1. 32 nd ICRC –Beijing – August 11-18, 2011 Silvia Vernetto IFSI-INAF Torino, ITALY On behalf of the ARGO-YBJ collaboration Observation of MGRO J1908+06 with ARGO-YBJ

2. Tibet ASγ ARGO The Yangbajing Cosmic Ray Laboratory Longitude 90° 31’ 50” East Latitude 30° 06’ 38” North 4300 m a.s.l.

3. Resistive Plate Chambers carpet

4. The ARGO-YBJ detector  Central carpet 78 x 75 m 2 (95 % of active surface)  Sampling ring surrounds the carpet up to 111 x 99 m 2 (20 % of active surface) Single layer of RPCs detectors The PAD (56  62 cm 2 ) is the space-time “pixel” Time resolution  1-2 ns ARGO has 18480 PADs

5. The ARGO-YBJ detector  Central carpet 78 x 75 m 2 (95 % of active surface)  Sampling ring surrounds the carpet up to 111 x 99 m 2 (20 % of active surface) The PAD (56  62 cm 2 ) is the space-time “pixel” Time resolution  1 ns ARGO has 18480 PADs Single layer of RPCs detectors

6. Duty cycle 86%  First data in July 2006  Full detector in stable data taking since November 2007  Trigger: Number of fired pad N pad > 20  Rate ~3.5 kHz - Dead time 4%  220 GB/day transferred to IHEP/CNAF data centers

7.  Shower core reconstruction Maximum Likelihood Method applied to the lateral density profile of the shower  Fit of the shower front Primary direction EAS data Space and time coordinates of the fired PADs

8. The Moon shadow An important tool to check the detector performances Deficit: 71 standard deviations  9 standard deviations /month Physics: antiproton / proton ratio in cosmic rays

9. Displacement of the shadow due to the Geomagnetic field Bending  1.57° Z / E (TeV) The Moon Shadow Angular resolution Energy calibration Error of energy scale < 13%

10. HST Crab Nebula dN/dE =(3.0 ± 0.3) 10 -11 E –  ± 0.09 ph sec -1 cm -2 TeV -1 3 years data

11. Mrk421 TeV  rays ARGO X- rays 2-12 KeV RXTE/AMS X –rays 15-30 KeV SWIFT/BAT Active periods Data sample: Nov 2007 – Feb 2011 Correlation with X rays Cumulative counting rate > 12 s.d.

12. MGRO J1908+06 discovered by MILAGRO MILAGRO Galactic plane survey, Abdo et al. 2007 2000-2006 data Median energy  20 TeV ARGO see poster by Chen S.Z. MGRO J1908+06 Flux  80% Crab Extended source with extension < 2.6 deg Cygnus region

13. MGRO J1908+06 confirmed by HESS Extension  0.34 ±0.04° HESS spectrum dN/dE = 4.14 10 -12 E -2.1 sec -1 cm -2 TeV -1 Aharonian et al., 2009

14. Fermi pulsar PSR J1907+0602 Abdo et al. 2010 Pulsar period 106.6 ms HESS Nebula flux FERMI upper limits to the nebula flux (pulsar off) FERMI pulsar

15. MGRO J1908+06 spectrum Disagreement between HESS and MILAGRO spectra  8  HESS HESS spectrum: Aharonian et al., 2009 dN/dE = 4.14 10 -12 E -2.1 sec -1 cm -2 TeV -1 Milagro spectrum: Smith et al., 2009 dN/dE = 6.2 10 -12 E -1.5 exp(-E/14.1) sec -1 cm -2 TeV -1 MILAGRO

16. ARGO data and analysis  From November 2007 to February 2011 (5358 observation hours)  Events zenith angle < 45°  Source culmination zenith angle = 24°  Source observation time = 5.4 hours /day  Events with N pad > 40  No gamma/hadron discrimination  Background evaluation : time swapping method  4 N pad intervals: 40 – 100 – 300 – 1000

17. Assuming a bidimensional Gauss shape In agreement with HESS  MGRO J1908+06 extension c Events Significance map Map centered on the HESS source Integral angular distribution Found extension:  = 0.50   0.35  N pad > 40

18. MGRO J1908+06 spectrum … but it is  3 times larger than the HESS one dN/dE =(2.2 ± 0.4) 10 -13 (E/7 TeV) –  ± 0.3 ph sec -1 cm -2 TeV -1 The ARGO flux is in agreement with MILAGRO… Systematic errors < 30%

19. . Possible causes of disagreement 1) Statistical fluctuation ? 2) Complex morphology or contribution from other sources ? 3) Contribution by the diffuse galactic gamma ray flux (< 20%) 4) Variable flux ? No, because of the extension d > 40 pc variability time scale > 130 years The problem is still open…

20. Backup slides

21. Determination of the flux and extension The observed extension is determined by  Intrinsic source extension  Detector PSF (that depends on the energy) But to evaluate the spectrum one should know the extension Iterative procedure

22. Determination of the flux and extension Iterative procedure:  Assumed a power low spectrum with slope  = 2.5  MC: evaluation of the PSF  Data: determination of the intrinsic extension ( fitting the angular distribution of events)  MC: evaluation of the best opening angles  Data: determination of the spectrum slope ( fitting the event rates vs. nhit) After a few iterations the procedure converges