1. A measurement of the diffuse TeV gamma ray emission from the Galactic Plane with the ARGO-YBJ experiment
Lingling Ma
Institute of High Energy Physics (IHEP),CAS
on behalf of the ARGO-YBJ collaboration
32nd ICRC, Beijing, August, 2011

2. Outline
Introduction
Data analysis
Results
Discussion
Summary

3. The physical goals of the study of the diffuse gamma rays
The production mechanism of the diffuse gamma rays
π0 decay:
Inverse Campton scattering:
The physical goals
To study the cosmic ray spectrum
To study the density of the interstellar medium and cosmic rays
To study of point sources

4. status of the study of the diffuse gamma rays
GeV: EGRET, Fermi/LAT
TeV: HESS ,Milagro results

5. Advantages of ARGO-YBJ experiment
Resistive Plate Chambers (RPC)
Wide FOV
Zenith<50o
dl: 25o-110o,
dl: 140o-210o
Duty cycle: ≥ 85%
Low energy threshold : 300GeV
Long term Stable operation : 4 years

6. Data analysis Data selection: Background estimation: DL selection:
zenith <50, optimal cut
Background estimation:
Direct Integral method
DL selection:
The inner Galactic plane (25o<dl<110o)
25o<dl<65o 65o<dl<85o 85o<dl<110o
Estimation of the anisotropy of the cosmic ray
Both sides of the db belt (8o)
Two sources (>6σ)observed by ARGO are excluded
MGROJ , TeVJ

7. Results: ---- flux profile along the Galactic latitude
Flux profile (1TeV )
25o<dl<110o
3o width in the Galactic latitude
Red line: the fluxes estimated by Fermi 100GeV
The effect of point sources:25%

8. Results: --flux profile along the Galactic longitude
Db belt selection:
|db|<2o based on Milagro’s results
10o width bin in the longitude
Red line: the fluxes estimated by Fermi 100GeV
The effects of point sources: 25%

9. Results: ----energy spectrum

10. Discussion The effects of the anisotropy of cosmic ray
The width of the db belt: from 5o to 10o
Effects to the results is about 10%
The effects of the un-detected sources
The Galactic plane is rich in sources
The limitation of the sensitivity of ARGO
IACTs discovered 6 sources in the two regions
For the region 25o<dl<65o
5 sources
25% at low energy, >50% at higher energy
For the region 65o<dl<85o
Cyg X-3
Can be neglected

11. Summary: The significance of the inner Galactic plane is 7.6σ
The flux profiles along the Galactic longitude and latitude are measured
The energy spectra of two regions are measured
The effects of the anisotropy and the week point sources are discussed.

12. Thanks