On A Large Array Of Midsized TelescopesStephen Fegan Vladimir Vassiliev UCLA

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Primary Science GoalsDetect and measure VHE transients at cosmological distancesSelf triggeringMeasure lightcurve from Mrk-421 at z=1 with few minute resolutionSurvey of VHE sky to level of 1-2 mCrabDetailed observations of Galactic sources in the energy range 20GeV to >50 TeV

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Requirements From Science GoalsTo resolve a few min variability time scale in the emission of a Mrk 421-like AGN at z=1 the collecting area must be ~1km2.To survey the sky to 1-2 mCrab over a few years of operation, must have VERITAS sensitivity over full sky1km2 collecting area Crab Nebula rate of 1g/min >10 TeV 2g/hr >100 TeVE Interval Rate [GeV] [min`1] 25-501.3 50-1000.7 100-2000.3

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Baseline DesignDistance From Center Of Array [m]Distance From Center Of Array [m]Array217 telescopes 8 hexagonal rings + 180m separation

Telescope and Detector10m equivalentQE = 0.25 (Bialkali)15 field of view

Facts and FiguresOuter radius: 640mSingle cell area: 5543m2 Total area: 1.06km2

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Collecting Area vs. Field Of ViewField of view [ sr]Field of view [deg]Collecting Area [km2]Current IACTAsNarrow field of view

All Sky Coverage: Flys Eye ModeEach telescope points in different direction. If position of telescope n on ground is (xn,yn)Zenith = ( xn2 + yn2 )1/2Azimuth = tan-1( xn / yn )

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Question(s)How can an array of mid-sized telescopes operate in the E~30 GeV range?Why is the collecting area of instruments like VERITAS so large at E>100GeV?OR

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Cell Effect Collecting AreaGamma-rays INSIDE detectorInstrument has efficiency (E) such that effective area is:AI=(E)RI2

Gamma-rays OUTSIDE detectorInstrument detects s to radius RO(E) such that effective area is:AO=(E)RO(E)(2RI+RO(E))

Energy Dependence(E):0.4 @ 20 GeV0.8 @ 40 GeVRO(E):

Cell Effect Small Impact ParameterInfinite Array Of Telescopes3500m ASL RCherenk = 85mDScopes = 80mDistance [m]Distance [m]Geometry Dictates ThatImpact point of every shower is in some cell BMax = 47mAt least 3 telescopes contained in Cherenkov light pool

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Cell Effect Cherenkov PE DensityPE density after:AtmosphereMirror reflectionPhotocathodeCell GeometryConsider only thedensity within 80mof coreMidsized telescopes10m, A=78m2 E=32 GeV, b=80mnPE=78Distance from shower core [m]Photoelectron density [PE/m2]

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Trigger Threshold vs. Pixel SizeTrigger Pixel Size [degree](nth-Nnsb) / QQE=0.25, FoV=15o, Rnsb=0.1 kHzQE=0.25, FoV=10o, Rnsb=0.1 kHzQE=0.25, FoV=15o, Rnsb=1.0 kHzQE=0.5, FoV=15o, Rnsb=0.1 kHzQE=0.5, FoV=10o, Rnsb=0.1 kHzQE=0.5, FoV=15o, Rnsb=1.0 kHzQE=0.25, FoV=10o, Rnsb=1.0 kHzQE=0.5, FoV=10o, Rnsb=1.0 kHzImportance of effect:1) QE2) Rate3) FoVNormalized trigger threshold for given QE, NSB rate and FOV

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Trigger Efficiency vs Pixel Size ICentral Telescope Trigger EfficiencyTrigger Pixel Size [degree]Parameters:Eg=42 GeVFoV=15oRnsb=1kHzOptimumtrigger sensorpixel size is 0.07o-0.3oWeakdependence on QE, D, El(Central Telescope)QE: 1.0, D=7mQE: 0.5, D=10mQE: 0.5, D=7mQE: 0.25, D=10mEl: 3.5 km

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Trigger Efficiency vs Pixel Size II Array Trigger EfficiencyPhoton Energy [GeV]Array Trigger: Three telescopesabove operational thresholdArray Parameters:Elevation: 3.5 kmQE: 0.25Reflector: 10 mFoV: 15op=0.05op=0.08op=0.10op=0.13op=0.16op=0.20o(Full Array)

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Trigger Peak Detection EnergyTrigger EfficiencyPhoton Energy [GeV]Photon Energy [GeV]Diff. RateEl=4.5km, QE: 1.0, D=7mEl=4.5km, QE: 0.5, D=10mEl=3.5km, QE: 1.0, D=7mEl=3.5km, QE: 0.5, D=10mEl=4.5km, QE: 0.5, D=7mEl=4.5km, QE: 0.25, D=10mEl=3.5km, QE: 0.5, D=7mEl=3.5km, QE: 0.25, D=10mParameters:Trigger pixel size: 0.146oUn-localized source (FoV=15o)Rnsb: 1kHzDiff. spectral index: 2.5 12 GeV15 GeV20 GeV27 GeVEffects:1) Cell operation mode2) Optimum trigger pixel size3) QE, Reflector Size4) Elevation 5) Rnsb

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Trigger Proton Rate

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Trigger Telescope MultiplicityAverage Number of Telescopes in TriggerPhoton Energy [GeV]30 GeV g triggers 5 telescopes

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Cleaning Sample EventPhoton direction [deg]Photon direction [deg]Photon direction [deg]Event 1 (42 GeV)Event 2 (42 GeV)

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Cleaning Voronoi DiagramEvent 1 (42 GeV)Event 2 (42 GeV)0.0-0.1-0.2-0.3-0.4-0.5-0.6-0.7-0.8-0.9-0.4-0.3-0.2-0.10.00.10.20.30.4-0.10.00.10.20.30.50.50.60.70.80.30.20.10.0-0.1-0.2-0.3-0.4-0.5-0.6Photon direction [deg]Photon direction [deg]Photon direction [deg]

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Cleaning P.E. Separation Scalesg: 21 GeVNSB: 150 g/deg2g: 42 GeVNSB: 150 g/deg2g: 100 GeVNSB: 150 g/deg2QE: 0.25Reflector Diameter: 10mElevation: 3.5 kmTrigger pixel size: 0.146oVoronoi DiagramP.E.-P.E. separation scalesin Image: 0.015o-0.045oDiff. density [Arbitrary]P.E. separation [deg]

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Reconstruction Angular Acceptanceq radius [deg]Event containment fraction [1]21 GeV42 GeV100 GeVCROptimum cut:4 photons within circle of 0.02o radius

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Cleaning Sample EventSingle 42 GeV eventView from 4 telescopesOptimal cleaning (from consideration of angular reconstruction) keeps only photons near core

Multiple cleaning schemes may be appropriate.Shower axisShape cutEnergy estimate

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Background Rejection Shape Cut21 GeV42 GeV100 GeVCRNPE [1]Mean cascade radius [m]Parameter gives the width of the emission region in spaceElectromagneticshowers: tightly confined along shower axis, have small Hadronic events: reconstructed cascade radius is larger than for gamma-rays

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Background Rejection Shower Maxq < 0.2o Mean emission height above array [m]Ln(Ng) [1]No q cutParameter gives the mean emission height of the Cherenkov photons.21 GeV42 GeV100 GeVCR1st interactionProton: 70g/cm2Gamma: 37g/cm2Distribution of reconstructed different for each species.

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Background Rejection Shower Max

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

LessonsCell Effect: operation in 20-30 GeV range possible with midsized telescopesOptimum trigger pixel size is ~0.1Optimum image pixel size is ~0.01Very hard cleaning required to optimize reconstruction of shower axisMultiple cleaning regimes is suggested Reconstructed emission height can be used to reject protons

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Comparison Collecting AreaEnergy [GeV]Collecting Area [m2]

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Comparison Differential RateEnergy [GeV]Differential Rate [arbitrary]

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

All Sky Survey One Year SensitivitySensitivity [mCrab]

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA

Summary Of Array ParametersArray of 217 telescopesElevation 3.5kmTelescopes coupling distance 80mArea ~1.0km2 (~1.6km2)Single Telescope Field of View ~15FoV area ~177deg2Reflector Diameter ~7mReflector Area ~40m2QE 50% (200-400nm)Trigger sensor pixel size 0.146Trigger Sensor Size ~31.2cmNSB rate per Trigger pixel ~3.2pe / 20nsSingle Telescope NSB Trigger Rate 1kHzEnergy Range 20200GeV Differential Detection Rate Peak ~30GeV Single Telescope CR trigger rate ~30kHzImage pixel size 0.0146Readout image 128 x 128 pixelsReadout Image size 1.875 x 1.875NSB per pixel 0.032 (20 nsec gate)ADC 8 bit (S/N improved, 10 >8)Pixel dimension 12mm x 12mmSensor area 12.3mm x 12.3mmShutter exposure a few msecImage integration time - 20nsOptical system TBDArray trigger protocol TBDData Rates ~80 Mb/secper nodeOnline data processing TBD

On A Large Array Of Midsized Telescopes Fegan & Vassiliev, UCLA