CTA大口径望遠鏡初号機によるブレーザーの観測：
マルチメッセンジャー天文学時代のブレーザー観測戦略

Joshua R. Baxter (ICRR, University of Tokyo)
On Behalf of the CTA-LST ProjectBlazars: Active Galactic Nuclei (AGN) jet pointing towards us
Only ~0.1% of all AGN③‣ Dominates the HE/VHE extragalactic sky‣ Signi cant variability across the entire EM spectrum‣ This talk will focus on GeV-TeV in particular as an individual engaged
in VHE experiments (Cherenkov Telescope Array, CTA)

Ghisellini+17

IceCube2018
fiJoshua Baxter for the CTA-LST project, CTA大口径望遠鏡初号機によるブレーザーの観測： マルチメッセンジャー天文学時代のブレーザー観測戦略2

What do we anticipate elucidating through the observation of blazars?

‣ Astrophysical studies:

Locationof‣ Leptonic (Synchrotron Self-Compton, External Compton)or hadronic (Proton synchrotron, Photomeson...)?

the emission‣ What is the structure/role of the magnetic eld in thejets?

‣ Where along the jet HE/VHE emission produced?

Hadronic vs Leptonic‣ Cosmological, fundamental physics:‣ Validation of galaxy and star formation models in theuniverse

Measurements of EBL
Measurements of H0,ΩmR. Primack et al. 2012

‣ Does the intergalactic magnetic eld exist?
‣ Axion-Like Particle?
‣ Towards the Hubble crisis; cosmological parameter
Dominguez et al (2015)'

measurement
fifi

Joshua Baxter for the CTA-LST project, CTA大口径望遠鏡初号機によるブレーザーの観測： マルチメッセンジャー天文学時代のブレーザー観測戦略3

Cherenkov Telescope Array (CTA)
Next generation ground-based instrumentfor gamma-ray astronomy at very-high energies③Larger collection area!

‣ Located in the northern and southern hemispheres with 71 telescopes‣ Northern CTA: 4 Large-Sized Telescopes + 9 Medium-Sized Telescopes‣ x10 better sensitivity + wide energy coverage of 20 GeV-300 TeV‣ LST-1 started observation since 2020
CTA northern site (Spain, La Palma)

MST

LST-1

MAGIC telescopex10 better sensitivity!

Credit: Gabriel Pérez Díaz, IAC

Joshua Baxter for the CTA-LST project, CTA大口径望遠鏡初号機によるブレーザーの観測： マルチメッセンジャー天文学時代のブレーザー観測戦略4

Large-Sized Telescope (LST)
LSTs are designed to give optimal performance in③
the lowest region of the energy range covered by CTA, down to ≃ 20 GeV- Reposition to any point in the sky within 20 seconds- A performance paper on LST-1 was published based on the observational data of the Crab Nebula- The energy threshold at trigger level estimated to be 20 GeV, increasing to ≃ 30 GeV after data analysis- Suitable for transient/soft/distant sources

LST-1
23 m mirror

High-QE PMTs
(peak QE > 40 %)Crédito: Iván Jiménez (IAC)

Differential Sensitivity of LST-1(assumed 50 hours observation of Crab Nebula)

MAGIC

arXiv:2306.12960

Joshua Baxter for the CTA-LST project, CTA大口径望遠鏡初号機によるブレーザーの観測： マルチメッセンジャー天文学時代のブレーザー観測戦略

5Blazar Observation: Recent Trends in Astrophysics
Gao et al. 2019

two zones?
③One zones?

92AeT
0onirtuenV

Xue et al. 2020

Hadronic component‣ Modeling TXS 0506+056/IC-170922A needs a leptonic genesis for γ-rays

Sol et al. (2013)[Ansoldi et al. 2018, Keivani et al. 2018, Cerruti et al. 2019, Gao et al. 2019]‣ photo-hadronic cascades in jets should manifest as X-ray/UVemissions, potentially a more reliable neutrino-activity indicator

EM emission observed
from the blazar is not between
coincident with thesiteObserving
a correlation
GeV-TeVgammaMeVrays and‣ Theof neutrino production

neutrinosfrom could
theleadsame
band observations
to modelblazar
rejection; can be quite challenging!
‣ MeV/UVobservations are awaited!

6Blazar Observation: Recent Trends in Astrophysics
Where is the location of γ-ray emission region?

③

Costamante et al. (2018)seidudtestaytiplii
cibt
ainraav
ylrneoi
gsai
Seeingvariability
helps
us
toconstraintsonDopplerfactor,particle
acceleration,andidentify
thelocationofthe‣ece
emission from the causality, further challenging the blazar models rerpahA
Gapoftensofpc
betweenRadioandOpticalEmission;
sources
like3C279
show
noγγ
absorption
byBLR
‣
Tgi
C
H-> Gamma rays from sub-pc regions?
ti hBlazars like PKS1504 exhibit minute time scale variability w
3C 454Sol et al. (2013)‣-> Gamma-ray emission region less than pc? How diverse are blazars?

7Active Galactic Nuclei Observation with LST-1
LST-1 detected (> 5 σ) 6 known TeV blazars:③
Mrk421, Mrk501, 1ES 1959+650, 1ES 0647+250, PG 1553+113, BL Lac- A paper is slated for publication,

Mrk421 Mrk 501 1ES1959+650

1ES0647+250

PG 1553+113

along with simultaneous dataacquired by the Fermi-LAT

AGN type

HBL

HBL

HBL

HBL

HBL

- LST-1 detected a are from BL

Redshift

0.031

0.034

0.048

0.45±0.05

0.433

Obs. date

2020/12/12 2020/07/10-2022/05/23 -2022/06/29

2020/07/11-2022/05/05

2020/12/16-2020/12/21

2021/04/08-2022/05/23

Obs. time
68.5/32.4
67.2/39.7
BF/AF cut (h)21.3/11.8

8.8/8.2

12.2/9.9

12 σ

7σ

16 σ

Lac in 2021 [icrc2023_pos]. Thisis a separate project and will not
be covered in this talk

LST-1

SignificanceCondition

34 σ

21 σ

Dark (No Moon) + Clear Sky

flJoshua Baxter for the CTA-LST project, CTA大口径望遠鏡初号機によるブレーザーの観測： マルチメッセンジャー天文学時代のブレーザー観測戦略

8Seeing Variabilities: Mrk421 Flare in 2022-05-18
Mrk421 are was detected in 2022/05/18~3 times brighter than Crab Nebula's ux at > 100 GeV③- Spectra are measured down to ~25 GeV, and well tted by the exponential cutoff power law (ECPL) function- Concurrently, intra-night light curve and ux variability time scale are under examination
Preliminary

5 min.

PreliminaryIndex Γ: -1.86±0.05

Crab Nebula flux

Upcoming minute-level variability studies
by CTA could lead to locate the emission
region, and further model constraints
Joshua Baxter for the CTA-LST project, CTA大口径望遠鏡初号機によるブレーザーの観測： マルチメッセンジャー天文学時代のブレーザー観測戦略

A single LST can already reconstruct LCs with atime-scale precision comparable to the current
gamma-ray telescope MAGICfiflflfl

9Distant VHE sources: 1ES 0647+250 and PG 1553+113
Effectively reconstructed a spectrum that seamlessly connects ③with the Fermi-LAT observational data from the corresponding time period- Joint- t with Fermi-LAT data using dedicated pipeline Asgardpy https://asgardpy.readthedocs.io/en/latest/- Variability of these two sources is currently not con rmed by LST-1- The variation in PG 1553+113 has already been ascertained in Fermi-LAT observations, making it
scienti cally imperative to maintain ongoing surveillance through LST-1
1ES 0647+250 (z ~ 0.45)

Preferredlog-parabola

PG 1553+113 (z = 0.433)

Preferred
ECPL model

Preliminary

Preliminary

fififi10

Why Distant VHE sources?
No detection of FSRQ by LST-1 so far, but...

③
C. Righi et al (2020)

C. Righi et al (2020)

Y. Sotnikova et al. (2023)‣ FSRQ is a promising candidate in producing neutrino, but no signi cant detection of FSRQs up to now‣ EeV neutrino production in FSRQs?
‣ Simply gone unobserved due to the sensitivity-wise limitations of current neutrino detection facilities?
‣ Given FSRQs tend to be observed at high redshifts (z > ~ 0.5), employing low-energy-threshold γ-ray telescope
like LSTs to increase FSRQ statistics is crucialfiJoshua Baxter for the CTA-LST project, CTA大口径望遠鏡初号機によるブレーザーの観測： マルチメッセンジャー天文学時代のブレーザー観測戦略11

Summary‣ MWL observations are essential for constraining blazar emission models‣ First neutrinos tied to a blazar observed: TXS 0506+056/IC-170922A‣ γ-rays likely of leptonic origin, making γ-neutrino correlation challenging‣ UV/X-ray observations are awaited‣ Monitoring variability crucial for pinpointing gamma-ray emission site③> pc or < pc? Are blazars diverse? Precise time-tracking by CTA is the key‣ FSRQ may product EeV neutrinos‣ Given FSRQs tend to exist at high redshifts, using low-energy-threshold LSTs to increase
FSRQ statistics is crucial‣ LST-1 initiated scienti c observations since 2020 and has already detected several known AGNs
‣ Achieved reconstruction of minute-scale variability in blazars, and detection of sub-100 GeV γrays from distant blazars
fiJoshua Baxter for the CTA-LST project, CTA大口径望遠鏡初号機によるブレーザーの観測： マルチメッセンジャー天文学時代のブレーザー観測戦略

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