“Gamma Astronomy with the ARGO-YBJ experiment"

1. “Gamma Astronomy with the ARGO-YBJ experiment" G. Marsella Università del Salento and INFN Lecce - Italy on behalf of ARGO-YBJ Collaboration XLIVth Rencontres de Moriond 2009, La Thuile - Italy

2. Outline • Detector features and performances • Moon and Sun shadows • γ-astronomy • Conclusions XLIVth Rencontres de Moriond 2009, La Thuile - Italy

3. ARGO-YBJ collaboration INFN and Università del Salento IHEP, Beijing INFN and Università “Federico II” di Napoli Shandong University,Jinan INFN Catania, Univ. and INAF/IASF di Palermo South West Jaotong Univ., Chengdu INFN and Università di Pavia Tibet University, Lhasa INFN and Università “Tor Vergata” di Roma Yunnan University, Kunming INFN and Università “Roma Tre” di Roma Zhengzhou University INFN and INAF/IFSI di Torino Hongkong University Spokesmen Prof. B. D’Ettorre Piazzoli Prof. Cao Zhen XLIVth Rencontres de Moriond 2009, La Thuile - Italy

4. Tibet 4300 m a.s.l. High Altitude Cosmic Ray Laboratory @ YangBaJing (Site Coordinates: longitude 90° 31’ 50” E, latitude 30° 06’ 38” N) XLIVth Rencontres de Moriond 2009, La Thuile - Italy

5. The Yangbajing Cosmic Ray Laboratory ARGO Tibet ASγ The ARGO-YBJ experiment An Extensive Air Shower detector exploiting the full coverage approach at very high altitude, with the aim of studying • VHE g-Ray Astronomy • Gamma Ray Burst Physics • Cosmic Ray Physics XLIVth Rencontres de Moriond 2009, La Thuile - Italy

6. 12 RPC =1 Cluster ( 5.7 ´ 7.6 m2 ) 99 m 74 m Central Carpet: 130 Clusters 1560 RPCs 124800 Strips 78 m 111 m Layer of RPC covering 5600 m2 (  92% active surface) + 0.5 cm lead converter + sampling guard-ring 8 Strips = 1 Pad (56 ´ 62 cm2) 10 Pads = 1 RPC (2.80 ´ 1.25 m2) Gas Mixture: Ar/ Iso/TFE = 15/10/75, HV = 7200 V BIG PAD Read-out of the charge induced on “Big-Pads” ADC XLIVth Rencontres de Moriond 2009, La Thuile - Italy RPC

7. Operation modes Shower mode Detection of Extensive Air Showers (direction, size, core …) Trigger : minimum number of fired pads within 420 ns ³20 fired pads on the central carpet: rate ~4 kHz Aims : cosmic-ray physics (threshold : ~1 TeV) VHE g-astronomy (threshold ~300 GeV) gamma-ray bursts Scaler mode counting rates ( ³ 1, ³ 2, ³ 3, ³ 4 coincidences) for each cluster Aims: detector and environment monitor transient phenomena (GRB, solar flares) with a threshold of few GeV XLIVth Rencontres de Moriond 2009, La Thuile - Italy

8. Main detector features and performance • Active element: Resistive Plate Chamber  time resolution 1 ns • Time information from Pad (56 x 62 cm2) • Space information from Strip (6.5 x 62 cm2) • Full coverage and large area ( 10,000 m2) • High altitude (4300 m a.s.l.) • ▼ • good pointing accuracy (≤0.5°) • detailed space-time image of the shower front • capability of small shower detection ( low E threshold) • Field of view (~2 sr) and high “duty-cycle” (~100%) •  continuous monitoring of the sky (-10°< <70°) XLIVth Rencontres de Moriond 2009, La Thuile - Italy

9. Number of Fired Strips ARGO-YBJ performances The number of pixels, the time resolution and the full coverage of the central carpet allow to reconstruct the shower with unprecedented details The detailed shower topology allows g/h discrimination XLIVth Rencontres de Moriond 2009, La Thuile - Italy

10. meters meters High space/time granularity (different topologies and time structures) •  Deeply inspects a wide and possibly unexpected EAS phenomenology. Same trigger: two showers Conical shape High energy Conical shape in small shower XLIVth Rencontres de Moriond 2009, La Thuile - Italy

11. Moon Shadow XLIVth Rencontres de Moriond 2009, La Thuile - Italy

12. The largest signal: a “negative” source...The Moon shadow on cosmic rays Moon Shadow A powerful tool to check the detector : • Size of the deficit  angular resolution • Position  pointing accuracy • West displacement  Energy calibration Geomagnetic bending  1.6° / E (TeV) towards West Physics:antiproton / proton ratio in cosmic rays XLIVth Rencontres de Moriond 2009, La Thuile - Italy

13. Moon Shadow E50 ≈ 2 TeV Emode ≈ 0.5 TeV (for protons) Nstr > 40 θ < 50° Sample 2007 day 347 - 2008 day 229 (802 h) ns ≈ 26 ns ≈ 26 XLIVth Rencontres de Moriond 2009, La Thuile - Italy

14. Nstr > 40 Nstr > 60 Nstr > 100 Nstr > 300 Moon Shadow XLIVth Rencontres de Moriond 2009, La Thuile - Italy

15. Moon Shadow analysis The displacement towards West is due to the Earth’s Magnetic Field XLIVth Rencontres de Moriond 2009, La Thuile - Italy

16. Sun shadow 2007 day 347 - 2008 day 229 (954 h) ≈25σ All triggered events Nstr > 40 θ < 50° XLIVth Rencontres de Moriond 2009, La Thuile - Italy

17. γ-astronomy XLIVth Rencontres de Moriond 2009, La Thuile - Italy

18. γ-ray astronomy • In this preliminary analysis • All events are considered without any internal shower selection • No lead converter on the RPC carpet (with Pb the ang. resol. improves by about 50% at TeV energies) • TheCR background rejection is performed by exploiting • the good angular resolution of the detector • the fact that at very high altitude the trigger efficiency of TeV γ-rays is about 2 times larger than protons one at fixed energy NO additional γ/hadron discrimination algorithms have been yet applied (Qf ≈ 1.5 – 1.8 with topology-based algorithms) XLIVth Rencontres de Moriond 2009, La Thuile - Italy

19. Crab • From 2007 day 347 to 2008 day 357 • observation time: 2186.7 h (equivalent time: 341.7 days -> 91% Duty Cycle) XLIVth Rencontres de Moriond 2009, La Thuile - Italy

20. Event selection: No Cut nhit > 60 ω= 1.0° Preliminary 7.0 σ XLIVth Rencontres de Moriond 2009, La Thuile - Italy

21. Event selection: No Cut Crab nhit > 40 w= 1.2° nhit > 100 w= 0.7° nhit > 60 w= 1.0° nhit > 200 w= 0.6° nhit > 300 w= 0.5° nhit > 500 w= 0.5° Preliminary XLIVth Rencontres de Moriond 2009, La Thuile - Italy

22. Quality Cuts on conical fit Event selection nhit > 60 ω= 1.0° Preliminary XLIVth Rencontres de Moriond 2009, La Thuile - Italy

23. Mrk421 – all data • From 2007 day 347 to 2008 day 357 308.0 days < 40 nhit > 40 w= 1.2° nhit > 60 w= 1.0° nhit > 100 w= 0.7° nhit > 200 w= 0.6° nhit > 300 w= 0.5° No event selection Preliminary XLIVth Rencontres de Moriond 2009, La Thuile - Italy

24. Mrk 421 X rays RXTE Count/s 1 day average Count/s 10 days average XLIVth Rencontres de Moriond 2009, La Thuile - Italy

25. Mrk421 – Flaring state • From 2008 day 37-191 131.2 days < 40 nhit > 40 w= 1.2° nhit > 60 w= 1.0° nhit > 100 w= 0.7° nhit > 200 w= 0.6° nhit > 300 w= 0.5° No event selection XLIVth Rencontres de Moriond 2009, La Thuile - Italy

26. Mrk 421 Observation of a flare period 10 days: 86-95 Day 1-130: Flux  Crab Day 86-95: Flux  3 Crab events/day 10 days 130 days 10 obs. time  42 hours min. PAD multiplicity NPAD > 100 XLIVth Rencontres de Moriond 2009, La Thuile - Italy

27. Search for GRBs in Scaler Mode GRBs are observable as a statistically significant excess of events in coincidence with a satellite event No arrival direction measurement 39 GRBs observed by satellites (mainly SWIFT) Dec. 2004 – June 2008(ARGO f.o.v.: θ < 45°) No excess observed Fluence upper limits down to10-5 erg/cm2 (E = 1 – 100 GeV) [T. Di Girolamo et al., European Cosmic Ray Simposium 2008] XLIVth Rencontres de Moriond 2009, La Thuile - Italy

28. Conclusions • ARGO-YBJ detector has been completely installed • Data taking with duty cycle > 95% since Dec 2007 • Results from first data: • Moon and Solar shadows observed • Mrk421 flare observed in 2006 and 2008 flares • Crab Nebula observed at ~ 7 s.d. Sky survey going on • Upper limits to GRBs flux at VHE range • Next future: • Optimize the reconstruction • Gamma-hadron discrimination • Sky Map and VHE Gamma sources monitoring and search ARGO-YBJ is a unique device for a continuous monitoring of the sky @ TeV energies in the declination band -10°<  <70° XLIVth Rencontres de Moriond 2009, La Thuile - Italy