Tidal Disruption Events
as a probe of super-Eddington accretion
Jane Lixin Dai
戴丽⼼心Niels Bohr Institute

UMD:
Jonathan McKinney,
Cole Miller, NathanRoth, Erin KaraUCSC/NBI:
Enrico Ramirez-Ruiz
1

Tidal disruption of a star by
a supermassive black hole

Tidal force from SMBH
> Self-gravity of the star2

Motivation for Studying Tidal Disruption Events (TDEs)
probe non-active SMBHs✦ detect IMBHs & binary SMBHs✦ study stellar dynamics✦Swift J1644✦study transition between
different accretion states& super-Eddington
accretion at peak3

Outline• Theoretical foundation of TDE physics (1970s - )• Current observational status (~2000 - )• New theoretical development (past few years)➡ TDE disk assembly➡ TDE disk (super-Eddington) accretion4Tidal Disruption Radius
RT / Rg ∝ MBH-2/3 ρ★-1/3

Rees 1988

GM★ /R★2 ≈GMBH/RT2 (R★ /RT)
GR is important!
BH Spin also affects RT

RT ≈ R★ (MBH / M★)1/3
5

Stellar Debris “Fallback” Ratet

ε>0ε=05/3ε<0Timescale: years
Rees 1988

dm/dt = (dm/dε) (dε/dt)
Fallbackrate

Stellarstructure

Kepler’s Law~ P-5/3
6Phinney 1989
Evans & Kochaneck 1989
Lodato+ 2009
Guillochon+ 2013

How is a TDE observationally identified?
Early theoretical predictions (e.g., Rees 88, Ulmer 99)• From the center of a previously quiescent galaxy

didates in X-rays• Light curve follows the fallback rate ∝t-5/3• Blackbody temperature: LEdd = 4𝜋 RT2𝜎T4$,%/%!"*#'/%"4'-%%'*I-M-%%GFb%c%[/%@0-.-%*XG%.@%
1%I)3)[/%04'3-%

T ~ 105K, soft X-ray & UVSoft X-ray TDEs
ROSAT, XMM-Newton, Chandra

kTBB ∼ 0.04 - 0.1 keV
Komossa & Bade 1999
Komossa & Greiner 1999
Grupe et al. 1999
Greiner et al. 2000

c0L0--)%CFF\%

7

TDE Multi-wavelength Observations• Wide-field transient surveys (GALEX, Pan-STARRS, PTF/

ZTF, ASASSN & SDSS, Swift)• Photometric and spectroscopic data, multiple epochs

observed for each event• Now: 30-50 TDEs discovered, different classes• ~2020: LSST - thousands of TDEs expected to be foundPan-STARRS

LSST8

Optical / NUV TDEs
TBB ~ few 104 K
H / He broad emission lines

PS 10-jh: Gezari+ 12

9Arcavi + 14

Optical / NUV + Soft X-ray TDEs
Multi-temperature blackbody:
Toptical ~ 104 K
TX-ray ~ 105 K

Miller+ 15
Holoien+ 16

ASASSN 14-li
10van Velzen+ 16

Jetted TDEs

Photons cm-2 s-1 keV-1

Strong non-thermal X-ray emission
Lx, iso ~ 1047-48 erg/sRadio afterglow→ Transient relativistic jet

Burrows+ 11, Bloom+ 11, Levan+ 11, Zauderer+11

Energy (keV)
11

TDE Multi-wavelength Observations~ 50 TDE
candidates

If TDE physics is universal,
why do we observe
different classes of TDEs?

Optical / UV:Soft X-ray: ROSAT,GALEX, Pan-STARRS, SDSS, PTF, ASASSN...

XMM-Newton, Chandra

Optical + Soft X-ray

Hard X-ray / Jetted: Swift(radio / sub-mm signals)
12

Recent TDE Theory Development
Circularization
Debris loses orbitalenergy & assembles
a diskDisruption

Accretion

I. How does debris assemble a disk?
II. How does the TDE disk produce emissions?
13

I. Debris Circularization:
stream self-collision due to general relativity

BH

Hydrodynamical simulations:
Guillochon+15, Shiokawa+15,Hayasaki+15, Bonnerot+15,17…

No GR14

I. Debris Circularization:
stream self-collision due to apsidal precession
Shocks

BH
Hydrodynamical simulations:
Guillochon+15, Shiokawa+ 2015,Hayasaki+ 2015, Bonnerot+ 2015, 2017…

GR apsidal precession
15Dai, McKinney,Miller, 2015

𝜷 = 1, 2, 4, 8, 16

105

106

107108Deeper plunge (𝜷= RT/Rp) or bigger black holecloser debris stream self-intersection
faster circularization
Light curve behaves more like fallback rate
16

II. Super-Eddington TDE disk emission• If efficient circularization, thenthe peak accretion rates in mostTDEs are super-Eddington.
• Super-Eddington accretion:
Ṁ >ṀEdd
Eddington luminosity:
FG = FRadLEdd = 4𝜋GMBH mp c/𝜎T
= 1.26⨉1038 (MBH /M☉)erg/s
Eddington Accretion rate:17

L = η Ṁ c2ṀEdd = LEdd / η c2
η~10-40% (depends on BH spin)

II. Super-Eddington TDE disk emission- Physics involved:• Non-spherical, non-axisymmetricdisk structure• General relativity• Magnetic field: magneto

rotational instability (MRI)• Optically thick: evolve gas inTheory:
Begelman 78, Abramowicz+ 88

parallel to radiation- Code needed: 3D general

Simulations:
Ohsuga+05,10, Jiang+ 14, Sadowski+15, 16,
McKinney, Dai & Avara 15…

relativistic radiation magneto
hydrodynamics (GRRMHD)

one simulation of footage of a few days
= 1 million CPU hours (1 month running on 1000 processors)
18

TDE super-Eddington accretion disk and jet:
GRRMHD simulations•HARMRAD: fully 3D GRMHD code with M1
radiative transfer scheme, grey opacity for emission
and absorption, also includes Comptonization•Previous studies: large disk + stellarmass black holeDai, McKinney, Roth &Ramiraz-Ruiz, in prep•

Our set up: small TDE disk + SMBH
19• SMBH: 5 million solar masses, spin parameter 0.8• Accretion rate: ~15 ṀEdd (similar to fallback rate)

color:gas density
black line:
magnetic field

Mdot & L

Efficiency
20

jet• Thick (geometrically andoptically) disk
• Relativistic jet (BlandfordZnajek processes)• Wide-angle, fast outflows• Luminosity: ~3LEdd• Radiative efficiency~3%,
total efficiency ~ 43% (20%jet, 20% wind)

ow
flt
ou

utflow
slow odisk

disk

debris stream

outfl
owjetw
flotou21

stfaoutfl
ow

debrisdebrisstream
streamfunnelSimulation Results

Kinetic energy luminosityand gas velocity flux lines

Radiation energy dL/dθ
and radiation flux lines

L ~ 3LEdd

L ~ LEddcolor:
dLKE/dθcolor:
dLrad/dθ

22

A Unified TDE model: viewing-angle dependence
missionntrinsice

fun
nel:
ijet

X-rayoutfl
ow: gwo ssinflt oceuo r

st ic repaf atbiaad

flow: singtu
ooces
slow

izationnoiot
phodebrisdebrisstream
stream

disk

disk

repr

Opticaldebris stream

outfl
ow

jetwotfluo23

Dai, McKinney,Roth, & RamirazRuiz, in prep

Observational evidence of TDE
super-Eddington accretion 1:
relativistic jet

When Do We Observe Jets?

= L/Leddh/r ⇠ 1⌧1

Radiatively-Inefficient(super-Eddington)

100%

10%h/r ⌧ 1⌧
1h/r ⇠ 1⌧ ⌧1
Alexander (Sasha) Tchekhovskoy

Thin Disk(High/Soft or Thermal state)

1%

Radiatively-Inefficient(sub-Eddington)

Disk transition — Jet shutoff(Low/Hard state)
YCAA Seminar

24

Tchekhovskoy + 2013

Observational evidence of TDE
super-Eddington accretion 1I:
ultra-fast outflows in jetted TDE
250

Sw 1644 reverberation lag

200

Lag (s)

150
100
50
0−50
1

5

10

Rest frame energy (keV)• Outflow speed 0.1-0.5c• X-ray reverberation found forthe first time from a TDE /super-Eddington disk

Kara, Miller, Reynolds, Dai, Nature, 201625

Observational evidence of TDE super-Eddington accretion 1I:
ultra-fast outflows in non-jetted TDE
Sw 1644 reverberation lag• P Cygni-like absorption
features from ASASSN 14-li• Outflow speed ~ 0.2c
• Consistent with the outflow
speed from radio signals(Alexander+16)

Kara, Dai+, submitted26

Super-Eddington Astrophysical Systems
High redshift quasars

Ultra Luminous X-ray Sources?
27

Summary
TDEs provide a unique opportunity toprobe dormant SMBHs and study superEddington accretion etc.
After disruption, stellar debris falls back tothe SMBH with a characteristic t-5/3 delay.
Stream self-interaction due to GR apsidalprecession leads to these material
assembling an accretion disk.

missionw: singo
tfl ceso u rost repfa atic

iab
ad:
utflow
slow oon reprocessingtiionizaphotodisk

disk

Opticaldebris stream

ou
tfl
ow

w
flot
ou

jet

28

ntri
nsic
e

jet
ou
tfl
ow

debrisdebrisstream
streamThe viewing angle dependence of theemissions from TDE super-Eddington disks
can provide a unified model for TDEs.

funnel:i

Observationally, TDEs producing different
types of emissions have been observed,
challenging theoretical understanding.

X-ray