GRB Science with XTP Xuefeng Wu Purple Mountain Observatory collaborators: Zigao Dai (NJU), Feng Yuan (SHAO), Enwei Liang (GXU), Yunpeng Men (PKU), & XTP+eXTP science team eXTP Meeting, Beijing, IHEP, Oct. 26-27, 2015 I am Dai Zigao in Astron. Dept. of Nanjing University. Today I talk about GRBs.

Physical Picture of Gamma-Ray Bursts v ≥ 0.9999c Gehrels et al., 2002, Scientific American

Magnetic Field Configuration I. Ordered B-field in large-scale from central engine Large-scale B-field may exist in Prompt GRB emission; Early afterglows (reverse shock) X-ray flares X-ray plateaus Moll 2009

Magnetic Field Configuration II. Disordered B-field by shock amplification Relativistic Weibel instability electron saturation ion saturation Electrons and ions separates into different currents in a disturbed seed B-field, which amplify the B-field in a positive feedback way. Medvedev & Loeb (1999)

Numerical simulation of the Weibel instability Frederiksen et al. (2004) random B-field may exist in Baryon dominated GRB fireball (prompt+flares); late afterglows (forward shock) X-ray plateaus with matter-dominated energy injection

Models on GRB polarization Nonthermal emission: - synchrotron - (inverse-) Compton large-scale B and syn: PL=(p+1)/(p+7/3)~70% Shock accelerated electrons (p=2) Waxman, 2003, Nature, 423, 388

Milestones in GRB polarization detections 1、Prompt gamma-rays： GRB 021206：P =80+/-20% (Coburn & Boggs, 2003, Nature) optical flash: reverse shock Log(Flux) t^-2 forward shock 2、Optical afterglows： Log(t) GRB060418: 1st poln upper limit on the forward shock emission P<8% (Mundell et al., 2007, Science) GRB090102: 1st polarization detection of reverse shock emission P=10.1%+/-1.3% (Steele et al., 2009, Nature) GRB120308A: 1st poln detection of reverse+forward shock emission (Mundell et al., 2013, Nature) GRB121024A: 1st circular poln detection of forward shock emission Pcirc=0.64%+/-0.13%，Pcirc/Plinear=0.15 (Wiersema et al., 2014, Nature)

Swift Canonical X-ray lightcurve X-ray polarimeter – a new era for GRBs！ I. steep decay V. X-ray flare III. Normal decay II. plateau IV. jet phase Zhang, Fan, Dyks et al. 2006, ApJ, 642, 354

GRB Science with XTP Polarization of GRB X-ray emission X-ray observation of ultra-long GRBs X-ray micro-flares in GRBs Late X-ray observation and jet breaks

GRB Science with XTP Polarization of GRB X-ray emission X-ray observation of ultra-long GRBs X-ray micro-flares in GRBs Late X-ray observation and jet breaks

X-ray flares Burrows et al. 2005, Science, 309, 1833 Explanation: late internal shocks (Burrows et al. 2005; Fan & Wei 2005; Zhang et al. 2006; Wu, Dai, Wang et al. 2005), implying a long-lasting central engine.

fast rise + steep decay Chincarini et al. (2007, ApJ, 671, 1903): ~ 1/3 of the detected GRB afterglows. fast rise + steep decay

X-ray flare sample duration ~ peak time Swift XRT observations (May 1 2005 – April 30 2015) 476 flares in 201 GRBs (1/5 Swift triggered GRBs in 10 years) duration ~ peak time duration time centered at ~300 s； for a small fraction, duration > 1 ks Peak time centered at ~300 s； for a small fraction, peak time > 1ks

X-ray flare sample Swift XRT observations (May 1 2005 – April 30 2015) 476 flares in 201 GRBs (1/5 Swift triggered GRBs in 10 years) Peak time centered at ~300 s； for a small fraction, peak time > 10 ks Peak flux centered at ~3e-9 erg/cm^2/s

X-ray flare sample: expected XTP detection possibility Swift XRT observations (May 1 2005 – April 30 2015) 476 flares in 201 GRBs (1/5 Swift triggered GRBs in 10 years) Assume XTP flux sensitivity = 4.4e-15 (t/10^4 s)^(-1/2) erg/cm^2/s XTP slewing speed = (3 – 10) degrees per minute whole flare peak flare (angle between the GRB and XTP boresight)

X-ray flare sample: expected XTP detection possibility Swift XRT observations (May 1 2005 – April 30 2015) 476 flares in 201 GRBs (1/5 Swift triggered GRBs in 10 years) Earth occulation P=50%, R=8 degree/min

fluence distribution of X-ray flares Minimum Detectable Polarization: MDP~19.5% ~ (fluence*S) ^-0.5 S=200 cm^2 MDP~6.2% MDP~62% XTP can do polarization detection for bright X-ray flares if it slews to the GRB within ~1 ks after the trigger! fluence ~ Fp*Tp/3 peaked at 1e-7 erg/cm^2

Two Models for GRB X-ray Polarizations (1) SO：synchrotron with ordered B-field (2) SR：synchrotron with random B-field following Toma et al. (2009, ApJ) SO SR

Input of X-ray flare simulation GRB redshift distribution 1997 Feb. – 2015 Oct.

Input of X-ray flare simulation GRB redshift distribution Gaussian Fit In our simulation: xc=0.3, w=0.1

Input of X-ray flare simulation GRB redshift distribution GRB jet half-opening angle distribution Lu et al., 2012, ApJ

Input of X-ray flare simulation GRB redshift distribution GRB jet half-opening angle distribution Viewing angle distribution p(θv) dθv =sin θv dθv, 0<θv <θj+1/Γ

Input of X-ray flare simulation GRB redshift distribution GRB jet half-opening angle distribution Viewing angle distribution X-ray flare energies (analogue to Frail relation)

X-ray flares statistics: <Ex,iso> ~ 0.01<Eg,iso> Prompt: Margutti, et al. 2011, MNRAS

Input of X-ray flare simulation GRB redshift distribution GRB jet half-opening angle distribution Viewing angle distribution X-ray flare energies (analogue to Frail relation) Band spectrum and Ep - Eiso relation

X-ray flares statistics: Ep - Ex,iso relation Band spectrum X-ray flares 10 Amati relation Prompt GRBs Ep Falcone et al., 2007, ApJ Margutti, et al. 2010, MNRAS

Input of X-ray flare simulation GRB redshift distribution GRB jet half-opening angle distribution Viewing angle distribution X-ray flare energies (analogue to Frail relation) Band spectrum and Ep - Eiso relation Lorentz factor – peak time relation

X-ray flares statistics: Lorentz factor – Tp relation Prompt GRBs X-ray flares Mu, H. J. et al., 2015, ApJ submitted

Preliminary Preliminary simulated X-ray flares X-ray flares simulations: Ex,iso & fluence distribution simulated X-ray flares Preliminary Preliminary

Preliminary XTP simulations for X-ray flares: polarization No SR! XTP can help to distinguish the magnetic field configuration in GRBs by detecting a large sample of X-ray flare polarizations!

Preliminary XTP simulations for X-ray flares: polarization only 14% of SO flares XTP with higher polarization sensitivity can increase the detected number of polarized X-ray flares!

X-ray Plateaus - Swift discovery and hydrodynamic origin external plateau by energy injection: matter-dominated？-> low poln Poynting flux – domianted ？-> high poln Internal plateau magnetic dissipative process？-> high poln GRB070110 GRB050319 post-plateau t -1.14ν-0.800.08 sharp drop steep decay plateau steep decay t -5.5ν-1.60.22 plateau t -0.54ν-0.690.06 Cusumano et al., 2006, ApJ, 639, 316 Troja et al., 2007, ApJ, 665, 599

A large sample ~ half of the detected GRB afterglows have shallow decay/plateau for a detailed analysis of Swift GRBs, see Liang et al., 2007, ApJ, 670, 565,

X-ray plateau sample Swift XRT observations (March 2005 - October 2010) 46 X-ray plateaus (1/10 Swift triggered GRBs in 5 years) flux centered at 1e-11 erg/cm^2/s duration ~ 1 – 100 ks, typically ~10 ks

X-ray plateau sample: expected XTP detection possibility Swift XRT observations (March 2005 - October 2010) 46 X-ray plateaus (1/10 Swift triggered GRBs in 5 years) Earth occulation P=50%, R=2 degree/min

fluence distribution of X-ray plateaus Minimum Detectable Polarization: MDP~19.5% MDP~6.2% ~ (fluence*S) ^-0.5 S=200 cm^2 MDP~62% XTP can do polarization detection for bright X-ray plateaus if it slews to the GRB within ~1 ks – 100 ks after the trigger! fluence ~ Fb*Tb peaked at 1e-7 erg/cm^2

X-ray plateau polarization: theoretical expectation Poynting-flux-dominated energy injection high polarization (20%-50%) Matter-dominated energy injection low polarization (<5%) random B-field aligned B-field Lan, M. X., Wu, X. F., & Dai, Z. G., 2015, ApJ to be submitted

Preliminary XTP simulations for X-ray plateaus: polarization MDP XTP can help to distinguish the magnetic field configuration and the physical origin of X-ray plateaus if a large sample of polarizations of X-ray plateaus has been detected!

GRB Science with XTP Polarization of GRB X-ray emission X-ray observation of ultra-long GRBs X-ray micro-flares in GRBs Late X-ray observation and jet breaks

Ultra-long GRBs Levan et al., 2013, arXiv: 1302.2352

Polarization of ultra-long GRBs GRB 121027A （1）Bright X-ray emission lasts for 10 ks (e.g., GRB 121027A) （2）Fall-back (a massive progenitor) accretion + Blandford-Znajek mechanism was proposed, which successfully interprets the long-lasting X-ray emission in super-long GRB 121027A (Wu, Hou & Lei, 2013, ApJ, 767, L36) -> high polarization of X-ray emission?

GRB Science with XTP Polarization of GRB X-ray emission X-ray observation of ultra-long GRBs X-ray micro-flares in GRBs Late X-ray observation and jet breaks

GRB optical micro-flares Swenson, et al., 2013, arXiv:1303.0286

GRB optical micro-flares flux of flare Flux ratio = ------------------------------------ flux of underlying component micro-flare: Flux ratio < 0.5 Swenson, et al., 2013, arXiv:1303.0286

GRB X-ray flare amplitudes Where are microflares? Chincarini et al., 2010, MNRAS

XTP vs Swift/XRT: larger detection area, higher temporal resolution  identify X-ray micro-flares from underlying external-shock afterglows  unveiling the central engine activities in smaller time scales GRB 070110

GRB X-ray flares statistics Differential duration time distributions of solar flares and X-ray flares. The slopes: (-2.00±0.05, -1.10±0.15). microflares dominate, but lack … Wang & Dai, 2013, Nature Physics

GRB X-ray flares statistics Left: differential energy distribution of solar flares Right: cumulative energy distribution of X-ray flares The slopes: (-1.65±0.02, -1.06±0.15) microflares dominate， but lack … Wang & Dai, 2013, Nature Physics

GRB X-ray flares: underlying physics Self-organized criticality (SOC): subsystems will self-organize to a critical state at which a small perturbation can trigger an avalanche of any size within the system (Bak et al. 1997). The slopes of frequency distributions for energies and durations depends on the Euclidean dimensions S (Aschwanden 2012): S ≈ 1 for X-ray flares, and S ≈ 3 for solar flares. Wang & Dai (2013) suggest that magnetic reconnection from ultra-strongly magnetized millisecond pulsars (Dai et al. 2006) may trigger an S ≈ 1 SOC process. microflares affect the evaluation of the S value

GRB Science with XTP Polarization of GRB X-ray emission X-ray observation of ultra-long GRBs X-ray micro-flares in GRBs Late X-ray observation and jet breaks

~ 90% GRBs with XRT promptly slewing to the GRB position have been detected with X-ray afterglows since Swift was launched in 2004 (2) Limited by the sensitivity of Swift/XRT, most X-ray afterglows are not well detected during late times (say, a few days since the trigger), and little X-ray jet breaks have been discovered, which is important for estimating the beaming factor and calculating the true energies of GRBs. GRB 060729： longest X-ray afterglow up to date Chandra deep observations possible jet break potential spectral softening Grupe et al., 2010, ApJ

GRB Science with XTP: Summary Polarization of GRB X-ray emission most GRBs have X-ray flares or plateaus large-scale B-field & physical origins polarization of 10%-20% SO flares can be detected slewing speed: (3 – 10) degree/min acceptable X-ray observation of ultra-long GRBs physical origin and mechanism of ULGRBs X-ray micro-flares in GRBs all-scale activities of GRB central engine Late X-ray observation and jet breaks jet angle and true energy of GRBs

Thanks