Detection of Gamma Rays with the LHAASO Experiment › ... › LHAASO_gamma_Taiwan.pdf · Physics...

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