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利用 ARGO-YBJ 实验对时变 现象的研究 PowerPoint PPT Presentation


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利用 ARGO-YBJ 实验对时变 现象的研究. 陈垚,姚志国,查敏 代表 ARGO-YBJ 实验 2010 年 4 月 18 日. 主要内容. 高能伽玛天文和时变现象; ARGO 数据质量检查; 背景估计法介绍; 观测结果和讨论。. H. E. S. S. 高能伽玛天文和时变现象. 高能伽玛天文是研究宇宙线的起源、加速和传播; 研究对象 : 稳定高能伽玛源 ; 高能伽玛源时变现象,如耀类星体 ; GRB; …… 伽玛天文的观测实验: 基于卫星探测器 ( Fermi ); 成像大气契伦克夫望远镜 (H.E.S.S. ); 广延大气簇射阵列;

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利用 ARGO-YBJ 实验对时变 现象的研究

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Argo ybj

利用ARGO-YBJ实验对时变 现象的研究

陈垚,姚志国,查敏

代表ARGO-YBJ实验

2010年4月18日


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主要内容

  • 高能伽玛天文和时变现象;

  • ARGO数据质量检查;

  • 背景估计法介绍;

  • 观测结果和讨论。


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H. E. S. S.

高能伽玛天文和时变现象

  • 高能伽玛天文是研究宇宙线的起源、加速和传播;

  • 研究对象:

    • 稳定高能伽玛源;

    • 高能伽玛源时变现象,如耀类星体;

    • GRB;

    • ……

  • 伽玛天文的观测实验:

    • 基于卫星探测器( Fermi );

    • 成像大气契伦克夫望远镜 (H.E.S.S. );

    • 广延大气簇射阵列;

      • As-gamma, ARGO;

      • Milagro。

Fermi Gamma-ray Space Telescope

Milagro

ASγ


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耀类星体的时变现象

  • 耀类星体的TeVγ射线发射是快速时变的,在爆发态时流强可达10倍Crab量级。如:Mkn421, Mkn501, 1ES 1959+650, PKS2155-304, BL Lacetae等;

  • 由于契伦克夫技术的限制,例如有效观测时间所占比例小、视场小,成像大气契伦克夫望远镜在某一时刻只能观测一个候选目标;

  • EAS Arrays(广延大气簇射阵列)有着长工作时间、宽视场的优点,使得连续的全天区扫描成为可能;

  • ARGO-YBJ属于后者,将能够对这类源的γ射线发射做很好的观测。

Mkn421: 2007 day 347 - 2008 day 229

X-ray

by RXTE

ARGO(nhit>40)

ARGO(nhit>100)


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数据质量检查

  • 由于时变现象的特性,对数据质量要求较高,需要进行数据质量检查;

  • 原理:

    • 数据质量低时,某些统计量将变异常;

    • 由统计量的值来判定数据质量。

  • 一些用到的统计量:

    • Event rate;

      • Reconstructed events number / live time;

    • Mean Chi-square value;

    • Mean Nhits;

    • Proportion of events with:

      • zenith in certain range;

      • azimuth in certain range;

      • Core in certain quadrant.

@ May 25, 2008

某channel掉高压时某些统计量异常


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Original data

Run level

1% cut off

Slice level: rate

1% cut off

2% cut off

Slice level: chi2_cn

Total: 3.1%

Final data

事例率随时间变化

逐级检查

  • 约排除 3% 的事例 ;

  • ARGO运行日志里记载的导致数据质量降低的事件都被排除;

  • 一些统计量的分布变得正常,见下图。

方位角0-PI的事例所占比例


Surrounding bins method



1.5

2+4

αi

1.5/*αi

(2+4)/*αi

背景估计方法:Surrounding bins method

  • 将天区划分为许多矩形的格子:

    • 各个格子接收度基本相等, 为赤纬方向上长度,αi 为赤经方向上长度, ~  /cosi;

    • 格子大小 ~ 角分辨率~ 能段;

  • 每一个格子都有一个对应的环绕的区域用于估计该格子的背景事例数:

    • 能将事例率随时间变化带来的影响最小化;

    • 基本不受方位角不均匀性影响。

    • NB = ini  inioffRi;

Astroparticle Physics 33 (2010) 24-39


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 =1.5 degree

Ri

  • 其中,格子和背景区域的接收度的比率R需要确定;

  • 在当地赤道坐标系下,R是位置的函数(如右上图),需要用一段较长时间的真实数据进行标定;

    • Ri = Nicenter(T)/ Nioff(T);

    • Ri ~ 立体角比值Rgeom;

    • R相当地稳定(如右下图):

      • 由2008170-366数据和由2009001-199数据标定得到的两组Ri一致性好;

(Ri1-Ri2)/Ri2


Mkn421

1.显著性值稳定;

2.与其它方法符合

时间交换法 ~ 4.2σ;

直接积分法 ~ 4.2σ.

Mkn421的观测

  • 数据: 2008163-165 ( mjd 54628-54630);

  • 事例选择条件:

    • nhit_ca: >100;

    • 天顶角: <40度;

  • Δδ:1.5 度;

  • 用不同的数据用做标定,得到的显著性:


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2008163-165

Mkn421 (166.114, 38.209)

Sun (80.65,23.16)

显著性全天区图


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显著性一维分布

2008163-165


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观测稳定源Crab

  • 数据: 2008170-2008366;

  • 事例选择条件:

    • Nhit: >100;

    • Core: 芯内;

    • 天顶角:<40度;

    • Δδ= 1.5;

  • 显著性:4.15σ。


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总结与讨论

  • 用该分析方法观测到已知时变源Mkn421的γ射线发射;

  • 用该分析方法观测到月亮阴影缺失和稳定源Crab;

  • 该方法将用于ARGO-YBJ对Mkn421的长期监测;

  • 并用于监测时变现象、找寻未知时变源。


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谢谢!


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稳定源Crab的观测

  • 数据: 2008170-2008366;

  • 选择条件:

    • Nhit: >100;

    • Core: 芯内;

    • 天顶角:<40度;

    • Δδ=1.0, 1.5, 2.0, 2.5 度.


Crab s location at cells

Crab's location at cells

Δδ= 1.5

Δδ=1.0

Δδ= 2.5

Δδ=2.0


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  • Note:

  • Cut dition is different;

  • Significance is maximized for equi-zenith and direc-integral.


Discussion

Discussion

  • The method is applied to monitor mkr421;

  • And search unknown flares.


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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 cells1

Crab's location at cells

Δδ= 1.5

Δδ=1.0

Δδ= 2.5

Δδ=2.0


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  • Note:

  • Cut dition is different;

  • Significance is maximized for equi-zenith and direc-integral.


Sun s orbit from 2008153 to 2008182 mjd54618 54647

Sun’s orbit from 2008153 to 2008182 (mjd54618-54647)

Δδ= 1.5

Δδ=1.0

2008163-165

Δδ=2.5

Δδ=2.0


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Δδ=3.0

2008161-164

Sig: -4.2σ


Mkn421 s location at cells 1 5degree

Mkn421’s location at cells (1.5degree)


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3510

Check on different levels

Check on run levels

Period level

Cut the run while statistics are abnormal.

Run level

Slice level (minute)

Check on period levels

Cut the period with statistics abnormal.

The runs with the statistics events rate<3510 are cut;

All the cut runs can find counterpart in LogBook;

Data is from March to May, 2008.


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After checking, slices with lower or higher rate are almost found.

Event rate with time

And, some other statistics behave better.

Red: slices cut off; Green: slices reserved.


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Check on slice levels

After cut, certain statistics become normal simultaneously.

Cut the slice with statistics “chi2_cn” abnormal.

140

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;


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  • 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;

      • >=20 hits ~ 4khz;

      • gamma-ray bursts;

      • VHE γ-astronomy (threshold ~300 GeV) ;

      • cosmic-ray physics (threshold ~1 TeV).


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ARGO-YBJ实验

  • ARGO特点:

    • 高海拔 4300 m a. s. l.);

    • 全覆盖RPC;

    • 低能阈(300GeV) ;

    • 大视场 ( > 2 sr);

    • 高duty cycle ( 93%);


1 0 degree nhit 100

Δδ = 1.0 degree; nhit>100

  • Crab: 4.87σ;

  • Direct- 1.0 >100 08年6.8 1degree

    >60 7.5 1.1 1.2degree

    Time-swap 6.29


3 0 degree nhit 60

Δδ = 3.0 degree; nhit>60

  • Crab: 4.86σ;


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temp


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Source numbers versus time in the X-ray, high-energy gamma-ray and VHE gamma-ray domains.


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