The islands method in the image analysis of atmospheric Cherenkov Telescopes data

The islands method in the image analysis of atmospheric Cherenkov Telescopes data

Nadia Tonello and Keiichi MaseMax-Planck-Institut für Physik München

Nadia TonelloMPI for Physics, Munich

DPG Spring Meeting 2004 Mainz, March 29th -April 1st



Previous generation of Cherenkov Telescopes (energy range TeV) successfully adopted Standard Image Cleaning and Hillas Parameters to analyze data.

New generation of Cherenkov Telescopes can record images produced by atmospheric showers initiated by (100-100) GeV particles.

Sometimes, the images are fragmented and the standard image cleaning miscalculates the image parameters.

An Island is defined as a group of pixels connected with each other above a certain threshold (noise RMS units = sigma).

The image parameters are calculated for each island and used for the g/h separation.

Using islands parameters more detailed informations can be potentially extracted.

m

h (m)

Gamma shower( narrow, points to source )

Proton shower( wide, points anywhere )



Width

LengthAlpha

Width

Length

Alpha

100 GeV proton

h(m)

CT1 Camera



MC gammas Real data (hadrons)

26.1 68.2 93.6 98.2 99.4 99.7 99.8

39.4 27.1 6.2 1.7 0.5 0.2 0.2

25.0 4.3 0.2 0.1 0.1 0.1

28.9 54.9 76.2 87.5 92.2 94.3 96.0

37.7 33.1 20.5 11.3 7.3 5.5 3.8

22.6 9.5 3.0 1.0 0.5 0.2 0.2

Distributions of the Number of IslandsHEGRA CT1

10.8 2.5 0.3 0.2 9.5 0.4

Energy threshold : 750 GeV



26.1 68.2 93.6 98.2 99.4 99.7 99.8

39.4 27.1 6.2 1.7 0.5 0.2 0.2

25.0 4.3 0.2 0.1 0.1 0.1

28.9 54.9 76.2 87.5 92.2 94.3 96.0

37.7 33.1 20.5 11.3 7.3 5.5 3.8

22.6 9.5 3.0 1.0 0.5 0.2 0.2

Standard AnalysisHEGRA CT1

10.8 2.5 0.3 0.2 9.5 0.4

After Supercuts : 97% of the survived events have only 1 main island

Distributions of the Number of IslandsMAGIC

Gammas

Hadrons

Number of pixels >2

Energy threshold:

30 GeV

Cleaning level:

2.5 sigma



Exam

ple

Alpha : -17.4°

Length : 143 mm

Width : 18.7 mm

Size : 494 photons

Standard I.C.

Islands AnalysisRecon. Alpha : -3.29°



Island1# pixels : 9 Alpha : -3.29°Length : 42.6 mm Width : 18.1 mmSize : 434 photons

Island2# pixels : 2 Alpha : 18.8°Length : -1 mm Width : -1 mmSize : 60 photons

MC Gamma

Energy : 35.7 GeV

I.P. : 112 m

MAGIC Camera

The Distribution of Alpha

Size > 300 ADC

Number of pixels >2

Standard I.C. Continent (Islands Analysis)

RMS = 26.0RMS = 22.5

RMS = 22.9

Reconstructed (Islands Analysis)

Islands analysis

The alpha distribution is slightly narrower

Better reconstruction power.



The Distribution of Width


gamma

hadron hadron

gamma

Size > 300 ADC



The Distribution of Length

Size > 300 ADC


Gammas

Hadrons Hadrons

Gammas



The islands information can be used as additional information.

G/h Separation

Input parameters

Standard Analysis Size Width Length Dist Conc2 Sgn(M3Long) Alpha

Islands Analysis Length of biggest island Width of biggest island

16% improvement for Size 600-1000 ADC

Size (ADC) Q (Std I.C.) Q (Islnd A.)0-300 1.2±0.038 1.3±0.040

300-600 2.1±0.084 2.1±0.086600-1000 3.2±0.26 3.7±0.311000-2000 3.5±0.33 3.7±0.37

>2000 17±11 12±2.8



SummaryAt TeV energies the shower images are compact and the standard analysis is working fine.

Al lower energies, the standard image cleaning miscalculates the Hillas parameters due to the fragmentation of the shower images.

The different parts are called ISLANDS.

Islands analysis is hardly affected by NSB. That's why the islands parameters are calculated correctly. More informations can be potentially extracted.

Island analysis is promising to analyze low energy showers



Outlook



Systematic study on

different cleaning levels

potential rejection power of different islands parameters

Example 4

Alpha : 6.97°

Length : 71.7 mm

Width : 69.4 mm

Size : 707 photons

Gamma (#13)

Energy : 61.9 GeV

I.P. : 62.1 m

# islands : 4

Island1

# pixels : 9

Alpha : -4.64°

Length : 31.4 mm

Width : 21.5 mm

Size : 300 photons

Island2

# pixels : 7

Alpha : -4.04°

Length : 29.8 mm

Width : 14.7 mm

Size : 371 photons

Standard I.C. Islands Analysis

Island3

# pixels : 2

Alpha : 0°

Length : -1 mm

Width : -1 mm

Size : 63 photons

Recon. Alpha : -2.67°Nadia TonelloMPI for Physics, Munich


Example 2

Alpha : -2.4°

Length : 27.0 mm

Width : 13.4 mm

Size : 954 photons

Gamma (#19)

Energy : 50.6 GeV

I.P. : 108 m

# islands : 3

Island1

# pixels : 9

Alpha : -2.4°

Length : 27.0 mm

Width : 13.4 mm

Size : 954 photons

Island2

# pixels : 2

Alpha : -29.0°

Length : -1 mm

Width : -1 mm

Size : 51 photons


Island3

# pixels : 2

Alpha : 0°

Length : -1 mm

Width : -1 mm

Size : 54 photons

Recon. Alpha : -2.4°



Example 3

Alpha : -1.03°

Length : 44.4 mm

Width : 12.6 mm

Size : 290 photons

Gamma (#23)

Energy : 19.3 GeV

I.P. : 88.3 m

# islands : 3

Island1

# pixels : 4

Alpha : -34.2°

Length : 19.6 mm

Width : 9.6 mm

Size : 155 photons

Island2

# pixels : 3

Alpha : 31.4°

Length : 13.0 mm

Width : 10.6 mm

Size : 135 photons


Island3

# pixels : 3

Alpha : 28.1°

Length : 12.5 mm

Width : 12.0 mm

Size : 83 photons

Recon. Alpha : -4.02°Nadia TonelloMPI for Physics, Munich


The islands method in the image analysis of atmospheric Cherenkov Telescopes data

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