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

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

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%

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

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

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

3. Result 4 sources with significance larger than 5 sigma: Crab (17.9σ) , Mrk421 (13.2σ), MRGOJ1908+06 (5.8σ), MGRO J2031+41/TeV J2032 +4130 (6.3σ) After large scale anisotropy removed latitude ±5º σ=0.99 Mean=0.0065 Mean 0.006 RMS 0.99

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.

ARGO-YBJ result MGRO J2031+41/TeV J2032 +4130 MRGOJ1908+06 (see Vernetto, S.’s talk ) MGRO J2031+41/TeV J2032 +4130 No signal from MGRO J2019+37

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!

Estimates of Systematic error for SED of Crab Nebula Origin flux index G4argo vs Data: 6.08% … variability of trigger rate 3.43% (RMS/mean) … Time resolution 11.22%(1.4-2.6ns) 0.040 Data selection 2.16% 0.098 Pointing error(0.3degree) 4.30% 0.054 anisotropy correction <0.7sigma … Different methods 0.495sigma ?? Others ???? Total 16.5% 0.1 (3°-5°) humped up background: 25% overestimated Not enough to understand the discrepancy

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.

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 J2019+37 VERITAS: a deeper survey of 0.01 Crab unit, some faint sources are found in this region.

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

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)

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 J2031+41 is much higher than that determined by IACT. The reason of the large discrepancy in the fluxes is still unclear. No signal from MGRO J2019+37. The upper limit of MGRO J2019+37 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

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