Black Hole Candidates in Gamma-Ray Bursts Xuefeng Wu Purple - - PowerPoint PPT Presentation

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Black Hole Candidates in Gamma-Ray Bursts Xuefeng Wu Purple - - PowerPoint PPT Presentation

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Black Holes and Friends Fudan University,2015.3.30-4.1 Black Hole Candidates in Gamma-Ray Bursts Xuefeng Wu Purple Mountain Observatory Chinese Academy of Sciences Collaborators Collaborators Liang Li, Weihua Weihua Lei, Lei, Zigao

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Black Hole Candidates in Gamma-Ray Bursts

Xuefeng Wu

Purple Mountain Observatory Chinese Academy of Sciences Collaborators Collaborators：Liang Li, Weihua Weihua Lei, Lei, Zigao Zigao Dai, Dai, Enwei Enwei Liang, and Bing Zhang

Black Holes and Friends

Fudan University,2015.3.30-4.1

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Basic Features of GRBs

  • - spatial features
  • - detection rate:
  • - temporal features
  • - spectral features
  • Profiles

Complicated

  • Durations

5 ms ─ 10 s ─ 5×103 s

  • Variability

0.1ms ─1ms ,

  • No repetition

1-2 events per day by CGRO/BATSE

  • Photon Energy

1 eV ─ 1 MeV ─ 30 GeV

  • Non-thermal:

N(E) ∝ E-α

  • High Energy Tail:

no cutoff above 1 MeV

  • Fluence:

10-10 ─ 10-8 J /m2

log

Isotropic

Lack of weak GRBs

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Short vs. Long GRBs

Long Bursts: collapsars Young (few million yrs) Star-forming regions Short Bursts: mergers Old (few billion yrs) Outside galaxies Short Bursts: mergers Old (few billion yrs) Outside galaxies Long Bursts: collapsars Young (few million yrs) Star-forming regions

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Gehrels, Piro & Leonard 2002, Scientific American

How to identify black holes in GRBs?

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Outline

  • 1. GRB X-ray shallow-decays/plateaus and the

magnetar model

  • 2. GRB X-ray shallow-decays/plateaus and the black

hole candidates

  • 3. Summary

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X-ray shallow-decay/plateaus

  • Swift/XRT discovery in 2005 and hydrodynamic origin

t -5.5ν-1.60.22

GRB050319

t -0.54ν-0.690.06 t -1.14ν-0.800.08

Cusumano et al., 2006, ApJ, 639, 316

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a large sample

~ about 50% GRBs have X-ray shallow decay/plateaus for more details of data analysis on X-ray plateaus

  • f Swift GRBs, see

Liang et al., 2007, ApJ, 670, 565,

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2 classes of X-ray plateaus

external origin

  • vs. internal origin

Cusumano et al., 2006, ApJ, 639, 316 Troja et al., 2007, ApJ, 665, 599 Energy injection: Matter-dominated？ Poynting dominated？

GRB050319

Magnetic dissipation？

GRB070110

1、most plateaus are of external origin 2、no quantitative internal plateau model

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Matter-dominated energy injection model

Forward Shock

end of injection

Lorentz factor distribution (Rees & Meszaros 1998):

s

M

 

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Poynting-flux dominated energy injection model

millisecond magnetar

  • r

fast-rotating black hole B-field Forward Shock

Injected luminosity (Dai & Lu 1998):

2

( / ) , ( / ) ,

q

L t T t T L L t T t T

    

       

end of injection

Forward shock energy: Ek,iso ∝ t1-q,

Poynting flux Poynting flux see Zhang et al., 2006, ApJ Nousek et al., 2006, ApJ

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Dai & Lu 1998; Zhang & Meszaros 2001; Fan & Xu 2006; Dall’Osso et al. 2011, etc.

Poynting-flux dominated injection by millisecond magnetar

numerical calculations and fittings to the observations

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Termination Shock External Shock Contact Discontinuity Shocked ambient medium

Relativistic e-e+ wind

Shocked e-e+ wind

Relativistic wind bubble (RWB) model

Black hole

Dai (2004, ApJ)

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Yu & Dai (2007) numerical light curves Dai (2004) analytical light curves

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Dai (2004)：X-ray plateaus may be highly polarized detectable by future X-ray polarimeter (such as XTP)

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Lv & Zhang Sample for GRB Magnetars

Gold: internal plateaus, (3 known z & 6 unknown z) Silver: external plateaus, (33 known z)

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Short GRBs

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Magnetars in short GRBs

X-ray plateau traces the spin-down of the magnetar? Collapse of the magnetar?

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Magnetars in short GRBs

Rowlinson et al. (2013)

X-ray plateaus

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Magnetars in short GRBs

Rowlinson et al. (2013)

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Gehrels, Piro & Leonard 2002, Scientific American

Where are black holes in GRBs?

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Outline

  • 1. GRB X-ray shallow-decays/plateaus and the

magnetar model

  • 2. GRB X-ray shallow-decays/plateaus and the black

hole candidates

  • 3. Summary

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Plateau Model Comparison：Magnetar vs. BH

GRB afterglow jet GRB afterglow jet isotropic injection low efficiency collimated injection high efficiency

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Magnetar parameters

2 observables，2 variables： （1）dipole magnetic B-field; （2）initial rotational Period。

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Lv & Zhang Sample for GRB Magnetars

Magnetar isotropic injection

Gold: internal plateaus, 3 known z & 6 unknown z Silver: external plateaus, 33 known z Aluminum: other plateaus

？

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Magnetar collimated injection

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Collimated wind from magnetar

Bucciantini et al., 2008, MNRAS, 383, L25 Bucciantini et al., 2009, MNRAS, 396, 2038 After plateau

/ >>

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Lv & Zhang Sample for GRB Magnetars

Gold: internal plateaus, 3 known z & 6 unknown z Silver: external plateaus, 33 known z Aluminum: other plateaus

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Magnetar isotropic injection Magnetar collimated injection

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Bucciantini et al., 2008, MNRAS, 383, L25 Bucciantini et al., 2009, MNRAS, 396, 2038 平台相结束后

/ >>

Assumptions of Bucciantini et al. simulations （1）GRB prompt phase，progenitor envelope exist X-ray plateaus，1 – 10 ks after the prompt phase （2）B >=10^15 G，magnetar luminosity about 10^51 erg/s，at least 10^50 erg/s。 X-ray plateaus, much lower B and luminosity (10^47 – 10^49 erg/s) （3）highly magnetization, Lorentz factor about 10 X-ray plateaus, unknown magnetization, higher Lorentz factor （4）toroidal magnetic field outside the magnetar, toothpase effect （kink instability?） X-ray plateaus, still toroidal magnetic field? No conclusive words about isotropic or collimated magnetar wind during the plateau phase

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Collimated wind from magnetar

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More reasonable criteria for magnetar/BH

GRB afterglow model has a lot of parameters Lower limit on E_k,iso (unknown radiation efficiency) Gold: Ex,iso > 2x10^52 erg, Ek,iso > 2x10^52 erg Black holes ?! （4 GRBs） Silver: Ex,iso < 2x10^52 erg, Ek,iso > 2x10^52 erg Black holes ? （62 GRBs） Bronze: Ex,iso < 2x10^52 erg, Ek,iso < 2x10^52 erg Magnetar ? （13 GRBs）

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BH candidates in GRB X-ray plateaus

(4 GRBs) (62 GRBs) (13 GRBs)

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Spin parameter of GRB BH candidates

a<0.1

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GRB afterglow jet

Blandford-Znajek mechanism

2、BZ power： Ratio of B-field angular velocity to BH spin 1、BH rotational energy：

其中黑洞自转参数： 其中： Lei, W. H., Zhang, B., & Liang, E. W., 2013, ApJ

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Wang, D. X., Lei, W. H., Xiao, K., & Ma, R. Y., 2002, ApJ

BH spin evolution in Blandford-Znajek process (1) k=0.5, maximum BZ power (2) Region I(IA, IB)， spin down LBZ,iso ∝ t -q q>0 (3) Region II ， spin up LBZ,iso ∝ t -q q<0

BH spin evolution： spin up spin down

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Wang, D. X., Lei, W. H., Xiao, K., & Ma, R. Y., 2002, ApJ solid line: k=0.6 dashed line: k=0.5 (upper and lower limits depends on k value as well as the inner radius of the accretion disk)

initial condition： BH spin evolution (BZ)：

(1) initial spin of X-ray plateau

  • after the prompt GRB；

(2) When k=0.6, and BH spin up, and X-ray plateau with q<0； (3) Otherwise，X-ray plateau with q>0

LBZ,iso ∝ t -q 32 BH spin evolution in Blandford-Znajek process

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Outline

  • 1. GRB X-ray shallow-decays/plateaus and the

magnetar model

  • 2. GRB X-ray shallow-decays/plateaus and the black

hole candidates

  • 3. Summary

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  • Both magnetar and BH models can explain the X-ray

shallow-decay/plateaus of GRBs well；

  • Less energetic (smaller than the NS maximum rotational

energy, 2e52 erg) X-ray plateaus may originate from magnetars

  • More energetic (larger than the NS maximum rotational

energy, 2e52 erg) X-ray plateaus may originate from black holes

  • We plan to apply detailed BZ mechanism to constrain BH

parameters with X-ray plateaus

Summary