1. Background treatment in spectral analysis of low surface brightness sources Alberto Leccardi & Silvano Molendi Garching, 2 nd May 2006 EPIC background working group meeting

2. 1.SPECTRAL ANALYSIS OF LOW SURFACE BRIGHTNESS SOURCES 2.BACKGROUND MODELING IN A HARD BAND (ABOVE 2 keV) SUMMARY

3. OUTER REGIONS OF CLUSTERS R max R max = 5’  0.9 Mpc  30% r 180 A1689 z = 0.183 kT  9 keV ObsID 0093030101 Exposure time 36 ks (MOS) 29 ks (pn)

4. OUTER REGIONS OF CLUSTERS Inner region source >> background Outer region source  background

5. SYSTEMATIC UNCERTAINTIES STATISTICAL (RANDOM) UNCERTAINTIES

6. SYSTEMATIC UNCERTAINTIES STATISTICAL (RANDOM) UNCERTAINTIES

7. SYSTEMATIC UNCERTAINTIES Cross-calibration MOS-pn Background knowledge

8. SYSTEMATIC UNCERTAINTIES Cross-calibration MOS-pn relatively good in the hard band 2-10 keV

9. SYSTEMATIC UNCERTAINTIES Background knowledge NXB – continuum + fluorescence lines SP – highly variable component hard & soft light curves + IN FOV / OUT FOV ratio

10. SYSTEMATIC UNCERTAINTIES Background knowledge NXB – continuum + fluorescence lines SP – highly variable component hard & soft light curves + IN FOV / OUT FOV ratio

11. SYSTEMATIC UNCERTAINTIES Background knowledge NXB – continuum + fluorescence lines SP – highly variable component hard & soft light curves + IN FOV / OUT FOV ratio (De Luca & Molendi, 2004)

12. IN FOV / OUT FOV DIAGNOSTIC MOS2 IN FOVOUT FOV InstrumentIn FoVOut FoVBand (keV) MOSR > 10’R > 14’40”6-12 pnR > 10’R > 15’50”5-7.3 + 10-14

13. IN FOV / OUT FOV DIAGNOSTIC NO SP contaminationR ≈ 1 LOW SP contaminationR ≤ 1.3 HIGH SP contaminationR ≥ 1.3

14. SYSTEMATIC UNCERTAINTIES STATISTICAL (RANDOM) UNCERTAINTIES

15. What are the effects of the pure statistical uncertainties in determining interesting parameters, as temperature and density of the ICM, in the case of few counts/bin and a low S/N ratio, as in the outer regions of clusters of galaxies?

16. ANALYSIS DIFFERENT METHODS ACCUMULATES “REAL” SPECTRUM THERMAL + POWER LAW as BACKGROUND GENERATION SIMULATION SIMULATES N≈1000 DIFFERENT MEASURES PERTURBING REAL SPECTRUM WITH A POISSONIAN DISTRIBUTION

17. WEIGHTED AVERAGE OF SINGLE MEASURES RENORMALIZED BACKGROUND SUBTRACTION STANDARD ANALYSIS METHODS χ 2 STATISTIC

18. STANDARD METHOD TEMPERATURENORMALIZATION (keV)(arbitrary units) REALMEASUREDREALMEASURED 5.004.29 ± 0.025.505.27 ± 0.02 10.007.64 ± 0.065.505.38 ± 0.01 Normalization is UNDERESTIMATED by few percent Temperature is UNDERESTIMATED by 15-25%

19. WEIGHTED AVERAGE OF SINGLE MEASURES BACKGROUND MODEL CASH + MODEL ANALYSIS METHODS CASH STATISTIC

20. CASH + MODEL METHOD TEMPERATURENORMALIZATION (keV)(arbitrary units) REALMEASUREDREALMEASURED 5.004.45 ± 0.035.505.30 ± 0.02 10.007.97 ± 0.075.505.46 ± 0.01 Normalization is UNDERESTIMATED by few percent Temperature is UNDERESTIMATED by 10-20%

21. JOINED PROBABILITY DISTRIBUTION BACKGROUND MODEL BEST ANALYSIS METHODS CASH STATISTIC WEIGHTED AVERAGE OF “TRIPLETS”

22. ANALYSIS METHODS P(T) Temperature (keV) Peak = 7.1 Med = 8.4 Mean = 9.3 Peak = 14.1 Med = 17.1 Mean = 21.1 Probability distributions of the temperature are strongly ASYMMETRIC

23. P 1 (T)P 2 (T)P 3 (T) P tot (T)= P 1 +P 2 +P 3 ANALYSIS METHODS Median 68%

24. BEST METHOD TEMPERATURENORMALIZATION (keV)(arbitrary units) REALMEASUREDREALMEASURED 5.004.99 ± 0.045.505.48 ± 0.02 10.009.96 ± 0.115.505.55 ± 0.01 Normalization is nearly correct (≈1%) Temperature is REMARKABLY correct (<0.5%)

25. SUMMARIZING... TT NN T = 5 keVT = 10 keV best C + M standard

26. Background has to be modeled Cash statistic has to be used Probability distributions have to be joined in a particular way SUMMARIZING...

27. FURTHER ADVANTAGES IN MODELING BACKGROUND NO pn OoT subtraction NO errors propagation MORE information about BKG

28. NO pn OoT subtraction means... Background subtraction Grouping of pn normal and OoT spectra to approximate gaussian errors Direct subtraction of pn OoT spectrum with mathpha Some error propagation Loss of information on the original spectrum modeling Pn OoT is associated by grppha NO information lost

29. 1.SPECTRAL ANALYSIS OF LOW SURFACE BRIGHTNESS SOURCES 2.BACKGROUND MODELING IN A HARD BAND (ABOVE 2 keV) SUMMARY

30. 1.SPECTRAL ANALYSIS OF LOW SURFACE BRIGHTNESS SOURCES 2.BACKGROUND MODELING IN A HARD BAND (ABOVE 2 keV) SUMMARY

31. OUR BACKGROUND MODEL NXB continuum NXB fluorescence emission lines Cosmic extragalactic background

32. OUR BACKGROUND MODEL

33. NXB continuum + fluorescence lines Cosmic X-ray background

34. OUR BACKGROUND MODEL NXB continuum + fluorescence lines Cosmic X-ray background

35. OUR BACKGROUND MODEL NXB EPIC - MOS1 N σ N EPIC – MOS2 N σ N EPIC - pn N σ N Closed57.71.757.31.797.53.9 Blank fields57.5 ± 1.44.357.2 ± 1.75.195.1 ± 2.47.1 Clusters60.9 ± 1.48.060.9 ± 1.26.6100.1 ± 2.514.1 CXB EPIC - MOS1 N σ N EPIC – MOS2 N σ N EPIC - pn N σ N Expected7.821.87.841.84.581.3 Blank fields7.65 ± 0.471.47.26 ± 0.521.64.38 ± 0.481.4 Clusters10.17 ± 0.422.49.72 ± 0.432.46.54 ± 0.291.7

36. OUR BACKGROUND MODEL NXB EPIC - MOS1 N σ N EPIC – MOS2 N σ N EPIC - pn N σ N Closed57.71.757.31.797.53.9 Blank fields57.5 ± 1.44.357.2 ± 1.75.195.1 ± 2.47.1 Clusters60.9 ± 1.48.060.9 ± 1.26.6100.1 ± 2.514.1 CXB EPIC - MOS1 N σ N EPIC – MOS2 N σ N EPIC - pn N σ N Expected7.821.87.841.84.581.3 Blank fields7.65 ± 0.471.47.26 ± 0.521.64.38 ± 0.481.4 Clusters10.17 ± 0.422.49.72 ± 0.432.46.54 ± 0.291.7

37. OUR BACKGROUND MODEL NXB continuum + fluorescence lines Cosmic X-ray background

38. NXB continuum + fluorescence lines Cosmic X-ray background OUR BACKGROUND MODEL NXB continuum + fluorescence lines Cosmic X-ray background Cluster residual thermal component

39. OUR BACKGROUND MODEL NXB EPIC - MOS1 N σ N EPIC – MOS2 N σ N EPIC - pn N σ N Closed57.71.757.31.797.53.9 Blank fields57.5 ± 1.44.357.2 ± 1.75.195.1 ± 2.47.1 Clusters60.9 ± 1.48.060.9 ± 1.26.6100.1 ± 2.514.1 CXB EPIC - MOS1 N σ N EPIC – MOS2 N σ N EPIC - pn N σ N Expected7.821.87.841.84.581.3 Blank fields7.65 ± 0.471.47.26 ± 0.521.64.38 ± 0.481.4 Clusters10.17 ± 0.422.49.72 ± 0.432.46.54 ± 0.291.7

40. OUR BACKGROUND MODEL NXB EPIC - MOS1 N σ N EPIC – MOS2 N σ N EPIC - pn N σ N Closed57.71.757.31.797.53.9 Blank fields57.5 ± 1.44.357.2 ± 1.75.195.1 ± 2.47.1 Clusters60.9 ± 1.48.060.9 ± 1.26.6100.1 ± 2.514.1 CXB EPIC - MOS1 N σ N EPIC – MOS2 N σ N EPIC - pn N σ N Expected7.821.87.841.84.581.3 Blank fields7.65 ± 0.471.47.26 ± 0.521.64.38 ± 0.481.4 Clusters8.51 ± 0.583.37.71 ± 0.573.24.76 ± 0.412.5

41. OUR BACKGROUND MODEL EPIC – MOS1EPIC – MOS2EPIC - pn CLBFSOCLBFSOCLBFSO Cr8.510.412.23.89.210.46.811.010.6 Mn6.67.610.48.57.56.2--- Fe9.38.27.67.99.37.59.012.411.7 Ni4.04.13.67.96.15.1126.128.126. Cu4.65.05.52.24.53.9883.887.877. Zn9.33.66.93.44.15.497.997.193.9 Au10.310.612.412.28.97.9--- NXB FLUORESCENCE LINES CL = closed – BF = blank fields – SO = sources (clusters)

42. Background has to be modeled Cash statistic has to be used Probability distributions have to be joined in a particular way SUMMARY