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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),

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Presentation on theme: "High-energy emission from the tidal disruption of stars by massive black holes Xiang-Yu Wang Nanjing University, China Collaborators: K. S. Cheng(HKU),"— Presentation transcript:

1 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

2 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

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  ~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

12 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

13 The expected detection rate by LAT The rate of capture events Within, the number of capture events

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

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

16 Greisen, Zatsepin and Kuzmin(GZK) effect

17 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

18 Sources: Acceleration R B v v 2R  t RF =R/  c) l =R/  22 22 [Waxman 04] AGN:  ~ few  L>10 45 erg/s GRB:  ~ 300  L>10 51 erg/s

19 AGNs as a candidate of UHECRs Hillas Plot

20 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

21 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 !

22 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

23 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

24 The maximum energy of accelerated protons particle acceleration in the blast wave

25 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

26 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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