Probing Black Hole Spacetime andDynamics of Accretion Flow with Relativistic Jet
via General Relativistic Multi-Wavelength Radiative Transfer
Tomohisa KAWASHIMA(HEA group, ICRR)
Collaborators (order of alphabet)
K. Akiyama (MIT), M. Kino (Kogakuin U/NAOJ),
K. Moriyama (MIT), M. Nakamura (Hachinohe C),
K. Ohsuga (U of Tsukuba),
H. R. Takahashi (Komazawa U), K. Toma (Tohoku U),
and EHT Collaboration members

General Relativistic Magnetohydrodynamic simulation (UWABAMI code) +General Relativistic Radiative Transfer calculation (RAIKOU code)relativistic jetaccretion flow

Accreting black holes (BHs) inastrophysics© NASA's Goddard Space Flight Centermechanical/radiative feedback→ co-evolution of BHs and hostgalaxies, cosmology© NASA/WMAP

acceleration of cosmic rays
→ possible origin of UHECR,
VHE gamma-ray, neutrino© Simon Swordy (U. Chicago), NASA

analogy of physics of jets
→ gamma-ray burst as a EM
counter part GW events© NSF LIGO Sonoma State University / A. Simonnet

Key questions in black hole (BH) astrophysics(1) BH spacetime?

(2) Physics ofaccretion flow?

(3) Formation andacceleration ofrelativistic jets?

(1) - (3) are related each other.
general relativity,magnetohydrodynamics (kinetics ofplasma), and Radiative Transfer areneeded.
© NASA's Goddard Space Flight CenterPower of radiative transfer
Theory/Simulation

Observation

what we know：fluid properties(i.e, density, temperature, etc.)
Takahashi et al. 2016

Large gap!
We need radiative transfer calculations ofWhat we know: radiation(i.e., image, SEDs)

EHT collaboration 2019

•Imaging•Spectral Energy Distribution (SED)

The detailed calculation of generalrelativistic radiative transfers will enable
us to study
・BH spacetime (mass and spin)
・dynamics of accretion flow and jetWalton et al. 2014

RAIKOU(来光): a general relativistic, multi-wavelength
radiative transfer code Kawashima, et al. (in prep.), EHT GRRT code comparison paper (2020)
RAIKOU: Radiative trAnsfer In Kerr-spacetime for accretiOn and oUtflow
ν = 350GHz•Ray-tracing法:

1013

10

w/ adoptive stepsize control• Radiative processes:- Cycle-synchrotron via thermal electrons- Synchrotron via non-thermal electrons- Bremsstrahlung via thermal electrons✓ scattering (Monte-Carlo method)- Compton/inverse-Compton scattering
via thermal and non-thermal electrons✓ Polarization (now implementing)computed SED
()

1015

1014

✓ 8th order embedded Runge-Kutta method✓ emission/absorption1016

ν = 86GHzcomputed SED()

1210111010

ν = 43GHz

10incident blackbody photons

91x10121x10141x10161x10181x1020(Almost) all the important continuum processes near BHs are implemented1x1022

First detection of BH shadow in M87(EHT Collaboration 2019 incl. T Kawashima)

BH shadow
Photon ringEvent Horizon Telescope (EHT) has successfully
detected the BH shadow in M87, which is one of themost famous relativistic jet source!

Formation of photon ring and BH shadow• Photon ring：gravitationally lensed image of (unstable) spherical orbit of photons• Photons passing through near the spherical orbit gain the intensity via "emissivity x length”, then,the bright photon ring is formed and it rims the BH shadow.
※ rg：gravitational radius, rs：Schwarzschild radius (rg = 0.5 rs)
6lan4iotiv ta nsra le-14-12-10-8-6-4-202# Example of non spinning BH
y4-6-4-2

BH0Spherical orbit(Radius = 3rg =1.5rs)

x2

GPhoton ring(radius=5.2rg=2.6rs)

Calculation of photon ring in M87 EHT Collaboration (inc. Kawashima T.) 2019
GRRT calculation
GRMHD
Simulation

GRRT calculation (blurred)

ジェットの方向

Observed image→

General Relativistic MagnetoHydroDynamic (GRMHD) simulation +General Relativistic Radiative Transfer (GRRT) calclualtion• The mass of M87 BH has 6.5x109 M_sun.
• Powerful evidence of the presence of supermassive BHWhat we achieved and remaining works• Remaining (important) works✓ value of BH spin
✓ BH has detected.
✓ Formation mechanism of jets
✓ BH mass is constrained to be ~ 6.5x109 M_sun. ✓ Dynamics of accretion flow
✓ Powerful evidence of the presence of✓ Emission region is jet or accretion flow?
supermassive BH✓ Other sources (e.g., Sgr A*)• What we achieved：

Theoretical images w/ various BH spin

BH
スピンa = -0.94

EHT2017 observation

降着円盤a=0a = 0.94

Towards future EHT:Exploring BH spin and launching of relativistic jets

Dependence of BH shadow (photon ring) on BH spin
a=0

BH shadow

a=0.998
a = 0, 0.5, 0.998

BHevent horizon

analytic solution of shadow-surface• Dependence of size of photon ring on BH’s
• mass：STRONG (it is proportional to BH mass)• spin：WEAK (the difference is within only ±5%)
The center of the photon ring just slide to the direction perpendicular to the BH-spin axis.
• Good for evaluating BH mass, but not good for estimating BH spin.

A new method constraining the BH spin
Kawashima Kino, & Akiyama 2019

We calculate the BH shadow in a flaring state, in which the mass accretion rate is moderately higher thanthat observed by EHT2017, to explore a new signature of the BH spin
Observer screen @ 104rg

accretion disk
BH

• For simplicity, we consider accretion flow only as in some previous works (Keplearian shell model:
Broderick & Loeb 2006)• Cyclo-synchrotron emission/absorption• BH mass: 6.2 x 109 solar mass
• BH spin: a = 0.5, 0.75, 0.998,

viewing angle i = 15, 30 degree• Relatively higher mass accretion rateBH shadow in flaring state (a=0.998)
OpticallythickSSA-thick
ISCO ring
innermostdisk• Optically thick ring image appears when thephoton
ring mass accretion rate is a bit higher.
Photon ring
• Photon ring also appears because theplasma is optically thin outside the inner
region of accretion flow.

BH“dark crescent”
CrescentShadow「三日月状シャドウ」

Crescent shadow
appears between the
optically thickinnermost disk andphoton ring

Dependence of BH shadow images on BH spinHigh spin

a=0.5

a=0.75a=0.998

photon-ring

SSA-thick
ISCO-ring
SSA-thick
Optically thick,
ISCO-ring
Innermostdisk photon
photon-ring
Photonringring“dark-crescent”“dark-crescent”
dark-crescent“darkcrescent”

SSA-thick
ISCO-ring• When the BH spin is high, the center of photon ring shifts.
→ The dark crescent appears.
This feature can be a new method constraining the BH spin.

a = 0, 0.5, 0.998

Synthetic Images of dark crescent,assuming
mass model(a)(a) fiducialmassmodelmass(a) fiducial
fiducialmass
modelmodelcurrent and future EHT array
230 GHz230 GHzGHz
230EHT
Model2017ModelModel350 GHz

350 GHz
GHz
350

3030µasµas 30 µas

3030µasµas 30 µas

EHT
EHT
2020
EHT 2017
EHT20172017

×EHTEHT
2020+1MEO
2020
EHT 2020 EHTEHT
2020+1MEO+1GEO
2020+1MEO
EHT 2020+1MEO
EHT
EHT 2020
EHT
2020
EHT
2020+1MEO
EHT2020+1MEO
2020+1ME××•It canss model(b)high(b)mass
high model
mass
model
detected
byusing extend EHT with space VLBI after 2020s! (2030s?)(b)behighmass
model•Both of 230GHzand 350GHzobservations
areimportant.
EHT
Model
2017ModelEHT
EHT
2020
EHT 2017
EHTEHT
2020+1MEO
2020
EHT
2020 EHTEHT
2020+1MEO+1GEO
2020+1MEO
EHT 2020+1MEO
EHT
EHT 2020
ModelEHT2017
2017
EHT
2020
EHT
2020+1MEO
EHT2020+1MEO
2020+1ME

Is the jet-base emission important for ring image?

Blandford + 2019 (ARAA)•The emission at the jet base would be important for formation of the ring-like image?

Overview of the model•

Electron-positron plasma
may be injected near thestagnation surface inside thejet funnel.(Broderick &Tchekhovskoy 2015)•We explore the importance ofthe emission from theelectron-positron plasma at
the jet-base for the formationof the ring-like image at
230GHz in M87!

Photon sphere of highly spinning BH

Appearance of jet injection point

CounterApproaching

WholeHigh spin

• Large BH spin→Direct image of jet tends
to overlap to the photon ring

• For a=0.99, diirect image of counter jet
overlaps to the photon ring, but inner ring
due to approaching jet still appears.
→ Conflict with EHT 2017? Let us
examine assuming the array of EHT

Synthetic image of jet-base emission
True imageEHT2017EHT2020

EHT2023• “Photon ring + jet-base image” can reproduce the observed image with EHT2017 (Itshould be emphasized that this a fine tuning model).
• This means that the observed image may include the important information of the jetbase.
• We can examine our models using forthcoming EHT!

Explore the global jet structure(Blackburn et al.
2019, astro2020
white paper
GRRMHD
simulation Chael +2019)

We are performing multi-wavelength simulations including non-thermal electrons!
(Kawashima + in prep.)
10230 GHz(log)

10.1

Jy86GHz(log)

Calculation
Obs (exept EHT2017)
EHT2017

0.01

0.001

0.0001

1e-05
1e+10

1e+11

1e+12

1e+13nu

1e+14

1e+15

1e+16

Towards multi-wavelength study
from radio to gamma-ray

Is it possible to determine the spin using X-ray, γ-ray?
Model setup
Photoninverse-Compton
scattering
Accretionflow

BH• Keplearian shell model (Falcke + 2000, Broderick & Loeb 2006, Pu + 2016)• cyclo-synchrotron emission/absorption + Compton/inverse-Compton scatteing, calculated by MC transport solver
implemented to RAIKOU (来光)• BH mass 4.3 x 106 M_sun• BH spin a = -0.9, 0, 0.9• viewing angle i = 30 degree

BH shadow + Multiwavelength SED

BH shadow(preliminary)

w/o GRa=0a=0.9

a=-0.9

X-rayγ-ray• Simple RIAF model for SgrA*• BH spin signifiantly affect the SEDs, especially in X-ray and γ-ray→ Even if the BH-shadow morphology is difficult to distinguish the BH spin, it may be possible toconstrain the BH spin.

Where does the inverse-Compton scattering take place ?
Retrograde BHa = -0.9

Prograde BH
a=0a = 0.9Viewing angelis 30 degree

ISCO• Color displays where the how many photons are upscattered with recording the highest frequency and escape to the observer at30deg (red/bule: large/small amount)• We speculate that retrgrad BH →outer location of ISCO →significant inflow motion → scattered photons are beamed into the BH→ less X-ray emission

Towards GRMHD simulation study
BH shadow
BH shadow (230GHz)+

MWL SED
1043

Compton ON
Compton OFF
EHT2017 data (230GHz)

1042

1041

1040

230 GHz

1039

Magnetically Arrested Disk(GRMHD code: UWABAMI)

1038108X-ray

γ-ray1010 1012 1014 1016 1018 1020 1022 1024

• Using GRMHD simulation (using UWABAMI code), we have started the calculation of BH shadow +MWL SEDs.
• Using the MWL SEDs, we are planning to explore the possibility of feature extraction.

Towards (Very High Energy) gamma-ray
Fermi(LAT) MAGIC©Fermi©MAGIC• The calculation module for Compton scattering w/ non thermal electrons have been implemented!
• We are planning to study the origin of jets and the physics of accretion flow in future work.

Towards lower photon frequency (preliminary)

43GHz

86 GHz230 GHz (EHT)
Sgr A*
Light curve• Time variation w/ ~100rg/c ~ 30 min have beenobserved in GRMHD simulation.
• What is the origin? It would be the imprint ofimportant physics of accretion flow.

~100rg/c ~ 30 min
230 GHz86 GHz43 GHzSummary• EHT 2017 successfully observed BH shadow in M87*, and the BH mass is••determined to be ~6 billion solar mass.
Big issues still remain, e.g., BH spin, jet and accretion physics.
Using multiwavelength, general relativistic radiative transfer code RAIOKOU,
we are studying these issues.
✓ Suggestion of a new method to constrain the BH spin with crescentshadow in luminous state of M87. (future space-VLBI can detect).
✓ Jet emission may be included in the ring-like image of EHT 2017 (ngEHT
can identify our model)

Multiwavelength study inc. X/γ-ray may enable us to understandthe physics near event horizon.