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Detection of Gamma Rays with the LHAASO Experiment
Zhen Cao
IHEP, Beijing
VHEPA2015 Taipei 4/2015
Outline
LHAASO & Gamma Ray Detectors
Physics & Competition
Gamma/Proton Discrimination
Performances
On Flares & Extended sources
On Known & Unknown Sources
Summary
LHAASO site
LHAASO for Gamma Astronomy • Two Gamma Ray Astronomic Devices
– A Wide FOV Survey Facility
– A Spectrometer for Interesting Sources
+ WCDA
KM2A
1-km2 Array: Plus scintillator detectors every 15 m
and –detectors every 30 m
Water Cherenkov
Detector
90,000 m2
Electromagnetic Particle Detector (ED)
1 2
3 4
15 m 15 m 15 m
ED Specifications Item Value
Effective area 1 m2
Thickness of tiles 2 cm
Number of WLS fibers 8/tile16 tile
Detection efficiency (> 5 MeV) >95%
Dynamic range 1-10,000 particles
Time resolution <2 ns
Particle counting resolution 25% @ 1 particle 5% @ 10,000 particles
Aging >10 years
Spacing 15 m
Total number of detectors 5635
Muon Detector (MD) 2.5
m
1.2
m
PMT: 8” or 9”
LDPE LDPE
PP
tyvek
MD Specifications
Item Value
Area 36 m2
Depth 1.2 m
Molasses overburden 2.5 m
Water transparency (att. len.) > 30 m (400 nm)
Reflection coefficient >95%
Time resolution <10 ns
Particle counting resolution 25% @ 1 particle 5% @ 10,000 particles
Aging >10 years
Spacing 30 m
Total number of detectors 1221
WCDA
WCDA Specifications
Item Value
Cell area 25 m2
Effective water depth 4 m
Water transparency > 20 m (400 nm)
Precision of time measurement 0.5 ns
Dynamic range 1-4000 PEs
Time resolution <2 ns
Charge resolution 40% @ 1 PE 5% @ 4000 PEs
Accuracy of charge calibration <2%
Accuracy of time calibration <0.2 ns
Total area 90,000 m2
Total cells 3600
Gamma/proton Discrimination – KM2A
nHit log10(E) GeV Q-factor
20-30 3.60 2.67
30-45 3.87 5.62
45-65 4.12 11.9
65-90 4.35 20.7
90-120 4.55 46.4
120-180 4.76 86.6
180-260 5.03 backgroud free
260-360 5.28 backgroud free
360-500 5.53 backgroud free
500-700 5.82 backgroud free
700-1000 6.11 backgroud free
Gamma/proton Discrimination - WCDA
Proton Gamma
Brightest “sub-core”:
Signal of the brightest PMT outside the shower core region (e.g., 45 m);
“Compactness” can be employed to reject cosmic ray background efficiently.
Effective Area
KM2A
WCDA
Angular Resolution
KM2A
WCDA
Energy Resolution
Down trend: effect of
the trigger threshold
Take notice that KM2A can reach the background free above 100 TeV, so the spectrum can be well measured…
WCDA aims to be well calibrated, so that the spectrum can be well fitted if assuming it obeys a power law…
Integral Sensitivity
KM2A WCDA
Map and
number of
the γ ray
sources
147 sources FERMI
Catalog
releasing
HESS
Switched on
MAGIC
Switched on
Two directions
1. Survey for more sources
2. Deep study on interesting sources:
spectroscopy & morphology
A. 34 Pulsar
Wind Nebula
A&A 548, A46 (2012)
Evolution Spatial drifting
Standard
Candle Crab
Nebula
RXJ 1713.7-3946 Morphology is important, Spectroscopy is even more!
B. 23 SNRs
(Shell or Composite w/clouds)
SNRs
Science 339, 807 (2013)
Young SNRs
Old SNRs
CR sources?
GeV&TeV~ dominated by π0 decay
(2)W51C:
a "mixed-morphology" type of SNR, shocked atomic and molecular gases show the
interaction between shock and molecular.
W51C
Age=30kyr
D~4.3kpc W51C
~3%Crab
reference~ APJ, 761:133(2012) &&
Mon.Not.R.Astron.Soc, 421,935-942(2012)
(4) W41(southern sky)
reference~ APJ, 761:133(2012) &&
Mon.Not.R.Astron.Soc, 421,935-942(2012)
The most active region in the northern sky
C. Big objects (regions) in the sky
Cygnus Cocoon (FERMI Cocoon)
FERMI Cocoon
ARGO J3031+4157
The first γ ray Superbubble
it is too big to IACT
Could be a possible hadronic
source w/ total hadronic energy of
1.5x1050 erg,Ecut=150TeV
To be submitted to ApJ
Science 334, 1103 (2011)
7.6
kpc
42°
LHAASO FOV
D. Galactic plane diffuse gamma-ray
Diffuse gamma rays produced by interactions of cosmic rays with the interstellar medium and radiation fields. They can be used to probe the cosmic ray spectrum and density throughout the whole Galaxy.
Inverse Compton p0-decay
Bremsstrahlung
Diffuse γ rays: EGRET, FERMI,
ARGO-YBJ and MILAGRO
From 30MeV to 20TeV, traces CR propagation well.
To be submitted to ApJ
Cygnus region
Sensitivity to Extended Sources
MGRO J1908+06 spectrum – can be measured well by KM2A, under assumption of different cutoff values. (Xinhua Ma et al., APP, 2014)
Sensitivity of WCDA to
extended sources as a function
of size. The angular bin is
optimized for the WCDA only.
67 of 148 known TeVCat sources are in the LHAASO FOV;
For a very simple estimation, the EBL absorption and the spectrum cut-off is ignored;
80% of these sources can be detected by LHAASO in 1-2 year’s operation.
TeVCat Sources
E. AGNs
Different models will predict different correlations between low and
high energy components. Thus, long-term continuously multi-
wavelength observations, especially at X-ray and TeV band,
are crucial to understand the emission mechanisms and underline
processes of the outbursts.
?
Leptonic SSC,
EC? Hadronic?
Transient AGNs: Mrk421
Survey of
transient AGNs
The evolution
of the Spectrum
during flares
IGMF measurement
Emitting Mechanism
2011flare of
Mrk501
S=7.7σ
SSC is good for steady emission
It is not easy to fit the spectrum during flare
ApJ 758:2(2012)
Mrk 501
Extra-galactic CR accelerators
From Gianfranco Brunetti, IRA , INAF
Galaxy Clusters ~ 100Mpc G. Vannoni, F. A. Aharonian, S. Gabici, S. R. Kelner, and A. Prosekin, A&A 536, A56 (2011)
Proton can be accelerated up
to 1019eV
P+CMB ->e+e-
Detectable x-ray and
γ-Ray spectrum
CTA
LHAASO
Sensitivity to Flares / GRBs - WCDA
Requirements:
30 events;
5 s.d.;
Calculation based on a power law spectrum (=-2.62).
Partly limited by statistics.
Duration Sensitivity (Crab)
1 year 0.0066
6 months 0.0094
3 months 0.013
1 month 0.039
10 days 0.10
3 days 0.36
1 day 1.0
2 hours 3.5
1 hour 5.4
30 minutes 13
10 minutes 67
3 minutes 410
1 minute 2100
3 days’ flare
Physics not only for Gamma Astronomy
VHE gamma sky survey (100 GeV-1 PeV): Galactic sources; Extragalactic sources & flares; VHE emission from Gamma Ray Bursts; Diffused Gamma rays.
Spectrum measurement at the high end: Nature of the acceleration: leptonic or hadronic; Origin of cosmic rays – 100 years’ mystery.
Cosmic rays Anisotropy of VHE cosmic rays; Cosmic electrons / positrons;
Miscellaneous: Gamma rays from dark matter; Sun storm & IMF.
A Clear Break of the Spectrum at (640±87) TeV
~6σ deviation from the single-index power law spectral index is >3.3 above the knee LHAASO-prototype + ARGO-YBJ
Ass. H:He = 1:1
118 35
9
21
64
Status of LHAASO
LHAASO has been included in the roadmap of the infrastructure construction for basic science in a short term (5 years). Total 16 projects are included.
• The local government has approved the LHAASO site in August with the local funding for infrastructures.
• Geo survey is done last month
• Civil construction design is started for both field preparation and buildings
environment impact evaluation and feasibility reviewing are started by professional teams
The detector designers are finishing the TDR report based on the Engineering arrays at scales of 1% of the full project done at ARGO-YBJ site in Tibet
Construction is expected to start this year
The Site Precipitation: 600~700 mm, >80% of it is in June, July and August
迪庆
新都桥
羊八井
稻城
玉树
Geo Location:Near S217, in the Haizishan Reservation N2921’30.7”,E100 08’14.65” 4400 A.S.L. Chengdu: 708km Litang: 98km Daocheng: 50km (living base @3700m) 稻城亚丁机场
4410m
LHAASO 4410m
Configuration and Schedule
¼阵列建成
物理运行
大门
44
Detector R/D: 1.5yr Electronics R/D: 2 yr Production: 1.5 yr DAQ R/D 0.5 yr Deployment: 4 yr 1%prototype Oper: 1 yr ¼ operation: 2 yr
Time Schedule now
Deployment
¼
operation
LHAASO construction (month)
Civil construction 24
Detector production 36
Deployment 36
¼ operation 28
Full operation 2
高能所
清华大学
北京大学
河北师范大学 山东大学
南开大学
云南天文台
云南大学
西南交通大学
西藏大学
中国科技大学
南京大学
国家天文台
LHAASO
大气所
Domestic Collaboration
20 institutions
四川大学
广西大学
紫金山天文台
空间中心
International collaboration France:IPNO
OMEGA
U. Montpellier
Italy:U. Rome I, II, III
U. Torino
U. Naples
Russia:RAS
INPR
Thailand:
成都分院:山地所
生物所
International Collaboration • Physicists (IPN-Orsay)
• Yingtao Chen (PhD student funded by CSC), Olivier Deligny, Isabelle Lhenry-Yvon, Tiina Suomijärvi, Francesco Salamida (post-doc)
• New PhD student, Zizhao Zong, currently applying funds from CSC
• Technical group
• Valérie Chambert, Bengyun Ky, Emmanuel Rauly, Thi Nguyen Trung, Eric Wanlin (IPN-Orsay)
• Gisèle Martin-Chassard, Frederic Dulucq, Christophe de la Taille (OMEGA)
• CAS Project for the China-France collaboration is
approved (1.1 M CNY) this year
• Italian colleagues are proposing for G-astro, GRBs,DM,CRs
(submitting to INFN)
• Working group with Russian for neutron detectors
• Thailand solar CR group (working together)
ASIC appl.
Summary LHAASO construction is going to be started next
year at Haizishan, Sichuan Province;
Two detector arrays (KM2A & WCDA) of the LHAASO project will mainly focus on Gamma astronomy;
The sensitivity of the two arrays can reach to 1% Crab flux at ~1 TeV and ~100 TeV, respectively;
LHAASO will play an important role in surveying, detecting, observing and measuring various VHE Gamma ray sources.
VHE -astronomy: Two Techniques IACTs: H.E.S.S., VERITAS, MAGIC, …
Good angular resolution (~0.1); Fair background rejection power; Short duty cycle (~10%); Narrow FOV (<5); Low energy threshold (~100 GeV);
Mainly focused on deep observation.
Ground particle array: AS, ARGO-YBJ, Milagro, HAWC, … Not-so-good angular resolution (~0.5); Poor background rejection power (but much elaborated in water Cherenkov); Full duty cycle (>95%,~10 IACT); Wide FOV(>2/3p,~150 IACT); High energy threshold improved by construction at high altitude (~1 TeV);
Good at sky survey, extended sources and flares.
Instrumentation History
2007
1980 Whipple (0.2 Crab)
Crab detected!
VERITAS (0.008 Crab)
ARGO-YBJ (0.6 Crab)
Tibet-AS (1.5 Crab)
Milagro (0.9 Crab)
2014
2015 HAWC 0.06 Crab
2004 H.E.S.S. (0.008 Crab)
MAGIC (0.02 Crab)
2009
2001
1989
CTA (0.001 Crab)
LHAASO (0.01 Crab)
IACTs are typically 10 better in sensitivity, gained from the lower energy threshold (stat.)
~150 Sources observed ~10 Sources
2018?
HEGRA, CANGAROO, CAT … 0.04 Crab
10 years delay!
AS+MD 0.06 Crab
KM2A:
5635 EDs
1221 MDs
WCDA:
3600 cells
90,000 m2
WFCTA:
24 telescopes
1024 pixels each
SCDA:
452 detectors
Gamma Ray Detectors
KM2A-MD
KM2A-ED
WCDA
Layout of the Detectors
1.2
7 k
m
Location: Haizishan (Lakes Mountain)
Beijing
Chengdu
Haizishan
Location: 2921’30.7”N, 10008’14.7”E; 4407 m a.s.l; 8 km to airport; 50 km to Daocheng City, Sichuan Province.
Fermi-LAT Sources Yi Zhao et al., RAA, 2014
101 AGN sources with known redshift and z < 0.5 from 2nd catalogue of Fermi-LAT;
5 EBL models adopted for the absorption of Gamma rays, but no cutoff is applied;
20-30 sources could be observed by LHAASO in several years’ operation.
Kifune’s plot: new detectors on TeV Gamma rays are awaited to keep the discovery pace. The LHAASO detectors will do help.
Can the number of sources climb to ~1000 by 2020?
Unknown TeV Sources
LHAASO