Science with LSTs inCherenkov Telescope Array South
Takeshi Nakamori (Yamagata U)
for the CTA consortium
and Many thanks to the LST teamcredit : Gabriel Pérez Díaz

2/21CTA-South
cta-observatory.org

4 Large-Sized Telescopes
25 Medium-Sized Telescopes

Paranal, Chille

70 Small-Sized Telescopes(see Akiraʼs talk)credit : Gabriel Pérez Díaz

Large-Sized Telescope

Covers the lowest energy bands down to 20 GeV.
complemental/competing with Fermi/LAT
Fast pointing ̶ 180 deg in 20 sec
4 LSTs are planned in CTA SouthFoV=5 degrees radius

4/21

v.s. LAT sensitivity
cta-observatory.org

LAT 10 yrs (low b)
LAT 10 yrs (high b)• better sensitivity > 50 GeV• wide overlap enablesprecise cross calibration

LSTs responsible

North 50h

South 50h
sensitive, but MSTs are betterreconstructed Energy (TeV)5/21

Ang&E resolutions
cta-observatory.org

cta-observatory.org

LSTs responsible

sensitive

LAT

LAT

LSTs responsible
sensitive

reconstructed Energy (TeV)

reconstructed Energy (TeV)6/21

short time scale
cta-observatory.org

Simulated LST light curvefor GRB 080916C
Inoue+13= LST x10000• Thanks to much larger eﬀective area, plenty ofphotons will be observed in a short time

• Powerful tool to probe high-z transients

7/21

LSTs are mainly expected forlong~ size of the systemtime scale

short•quick follow-up of•GW events•GRBs•search for FRBs
•Galactic transients•Crab ﬂare
•Novae ?
•Extragalactic transients•IceCube nu events

OhashiTakahashi

Ioka

Totani

Kawai

VovkInoue• search for DM through gamma rays
Kohri, Inada, Hütten

What else should I talk about ?

8/21

Galactic Plane Survey
Simulated GP image with CTA (full array)

arXiv:1709.07997

9/21

GPS as a Key Science Project
arXiv:1709.07997
log N - log S• roughly ~50h exposure for Southern sky• Systematic view of the Galaxy to facilitate our understanding of
Galactic sources populations and diﬀuse emission.

• Can expect discoveries of new/unexpected phenomena• expecting 3-500 sources, mainly SNRs and PWNe
• Making catalogs, useful for further deep investigations

10/21

Pulsars• Pulsed gamma-ray emission with an exponential cut-oﬀ in Fermi/LAT
energies supporting outer gap related emission models.
• IACTs have reported the Crab has a spectral extension up to TeV• Challenge to probe the pulsar wind and e- acceleration scenario• Other pulsars ?

Aharonian+12

11/21

Pulsars in southern sky• Fermi/LAT pulsars with E>25 GeV emissions are selected.
• 6/12 pulsars are seen from South• assumed 50 h observations for each PSRs
• Phase-averaged, On-pulse and Oﬀ-pulse spectral analysis• Vela is promising, others may need more exposure
PulsedPulsed

Burtovoi+, MNRAS, 431, 446 (2017)

J0614-3329
J0835-4510
J1082-5819
J1048-5832
J1413-6205
J1809-2332

12/21VHE SNRs?

based on TeVCat http://tevcat.uchicago.edu/

H.E.S.S.
GP survey

CTA
GP survey
w/ MCRX J1713
shell-likestereo imaging

Cas A
Fermi launch13/21

Who can touch knees ?
• Older SNRs with Ecut in GeV, dim in TeV• Even younger SNRs not confirmed as PeVatrons• Galactic Center ?
t~20 kyrw/ MCt~2 kyrFunk(2015)

CTA Southt<1000 yr50hknee p → γ14/21

Footprints of Escaping CRs• Gamma-ray halo surrounding W44 was seen

when removing the emission from the SNR itself• Harder specta than the SNR

Collision of escaping (energetic ) CR and MCs

LST+ will derive more precise specta/morphology
LAT
2-100 GeV

Contour : radio
Uchiyama+12

LSTLST15/21young SNR J1713• Despite its brightness, the emission scenario has long been inquestion.
• CTA simulation with leptonic/hadronic scenario expects moreextension than X-ray morphology.
• H.E.S.S. observed such extension.
• Escape of the CR e- ? But no signiﬁcant energy dependence

Acero+17 (C.A. TN+)

H.E.S.S. collaboration (2017 )16/21

Search for PeVatron clues
Can we detect a “hidden” hadronic component up to knee ?
— even if the leptonic emission is dominatedWe demonstrated the possibility in 50h observations, if hadronic flux
occupies 10% of the total flux.
Mainly SSTs are responsible,
but with LSTs wider band spectroscopy will realized.
Fp/Fe~10% case

CTA Simulation
50 hr, E>500 GeVAcero+17 (C.A. TN+)

17/21Time evolution of Ec
Maximum energy

Ecelectron caseacceleration
escapecoolingtime variation of Ec→ magnetic field strength→ shock parameters→ acceleration model
ΔEc ~ 5−10％ in 20 yr
electron>proton(Ohira+12)
might be faster
when interacting with MCs

18/21

Acero+17 (C.A. TN+)

Search for Ec variations• only Ec is modified, E>200 GeV analysis• Combination of obs. time in each epoch examined• -10% case is easier to detect• >5-60 hrs in the 1st epoch is necessary for 3σ• By using LST, higher significance could be expected-10% case+10% case

3σ
3σ
100 times avr.

100 times avr.

PERSONAL REMARKS

19/21

Pulsars as CR source ?
Apart from knee CRs, do we already know suﬃcientCR source in the Galaxy ? Are SNRs enough?
Hadronic gamma-ray emission fromRCW89

PWNe has ever been discussede.g., Bednarek+, Horns+

But not conﬁrmed yet.
RCW89 is a HII region interactingwith pulsar jet (Yatsu+05)

Challenge toHidden emission
at RCW89 by CRs?

PSR B1509-58
Aharonian+05

20/21

similar to SS 433/W50 ?
• accreting BH or NS• bipolar jets terminated at the SNR shell• leptonic gamma rays dominate ?

B=16 uG
Eemax=3.5 PeV

A. U. Abeysekara+18, Nature 562, 82

21/21

Summary• 4 LSTs are planned to be built in CTA South• With their low energy threshold and fast driving system, the LSTs
are a very powerful tool probing short time-scale transients.

• Extragalactic transients are one of the major targets; follow-ups
for GW, GRB, neutrino sources.

• Even for steady sources, the sensitivity is better than Femri/LAT
with E>50 GeV• Never forget LSTs are important/crucial instruments to study
Galactic HE sources like pulsars.