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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) ---preliminary results
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The basic picture Rees 1988: When r<r_t, the star is captured by the BH r_t---tidal radius Applicable to 10 6-7 M SMBH A transient accretion disk is formed Artists conception of tidal disruption of star
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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
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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
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Jet-driven blast wave emission in GRB- --the afterglows ~300
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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
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The dynamic of the blast wave
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Synchrotron radiation The magnetic field The spectrum
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Maximum synchrotron photon energy ---a parameter describing the efficiency of the shock acceleration Synchrotron radiation can not produce photons with energy >50 MeV !
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Synchrotron self-Compton emission
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The calculated flux at 100MeV Fermi/LAT sensitivity 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
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The expected detection rate by LAT The rate of capture events Within, the number of capture events
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2. Ultra-high energy cosmic rays from the jet resulted from the tidal disruption
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Ultra-high energy cosmic rays (UHECRs) Ultra-high energy cosmic rays E>10^18-10^19 eV Extragalactic origin
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Greisen, Zatsepin and Kuzmin(GZK) effect
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HiRes result Summary of spectral indices and break points from the fits to the HiRes monocular data ankleGZK slope below3.22 ±0.032.81 ± 0.03 break point (logE eV ) 18.65 ± 0.0419.75 ± 0.04 slope above2.81 ± 0.035.1 ± 0.7 HiRes Collaboration, PRL D. Bergman and J. Belz, arXiv:0704.3721
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Sources: Acceleration R B v v 2R t RF =R/ c) l =R/ 22 22 [Waxman 04] AGN: ~ few L>10 45 erg/s GRB: ~ 300 L>10 51 erg/s
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AGNs as a candidate of UHECRs Hillas Plot
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Super-galactic plane galactic coordinates Border of the f.o.v. 27 events E > 57 EeV 3.2 0 radius Véron &Véron-Cetty catalogue 442 AGN (292 in f.o.v.) z<0.017 (71 Mpc) Relative exposure Auger result
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Auger UHECR correlation with Veron-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 !
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Diffusion of the UHECRs induced by the intergalactic B CR dispersion time But, there could be past transient sources with a high luminosity above 10^45 erg/s p D B
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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
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The maximum energy of accelerated protons particle acceleration in the blast wave
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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
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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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