A fast online and trigger-less signal reconstruction

A fast online and trigger-less signal reconstruction

Arno GadolaPhysik-Institut Universität Zürich

Doktorandenseminar 2009

05.06.09, Arno GadolaDoktorandenseminar

Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich

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Outline

Introduction into γ-ray astronomy

Characteristics and detection of γ-ray induced Cherenkov pulses

Reconstruction of detected Cherenkov pulses

Results of reconstruction algorithm

Summary and Outlook



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γ-rays

SNR

Dark Matter

GRBs

AGNs

PulsarsPWN

Micro quasarsx-ray binaries

Energy range:103 – 1020 eV

HE and VHE: 107 – 1012 eV

Wavelength: 10-13 – 10-18 m

Visible light: 3.2 – 1.6 eV 380 – 750 nm

Production mechanisms: inverse Compton, π0 → γγ, decay of heavy particles, etc.

Low rates: 1γ/min (Vela pulsar)

Not affected by magnetic fields Probing non-thermal universe



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Cherenkov light production

X0 = typically 330m in atmosphere

Bremsstrahlungve>c/n=cn

E0

½E0

¼E0

θ≈1˚ 45‘000m2 illuminated on sea level, but θ(n)!

e



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Cherenkov light productionSome values for relativistic electrons:

Characteristics of Cherenkov pulses: Duration: ≈ 5ns Time spread: 0 – 10ns Intensity: 4.6 – 74γ/m2 for Eγ = 0.1 – 1TeV (A. M. Hillas, 2002)

i.e. for a 12m telescope = 110m2 mirror = 500 – 8’140 γ Wavelength: 300 – 600 nm

Water Atmosphere @ sea level

n 1.33 1.00029

θmax 40° 1.3°

ETresh 260 keV 21’000 keV

X0 430 m 330 m

#γ/m 2500 30

#γ/X0 1’075’000 10’000



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Cherenkov telescope

MAGIC I, La PalmaMirror ø 17m

Noise: □ stars□ airplanes□ cities

Signal: □ γ-rays□ protons□ muons

H.E.S.S., Namibia

MAGIC I cameraø 1.5m, 450kg



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Camera readout chain



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Cross-Correlation

m

mngmfngf ][][])[*( *

dtgftgf )()())(*( *

For two continuous functions:

For two discrete functions:

The second derivative:

Better resolution of pile-up



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Simulation

≈

TemplateSimulated measurement

fNSB= 3000 MHz (full moon)

m

mngmfngf ][][])[*( *



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Reconstruction

Output at threshold of 2γSignal: 4.6γ @ t=250ns

Input sampleSignal: A=5γ @ t=250nsNSB: 60MHz

(After ADC): Second derivative of the discrete cross-correlation

Reconstruction of sample with time and amplitude stamps



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Time resolution: (0.0 ± 0.4)ns for 12bits, 1000MHz ADC(-0.5 ± 1.5)ns for 10bits, 250MHz

ADC Amplitude resolution: (0.7 ± 1.5)γ for 12bits, 1000MHz ADC

(1.5 ± 2.0)γ for 10bits, 250MHz ADC Reconstruction efficiency increases with:

higher ADC resolution or higher ADC sampling rate higher Cherenkov signal amplitude higher NSB frequency

Noise rate for 3000 MHz NSB and sampling rate fs = 1 GHz: 8 bits → noise rate = 360 MHz 10 bits → noise rate = 240 MHz 12 bits → noise rate = 125 MHz

Results Simulation parameters:

ADC resolutions: 8 – 12bit ADC sampling rates: 250 – 1000 MHz NSB: 40 – 3000MHz Cherenkov signal amplitudes: 1 – 100γ

This ratio of 3:2:1 shows up for all sampling rates fs



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Summary & Outlook

Good reconstruction efficiency for an ADC setup with 300 MHz and 9 - 10 bit sampling: 5γ pulse @ noise rate < 100 kHz for low NSB (100 MHz) 5γ pulse @ noise rate < 5 MHz for large NSB (3000 MHz)

Further investigations on reconstruction algorithm behavior (time jitter, real data)

Investigation of a hardware based implementation of the reconstruction algorithm

Designing a toy camera readout chain for testing the signal reconstruction algorithm

Research on “new” light collector design together with ETHZ



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Questions

?



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Backup Slides Shower development Propertier of Cherenkov light Propertier of the atmosphere Photon interactions Simulation examples Time resolution Amplitude resolution



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γ-ray sources Supernova remnants (SNRs) A supernova is the explosion of a massive star (mass of 8 to 150 solar masses) at the end of its life. Cosmic-rays are accelerated in the supernova explosion shocks which are non thermal processes. The

gamma-ray energies reach well beyond 1013 eV. • Pulsars and associated nebulae Pulsars are rotating neutron stars with an intense magnetic field. The pulsar’s magnetosphere is known to act as an efficient cosmic accelerator with gamma-ray emission in the range of 10 to 100 GeV. Pulsar wind nebulae are synchrotron nebulae powered by the relativistic winds of energetic pulsars. Their VHE gamma-ray emissions originate most probably from electrons accelerated in the shock formed by the interaction of the pulsar wind with the supernova ejecta. The most famous pulsar wind nebula is the Crab Nebula which, due to its strong and steady emission of gamma-rays, is used as calibration candle for almost all VHE gamma-ray detectors. • Binary systems A binary system contains a compact object like a neutron star or a black hole orbiting a massive star. Such objects emit mostly VHE gamma-rays. • Active galactic nuclei (AGNs) An AGN is a galaxy with a super massive black hole at the core. AGNs are known to produce outflows which are strong sources of high energy gamma-rays. Other possible sources of gamma-rays are synchrotron emission from populations of ultra-relativistic electrons and inverse Compton emission from soft photon scattering. • Gamma ray bursts (GRBs) GRBs are still a not completely resolved phenomenon. Their pulses are extremely intensive and have a duration of about 0.1 seconds to several minutes. They are known as the most luminous electromagnetic events occurring in the universe since the Big Bang and they all originate from outside our galaxy (as known so far). Investigation of gamma-rays coming from GRBs would help to establish a reliable model for GRBs. • Dark matter Dark matter particles accumulate in, and cause, wells in gravitational potential, and with high enough density they are predicted to have annihilation rates resulting in detectable fluxes of high energy gamma-rays.



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Shower development

Astroparticle Physics, Claus Grupen



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Shower development

Very High Energy Gamma-ray Astronomy, T.C. Weekes



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Properties of Cherenkov light




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Properties of the atmosphere




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Photon interactions



Dominations of photon interactions

Observation of UHE gamma-rays only possible for near sources due to attenuation through γ + γ e+ + e- (e.g. cosmic background γ’s)



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Simulation examples

≈

NSB of frequency fNSB superposed by two 5γ showers

fNSB= 40 MHz (newmoon) fNSB= 3000 MHz (full moon)



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Time resolution



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Amplitude resolution

A fast online and trigger-less signal reconstruction

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