Gamma-Ray Astronomy with the ARGO-YBJ experiment G. Di Sciascio INFN – Sez. Roma “TorVergata” On behalf of ARGO-YBJ Collaboration 5th AGILE Workshop 2008 – Frascati, June 12-13, 2008

G. Di Sciascio 5th Agile Workshop Why is this talk relevant to AGILE/GLAST ? ARGO detects air-shower particles at ground level wide field of view gamma-ray telescope which operates in “scanning mode”ARGO is a wide field of view gamma-ray telescope which operates in “scanning mode” ARGO is optimized to work with showers induced by primaries of energy E > a few hundreds GeV Excellent complement to AGILE/GLAST to extend satellite measurements at > 100 GeV This low energy threshold is achieved by:  operating at very high altitude (4300 m asl)  using a “full coverage” detection surface

G. Di Sciascio 5th Agile Workshop Longitude 90° 31’ 50” East Latitude 30° 06’ 38” North 90 Km North from Lhasa (Tibet) An Extensive Air Shower detector exploiting the full coverage approach at very high altitude, with the aim of studying The ARGO-YBJ experiment Tibet AS γ ARGO The Yangbajing Cosmic Ray Laboratory VHE  -Ray Astronomy Gamma Ray Burst Physics Cosmic Ray Physics 4300 m above the sea level

10 Pads = 1 RPC (2.80  1.25 m 2 ) Gas Mixture: Ar/ Iso/TFE = 15/10/75, HV = 7200 V 78 m 99 m74 m 111 m Layer of RPC covering  5600 m 2 (  92% active surface) cm lead converter + sampling guard-ring Central Carpet: 130 Clusters 1560 RPCs Strips BIG PAD ADC RPC Read-out of the charge induced on “Big-Pads” 12 RPC =1 Cluster ( 5.7  7.6 m 2 ) 8 Strips = 1 Pad (56  62 cm 2 )

G. Di Sciascio 5th Agile Workshop Operation Modes Aims: flaring phenomena (high energy tail of GRBs, solar flares) detector and environment monitor The counting rates (N hit ≥1, ≥2, ≥3, ≥4) for each cluster is recorded every 0.5 s, within 150 ns. Measured counting rate: ~40KHz, ~2KHz, ~300Hz, ~120Hz. No information on the arrival direction and spatial distribution of the detected particles. Threshold energy ≈ GeV. Scaler Mode:  Scaler Mode: Coincidence of different detector units (pads) within 420 ns Trigger : ≥ 20 fired pads on the central carpet (rate ~4 kHz) Detection of Extensive Air Showers (direction, size, core …) Aims: Cosmic Ray physics VHE γ-astronomy Shower Mode:  Shower Mode:

G. Di Sciascio 5th Agile Workshop First Results At present: Stable Data Taking since Nov (d.c. > 90%) with the full detector Central Carpet (130 Clusters) + Guard Ring highly fragmented and preliminary Despite the highly fragmented and preliminary data taking (up to Nov. 2007), some remarkable results are available in different items even with small duty-cycle due to very aggressive cuts applied to select “good” data The analyses presented here are based on data collected in the period July 2006-April These data were mainly used to calibrate and debug the detector and the DAQ. Moon Shadow Gamma ray sources High Energy GRBs p-air cross section Antip/p ratio measurement …

G. Di Sciascio 5th Agile Workshop The Moon Shadow Size of the deficit Position of the deficit Angular Resolution Pointing Error Geomagnetic Field: positively charged particles deflected towards the West and negatively charged particles towards the East. Ion spectrometer The observation of the Moon shadow can provide a direct check of the relation between size and primary energy Energy calibration Cosmic rays are hampered by the Moon Deficit of cosmic rays in the direction of the Moon Moon diameter ~0.5 deg

G. Di Sciascio 5th Agile Workshop Moon Shadow 2008 All triggered events N hit > 40 θ < 50° E 50 ≈ 1.8 TeV E mode ≈ 1 TeV (for protons) 2008: ~292 hours ≈16 σ ≈100 h/month ≈ 10 s.d./month

G. Di Sciascio 5th Agile Workshop Moon Shadow analysis Residual systematic shift towards North of about 0.2 deg The displacement towards West is due to the Earth’s Magnetic Field

G. Di Sciascio 5th Agile Workshop γ-ray astronomy In this preliminary analysis 1.All events are considered without any internal shower selection 2.No lead converter on the RPC carpet (with Pb the ang. resol. improves by about 50% at TeV energies) CR background rejection The CR background rejection is performed by exploiting angular resolution 1.the good angular resolution of the detector the trigger efficiency of TeV γ - rays is about 2 times larger than protons’ one 2.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 (Q f ≈ 1.5 – 1.8 with “topological”-based algorithms) Continuous monitoring of the sky in the declination band -10°<  <70°

G. Di Sciascio 5th Agile Workshop Crab Nebula 2007 E γ 50 ≈ 2.4 TeV, E γ mode ≈ 700 GeV N hit > 100 θ < 40° ARGO observed Crab Nebula at ≈6 σ in ≈ 40 days 5.8 hours/day ω = 1.5° 66% ev Preliminary “quality cuts” applied to optimize the signal based on: χ 2, R core, particle density Only Central Carpet in DAQ ≈6 σ δ (deg) R.a. (deg) Sky map The Crab days 25 – 110: 241 hours

G. Di Sciascio 5th Agile Workshop Crab Nebula 2008 Preliminary E γ 50 ≈ 2.4 TeV, E γ mode ≈ 700 GeV N hit > 100 θ < 40° NO “quality cuts” yet applied days 1 – 104: 450 hours Central Carpet + Guard Ring in DAQ ≈4 σ δ (deg) R.a. (deg) Sky map

G. Di Sciascio 5th Agile Workshop Mrk 421 ASM / RXTE Mrk 421: 2006 July 2006 ARGO started recording data with the full central carpet during the X-ray flare of Mrk421 in July The detector was in its commissioning phase, therefore new analyses are in progress to properly evaluate the statistical significance of the observation. Evidence for TeV emission in coincidence with the X-ray flare E γ 50 ~ 1.6 TeV, E γ mode ~ 500 GeV days ( 137 hours ) R.a. (deg) N pad > 60 ≈6σ≈6σ δ (deg)

G. Di Sciascio 5th Agile Workshop Feb. - April 2008 Mrk 421: 2008 Preliminary Evidence for TeV emission in coincidence with the X-ray flare E γ 50 ~ 1.6 TeV, E γ mode ~ 500 GeV Mrk 421 ASM / RXTE Deeper analysis and further data integration are in progress ≈6σ days ( 472 hours ) N pad > 60 R.a. (deg) δ (deg)

G. Di Sciascio 5th Agile Workshop Correlation with X-rays in 2008 N hit >100 days from 1/1/08 RXTE counting rate day average ev/hour ARGO RXTE Correlation ? maybe… E γ 50 ≈ 2.4 TeV, E γ mode ≈ 700 GeV Preliminary

G. Di Sciascio 5th Agile Workshop Search for GRBs with Scaler Mode The counting rates (N hit ≥1, ≥2, ≥3, ≥4) for each cluster is recorded every 0.5 s. The corresponding upper limits on the fluence are of the order of – erg/cm 2 in the 1 – 100 GeV range, well below the energy range explored by the present generation of Cherenkov telescopes. We expect ~1 EGRET-like GRB (with spectrum >200 MeV) to occur in the ARGO f.o.v. (θ < 45°) in 1 year. 38 GRBs triggered by satellites (mainly SWIFT) analized in the period Dec – March 2008 (ARGO f.o.v.: θ < 45°) NO excess observed No information on arrival direction Trigger by satellite is needed to detect a transient emission as a statistically significant and coincident excess of events over the uniform bkg due to CRs

G. Di Sciascio 5th Agile Workshop Conclusions Detector setup: The ARGO-YBJ detector has been completely installed Stable data taking since Nov (d.c. > 90%) with the full detector Lead plate installation during 2008 Results from preliminary analysis: Moon shadow observed at >9 s.d. level per month Preliminary antiproton/proton ratio measurement at ≈1 TeV Mrk421 flares observed in July-August 2006 and Feb-April 2008 at > 5 σ Crab Nebula observed in 2007 and 2008 at >4 σ in ≈ 50 days (no γ/h discrimination yet !!) Preliminary “Hot Spots” catalogue (>4σ) in preparation Search for high energy tail of GRBs in the GeV range in progress Inelastic p-air cross section measurements at √s ~ 0.1 TeV