1. The islands method in the image analysis of atmospheric Cherenkov Telescopes data Nadia Tonello and Keiichi Mase Max-Planck-Institut für Physik München Nadia Tonello MPI for Physics, Munich DPG Spring Meeting 2004 Mainz, March 29 th -April 1 st

2. Nadia Tonello MPI for Physics, Munich DPG Spring Meeting 2004 Mainz, March 29 th -April 1 st  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.

3. m h (m) Gamma shower ( narrow, points to source ) Proton shower ( wide, points anywhere ) Nadia Tonello MPI for Physics, Munich DPG Spring Meeting 2004 Mainz, March 29 th -April 1 st Width Length Alpha Width Length Alpha 100 GeV proton h(m) CT1 Camera

4. Nadia Tonello MPI for Physics, Munich DPG Spring Meeting 2004 Mainz, March 29 th -April 1 st 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 Islands HEGRA CT1 10.8 2.5 0.3 0.2 9.5 0.4 Energy threshold : 750 GeV

5. Nadia Tonello MPI for Physics, Munich DPG Spring Meeting 2004 Mainz, March 29 th -April 1 st 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 Analysis HEGRA 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

6. Distributions of the Number of Islands MAGIC Gammas Hadrons Number of pixels >2 Energy threshold: 30 GeV Cleaning level: 2.5 sigma Nadia Tonello MPI for Physics, Munich DPG Spring Meeting 2004 Mainz, March 29 th -April 1 st

7. Example Alpha : -17.4° Length : 143 mm Width : 18.7 mm Size : 494 photons Standard I.C. Islands Analysis Recon. Alpha : -3.29° Nadia Tonello MPI for Physics, Munich DPG Spring Meeting 2004 Mainz, March 29 th -April 1 st Island1 # pixels : 9 Alpha : -3.29° Length : 42.6 mm Width : 18.1 mm Size : 434 photons Island2 # pixels : 2 Alpha : 18.8° Length : -1 mm Width : -1 mm Size : 60 photons MC Gamma Energy : 35.7 GeV I.P. : 112 m MAGIC Camera

8. The Distribution of Alpha Size > 300 ADC Number of pixels >2 Standard I.C. Continent (Islands Analysis) RMS = 26.0 RMS = 22.5 RMS = 22.9 Reconstructed (Islands Analysis) Islands analysis The alpha distribution is slightly narrower Better reconstruction power. Nadia Tonello MPI for Physics, Munich DPG Spring Meeting 2004 Mainz, March 29 th -April 1 st

9. The Distribution of Width Standard I.C. Continent (Islands Analysis) gamma hadron gamma Size > 300 ADC Nadia Tonello MPI for Physics, Munich DPG Spring Meeting 2004 Mainz, March 29 th -April 1 st

10. The Distribution of Length Size > 300 ADC Standard I.C. Continent (Islands Analysis) Gammas Hadrons Gammas Nadia Tonello MPI for Physics, Munich DPG Spring Meeting 2004 Mainz, March 29 th -April 1 st The islands information can be used as additional information.

11. 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 Nadia Tonello MPI for Physics, Munich DPG Spring Meeting 2004 Mainz, March 29 th -April 1 st

12. Summary  At 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 Nadia Tonello MPI for Physics, Munich DPG Spring Meeting 2004 Mainz, March 29 th -April 1 st

13. Outlook Nadia Tonello MPI for Physics, Munich DPG Spring Meeting 2004 Mainz, March 29 th -April 1 st Systematic study on different cleaning levels potential rejection power of different islands parameters

14. 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 Tonello MPI for Physics, Munich DPG Spring Meeting 2004 Mainz, March 29 th -April 1 st

15. 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 Standard I.C.Islands Analysis Island3 # pixels : 2 Alpha : 0° Length : -1 mm Width : -1 mm Size : 54 photons Recon. Alpha : - 2.4° Nadia Tonello MPI for Physics, Munich DPG Spring Meeting 2004 Mainz, March 29 th -April 1 st

16. 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 Standard I.C.Islands Analysis Island3 # pixels : 3 Alpha : 28.1° Length : 12.5 mm Width : 12.0 mm Size : 83 photons Recon. Alpha : -4.02° Nadia Tonello MPI for Physics, Munich DPG Spring Meeting 2004 Mainz, March 29 th -April 1 st