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
2
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
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
3
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
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
4
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
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
5
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
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
6
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
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
7
Camera readout chain
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
8
Cross-Correlation
m
mngmfngf ][][])[*( *
dtgftgf )()())(*( *
For two continuous functions:
For two discrete functions:
The second derivative:
Better resolution of pile-up
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
9
Simulation
≈
TemplateSimulated measurement
fNSB= 3000 MHz (full moon)
m
mngmfngf ][][])[*( *
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
10
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
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
11
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
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
12
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
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
13
Questions
?
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
14
Backup Slides Shower development Propertier of Cherenkov light Propertier of the atmosphere Photon interactions Simulation examples Time resolution Amplitude resolution
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
15
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.
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
16
Shower development
Astroparticle Physics, Claus Grupen
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
17
Shower development
Very High Energy Gamma-ray Astronomy, T.C. Weekes
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
18
Properties of Cherenkov light
Astroparticle Physics, Claus Grupen
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
19
Properties of the atmosphere
Astroparticle Physics, Claus Grupen
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
20
Photon interactions
Astroparticle Physics, Claus Grupen
Astroparticle Physics, Claus Grupen
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)
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
21
Simulation examples
≈
NSB of frequency fNSB superposed by two 5γ showers
fNSB= 40 MHz (newmoon) fNSB= 3000 MHz (full moon)
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
22
Time resolution
05.06.09, Arno GadolaDoktorandenseminar
Physik-Institut Universität ZürichWinterthurerstr. 190, 8057 Zürich
23
Amplitude resolution