Study with Sun Shadow Observed by the ARGO-YBJ experiment

祝凤荣

2010.07 @NOA

Content

ARGO-YBJ experiment

Motivation

Measurement of IMF with the ARGO

Solar magnetic field

Summary

ARGO-YBJ collaboration

INFN and Univeristà di Lecce IHEP, Beijing

INFN and Università “Federico II” di Napoli Shandong University,Jinan

INFN Catania, Univ. and INAF/IASF di Palermo South West Jaotong Univ., Chengdu

INFN and Università di Pavia Tibet University, Lhasa

INFN and Univ.ersità “Tor Vergata” di Roma Yunnan University, Kunming

INFN and Università “Roma Tre” di Roma Zhengzhou University

INFN and INAF/IFSI di Torino Hongkong University

Hebei Normal University

Spokesmen

Prof. B. D’Ettorre Piazzoli Prof. Cao Zhen

ARGO-YBJ is an Extensive Air Shower detector optimized to work with showers induced by primaries cosmic rays of energy

E > a few hundreds GeV

This low energy threshold is achieved by:

operating at very high altitude (4300 m)

using a “full coverage” detection surface

Current status

Data taking since Jul. 2006

Duty cycle ~ 90%

Trigger rate 3.6 kHz

Dead time 3%

220 GB/day transferred to IHEP

1. Motivation Solar magnetic measurement

Sunspot SMMF

Polar Field Strength IMF

ASr result 1. Sun’s shadow is strongly affected by the solar and interplanetary

magnetic fields changing with the solar activity. 2. Near solar minimum, the displacement of the Sun’s shadow

in the east-west direction is mostly caused by the effect of the dipole component of the solar magnetic field. When the dipole directions of the Sun and the Earth are parallel the Sun shadow would shift to west (in 2008-2009), otherwise when they are anti-parallel the two component will cancelled (in 1996-1997).

3. The displacement in the north-south direction is due to the effect of the IMF. The shadow will be shifted to the north by the away (from the Sun) IMF and to the south by the toward (to the Sun) IMF.

MotivationSolar surface is measured everyday by ground based detector. But,

from surface to 2.6 Rsun, the chromospheres magnetic field measurement is difficult, usually the surface measurement is extrapolated under some hypothesis (Like the PFSS model). Cosmic ray shadow by solar maybe provide some information about the magnetic of this region, like defected ratio.

From 2.5 Rsun to 1 AU, only measurement at 1 AU. The IMF usually is assumed a simple Archimedean spiral configuration as the Sun rotates. Sun shadow displacement could measure the magnetic of this region.

ARGO-YBJ have a higher event rate and wider sensitive energy range , so we could check ASr result, measure sun shadow short term variations and its energy dependence. Our final aim  is to give some independent quantitative measurement of the solar magnetic.

Sun shadow of 44.6σ

• Clear Off set of the position in N-S

• There is almost not off set in E-W.

• 6/2006-10/2009• 906 days • Θ<50 deg

• Nhit

>100

How the sun shadow shift in IMF?

The sun shadow of 1TeV proton is shift 1.5 degree when only IMF. Tracking the 1 TeV antiproton from earth to sun step by step could find how the sun shadow shift.

When distance <20 Rsun, the IMF effection on sun shadow could be neglected. So 2/3 of the shift is caused by IMF from 120Rsun to 215Rsun.

Deflected angle of particle

Deflected angle of sun shadow

1 TeV Proton

太阳整体磁场模型

IMF模型一：草帽

IMF模型二：涡轮

Potential Field Source Surface Model (PFSS)

• 势场模型、线性无力场模型和非线性无力场模型是无力场假设下的三种理论外推模型。

• “ ” 势场表面源 (PFSS)模型为势场模型：

1、光球以内的太阳内部的磁场受等离子体运动的控制，是磁场通过太阳发电机产生的区域。

2、光球以上的低日冕区存在着闭合的磁力线，假设了区域内的磁场是势场，即该区域的磁场满足 Laplace方程。

3、表面源模型认为，当磁场到达约r= 2.5 R0 “冕层，即所谓的 表面”源 时，由于太阳风的作用，磁力线

被拉成垂直于表面源，势场假设不再适用，即形成相对于行星际空间来说的所谓源 .

简单模型：阿基米得螺旋线按 400km/s速度摆出来

Carington Coordinate:solar

longitudes

Carington period: 27.3 days

Nhit>100

Ratio:(12584\14605) 116.06±0.89%（预期遮挡事例数 \实际遮挡事例数）

简单考虑角分辨 0.76度后缺失度： 101.34%

WE: -0.30±0.26 deg

SN: 0.50±0.56 deg

不同方位处（ 2）

不同方位处（ 3）

18 sectors with 20º each

Folding with Carington period of 27.3 days

Displacement vs. solar longitudes

Switching between 2-sector and 4-sector

sun shadow displacement in different sector

Measurement of IMF(with a conventional model)

• At 1AU: B0 is the

only parameter

• B(θ)=B0 sin(θ-θ0)

R-3

R-1

vr=450km/sB=B0' R0/r ,

• IMF模型（ r>5Rsun ）

Cosmic ray deflection method vs.direct measurements using orbiting

detectors

Study about Solar magnetic field

displacement Defected ratio

IMF and dipole affection

1o/E(TeV)/nTOnly IMF, N-S the deflected

angle as a function of energy 1o/E(TeV)/nT.

Only dipole, W-E deflected angle is not Direct proportion to 1/E(TeV).

But the geomagnetic field affection is Direct proportion to 1/E(TeV). So, the sun shadow for different energy region could confirm the dipole component?

Deficit ratio with PSFF

The magnetic around the solar is complicated and dipole hypothesis is too simple.

Harmonic coefficients to order 20 for PFSS model is published in web http://wso.stanford.edu/

We use the PFSS model from Rs

to 3.25Rs. We choose one data file to do our calculation. When only PFSS, the defected ratio is 80~90% in 2009. 60~70% in 2002.

Ratio=50%

2009: ~0.9TeV

2002: ~3.1TeV

Summary

ARGO-ybj experiment

Measurement of By component of IMF

Solar magnetic field study