1. “Gamma Astronomy with the ARGO-YBJ experiment"
G. Marsella
Università del Salento and INFN Lecce - Italy
on behalf of ARGO-YBJ Collaboration
19/09/2018
XLIVth Rencontres de Moriond 2009, La Thuile - Italy

2. XLIVth Rencontres de Moriond 2009, La Thuile - Italy
Outline
Detector features and performances
Moon and Sun shadows
γ-astronomy
Conclusions
19/09/2018
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
19/09/2018
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)
19/09/2018
XLIVth Rencontres de Moriond 2009, La Thuile - Italy

5. 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
Tibet ASγ
ARGO
The Yangbajing Cosmic Ray Laboratory
19/09/2018
XLIVth Rencontres de Moriond 2009, La Thuile - Italy

6. Read-out of the charge induced on “Big-Pads”
12 RPC =1 Cluster
( 5.7 ´ 7.6 m2 )
78 m
99 m
74 m
111 m
Layer of RPC covering 5600 m2
(  92% active surface)
+ 0.5 cm lead converter
+ sampling guard-ring
Central Carpet:
130 Clusters
1560 RPCs
Strips
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
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XLIVth Rencontres de Moriond 2009, La Thuile - Italy
RPC

7. XLIVth Rencontres de Moriond 2009, La Thuile - Italy
Operation modes
Shower mode
Detection of Extensive Air Showers (direction, size, core …)
Trigger : minimum number of fired pads within 420 ns
³ 20 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
Experimental hall
VHE astronomy (range : few hundreds GeV – few tens TeV) oppure (range : 300 GeV – 10 TeV)
Search for GRB’s (full GeV / TeV energy range)
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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°)
19/09/2018
XLIVth Rencontres de Moriond 2009, La Thuile - Italy

9. ARGO-YBJ performances
Number of Fired Strips
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
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XLIVth Rencontres de Moriond 2009, La Thuile - Italy

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

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

12. XLIVth Rencontres de Moriond 2009, La Thuile - Italy
Moon Shadow
The largest signal: a “negative” source... The Moon shadow on cosmic rays
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
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XLIVth Rencontres de Moriond 2009, La Thuile - Italy

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

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

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

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

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

18. (Qf ≈ 1.5 – 1.8 with topology-based algorithms)
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)
The CR 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)
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XLIVth Rencontres de Moriond 2009, La Thuile - Italy

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

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

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

22. Preliminary Quality Cuts on conical fit
Event selection nhit > 60 ω = 1.0°
Preliminary
19/09/2018
XLIVth Rencontres de Moriond 2009, La Thuile - Italy

23. XLIVth Rencontres de Moriond 2009, La Thuile - Italy
Mrk421 – all data
From day to day days  < 40
nhit > 40 w= 1.2°
nhit > 60 w= 1.0°
nhit > w= 0.7°
nhit > w= 0.6°
nhit > w= 0.5°
No event selection
Preliminary
19/09/2018
XLIVth Rencontres de Moriond 2009, La Thuile - Italy

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

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

26. Mrk 421 Observation of a flare period 10 days: 86-95
Flux  Crab
Day 86-95:
Flux  3 Crab
events/day
10 days
130 days 10
obs. time  42 hours
min. PAD multiplicity
NPAD > 100
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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 – June (ARGO f.o.v.: θ < 45°)
No excess observed
Fluence upper limits down to 10-5 erg/cm2
(E = 1 – 100 GeV)
[T. Di Girolamo et al., European Cosmic Ray Simposium 2008]
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XLIVth Rencontres de Moriond 2009, La Thuile - Italy

28. XLIVth Rencontres de Moriond 2009, La Thuile - Italy
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 TeV energies in the
declination band -10°<  <70°
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XLIVth Rencontres de Moriond 2009, La Thuile - Italy