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Particle Creation in GRB Central Region Strong Gravity and Electromagnetic Field Hyun Kyu Lee( ) Hanyang University 2008 Nanjing GRB Conference June 23-27, 2008

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Isotropic distribution Cosmic distances Isotropic energy Burst duration T ~ ms 100 s Gamma Ray Bursts(GRB) I. Introduction

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Central Region of GRB ?

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Probing GRB Central Region

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Black hole-Accretion disk Magnetic Braking II. A model for GRB central engine

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Rotational Energy of Kerr Black Hole

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Simple Exercise: black hole-accretion disk(Poynting-flux dominated flow) H.Kim & HKL, JKPS 42, S40(2003) turn-off profile HKL, PRD 64, 043006(2001) rapidly declining LC

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Ultra-Strong Magnetic Field GRB : B ~ 10^{15} G Magnetars : SGR(Soft Gamma Repeaters, AXP(Anomalous X-Ray Pulsars) : B > 10^{14} G Radio Pulsars : B ~ 10^{12} G Magnetically dominated system: E^2 B^2 < 0

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Data vs. Magnetar model (Lyons et al. 2008) We expect a relation between the pulsar initial spin period (P 0 ), dipole field strength (B p ), luminosity (L) and the characteristic timescale (T em ) for spin-down: L B p 2 / P 0 4 and T em P 0 2 / B p 2 (overestimated if final rapid decay due to collapse) B p (G) P 0 (msec) 10 16 10 15 Spin period too short? Too faint vs. X-ray plateau? B field too large or too brief? P. OBrien, 2008 Nanjing GRB

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III. Electromagnetic Vacuum Instability 3.1 QED e+ e- pair creation Schwinger 1951 Electric Effect: E 2 B 2 > 0

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3.2 Fermion Production with Pauli Interaction Astrophysical environment with storng magnetic field is magnetically dominant : B^2 E^2 > 0 No Schwinger process Fermion with Magnetic Moment : Pauli Interaction

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Effective potential for uniform magnetic field Critical magnetic field : HKL & Y. Yoon JHEP 03, 086(2007) Magnetic Effect: B^2-E^2 > 0

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HKL & Y. Yoon JHEP 03, 078(2007)

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IV. Neutrino Production in GRB Central Region Neutrino: 1. electrically neutral(beta decay) 2. massive(neutrino oscillation) 3. flavor mixing (neutrino oscillation) 4. Dirac or Majorana ? 5. magnetic moment ? 6. physics beyond standard model

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Theoretical and experimental bounds on neutrino magnetic moment Critical magnetic field Slow process Continuous source of neutrinos Production in mass eigenstate

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Model for neutrino magnetic moment Neutrino production inside fireball Neutrino emission in accretion torus Validity of effective theory for strong magnetic field

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V. e+e- pair production inside ergosphere Geometry around Kerr black hole with mass m and angular momentum J=am Event horizon Boundary of ergosphere Magnetically-dominated in preperation

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On equator plane inside ergosphere 1. f < 0 : magnetically dominated No Poyintng flux along the field lines

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2. non force-free equator: f > 0 pair creation of e + e - E > E C accretion flow of particles in negative energy orbit. (plasma effect is not included)

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Power from ergo region

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Out Looks New Laboratory Astrophysical Phenomena GRB, Magnetar Compact Objects Neutron star ~ 10 km Black Hole ~ 1.5 km (horizon) and Extreme Environment Strong Magnetic Field: B > 10^{15} G Strong Gravity : horizon, ergosphere Particle creation: Electromagnetic v acuum instability