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!