Performance evaluation of trigger algorithm forthe MACE telescope
Kuldeep Yadav
BARCMumbai
February 20, 2013
(On behalf of: N. Bhatt, N. Chouhan, S.S. Sikder, A. Behere, C.K. Pithawa, A.K. Tickoo, R.C.
Rannot, S. Bhattacharyya, A.K. Mitra, R. Koul )
Kuldeep Yadav (BARC, Mumbai) ASI-2013 February 20, 2013 1 / 16
Detection technique for very high energy γ-rays
Eγ < 100 GeV direct observations onsatellites
Eγ > 20 GeV indiret observations viaextensive air showers (EAS)
> 99% air showers produced in theatmophere are isotropic CR
Typically γ-ray : CR : : 1 : 103-104
Gamma-ray sources can be detectedIdentify a single photon event from thesea of background event (shower shape,muon contents)They emit so many photons that thenumber of particles from this directionstands out of the background (excess ofevents from certain sky positions)
Cherenkov light from chargedsecondaries can reach the ground withtight time structure and maintainingdirection of primary
Kuldeep Yadav (BARC, Mumbai) ASI-2013 February 20, 2013 2 / 16
Detection of atmospheric Cherenkov radiation
Purpose of detection of an EASexperimentally: Determine the type ofparticle (though difficult) andproperties of the primary particle e.g.direction, energy and chemicalcomposition in case of CR
IACT: most successful
Characteristic features ofCherenkov pulse:facilitate its detection in the presence of NSB
Narrow pulse width (∼ 5 ns)
Limited angular size (< 1) on the ground
Nature of its photon spectrum i.e.Cherenkov light peaks at shortwavelength (blue/UV) whereas NSBpeaks at longer wavelength
Example
A telescope with 1 field of view and 10 nstrigger formation time would receive∼ 5 photons/m2 from the NSB while a muchhigher expected value of ∼ 65 photons/m2 froma 1 TeV γ-ray shower. Thus, a 1 TeV showershould be detectable above NSB with atelescope having 1 m2 mirror area.
Kuldeep Yadav (BARC, Mumbai) ASI-2013 February 20, 2013 3 / 16
Bias Curve
Bias curve obtained from a simpledetector has two components
Both components can be fitted withpower law
Exponent of hard component is ≈ thatof CR spectrum
Kuldeep Yadav (BARC, Mumbai) ASI-2013 February 20, 2013 4 / 16
Trigger threshold of the telescope
The signal due to Cherenkov photons (pe)S = ργ A R ηpmt = yγ E A R ηpmt
where ηpmt : quantum efficiency of the PMT
The noise level in terms of fluctuationsN =
√
φLONS Ω A R ηpmt τNote: in actual case the wavelength dependence of both Cherenkov and LONS production
and collection should also we considered
The energy threshold: is the minimum γ-ray energy for which(S/N) is sufficient to adequately trigger the telescope. Thesmallest detectable light pulse is therefore inversely proportionalto S/N, i.e.
Eth ∝ (1/yγ)√
φLONS Ω τA R ηpmt
Kuldeep Yadav (BARC, Mumbai) ASI-2013 February 20, 2013 5 / 16
MACE telescope
Location: Hanle, Ladakh(32.7N, 79 E, 4200m asl)
Number of Photometric Nights:∼ 190/yr
Diameter: 21 m
Focal Distance: 25, m
Light collector configuration:Paraboloid with graded FL
Panel Size: 984 mm × 984 mm
Number of Panels: 352, Number ofFacets: ∼ 1500
Total light Collector Area: 337 m2
PSF: R95 at 0∼ 15 mm
R95 at 1∼ 43 mm
Telescope weight: ∼ 150 T
Kuldeep Yadav (BARC, Mumbai) ASI-2013 February 20, 2013 6 / 16
MACE camera
Integrated Camera (all signalprocessing instrumentation housedwithin the camera structure of2mx2mx1.2m size)
Temperature control of the cameraduring operation and standbycondition.
Conventional CDC/GHz Sampling
Kuldeep Yadav (BARC, Mumbai) ASI-2013 February 20, 2013 7 / 16
Trigger region of MACE camera
16 channel CIM module
Total PMTs: 1088 (68 CIM)
PMTs in the trigger region: 576 (36
CIM)
Kuldeep Yadav (BARC, Mumbai) ASI-2013 February 20, 2013 8 / 16
Implementation of trigger algorithm
SLT hardware
Two level trigger generation
FLT: within the CIM
SLT: sytem level trigger
Kuldeep Yadav (BARC, Mumbai) ASI-2013 February 20, 2013 9 / 16
Trigger configuration 4NN tight cluster
Table: Number of combinationsTrigger Mode Desired desired + undesired
Due to implimentationFULL 36 × 21 36 × 21N+N 240 6588S+W 210 5582
& +W+S 210 5612
N+2W – –4W – –
Kuldeep Yadav (BARC, Mumbai) ASI-2013 February 20, 2013 10 / 16
Estimates of chance trigger rates
SCR ( kHz)
100 1000
Ra
te (
Hz)
10-1
100
101
102
103
104
(1)
(2)
(3)
(4)
(1) Chance 4NN --full alone ( 5ns )
(2) Chance 4NN -- (N+N) alone ( 5ns , 10ns)
(3) Chance 4NN -- (S+W: W+S) alone ( 5ns , 10ns)
(4) Chance 4NN -- total (1)+(2)+(3)
(5) Rate at which trigger patterns need to be validated
Fu
ll
alo
ne
(4
9.0
5 %
pa
tte
rns
)
Fu
ll
+N
N+
SW
+W
S
(9
1.8
8 %
pa
tte
rns
)(5)
Chance rate : 20 Hz
Chance rate due to desired
combinations
1 Full triggers:36 × 21 × 4 × R4τ3
flt2 N+N triggers: 240 × 2 ×
(2R2τflt )(2R2τflt )τslt3 W+S triggers:
420 × 2 × (3R3τ2flt )(R)τslt
Total chance rate due to
implementation
1 N+N triggers:6588 × 2 ×
(2R2τflt )(2R2τflt )τslt2 W+S triggers: 11194 ×
2 × (3R3τ2flt )(R)τslt
TRIGGER INFORMATION IN TWOPHASES !
Kuldeep Yadav (BARC, Mumbai) ASI-2013 February 20, 2013 11 / 16
Effective area
Biggest advantage of groundbased Cherenkov telescopesLarge effective collection area
Satellite exp.: Geometrical areaCherenkov tel.: Cherekov pool(120 m radius)
Large collextion area isessential due to power lawnature of sources
Effective area for point γ-raysourcesAeff (E) = 2π
R
∞
0 R×p(R, E)dR
Discretized form Aeff (E) =P
∞
0 π(R2i − R2
i−1)p(Ri , E)
p(R,E): Probability of trigger
10000
100000
100
Effe
ctiv
e A
rea
(m2 )
Energy (GeV)
5pe-4NN-FullCascade7pe-4NN-FullCascade
7pe-4NN-Full10pe-4NN-FullCascade
Kuldeep Yadav (BARC, Mumbai) ASI-2013 February 20, 2013 12 / 16
Trigger Efficiency
Trigger Probability , p(R, E) =number of triggered showers
Total number of showers generated
depends on Cherenkovphoton density, trigger FOV,trigger multiplicity and singlepixel threshold
Kuldeep Yadav (BARC, Mumbai) ASI-2013 February 20, 2013 13 / 16
Trigger rates for Gamma-ray at various single pixelthresholds
Differential rate: Number of particles (E and E+dE)
trigger the telescope per unit time
0.01
0.1
1
10 100
Diff
. Rat
e (G
amm
a-ra
y/se
c)
Energy (GeV)
5pe-4NN-FullCascade7pe-4NN-FullCascade
7pe-4NN-Full10pe-4NN-FullCascade
D(E)dE = Aeff × N(E)dEPeak of differential trigger ratedetermines the energy thresholdNγ (e) = 2.79 × 10−7( E
GeV )−2.59
ph m−2 s−1 GeV−1
Trigger Threshold IntegralMode Energy rate
(GeV) (Hz)
5peFC 16 8.0
7peFC 21 3.4
7peF 23 2.2
10peFC 30 1.5
Kuldeep Yadav (BARC, Mumbai) ASI-2013 February 20, 2013 14 / 16
Simulation results: Effective area and trigger ratesEffective area
Particle Threshold Integraltype Energy rate
(GeV) (Hz)
Gamma-rays 18.78 11.86
Electrons 27.27 37.13
Differential rates
Particle Threshold Integraltpye Energy rate
(GeV) (Hz)Protons 127.1 818.8Alpha 660.8 137.7Total 1000.49rate
Kuldeep Yadav (BARC, Mumbai) ASI-2013 February 20, 2013 15 / 16
Summary
In the actual implementation of 4NN tight cluster trigger schemeprovides an integral trigger rate for gamma-rays which is less thanobtained from MC simulation of the MACE telescope. Whichmeans the total trigger rate should not exceed the estimated dataacquisition rate of cosmic-ray (∼ 1 kHz)
Data acquisition of the MACE telescope is capable of handling asustained trigger rate of 1 kHz.
Thank you
Kuldeep Yadav (BARC, Mumbai) ASI-2013 February 20, 2013 16 / 16
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