1. TeV γ-ray survey of the northern sky using the ARGO-YBJ experiment
Data analysis
Results (sources+ upper limits)
Summary
Zhen Cao
Institute of High Energy Physics (IHEP),CAS
On behalf of the ARGO-YBJ collaboration
32nd ICRC, Beijing Aug. 16, 2011

2. 1. The ARGO-YBJ experiment
RPC
111 m
8 Strips
(6.5 x 62 cm2)
for each Pad
78 m
99 m
74 m
(43 m2)‏
1 CLUSTER = 12 RPC
10 Pads
(56 x 62 cm2)‏
for each RPC
4300m a.s.l.
Tibet/China
Number of Fired Strips
Start from July 2006
Rate：3.5kHz
Threshold：~ 300 GeV
Duty cycle: >86%
FOV: 2 sr 2

3. Duty cycle Stable operation: since November 2007
Observation: since July 2006,
Stable operation: since November 2007
Effective observation time: >1265 days
The average duty cycle > 86%

4. Moon shadow
Npad>100, 74 s.d.
10 s.d. per month
Angular resolution

5. 2. Data analysis Data selection zenith <50º, quality cut
Background estimation:
Direct Integral method
Cosmic ray large scale anisotropy estimate
by smoothing over 11ºx11º
with central area of 5ºx5º excluded

6. ARGO-YBJ sensitivity
The cumulative sensitivity to the Crab like source is 28% Crab unit.
Milagro sources
>1000
>500
>200

7. 3. Result 4 sources with significance larger than 5 sigma:
Crab (17.9σ) , Mrk421 (13.2σ), MRGOJ (5.8σ),
MGRO J /TeV J (6.3σ)
After large scale anisotropy removed
latitude ±5º
σ=0.99
Mean=0.0065
Mean 0.006
RMS 0.99

8. ARGO-YBJ result for Milagro’s candidates
Recently, the Milagro experiment observed 14 of the 34 selected Fermi sources at a pre-trial significance of 3 S.D at 35 TeV.
9 out of 15 sources are observed by ARGO-YBJ with significance greater than 1.5 S.D., against 1 expected source from the normal Gaussian.

9. ARGO-YBJ result MGRO J2031+41/TeV J2032 +4130
MRGOJ (see Vernetto, S.’s talk )
MGRO J /TeV J
No signal from MGRO J

10. ARGO-YBJ result for MGRO J2031+41
Extension
Consistent with MAGIC and HEGRA results ,
(0.087±0.030)º and (0.103±0.025)º.
Flux is much higher than MAGIC and HEGRA results.
This difference is not due to statistic and systematic errors!

11. Estimates of Systematic error for SED of Crab Nebula
Origin flux index
G4argo vs Data: % …
variability of trigger rate % (RMS/mean) …
Time resolution %( ns)
Data selection %
Pointing error(0.3degree) %
anisotropy correction <0.7sigma …
Different methods sigma ??
Others ????
Total %
(3°-5°) humped up background: 25% overestimated
Not enough to understand the discrepancy

12. ARGO-YBJ result for MGRO J2019+37
The extension estimated by Milagro is (0.32±0.12)º , SED with a=-1.83 and cutoff at 22.4 TeV
90% c.l. upper limit derived from ARGO-YBJ data is lower than Milagro’s flux. This discrepancy might indicate a variation in the ray flux of the source.

13. VERITAS: a survey with an exposure of 0
VERITAS: a survey with an exposure of 0.1 Crab unit, there is no significant signal was found in the direction of MGRO J
VERITAS: a deeper survey of 0.01 Crab unit, some faint sources are found in this region.

14. Median energy Median energy (for α=-2.6) is from 0.56 ~2.2 TeV
Lower than Milagro (left)
Aktins, ApJ,608:680,2004

15. upper limits for a=-2.6 95% Upper limits: 10.5%~57% Crab units
95% upper limit was set
by Milagro at 27.5% Crab units
for a=-2.6
(Aktins,ApJ,608:680,2004)

16. 4. Summary
The cumulative sensitivity of ARGO-YBJ is 30% Crab unit and 4 known TeV sources is observed with significance greater than 5 s.d..
The flux of MGRO J is much higher than that determined by IACT. The reason of the large discrepancy in the fluxes is still unclear.
No signal from MGRO J The upper limit of MGRO J is lower than the flux determined by Milagro. This discrepancy might indicate a very rapid variation in the ϫ ray flux of the source.
We set the lowest upper limit for every point in the Northern sky

17. Thanks for your attention!