Modeling the X-ray emission and QPO of Swift J1644+57

1. Modeling the X-ray emission and QPO of Swift J1644+57 Fayin Wang (王发印） Nanjing University, China Collaborators: K. S. Cheng (HKU), Z. G. Dai (NJU), Y. C. Zou (HUST)

2. Outline • Tidal disruption event (TDE) and Swift J1644+57 observation • X-ray flares of Swift J164+57 • Long-term X-ray emission • Quasi-periodic oscillation (QPO) • Summary FAN4 Workshop

3. Galactic centers: some are active, most are dormant NGC 3115 M87; NASA/Hubble Canada-France-Hawaii Telescope Sgr A* Tidal disruption event (TDE) can light dormant SMBH. So TDE is promising tool to probe galactic center BHs. FAN4 Workshop Ghez et al. 2005

4. Unlucky Star tidal disrupted by SMBHs (Rees 88; Evans & Kochanek 89; Li et al. 02; Strubbe & Quataert 09; Lodato et al.09; …) When a star’s orbit in tidal radius (tidal force=self gravity) it is tidally disrupted. For a solartype star Rt Rt~1013(MBH,6 )1/3cm Rees 88 Rate of TDEs~10-5-10-3 yr-1gal-1 (e.g. Wang& Merritt 2004) Fallback time (most bound material): tf ~ days to weeks. FAN4 Workshop

5. Swift J1644+57: first TDE with a jet (Levan et al. 2011; Bloom et al. 2011; Burrows et al. 2011; Zauderder et al. 2011) • Triggered Swift BAT on March 28, 2011 • Triggered BAT 3 more times over next few days • Remains bright in X-rays • IR and Radio Brightening • Host galaxy at z = 0.35 /X-ray IR-Optical • NOT a (normal) GRB • low luminosity • duration ~ months Radio • NOT a normal AGN • no evidence for AGN or past activity Levan et al. 2011, Science FAN4 Workshop

6. Host Galaxy at z = 0.35 Levan et al. 2011 Not an AGN • Within < 150 pc of galactic center  SMBH origin • LX > 1048 erg s-1 > 10000 LEdd of 106M⊙ black hole  super-Edd accretion and/or beaming FAN4 Workshop

7. Zauderder et al. 2011 FAN4 Workshop

8. Blazar model for Swift J1644+57 Fermi LAT Emission from the accretion disk is Compton-upscattered, giving rise to the observed x-rays. Bloom et al. 2011 radio t ~ 3 days X-rays Av=3-5 • synchrotron self-absorption  Rradio > 1016 cm  Г~20  external shock from ISM interaction (Giannios & Metzger 2011) • X-ray variability  RX ~ c tX2 ~ 3x1014 (/20)2 cm  “internal” process (e.g. shocks, reconnection) FAN4 Workshop

9. 1.Internal model for X-ray flares Levan et al. 2011, Science X-ray flux increases 10 times in 200 seconds, from internal shocks. For Lorentz factor about 20, the critical frequencies of external shock (radio and optical) Many flares in the X-ray band! FAN4 Workshop

10. Internal-shock model for X-ray flares Two shocks structure: L1γ1 L4γ4 Forward shock Reverse shock 4 3 1 2 shocked material unshocked material unshocked material Yu & Dai 2009 See Prof. Z. G. Dai’s talk FAN4 Workshop

11. t=31 hrs t=3 days Wang & Cheng 2012 FAN4 Workshop

12. Internal shock Our model also predicts that the external shock will dominate the X-ray emission when the internal shock has ended. external shock Wang & Cheng 2012 Our prediction is confirmed by observation! external shock Zauderder et al. 2013 Chandra observation at 630 days FAN4 Workshop

13. 2. Long-term X-ray emission There are many pulses with long duration times (105-106 s) are found at later observation in the X-ray band. • jet precession? Possibly warped disk around rapidly spinning BH (Lei et al.2012; Bardeen-Petterson effect due to stellar orbit not being in BH equatorial plane, leads to jet precession) Saxton et al. 2012 Lei et al.2012 FAN4 Workshop

14. X-ray flares BH Internal Shocks External Shock How to produce late X-ray pulses? Combined shell X-ray pulse ISM FAN4 Workshop

15. The Lorentz factor of the external shock is Zou, Wang & Cheng 2013 The critical frequencies of the synchrotron emission are (for energy injection) The peak observed flux density is FAN4 Workshop

16. Light curve 1<α<1.5 Zou, Wang & Cheng 2013 FAN4 Workshop

17. Photon index evolution Zou, Wang & Cheng 2013 FAN4 Workshop

18. 3. Quasi-periodic oscillation(QPO) 3.8σ 2.2σ Q=15 QPO at ν=4.8 mHz Reis et al. 2012, Science FAN4 Workshop

19. FAN4 Workshop

20. a steady outflow plus a clumpy shells with a periodic modulation at a frequency ω0 β is the fraction of discrete shells in the total outflow gas. So the power spectrum τ gives the width of the QPO frequency, A is the amplitude. From the properties of QPO observed by Suzaku and XMM-Newton, We find β=0.3. The clumpy accretion scale is Wang et al. 2013 FAN4 Workshop

21. 4. Statistics of X-ray flares • Nearly half of GRBs have X-ray flares, including long and short GRBs. • But the physical origin is mysterious, many models have been proposed. GRB 050724 Burrows et al. 2005 Science Barthelmy et al. 2005, Nature FAN4 Workshop

22. Energy frequency distribution 83= 9 (short)+74 (long) Wang & Dai 2013, Nature Phys FAN4 Workshop

23. Duration time distribution Wang & Dai 2013, Nature Phys FAN4 Workshop

24. Waiting time distribution Wang & Dai 2013, Nature Phys FAN4 Workshop

25. Magnetic reconnection? Similar distributions between GRB X-ray flares and solar flares may reflect an underlying system in a state of self-organized criticality (Bak, Tang, & Wiesenfeld 1987) where many composite systems will self-organize to a critical state in which a small perturbation can trigger a chain reaction that affects any number of elements within the system. FAN4 Workshop

26. Self-organized criticality (SOC)? FAN4 Workshop

27. Summary • Swift J1644+57 is the first TDE with jet and QPO • The internal shock model can explain the X-ray flares of Swift J1644+57 • The energy injection can explain the long term X-ray emission • The clumpy component comprises about 30% of outflow • Strong relativistic jet results in unique properties of this event! • SOC property of GRB X-ray flares Thanks for your attention! FAN4 Workshop