Tidal Disruption Events

Transcription

1 Tidal Disruption Events as a probe of super-eddington accretion Jane Lixin Dai 戴丽 心 Niels Bohr Institute UMD: Jonathan McKinney, Cole Miller, Nathan Roth, Erin Kara 1 UCSC/NBI: Enrico Ramirez-Ruiz

2 Tidal disruption of a star by a supermassive black hole Tidal force from SMBH > Self-gravity of the star 2

3 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 peak 3

4 Outline Theoretical foundation of TDE physics (1970s - ) Current observational status (~ ) New theoretical development (past few years) TDE disk assembly TDE disk (super-eddington) accretion 4

5 Tidal Disruption Radius RT / Rg MBH -2/3 ρ -1/3 Rees 1988 GM /R 2 GMBH/RT 2 (R /RT) RT R (MBH / M ) 1/3 5 GR is important! BH Spin also affects RT

6 Stellar Debris Fallback Rate ε>0 t 5/3 ε=0 ε<0 Timescale: years Rees 1988 dm/dt = (dm/dε) (dε/dt) Fallback rate Stellar structure Kepler s Law ~ P -5/3 6 Phinney 1989 Evans & Kochaneck 1989 Lodato Guillochon+ 2013

7 How is a TDE observationally identified? Early theoretical predictions (e.g., Rees 88, Ulmer 99) From the center of a previously quiescent galaxy Light curve follows the fallback rate t -5/3 Blackbody temperature: LEdd = 4π RT 2 σt 4 T ~ 10 5 K, soft X-ray & UV Soft X-ray TDEs ROSAT, XMM-Newton, Chandra ktbb kev Komossa & Bade 1999 Komossa & Greiner 1999 Grupe et al Greiner et al

8 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: TDEs discovered, different classes ~2020: LSST - thousands of TDEs expected to be found Pan-STARRS LSST 8

9 Optical / NUV TDEs TBB ~ few 10 4 K H / He broad emission lines PS 10-jh: Gezari Arcavi + 14

10 Optical / NUV + Soft X-ray TDEs Multi-temperature blackbody: Toptical ~ 10 4 K TX-ray ~ 10 5 K Miller+ 15 Holoien+ 16 ASASSN 14-li 10 van Velzen+ 16

11 Jetted TDEs Strong non-thermal X-ray emission Lx, iso ~ erg/s Radio afterglow Transient relativistic jet Photons cm -2 s -1 kev -1 Burrows+ 11, Bloom+ 11, Levan+ 11, Zauderer Energy (kev)

12 TDE Multi-wavelength Observations If TDE physics is universal, ~ 50 TDE candidates why do we observe different classes of TDEs? Optical / UV: GALEX, Pan-STARRS, SDSS, PTF, ASASSN... Soft X-ray: ROSAT, XMM-Newton, Chandra Optical + Soft X-ray Hard X-ray / Jetted: Swift (radio / sub-mm signals) 12

13 Recent TDE Theory Development Circularization Debris loses orbital energy & assembles a disk Disruption Accretion I. How does debris assemble a disk? II. How does the TDE disk produce emissions? 13

14 I. Debris Circularization: stream self-collision due to general relativity BH Hydrodynamical simulations: Guillochon+15, Shiokawa+15, Hayasaki+15, Bonnerot+15,17 No GR 14

15 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

16 Dai, McKinney, Miller, 2015 β = 1, 2, 4, 8, Deeper plunge (β= R T /R p ) or bigger black hole closer debris stream self-intersection faster circularization Light curve behaves more like fallback rate 16

17 II. Super-Eddington TDE disk emission If efficient circularization, then the peak accretion rates in most TDEs are super-eddington. Super-Eddington accretion: Ṁ >ṀEdd Eddington luminosity: FG = FRad LEdd = 4πGMBH mp c/σt = (MBH /M )erg/s Eddington Accretion rate: 17 L = η Ṁ c 2 ṀEdd = LEdd / η c 2 η~10-40% (depends on BH spin)

18 II. Super-Eddington TDE disk emission - Physics involved: Non-spherical, non-axisymmetric disk structure General relativity Magnetic field: magneto rotational instability (MRI) Theory: Begelman 78, Abramowicz+ 88 Simulations: Ohsuga+05,10, Jiang+ 14, Sadowski+15, 16, McKinney, Dai & Avara 15 Optically thick: evolve gas in parallel to radiation - Code needed: 3D general relativistic radiation magneto hydrodynamics (GRRMHD) one simulation of footage of a few days = 1 million CPU hours (1 month running on 1000 processors) 18

19 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 hole Dai, McKinney, Roth & Ramiraz-Ruiz, in prep Our set up: small TDE disk + SMBH 19

20 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

21 Simulation Results Thick (geometrically and jet optically) disk Relativistic jet (Blandford- funnel fast outflow Znajek processes) outflow slow outflow Wide-angle, fast outflows debris stream disk disk debris stream Luminosity: ~3LEdd Radiative efficiency~3%, outflow outflow total efficiency ~ 43% (20% jet, 20% wind) jet 21

22 Kinetic energy luminosity and gas velocity flux lines Radiation energy dl/dθ and radiation flux lines L ~ 3LEdd L ~ LEdd color: dlke/dθ color: dlrad/dθ 22

23 A Unified TDE model: viewing-angle dependence X-ray outflow jet funnel: intrinsic emission fast outflow: adiabatic reprocessing slow outflow: photoionization reprocessing Optical debris stream disk disk debris stream outflow jet outflow Dai, McKinney, Roth, & Ramiraz- Ruiz, in prep 23

24 Observational evidence of TDE super-eddington accretion 1: relativistic jet When Do We Observe Jets? = L/L edd h/r 1 1 Radiatively-Inefficient (super-eddington) 100% h/r 1 1 h/r 1 1 Thin Disk (High/Soft or Thermal state) Radiatively-Inefficient (sub-eddington) (Low/Hard state) 10% 1% Disk transition Jet shutoff Tchekhovskoy

25 Observational evidence of TDE super-eddington accretion 1I: ultra-fast outflows in jetted TDE 250 Sw 1644 reverberation lag Lag (s) Rest frame energy (kev) Outflow speed c X-ray reverberation found for the first time from a TDE / super-eddington disk 25 Kara, Miller, Reynolds, Dai, Nature, 2016

26 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+, submitted 26

27 Super-Eddington Astrophysical Systems High redshift quasars Ultra Luminous X-ray Sources? 27

28 Summary TDEs provide a unique opportunity to probe dormant SMBHs and study super- Eddington accretion etc. After disruption, stellar debris falls back to the SMBH with a characteristic t -5/3 delay. Stream self-interaction due to GR apsidal precession leads to these material assembling an accretion disk. Observationally, TDEs producing different types of emissions have been observed, challenging theoretical understanding. The viewing angle dependence of the emissions from TDE super-eddington disks can provide a unified model for TDEs. outflow debris stream outflow disk jet X-ray funnel: intrinsic emission fast outflow: adiabatic reprocessing slow outflow: photoionization reprocessing disk outflow debris stream Optical 28 jet