Gamma Astronomy with the ARGOYBJ experiment"

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Gamma Astronomy with the ARGO-YBJ experiment"

• G. Marsella
• Università del Salento and INFN Lecce - Italy
• on behalf of ARGO-YBJ Collaboration

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Outline

• Detector features and performances
• Moon and Sun shadows
• ?-astronomy
• Conclusions

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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.
DEttorre Piazzoli Prof. Cao Zhen
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Tibet 4300 m a.s.l.
High Altitude Cosmic Ray Laboratory _at_
YangBaJing (Site Coordinates longitude 90 31
50 E, latitude 30 06 38 N)
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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

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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
RPC
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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
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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 (-10lt? lt70)

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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
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• 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
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• Moon Shadow

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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
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Moon Shadow
E50 2 TeV Emode 0.5 TeV (for protons)
Nstr gt 40 ? lt 50
Sample 2007 day 347 - 2008 day 229 (802 h)
ns 26
ns 26
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Moon Shadow
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Moon Shadow analysis
The displacement towards West is due to the
Earths Magnetic Field
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Sun shadow
2007 day 347 - 2008 day 229 (954 h)
25s
All triggered events
Nstr gt 40 ? lt 50
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• ?-astronomy

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?-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 ?-rays is about 2 times larger
  than protons one at fixed energy

NO additional ?/hadron discrimination algorithms
have been yet applied (Qf 1.5 1.8 with
topology-based algorithms)
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Crab

• From 2007 day 347 to 2008 day 357
• observation time 2186.7 h
• (equivalent time 341.7 days -gt 91 Duty Cycle)

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Event selection No Cut nhit gt 60 ? 1.0
Preliminary
7.0 s
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Crab
Event selection No Cut
nhit gt 40 w 1.2
nhit gt 60 w 1.0
nhit gt 100 w 0.7
nhit gt 200 w 0.6
nhit gt 300 w 0.5
nhit gt 500 w 0.5
Preliminary
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Quality Cuts on conical fit Event selection
nhit gt 60 ? 1.0
Preliminary
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Mrk421 all data

• From 2007 day 347 to 2008 day 357
  308.0 days ? lt 40?

nhit gt 40 w 1.2
nhit gt 60 w 1.0
nhit gt 100 w 0.7
nhit gt 300 w 0.5
nhit gt 200 w 0.6
No event selection
Preliminary
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Mrk 421 X rays
RXTE
Count/s
1 day average
Count/s
10 days average
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Mrk421 Flaring state

• From 2008 day 37-191
  131.2 days ? lt 40?

nhit gt 40 w 1.2
nhit gt 60 w 1.0
nhit gt 100 w 0.7
nhit gt 300 w 0.5
nhit gt 200 w 0.6
No event selection
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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
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obs. time ? 42 hours
min. PAD multiplicity
NPAD gt 100
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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. ? lt
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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Conclusions

• ARGO-YBJ detector has been completely installed
• Data taking with duty cycle gt 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 _at_ TeV energies in the
declination band -10lt ? lt70