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

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 Zigao Dai, Dai, Enwei Enwei Liang, and Bing Zhang 1

Basic Features of GRBs -- detection rate: -- temporal features -- spectral features -- spatial features • Photon Energy 1-2 events per day by CGRO/BATSE 1 eV ─ 1 MeV ─ 30 GeV • Profiles • Non-thermal : Complicated N(E) ∝ E - α • Durations • High Energy Tail: 5 ms ─ 10 s ─ 5 × 10 3 s • Variability no cutoff above 1 MeV • Fluence: 0.1ms ─1ms , Lack of weak GRBs 10 -10 ─ 10 -8 J /m 2 • No repetition Isotropic log

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

How to identify black holes in GRBs? Gehrels, Piro & Leonard 2002, Scientific American

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 5

X-ray shallow-decay/plateaus - Swift/XRT discovery in 2005 and hydrodynamic origin GRB050319 t -5.5 ν -1.6  0.22 t -1.14 ν -0.80  0.08 t -0.54 ν -0.69  0.06 Cusumano et al., 2006, ApJ, 639, 316 6

a large sample ~ about 50% GRBs have X-ray shallow decay/plateaus for more details of data analysis on X-ray plateaus of Swift GRBs, see Liang et al., 2007, ApJ, 670, 565, 7

2 classes of X-ray plateaus external origin vs. internal origin Energy injection: 1 、 most plateaus are of external origin Magnetic Matter-dominated ？ dissipation ？ 2 、 no quantitative internal plateau model Poynting dominated ？ GRB070110 GRB050319 Cusumano et al., 2006, ApJ, 639, 316 Troja et al., 2007, ApJ, 665, 599 8

Matter-dominated energy injection model end of injection Forward Shock Lorentz factor distribution ( Rees & Meszaros 1998 ):    s M

Poynting-flux dominated energy injection model Injected luminosity ( Dai & Lu 1998 ):    q ( / ) , L t T t T     0 L    2  L t T ( / ) , t T   0 Poynting flux millisecond magnetar end of injection or Forward Shock fast-rotating black hole Forward shock energy: Poynting flux E k,iso ∝ t 1-q , see Zhang et al., 2006, ApJ 10 B-field Nousek et al., 2006, ApJ

Poynting-flux dominated injection by millisecond magnetar numerical calculations and fittings to the observations Dai & Lu 1998; Zhang & Meszaros 2001; Fan & Xu 2006; Dall’Osso et al. 2011, etc. 11

Relativistic wind bubble (RWB) model Shocked ambient medium Shocked e-e+ wind External Relativistic e - e + wind Shock Black hole Termination Shock Contact Discontinuity Dai (2004, ApJ) 12

Dai (2004) analytical light curves Yu & Dai (2007) numerical light curves 13

Dai (2004) ： X-ray plateaus may be highly polarized detectable by future X-ray polarimeter (such as XTP) 14

Lv & Zhang Sample for GRB Magnetars Gold: internal plateaus, (3 known z & 6 unknown z) Silver: external plateaus, (33 known z) Short GRBs 15

Magnetars in short GRBs X-ray plateau traces Collapse of the the spin-down of the magnetar? magnetar?

Magnetars in short GRBs X-ray plateaus Rowlinson et al. (2013) 17

Magnetars in short GRBs Rowlinson et al. (2013)

Where are black holes in GRBs? Gehrels, Piro & Leonard 2002, Scientific American

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 20

Plateau Model Comparison ： Magnetar vs. BH GRB afterglow jet GRB afterglow jet isotropic injection collimated injection low efficiency high efficiency 21

Magnetar parameters 2 observables ， 2 variables ： （ 1 ） dipole magnetic B-field; （ 2 ） initial rotational Period 。 22

Lv & Zhang Sample for GRB Magnetars Magnetar Magnetar isotropic collimated injection injection ？ Gold: internal plateaus, 3 known z & 6 unknown z Silver: external plateaus, 33 known z 23 Aluminum: other plateaus

Collimated wind from magnetar >> After plateau / Bucciantini et al., 2008, MNRAS, 383, L25 24 Bucciantini et al., 2009, MNRAS, 396, 2038

Lv & Zhang Sample for GRB Magnetars Magnetar Magnetar isotropic collimated injection injection Gold: internal plateaus, 3 known z & 6 unknown z Silver: external plateaus, 33 known z 25 Aluminum: other plateaus

Collimated wind from magnetar 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 平台相结束后 >> / Bucciantini et al., 2008, MNRAS, 383, L25 26 Bucciantini et al., 2009, MNRAS, 396, 2038

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

BH candidates in GRB X-ray plateaus (4 GRBs) (62 GRBs) (13 GRBs) 28

Spin parameter of GRB BH candidates a<0.1 29

Blandford-Znajek mechanism GRB afterglow jet Lei, W. H., Zhang, B., & Liang, E. W., 2013, ApJ 1 、 BH rotational energy ： 其中黑洞自转参数： 2 、 BZ power ： 其中： Ratio of B-field angular velocity to BH spin 30

BH spin evolution in Blandford-Znajek process BH spin evolution ： spin up (1) k=0.5, maximum BZ power (2) Region I(IA, IB) ， spin down spin down L BZ,iso ∝ t -q q>0 (3) Region II ， spin up L BZ,iso ∝ t -q 31 q<0 Wang, D. X., Lei, W. H., Xiao, K., & Ma, R. Y., 2002, ApJ

BH spin evolution in Blandford-Znajek process initial condition ： BH spin evolution (BZ) ： (1) initial spin of X-ray plateau - after the prompt GRB ； (2) When k=0.6, and 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) BH spin up, and X-ray plateau with q<0 ； (3) Otherwise ， X-ray plateau with q>0 L BZ,iso ∝ t -q 32 Wang, D. X., Lei, W. H., Xiao, K., & Ma, R. Y., 2002, ApJ

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 33

Summary • 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 34