cork Institute of Technology; University System of Maryland; University of Maryland College Park; Durham University; Centre National de la Recherche Scientifique (CNRS); UDICE-French Research Universities; Sorbonne Universite; Universite Paris Cite; University of Alabama Tuscaloosa
    Between the beginning of its full-scale scientific operations in 2007 and 2012, the VERITAS Cherenkov telescope array observed more than 130 blazars; of these, 26 were detected as very-high-energy (VHE; E > 100 GeV) gamma-ray sources. In this work, we present the analysis results of a sample of 114 undetected objects. The observations constitute a total live-time of similar to 570 hr. The sample includes several unidentified Fermi-Large Area Telescope (LAT) sources (located at high Galactic latitude) as well as all the sources from the second Fermi-LAT catalog that are contained within the field of view of the VERITAS observations. We have also performed optical spectroscopy measurements in order to estimate the redshift of some of these blazars that do not have spectroscopic distance estimates. We present new optical spectra from the Kast instrument on the Shane telescope at the Lick observatory for 18 blazars included in this work, which allowed for the successful measurement or constraint on the redshift of four of them. For each of the blazars included in our sample, we provide the flux upper limit in the VERITAS energy band. We also study the properties of the significance distributions and we present the result of a stacked analysis of the data set, which shows a 4s excess.
  • Thumbnail Image
    Item
    VERITAS and Fermi-LAT Observations of TeV Gamma-Ray Sources Discovered by HAWC in the 2HWC Catalog
    (IOP Publishing) VERITAS Collaboration; Fermi-LAT Collaboration; HAWC Collaboration; University of Alabama Tuscaloosa
    The High Altitude Water Cherenkov (HAWC) collaboration recently published their 2HWC catalog, listing 39 very high energy (VHE; >100 GeV) gamma-ray sources based on 507 days of observation. Among these, 19 sources are not associated with previously known teraelectronvolt (TeV) gamma-ray sources. We have studied 14 of these sources without known counterparts with VERITAS and Fermi-LAT. VERITAS detected weak gamma-ray emission in the 1 TeV-30 TeV band in the region of DA 495, a pulsar wind nebula coinciding with 2HWC J1953+294, confirming the discovery of the source by HAWC. We did not find any counterpart for the selected 14 new HAWC sources from our analysis of Fermi-LAT data for energies higher than 10 GeV. During the search, we detected gigaelectronvolt (GeV) gamma-ray emission coincident with a known TeV pulsar wind nebula, SNR G54.1+0.3 (VER J1930+188), and a 2HWC source, 2HWC J1930+188. The fluxes for isolated, steady sources in the 2HWC catalog are generally in good agreement with those measured by imaging atmospheric Cherenkov telescopes. However, the VERITAS fluxes for SNR G54.1+0.3, DA 495, and TeV J2032+4130 are lower than those measured by HAWC, and several new HAWC sources are not detected by VERITAS. This is likely due to a change in spectral shape, source extension, or the influence of diffuse emission in the source region.
  • Thumbnail Image
    Item
    VERITAS Observations of the BL Lac Object TXS 0506+056
    (IOP Publishing, 2018-07-12) VERITAS Collaboration; Utah System of Higher Education; University of Utah; Washington University (WUSTL); Harvard University; Smithsonian Institution; University of California System; University of California Los Angeles; Columbia University; University of Potsdam; Helmholtz Association; Deutsches Elektronen-Synchrotron (DESY); California State University System; California Polytechnic State University San Luis Obispo; Iowa State University; Pennsylvania Commonwealth System of Higher Education (PCSHE); Pennsylvania State University; Pennsylvania State University - University Park; McGill University; Purdue University System; Purdue University; Purdue University West Lafayette Campus; University of Minnesota System; University of Minnesota Twin Cities; California State University East Bay; Ollscoil na Gaillimhe-University of Galway; University of California Santa Cruz; University of Delaware; University of Iowa; DePauw University; University College Dublin; University System of Georgia; Georgia Institute of Technology; University of Wisconsin System; University of Wisconsin Madison; University of Chicago; Cork Institute of Technology; University of Alabama Tuscaloosa
    On 2017 September 22, the IceCube Neutrino Observatory reported the detection of the high-energy neutrino event IC 170922A, of potential astrophysical origin. It was soon determined that the neutrino direction was consistent with the location of the gamma-ray blazar TXS 0506+056. (3FGL J0509.4+ 0541), which was in an elevated gamma-ray emission state as measured by the Fermi satellite. Very Energetic Radiation Imaging Telescope Array System (VERITAS) observations of the neutrino/blazar region started on 2017 September 23 in response to the neutrino alert and continued through 2018 February 6. While no significant very-high-energy (VHE; E > 100 GeV) emission was observed from the blazar by VERITAS in the two-week period immediately following the IceCube alert, TXS 0506+ 056 was detected by VERITAS with a significance of 5.8 standard deviations (sigma) in the full 35 hr data set. The average photon flux of the source during this period was (8.9 +/- 1.6). x. 10(-12) cm(-2) s(-1), or 1.6% of the Crab Nebula flux, above an energy threshold of 110 GeV, with a soft spectral index of 4.8. +/-. 1.3.