Numerical simulations of super-eddington accretion flow and outflow

Transcription

1 Numerical simulations of super-eddington accretion flow and outflow Ken Ohsuga (NAOJ), Shin Mineshige (Kyoto), Hiroyuki Takahashi (NAOJ) Collaboration with T. Ogawa, T. Kawashima, & H. Kobayashi

2 Today s Plan Overview of the numerical simulations of super-eddington accretion flows and outflows around BHs. Can reproduce the basic features of ULXs (luminosity, spectra, time variation, and ULX bubbles) and thus support that ULXs are powered by the super-eddington accretion onto BHs. Also support that ULSs are super-eddington accretor viewed from the large angle direction (to the rotation axis). Next talk GR-RMHD simulations of the super-eddington flows around BHs and NSs (by Takahashi). Super-Eddington model for ULX-pulsar (by myself).

3 Engine of ULX s? Intermediate mass black hole If the IMBHs exist, sub- Eddington disk can explain the huge luminosity of ULXs; 0.1LEdd (10 3 M sun ) ~10 40 erg/s. Super-Eddington Disk Even for normal BH mass (<< 100 M sun ) super-eddington disks can reproduce huge luminosity; 10 LEdd (10M sun ) ~10 40 erg/s. (c)kawashima

4 Super-Eddington Accretion M acc M Edd L Edd / c 2 ( m acc M acc / M Edd 1) Super-Eddington accretion is feasible in disk accretion, since the main directions of gas accretion and of outgoing radiation do not match (unlike the case of spherical accretion). accreting gas radiation pressure R sp accreting gas accreting gas Mass accretion rate can be L E /c 2. (Shakura & Sunyaev 1973) Apparent luminosity can exceed L E!

5 Key process 1 - outflow (Shakura & Sunyaev 1973; Poutanen+ 2007, ) Significant outflow from disk surface Radiation pressure-driven outflow inevitably occurs. disk wind outflow accreting gas BH accretion Critical radius = spherization radius:. R sp ~ (Mc 2 /L E ) r s Inside this radius: flatter T profile: T r -1/2

6 Key process 2 - photon trapping Photon trapping within disk center Low-energy photons Begelman (1978), Ohsuga et al. (2002) Photons are trapped within luminous accretion flow. High-energy photons BH trapped photons. Critical radius = trapping radius: R trap ~(Mc 2 /L E )(H/r) r s Inside this radius: flatter T profile: T r -1/2 K. Ohsuga

7 Why radiation-mhd simulation? One-dimensional models (e.g. standard disk, slim disk, ADAF) are quite useful for understanding the basics. However Multi-dimensional gas motions, such as circulation and outflow are totally neglected. Need 2-D/3-D global simulations Disk viscosity was treated by the phenomenological alpha model. Need MHD simulations Strong radiation-matter interactions at high luminosities are not properly treated. Need radiation-hydrodynamical simulations

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9 Basic eqs. of Radiation-MHD RHD terms MHD terms

10 Super-Eddington accretion Radiation-pressure supported disk + radiatively-driven jet Radiation energy & Magnetic field lines Lbol LEdd, M~60 LEdd/c 2 MBH=10Msun

11 Radiation-MHD Jet & outflow

12 Three accretion modes Ohsuga et al. 2009, Ohsuga, Mineshige 2011 RIAF Standard Slim Hot rarefied disk & Magnetized jet Cold thin disk & Magnetized wind Radiation Pressure Supported Disk & Jet Mass Accretion Rate

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16 Emergent spectra is sensitive to the MBH and inclination angle. Kawashima et al (data; Gladstone 2009) Simulated spectra nicely fit the observations.

17 Comparison with ULXs; Time variation Takeuchi, Ohsuga, Mineshige 2013 Schematic picture for explaining the time variation (Middleton et al. 2011) Our simulations succeeded in reporoducing the clumpy outfl ow. Super- Eddington disk+ Jet Time-dependent, Clumpy outflow with wide angle

18 Clumpy structure induced by the RT instability in radiation dominated atmosphere

19 Comparison with ULXs: outflow Mdot~100LEdd/c 2 L~3LEdd Poutflow~3LEdd ~3x10 39 erg/s RHD simulation with low resolution but large computational box (5000Rs). Radiation pressure force drives wideangle outflows. Hashizume et al. 2015

20 Comparison with ULXs: outflow BH wide-angle vr>vesc vr<vesc Wide W ide angle outflow is is accelerated by by radiation force. For At θ < <<45 we 45, we find find v > vr>vesc v near esc near the black the hole. hole. For θ =45-80 outflow velocity In ~ 45-80, gradually outflow increases velocity gradually as it travels, exceeding increases and the exceeds escape velocity vesc at r ~ at Rs. Hashizume et al. 2015

21 ULX bubbles Kinetic Power (vr>vesc) Poutflow~3x10 39 erg/s (10Msun) Wide angle outflow would produce the shock excited bubbles around ULX. Kinetic power is consistent with observations (3-5 x erg/s). 0 angle 90 Super-Eddington model would explain the shock excited bubbles.

22 Evidence of outflow Pinto, Middleton, Fabian, 2016 Blue-shifted absorption lines are for the first time detected in ULXs, implying the existence of the outflows. Outflow velocity of c nicely fits our results, ~0.3c. Blue-shifted absorption lines would be reproduced by the outflows from the super-eddington disks.

23 Large-box RHD simulation m input = ρ gas preliminary (Ogawa+16) T gas 10 6 K 10 6 K

24 How much gas to go out? (Ogawa+16) 10 5 preliminary m acc m 0.7 input 10 1 m outflow m 1.2 input m input

25 10 3 L kin or L rad? preliminary (Ogawa+16) L rad m 0.3 acc 10 0 L kin m 1.3 acc m acc

26 1000 Rs ULX vs. ULS? m acc =700 (Ogawa+16) T gas m acc =30 preliminary Rs 0.1 kev Photosphere (where tau_eff = 1 from outside) is located at r ~ 1000 Rs Super-Eddington objects will be identified as ULSs for the observers at theta > 45 deg.

27 What determines X-ray temp.? standard disk part:, H << r, slim disk part: H~r, T r -0.5 T r kev 0.1 kev disk temperature (at ~ L Edd ): T disk ( r) ~1( M/10M T disk ( R trap sun ) 1/4 ( r /3R s ) ) ~ 0.1( m /300) 1/2 1/2 [kev] [kev] Rtrap ~ m R s

28 Summary Our super-eddington simulations can reproduce the basic features of ULXs (Luminosity, spectra, time-variation, and ULX bubbles). Thus, our results support that ULXs are powered by the super- Eddington accretion onto stellar-mass BHs. Our simulations indicate that the powerful outflows, of which the maximum velocity is ~0.3c, is launched from the super-eddington disks. This is consistent with the recent observations which discovered the blueshifted absorption lines ( c) in ULXs. In our simulations, ULSs are also explained by super-eddington flows.

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30 Super-Eddington model for ULX pulsar(s) Shin Mineshige (Kyoto), Ken Ohsuga (NAOJ), Tomohisa Kawashima (NAOJ) Collaboration with T. Ogawa

31 Model for ULX-pulsar Super-Eddington accretion occurs also onto neutron stars (NSs). How about the cases with magnetized NSs? accretion occurs through an accretion column (or funnel) free fall zone Frank+02 shock radiation settling zone RHD simulation of an accretion column (half opening angle of π/6) initially filled with uniform gas (ρ= 10-4 g/cm 3 ) L~10 2 L Edd two-zone structure & strong radiation from the column side NS Basko-Sunyaev76

32 Radiation from the column side potential kinetic heat radiation

33 Summary & Issues Three types of super-eddington flow: central object photon luminosity final energy carrier black hole (BH) > L Edd trapped photons +outflow (+Poynting) non-magnetized NS ~ L Edd outflow (E kin ) magnetized NS >> L Edd (Ω/2π) outgoing radiation Issues: GR effects (Blandford-Znajek process, Lense ー Thirring effects ) Issues: Full radiation transfer (most of the existing simulations assume something uncomfortable) Issues: more comparison with multi-λ observation