Modeling the X-ray emission and QPO of Swift J1644+57

Fayin Wang (王发印）

Nanjing University, China

Collaborators: K. S. Cheng (HKU), Z. G. Dai (NJU), Y. C. Zou (HUST)

Outline

Tidal disruption event (TDE) and Swift J1644+57 observation

X-ray flares of Swift J164+57Long-term X-ray emissionQuasi-periodic oscillation (QPO)Summary

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Galactic centers: some are active, most are dormant

M87; NASA/Hubble

Ghez et al. 2005

Sgr A*

NGC 3115

Canada-France-Hawaii Telescope

Tidal disruption event (TDE) can light dormant SMBH. So TDE is promising tool toprobe galactic center BHs.

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Unlucky Star tidal disrupted by SMBHs

Rt

When a star’s orbit in tidal radius (tidal force=self gravity)

it is tidally disrupted.For a solar type star

1/3

BH*

*

~Mt

MR R

Rate of TDEs~10Rate of TDEs~10-5-5-10-10-3-3 yr yr-1-1galgal-1 -1

(e.g. Wang& Merritt 2004)

(Rees 88; Evans & Kochanek 89; Li et al. 02; Strubbe & Quataert 09; Lodato et al.09; …)

Fallback time (most bound material):tf ~ days to weeks.

Rees 88

Rt~1013(MBH,6 )1/3cm

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Swift J1644+57: first TDE with a jet

/X-ray/X-ray

IR-OpticalIR-Optical

RadioRadio

• Triggered Swift BAT on March 28, 2011

• Triggered BAT 3 more times over next few days

• Remains bright in X-rays

• IR and Radio Brightening

• Host galaxy at z = 0.35

(Levan et al. 2011; Bloom et al. 2011; Burrows et al. 2011; Zauderder et al. 2011)

• NOT a (normal) GRB

- low luminosity

- duration ~ months

•NOT a normal AGN

- no evidence for AGN or past activity

Levan et al. 2011, Science

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Host Galaxy at z = 0.35

Not an AGN• Within < 150 pc of galactic center SMBH origin

•LX > 1048 erg s-1 > 10000 LEdd of 106M⊙ black hole super-Edd accretion and/or beaming

Levan et al. 2011

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Zauderder et al. 2011

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Blazar model for Swift J1644+57

• synchrotron self-absorption Rradio > 1016 cm Г~20 external shock from ISM interaction (Giannios & Metzger 2011)

• X-ray variability RX ~ c tX 2 ~ 3x1014 (/20)2 cm “internal” process (e.g. shocks, reconnection)

t ~ 3 days

X-rays

radio Bloom et al. 2011 Fermi LAT

Av=3-5

Emission from the accretion disk is Compton-upscattered,giving rise to the observed x-rays.

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1.Internal model for X-ray flares

Levan et al. 2011, Science

Many flares in the X-ray band!

X-ray flux increases 10 times in 200 seconds, from internal shocks.

For Lorentz factor about 20, the criticalfrequencies of external shock (radio and optical)

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Internal-shock model for X-ray flares

Reverse shock Forward shock

Yu & Dai 2009

Two shocks structure:

shocked materialunshocked materialunshocked material

1234L1γ1L4γ4

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See Prof. Z. G. Dai’s talk

Wang & Cheng 2012

t=3 dayst=31 hrs

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Wang & Cheng 2012

Zauderder et al. 2013

Internal shock

external shock

external shock

Chandra observation at 630 days

Our model also predicts that the external shock will dominate the X-ray emission when the internal shock has ended.

Our prediction is confirmed by observation!

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2. Long-term X-ray emission

Saxton et al. 2012

There are many pulses with long durationtimes (105-106 s) are found at later observationin the X-ray band.

jet precession? Possibly warped disk around rapidly spinning BH (Lei et al.2012; Bardeen-Petterson effect due to stellar orbit not being in BH equatorial plane, leads to jet precession)

Lei et al.201223/4/22 13FAN4 Workshop

14

BH

How to produce late X-ray pulses?

ExternalShock

InternalShocks

X-ray flares

ISM

Combined shell X-ray pulse

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The Lorentz factor of the external shock is

The critical frequencies of the synchrotron emission are (for energy injection)

The peak observed flux density is

Zou, Wang & Cheng 2013

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Light curve

Zou, Wang & Cheng 2013

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1<α<1.5

Photon index evolution

Zou, Wang & Cheng 2013

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3. Quasi-periodic oscillation(QPO)

Reis et al. 2012, Science

3.8σ

2.2σQ=15

QPO at ν=4.8 mHz

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So the power spectrum

The clumpy accretion scale is

a steady outflow plus a clumpy shells with a periodic modulation at a frequency ω0

β is the fraction of discrete shells in the total outflow gas.

τ gives the width of the QPO frequency, A is the amplitude.

From the properties of QPO observed by Suzaku and XMM-Newton,We find β=0.3.

Wang et al. 2013

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4. Statistics of X-ray flares• Nearly half of GRBs have X-ray flares,

including long and short GRBs.

• But the physical origin is mysterious, many models have been proposed.

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Barthelmy et al. 2005, NatureBurrows et al. 2005 Science

GRB 050724

Energy frequency distribution

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83= 9 (short)+74 (long)

Wang & Dai 2013, Nature Phys

Duration time distribution

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Wang & Dai 2013, Nature Phys

Waiting time distribution

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Wang & Dai 2013, Nature Phys

Magnetic reconnection?

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Similar distributions between GRB X-ray flares and solar flares may reflect an underlying system in a state of self-organized criticality (Bak, Tang, & Wiesenfeld 1987) where many composite systems will self-organize to a critical state in which a small perturbation can trigger a chain reaction that affects any number of elements within the system.

Self-organized criticality (SOC)?

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Summary• Swift J1644+57 is the first TDE with jet and QPO

• The internal shock model can explain the X-ray flares of Swift J1644+57

• The energy injection can explain the long term X-ray emission

• The clumpy component comprises about 30% of outflow

• Strong relativistic jet results in unique properties of this event!

• SOC property of GRB X-ray flares

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Thanks for your attention!Thanks for your attention!