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

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


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

2
The basic picture
  • Rees 1988 When rltr_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
G300
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 gt50 MeV!
10
Synchrotron self-Compton emission
11
(No Transcript)
12
The calculated flux at 100MeV
  • parameters
  • E1052 erg
  • t_b3106 s
  • d50Mpc
  • ep_e0.1
  • ep_B0.001
  • n1000 cm-3
  • p2.5

Fermi/LAT sensitivity
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)
  • Egt1018-1019 eV
  • Extragalactic origin

Ultra-high energy cosmic rays
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

HiRes Collaboration, PRL D. Bergman and J. Belz,
arXiv0704.3721
ankle GZK
slope below 3.22 0.03 2.81 0.03
break point (logEeV) 18.65 0.04 19.75 0.04
slope above 2.81 0.03 5.1 0.7
18
Sources Acceleration
Waxman 04
v
R
B
v
G2
G2
2R
l R/G
(dtRFR/Gc)
  • AGN G few ? Lgt1045 erg/s
  • GRB G 300 ? Lgt1051 erg/s

19
AGNs as a candidate of UHECRs
Hillas Plot
20
Auger result
27 events E gt 57 EeV 3.20 radius
Véron Véron-Cetty catalogue 442 AGN (292 in
f.o.v.) zlt0.017 (71 Mpc)
galactic coordinates
Border of the f.o.v.
Super-galactic plane
Relative exposure
21
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 dont work!

Actually, no observed objects with luminosity
gt1045 erg s-1 within d100Mpc !
22
Diffusion of the UHECRs induced by the
intergalactic B
g
  • CR dispersion time
  • But, there could be past transient sources with a
    high luminosity above 1045 erg/s

p
D
lB
23
UHECR production in transient Giant AGN flares
(Farrar Gruzinov, 2008)
  • Black Hole tidal disruption of a passing star
  • Occurs every 104-105 yr
  • In AGN, produces a Super-Eddington jet
  • Duration debris return time, 1 month
  • event energy 0.01 Msun gt 1052 ergs
  • Easily achieves L gt 1045 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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