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High-energy emission from the tidal disruption of stars by massive black holes

Explore the phenomenon of high-energy emission from the tidal disruption of stars by massive black holes, analyzing jet formation and cosmic rays acceleration. Discover the connection between gamma-ray emission, jet-driven blast waves, and ultra-high energy cosmic rays. Investigate the possibility of detecting these events using Fermi/LAT.

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High-energy emission from the tidal disruption of stars by massive black holes

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  1. ---preliminary results High-energy emission from the tidal disruption of stars by massive black holes Xiang-Yu Wang Nanjing University, China Collaborators: K. S. Cheng(HKU), Ruo-Yu Liu(NJU)

  2. The basic picture • Rees 1988: When r<r_t, the star is captured by the BH r_t---tidal radius • Applicable to 106-7 M SMBH • A transient accretion disk is formed Artists conception of tidal disruption of star

  3. Motivations • A jet may form along the axis of the accretion disk (Cheng et al. 06) • This jet may produce high-energy gamma-ray emission • Use Fermi/LAT to constrain this process

  4. Previous works on the jet emission • Disk may produce x-ray flares (Halpern et al. 2004) • Modelling with the jet-shock emission (Wong , Huang & Cheng 07) The spectrum should be very different

  5. Jet-driven blast wave emission in GRB---the afterglows G~300

  6. Our case— initial condition • Jet energy (Cheng et al. 06) • A long injection phase (Halpern et al. 04) • Initial bulk Lorentz factor • Density of surrounding medium

  7. The dynamic of the blast wave

  8. Synchrotron radiation • The magnetic field • The spectrum

  9. Maximum synchrotron photon energy ---a parameter describing the efficiency of the shock acceleration Synchrotron radiation can not produce photons with energy >50 MeV!

  10. Synchrotron self-Compton emission

  11. The calculated flux at 100MeV parameters • E=10^52 erg • t_b=3*10^6 s • d=50Mpc • ep_e=0.1 • ep_B=0.001 • n=1000 cm^-3 • p=2.5 Fermi/LAT sensitivity

  12. The expected detection rate by LAT • The rate of capture events • Within , the number of capture events

  13. 2. Ultra-high energy cosmic rays from the jet resulted from the tidal disruption

  14. Ultra-high energy cosmic rays (UHECRs) • E>10^18-10^19 eV • Extragalactic origin Ultra-high energy cosmic rays

  15. Greisen, Zatsepin and Kuzmin(GZK) effect

  16. HiRes result • Summary of spectral indices and break points from the fits to the HiRes monocular data HiRes Collaboration, PRL D. Bergman and J. Belz, arXiv:0704.3721

  17. [Waxman 04] v R Sources: Acceleration B v G2 G2 2R l =R/G (dtRF=R/Gc) • AGN: G~ few  L>1045 erg/s • GRB: G~ 300  L>1051 erg/s

  18. AGNs as a candidate of UHECRs Hillas Plot

  19. Augerresult 27 events E > 57 EeV 3.20 radius Véron &Véron-Cetty catalogue 442 AGN (292 in f.o.v.) z<0.017 (71 Mpc) galactic coordinates Border of the f.o.v. Super-galactic plane Relative exposure

  20. Auger UHECR correlation withVeron-Cetty Veron galaxies • VCV catalog -- mostly AGNs, but not pure or complete • L_bol : Most correlations are with too-weak AGNs (Zaw, Farrar, Greene 08) • Morphology of correlated galaxies: few have jets (Moskalenko, Stawarz, Porter, Cheung 08) • Standard Scenarios don’t work! Actually, no observed objects with luminosity >10^45 erg s^-1 within d=100Mpc !

  21. Diffusion of the UHECRs induced by the intergalactic B g p • CR dispersion time • But, there could be past transient sources with a high luminosity above 10^45 erg/s D lB

  22. UHECR production in transient Giant AGN flares (Farrar & Gruzinov, 2008) • Black Hole tidal disruption of a passing star – Occurs every 10^4-10^5 yr – In AGN, produces a Super-Eddington jet – Duration ~ debris return time, ~1 month – event energy: ~0.01 Msun > 10^52 ergs • Easily achieves L > 10^45 erg/s required for UHECR acceleration

  23. The maximum energy of accelerated protons • particle acceleration in the blast wave

  24. UHECR chemical composition--Auger result Elongation Rate measured over two decades of energy Pierre Auger Collaboration 2010, PRL Possible presence of intermediate-mass or heavy nuclei in UHECRs ? But inconsistent with HiRes result

  25. Summary • Stellar capture by massive BH may power a jet • The jet-driven expanding blast wave can produce high-energy gamma-ray emission through SSC process, which may be detected by Fermi/LAT up to distance ~ • Depending on the energy released, the expected detection rate is ~ • The same jet may also accelerate UHECRs

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