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利用不同背景估计方法对 Mrk421 的观测

利用不同背景估计方法对 Mrk421 的观测. 查敏，张建立，陈松战 (ARGO-YBJ) 2010.04.18 高能物理分会. 工作背景的介绍 方法的简介 结果和讨论. content. Introduction: Mrk421 single flare: 10 I Crab. ARGO has seen a 4 σ effect 2008/05/02 2010/02/18. Whipple. --continued. Multi-wave-length Observation of Flares of Mrk421.

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利用不同背景估计方法对 Mrk421 的观测

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  1. 利用不同背景估计方法对Mrk421的观测 查敏，张建立，陈松战 (ARGO-YBJ) 2010.04.18 高能物理分会

  2. 工作背景的介绍 方法的简介 结果和讨论 content

  3. Introduction: Mrk421 single flare: 10ICrab • ARGO has seen a 4σ effect • 2008/05/02 • 2010/02/18 Whipple

  4. --continued Multi-wave-length Observation of Flares of Mrk421

  5. Method (D.E. Alexandreas NIMA (1993)) • Optimize bin size method • Non & Nbg estimation + the formula to estimate statistical significance • Background estimation • Isotropic background from charged cosmic ray; • Event rate is constant except when changes in the detector configuration are made • A strong function of zenith angle; • Event rate may change with experimental conditions • Detector threshold / dead time • External changes (e.g. local atmospheric pressure) • Time-swapping method • Direct integral method; • Equi-zenith method

  6. Data information • 数据11-13 June 2008； • nHit on carpet > 100; • 400

  7. 时间交换法(time-swapping) • Assumption: A(h,,t) = A(h,,t0)(t), where (t0) = 1 • Effective acceptance map in local coordinate is tabulated within certain time period (Tw) • Artificial background events are created with the randomly combination of above map and arriving time within this time period; • advantage • Keep most properties of background • parameters • Time-shuffling length （Tw）? • Swapping times （Nsw）? • Possible correction? • 6.4%  180 minutes; • 6.4% *180./T; • limitation • Conservative result • Not applicable to the investigation of high declination sky.

  8. 3h + 10 + 3.8 Significance () Tw

  9. 直接积分法（Direct Integral） • E(ha, ): the acceptance distribution in Local Equatorial Coordinates (LEC) for certain period; • R(t): event rate of the detector; • (ha,ra,t) is 1 if events falls within this special bin or 0 othersize; • limitation • Time integration period?/ conservative result /Not applicable for the source near the North/South pole;

  10. 24h + 4.6  4h + 4.4 

  11. 等天顶角法（Equi-Zenith Method） • Minimize the detecting factors from detector and environmental variation • See Source/background at the same time; • Free from zenith dependence; • Free from acceptance/ efficiency changes; • Free from Pressure and tempreture; • Limitation: • Giving up small zenith angle data due to number of off-source windows • non-uniformity distribution for the azimuth angle

  12. 方位角的不一致性 • geomagnetic field; • other unknown factrors? • Zenith angle dependence and <2%

  13. 地磁场使带电次级粒子发生偏转，拉宽次级粒子的横向分布，使得芯区粒子密度降低，从而降低了原初簇射的触发率。地磁场使带电次级粒子发生偏转，拉宽次级粒子的横向分布，使得芯区粒子密度降低，从而降低了原初簇射的触发率。 • 地磁场因子  1-2% Ivanz, CPTL(1998), Zhouyuan (HEP&NP)

  14. equi-declination normalization • The correction happen within a day; • Repeat above measurement 35 times; • 35 dummy on-source windows on the orbit has the same Declination band with the on-source window. • The corrected background is obtained • The uncertainty of signal

  15. 10 off windows + 5.2 

  16. Summary & discussion

  17. --continued • Differences • difference from parameters: 0.3-0.4 • From method itself: 0.8 ; • For a fixed point source “seeing” in 2 ways • (s1-s2)=(1 + 2)1/2 =0.447 (here 1= 2=0.1) • Here (s1-s2)=0.8, thus not just statistical fluctuations • Data quality • Different method may have different dependence on data.

  18. Direct integral .vs. equi-zenith 2008 1 year Crab from SongZhan + JianLI

  19. The optimal smooth angle Point source Non-point source >1.58σ ~ 1.58σ+Rsource

  20. Angular resolution of proton • Φ70=1.58σ • Nhit>20: 2.90 deg • Nhit>60: 1.60 deg • Nhit>100: 1.14 deg • Nhit>500: 0.56 deg • Nhit>1000:0.48 deg

  21. Equi-Zenith Angle method The number of background are estimated using 10 off-source windows which are at the same zenith angle as the on-source direction in the azimuthal direction. Without considering the effect from non-uniform azimuth angle distribution, the number of background events can be estimated as Azimuth correction: Repeat the above measurement 35 times. Assigned as This 35 dummy on-source windows on the orbit has the same Decl. with the on-source window. The azimuth correction factor η is given by Using error spread law, the statistical error of the excess events in a on-source window is Finally, the corrected estimation of the number of background events is obtained as Detailed information refer to

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