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)
Ryuji Takeishi (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1

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 (Extragalactic Background Light)

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2

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 zone?

92AeT0onirtuenV

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‣ The EM emission observed from the blazar is not coincident with the site

MeVof neutrino production‣ MeV/UV band observations could lead to model rejection;observations are awaited!

6

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

two zones?
③One zone?

92Ae
T
0on
irtuenV

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-TeVgammaMeV
rays and‣ Theof neutrino production

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

7

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

③Costamante et al. (2018)

3C 454Sol et al. (2013)‣ Seeing variability helps us to constraints on Doppler factor, particle acceleration, and identify the location of theemission from the causality, further challenging the blazar models‣ Gap of tens of pc between Radio and Optical Emission; sources like 3C 279 show no γγ absorption by BLR-> Gamma rays from sub-pc regions?

‣ Blazars like PKS1504 exhibit minute time scale variability-> Gamma-ray emission region less than pc? How diverse are blazars?

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

③Costamante et al. (2018)seidudtestayti
plii
cibtainraav
ylr
neoi
gsai
Seeingvariability
helps
us
toconstraintsonDopplerfactor,particle
acceleration,and
identify
thelocation
of
the
‣ece
emission from the causality, further challenging the blazar models rer
pah
A
Gapof
tens
ofpc
betweenRadioandOpticalEmission;
sources
like3C
279
show
noγγ
absorptionbyBLR‣
Tgi
CH-> 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?

9

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

HBLHBLHBLHBL

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

10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.

Preliminary

Index 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 MAGICfifl

fl

fl

11

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)

Preferred
log-parabola

PG 1553+113 (z = 0.433)

Preferred
ECPL model

Preliminary

Preliminary

fifi

fi

12

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 limitation of the 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13

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14

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 site

③g?
nTi
Ss> pc or < pc? Are blazars diverse? Precise time-tracking by CTA is the keyLo/pCoIr
FSRQ
mayproduct
EeV
neutrinos‣GpAni
M
Given
FSRQs
tend
toexistat
highredshifts,
using
low-energy-thresholdLSTs
toincrease‣dhettiFSRQ statistics is crucialswersentoniI atv
alreadydetected several known AGNsr‣ LST-1 initiated scienti c observations since 2020 and hasesb‣ Achieved reconstruction of minute-scale variability
o 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15

③Backup

Joshua Baxter for the CTA-LST project, Observation of Active Galactic Nuclei through the eyes of CTA LST-116

Blazar Observation: Recent Trends in Astrophysics
SSC-dominant +pγ cascade

proton sync.-dominant +pγ cascade

Gao et al. 2019③Hadronic component‣ Modeling TXS 0506+056/IC-170922A needs a leptonic genesis for γ-rays [Ansoldi et al. 2018,Keivani et al. 2018, Cerruti et al. 2019, Gao et al. 2019] (one zone assumed)‣ Hadronic component covered under the leptonic component‣ γ-rays co-produced with IceCube neutrinos should initiate EM cascades, with their energy escaping
in the optical-UV-X-ray spectrum‣ Leptonic processes likely dominate their γ-ray emission, negating the need for γ-neutrino correlation‣ Instead, photo-hadronic cascades in blazar jets should manifest as X-ray/UV emissions,potentially a more reliable neutrino-activity indicator
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

17

Blazar Observation: Recent Trends in Astrophysics
Then why not two zones?

③Sol et al. (2013)

Xue et al. 2020

MeV

‣ Active research on modeling TXS 0506+056 assuming a two-zone framework [ Xue et al. 2020, Zhang et al. 2020,
Reimer et al. 2019]‣ The EM emission observed from the blazar is not coincident with the site of neutrino production‣ MeV/UV band observations could lead to model rejection; observations are awaited
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

18

Blazar Observation: Recent Trends in Cosmology, Fundamental Physics
Measurement of Cosmological Parameters using γ-ray's cosmological optical depth③‣ The opacity of gamma rays against Extragalactic background light (EBL) depends on H0 and Ωm.
By using this fact in reverse, they gave constraints on H0 and Ωm from the EBL attenuation data‣ The H0 dependence occurs at > 100 GeV and increases with energy
The strongest constraints on H0 come from the lower redshifts‣ Ωm dependence becomes stronger for the larger redshifts

TeV optical depth τ (Eγ, z) data (Desai+ 2015)
measured by using EBL model

Possible systematic error in the method?

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

19

Blazar Observation: Recent Trends in Cosmology, Fundamental Physics
Measurement of Cosmological Parameters using γ-ray's cosmological optical depth③‣ The opacity of gamma rays against Extragalactic background light (EBL) depends on H0 and Ωm.
By using this fact in reverse, they gave constraints on H0 and Ωm from the EBL attenuation data
‣ The H0 dependence occurs at > 100 GeV and increases with energy
The strongest constraints on H0 come from the lower redshifts‣ Ωm dependence becomes stronger for the larger redshifts

TeV optical depth τ (Eγ, z) data (Desai+ 2015)
measured by using EBL model

Possible systematic error in the method?

CTA could potentially offer the precision needed to tackle
the Hubble Tension, given its broad energy sensitivity
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

20

Seeing Variabilities: Mrk501 Light Curves and SEDs
Tracked the temporal evolution of a spectrum③
consisting of 11 blocks via the application of a Bayesian block algorithm- Data period: 2020/07/10 - 2022/05/22 (153 runs, 39.7 h)- The spectrum variation, already veri ed in VHE gamma, was also properly con rmed in our data set
Preferred model
Block 8: log-parabola + EBL Others: power-law + EBLNight-wise light curve (> 100 GeV)Preliminary

Preliminaryfifi

Joshua Baxter for the CTA-LST project, Observation of Active Galactic Nuclei through the eyes of CTA LST-121

LST-1 Data Analysis Method
Perform IRF interpolation to minimize the discrepancy between Simulation③and Data

- Reconstruction of primary particle information using Random Forest trained with MC simulation of gamma-ray
and cosmic-ray showers as input- The Estimation of the IRFs at given telescope pointing direction was performed through the interpolation ofMonte Carlo (MC) simulations, generated on a grid in the (zenith, azimuth) plane

MC grid for
IRF interpolation

Zenith (deg)1ES 1959+650

Mrk501
Mrk421

PG 1553+113

1ES 0647+250

Azimuth (deg)Joshua Baxter for the CTA-LST project, Observation of Active Galactic Nuclei through the eyes of CTA LST-1

22

LST-1 Data Analysis Method
We used cta-lstchain for creating IRFs and event list,and Gammapy for subsequent processes③- Python-based pipeline cta-lstchain v0.9.12/0.9.13 (dedicated analysis tool for LST data)- For the generation of high-level visualizations, including SED and Light Curves, we employed Gammapy v1.0.1- Gammapy: open-source Python package for gamma-ray astronomy built on Numpy, Scipy and Astropy

cta-lstchain

Gammapyhttps://github.com/cta-observatory/cta-lstchain

https://github.com/gammapy/gammapyrew

irAeoh
Siv
sent
Ex

es
on

Direction

nt
emu
rtsn

Gammaness

Cherenkov LightEnergy..
.
sev
ru
C
ht

ps
ReI

DES

gi,LK Satalecka at el (2010)

DL0DL1DL2

DL3

DL4Raw DAQ output

Image Parameters

Shower Parameters

IRF + event list

Scienti c Quantities

fiJoshua Baxter for the CTA-LST project, Observation of Active Galactic Nuclei through the eyes of CTA LST-123