利用argo-ybj實驗對時變現(xiàn)象的研究

1、利用ARGO-YBJ實驗對時變 現(xiàn)象的研究,陳垚，姚志國，查敏 代表ARGO-YBJ實驗2010年4月18日,主要內(nèi)容,高能伽瑪天文和時變現(xiàn)象；ARGO數(shù)據(jù)質(zhì)量檢查；背景估計法介紹；觀測結(jié)果和討論。,高能伽瑪天文和時變現(xiàn)象,高能伽瑪天文是研究宇宙線的起源、加速和傳播；研究對象:穩(wěn)定高能伽瑪源;高能伽瑪源時變現(xiàn)象，如耀類星體;GRB;……伽瑪天文的觀測實驗：基于衛(wèi)星探測器( Fermi );成像大氣契倫克夫望

2、遠鏡 (H.E.S.S. );廣延大氣簇射陣列；As-gamma, ARGO;Milagro。,Fermi Gamma-ray Space Telescope,H. E. S. S.,Milagro,ASγ,耀類星體的時變現(xiàn)象,Mkn421: 2007 day 347 - 2008 day 229,X-ray,ARGO(nhit>40),ARGO(nhit>100),by RXTE,耀類星體的TeVγ射線發(fā)射是快速時變

3、的，在爆發(fā)態(tài)時流強可達10倍Crab量級。如：Mkn421, Mkn501, 1ES 1959+650, PKS2155-304, BL Lacetae等；由于契倫克夫技術(shù)的限制，例如有效觀測時間所占比例小、視場小，成像大氣契倫克夫望遠鏡在某一時刻只能觀測一個候選目標(biāo);EAS Arrays（廣延大氣簇射陣列）有著長工作時間、寬視場的優(yōu)點，使得連續(xù)的全天區(qū)掃描成為可能;ARGO-YBJ屬于后者，將能夠?qū)@類源的γ射線發(fā)射做很好的觀測

4、。,數(shù)據(jù)質(zhì)量檢查,由于時變現(xiàn)象的特性，對數(shù)據(jù)質(zhì)量要求較高，需要進行數(shù)據(jù)質(zhì)量檢查；原理：數(shù)據(jù)質(zhì)量低時，某些統(tǒng)計量將變異常; 由統(tǒng)計量的值來判定數(shù)據(jù)質(zhì)量。,一些用到的統(tǒng)計量：Event rate;Reconstructed events number / live time;Mean Chi-square value; Mean Nhits;Proportion of events with: zenith in cert

5、ain range; azimuth in certain range;Core in certain quadrant.,@ May 25, 2008某channel掉高壓時某些統(tǒng)計量異常,約排除 3% 的事例 ;ARGO運行日志里記載的導(dǎo)致數(shù)據(jù)質(zhì)量降低的事件都被排除;一些統(tǒng)計量的分布變得正常，見下圖。,逐級檢查,事例率隨時間變化,方位角0-PI的事例所占比例,背景估計方法：Surrounding bins method,將

6、天區(qū)劃分為許多矩形的格子：各個格子接收度基本相等，?? 為赤緯方向上長度，?αi 為赤經(jīng)方向上長度, ~ ?? /cos?i;格子大小 ~ 角分辨率~ 能段;每一個格子都有一個對應(yīng)的環(huán)繞的區(qū)域用于估計該格子的背景事例數(shù)：能將事例率隨時間變化帶來的影響最小化；基本不受方位角不均勻性影響。NB = ?i?ni ? ?i?nioffRi ;,,Astroparticle Physics 33 (2010) 24-39,其中，格子

7、和背景區(qū)域的接收度的比率R需要確定；在當(dāng)?shù)爻嗟雷鴺?biāo)系下，R是位置的函數(shù)（如右上圖），需要用一段較長時間的真實數(shù)據(jù)進行標(biāo)定；Ri = ?Nicenter(T)/ ?Nioff(T);Ri ~ 立體角比值Rgeom;R相當(dāng)?shù)胤€(wěn)定（如右下圖）：由2008170-366數(shù)據(jù)和由2009001-199數(shù)據(jù)標(biāo)定得到的兩組Ri一致性好；,?? =1.5 degree,(Ri1-Ri2)/Ri2,Ri,Mkn421的觀測,數(shù)據(jù)： 20081

8、63-165 ( mjd 54628-54630);事例選擇條件: nhit_ca: >100;天頂角: <40度；Δδ：1.5 度;用不同的數(shù)據(jù)用做標(biāo)定，得到的顯著性：,顯著性全天區(qū)圖,2008163-165,顯著性一維分布,,觀測穩(wěn)定源Crab,數(shù)據(jù): 2008170-2008366；事例選擇條件: Nhit: >100;Core: 芯內(nèi);天頂角：<40度;Δδ= 1.5；顯著性：4.

9、15σ。,總結(jié)與討論,用該分析方法觀測到已知時變源Mkn421的γ射線發(fā)射；用該分析方法觀測到月亮陰影缺失和穩(wěn)定源Crab;該方法將用于ARGO-YBJ對Mkn421的長期監(jiān)測；并用于監(jiān)測時變現(xiàn)象、找尋未知時變源。,,謝謝！,,,,,,,穩(wěn)定源Crab的觀測,數(shù)據(jù): 2008170-2008366；選擇條件: Nhit: >100;Core: 芯內(nèi);天頂角：<40度;Δδ=1.0, 1.5, 2.0, 2.

10、5 度.,Crab's location at cells,,Δδ= 2.5,Δδ=2.0,Δδ= 1.5,Δδ=1.0,Note: Cut dition is different; Significance is maximized for equi-zenith and direc-integral.,Discussion,The method is applied to monitor mkr421;And sea

11、rch unknown flares.,,,,,,,Crab,Data: 2008170-2008366；Cut condition: Nhit: >100;Core: in the carpet;Event zenith: none;Cell’s zenith<40;Δδ=1.0, 1.5, 2.0, 2.5 .,Crab's location at cells,,Δδ= 2.5,Δδ=2.0,Δδ=

12、 1.5,Δδ=1.0,Note: Cut dition is different; Significance is maximized for equi-zenith and direc-integral.,,,Sun’s orbit from 2008153 to 2008182 (mjd54618-54647),,,Δδ= 1.5,Δδ=1.0,Δδ=2.0,Δδ=2.5,,,,2008163-165,Δδ=3.0,,,2

13、008161-164Sig: -4.2σ,Mkn421’s location at cells (1.5degree),,,,,,Period level,Slice level (minute),Run level,,,Check on different levels,Cut the run while statistics are abnormal.,Check on period levels,The runs with th

14、e statistics events rate<3510 are cut;All the cut runs can find counterpart in LogBook;Data is from March to May, 2008.,Cut the period with statistics abnormal.,Check on run levels,,Red: slices cut off; Green: sl

15、ices reserved.,After checking, slices with lower or higher rate are almost found.,Event rate with time,And, some other statistics behave better.,Check on slice levels,Cut the slice with statistics “chi2_cn” abnormal.,,14

16、0,Cut the slices with mean chi2_cn >140;Data from 200803- 200805.,Upper-right: ratio of zenith >50 degree;Lower-left: ratio of azimuth (0-PI);Red: slices cut off; Green: slices reserved;,After cut, certain sta

17、tistics become normal simultaneously.,,,,,ARGO-YBJ’ s mode: Scalar mode;counting rates for each cluster ( >= 1, >=2, >=3, >=4 coincidences);GRB and solar flares with a threshold of few GeV;Shower mode;&g

18、t;=20 hits ~ 4khz;gamma-ray bursts;VHE γ-astronomy (threshold ~300 GeV) ;cosmic-ray physics (threshold ~1 TeV).,,,,,ARGO-YBJ實驗,ARGO特點:高海拔 4300 m a. s. l.);全覆蓋RPC;低能閾（300GeV) ;大視場 ( > 2 sr);高duty cycle ( 93%);,

19、Δδ = 1.0 degree; nhit>100,Crab: 4.87σ; Direct- 1.0 >100 08年6.8 1degree >60 7.5 1.1 1.2degreeTime-swap 6.29,,Δδ = 3.0 degree; nhit>60,Crab: 4.86σ;,,,,,,temp,,,,,,Source numbers versus time in the X-r