A Northern Sky Survey for Both TeV CR anisotropy and -ray Sources
with Tibet Air Shower Array
Hongbo Hu
For Tibet AS collaboration
• The Tibet AS-gamma Experiment ;• Two Analyses Methods;• Preliminary Results;• Discussion and Conclusions.
2004.8 Institute of High Energy Physics
YangBaJing Observatory and its Experiments
– Located at an elevation of 4300 m (Yangbajing , China)
– Atmospheric depth 606g/cm2
– Wide field of view– High duty cycle (>90%)
ARGOExperimentalHall
ASγ air shower array
3,600m2 (in area)Tibet-HD Tibet array: ~250 x 250 m2
HD: 60 x 60m2
Tibet-III: ~150x150 m2
Tibet-III
Tibet-HD
Operation Time
Live TimeSelected
EventsMode Energy
Resolution (@3TeV) Area
Tibet-HD
1997.2~1999.9 555.9 days 1.5×109 ~3TeV 0.9o 3600m2
Tibet-III 1999.11~2001.5 456.8 days 5.5×109 ~3TeV 0.9o 22050m2
Tibet Air Shower Array
Method I -----Equal-zenith method Zenith
North Pole
On-source
Off-source
6.8°<zenith<40.0°
10
10
1* i OFFBG
iN
N
• Making use of the fact that events are uniformly distributed within equal-zenith belt;
• 10 off-source windows (side band) are chosen to estimate BKG.
, on onI N on
on
NI
Equal !
, off offI N off
off
NI
Method II----Global CR. Intensity fitting method
2
, ,2, 2
2 2, ,
1
1
on on off i off ii i
t on
on on off i off ii i
N I N I
N I N I
2 2,
,total i t on
t on
I
Zenith
Equal ?
All sky survey based on an anisotropy correction of relative CR intensity, which is obtained by LSQ fitting for the data in each of equal zenith ring
Tail-in and Loss-cone
DEC
RA.Duldig, PASA,Vol18,No.1
～±0.1%
Large scale anisotropy (by method II) I - 1
Large scale anisotropy of diff. Data sample
• Anisotropy measurements agree with each other from using HD detector or TibetIII detector, means small systematic effects.
Large scale anisotropy correction
σ=1.258
Before subtraction
After subtraction
σ=1.018
0
0
Sky Map
NO. R.A.(˚) DEC(˚) Signifi(σ) NO. R.A.(˚) R.A.(˚) Signifi(σ)
1 38.9 13.9 4.2 13 221.6 32.8 4.4
2 39.2 31.9 4.0 14 253.2 58.8 4.1
3 66.8 12.3 4.1 15 278.3 38.4 4.3
4* 70.1 11.9 4.6 16* 286.7 5.6 4.6
5 70.4 18.0 4.3 17 301.7 8.7 4.1
6 71.9 47.5 4.0 18* 304.3 36.7 4.2
7 78.9 18.9 4.2 19 309.5 49.1 4.4
8* 83.3 21.8 5.0 20 309.9 39.6 4.5
9* 88.8 30.2 5.6 21 318.0 40.6 4.7
10* 115.3 17.5 4.1 22 330.3 50.3 4.0
11* 165.5 38.4 5.3 23 333.0 34.7 4.0
12 199.9 29.7 4.0 24 336.9 12.7 4.0
Crab
Mrk421 List of sky cells with clustered directions (24)having statistic significance larger
than 4.0σ.
(88.8,30.2)
Discussion Hot point I ---evt. No.9 (88.8°, 30.2 °)
SNR counterpart G179.0+2.6,
RA : 88.42 DEC :31.08 Size (/arc min): 70 Type: Shell
3.7σ 4.5 σ
5.6 σ
b=+5˚
b=0˚
b=-5˚
b=+5˚
b=+5˚
b=0˚
b=0˚
b=-5˚
b=-5˚
Hot Point II -- No.18(304.3 °, 36.7 °), No19(309.9 °, 39.6 °)
• Amenomori,in Proc.27th ICRC,2315. Observed 4.15 σ;
• S.W. Cui and C.T. Yan, in Proc. 28th ICRC, 2315. Observed 4 σ; EGRET counterpart 3EG J2016+3657 RA :304.008 DEC : 37.2 Milagro (306.6,38.9) 4.2 σ (Atkins,R., et al 2004, ApJ, 608,680)
~0 σ
4.2 σ
b=+5˚b=0˚
b=-5˚
b=+5˚b=0˚
b=-5˚
b=+5˚b=0˚
b=-5˚
3.9 σ
4.4 σ
4.5 σ
2.9 σ
Up flux limit (by method I)
(30 degree of declination related to YBJ zenith direction)
Conclusions
• Large scale anisotropy of CR. intensity with a magnitude about 0.1% are observed in two dimensions in TeV energy range.
• Crab and Mrk421 are detected with 5 σ level.
• No other significant point source is found, and an upper-flux limit curve is given
