1. Models of GRB GeV-TeV emission and GLAST/Swift synergy Xiang-Yu Wang Nanjing University, China Co-authors: Peter Meszaros (PennState), Zhuo Li (PKU), Hao-ning He (NJU) TeV Particle Astrophysics IV Sept. 24-28, 2008; Beijing, China

2. Xiang-Yu Wang TeVPA08 Outline GRB high-energy observations Models for GeV-TeV emission from GRBs Swift new discoveries and high-energy predictions with GLAST

3. Xiang-Yu Wang TeVPA08 I. GRB high-energy observations GRB930131 GRB940217 EGRET on CGRO 1) Prompt 2) Delayed

4. Xiang-Yu Wang TeVPA08 GRB941017 − 18 s – 14 s 14 s – 47 s 47 s – 80 s 80 s – 113 s 113 s – 211 s High-energy emission lasts longer than KeV-MeV emission

5. Xiang-Yu Wang TeVPA08 A recent burst detected by AGILE GRB080514B Similar to GRB941017, common phenomena?

6. Xiang-Yu Wang TeVPA08 GCN reports on GLAST Obs. GRB080825C: LAT detection, photons with energy lower than 1 GeV (GCN No.8183) GRB080916C : LAT detection, more than 10 photons are observed above 1 GeV (GCN No.8246)

7. Xiang-Yu Wang TeVPA08 E>100GeV: only upper limits Magic: upper limits for several Swift bursts (Albert et al., 06) Whipple: upper limits (Horan et al. 07) Milagro: upper limits fro short GRB (Abdo et al. 07) ARGO-YBJ array find only upper limits (Di Sciascio, et al., 06) HESS: upper limits of GRB060602B (Aharonian et al. 08)

8. Xiang-Yu Wang TeVPA08 Example: HESS GRB060602B very soft BAT spectrum and proximity to the Galactic center More likely to be a Galactic X-ray transient

9. Xiang-Yu Wang TeVPA08 GRB model: Internal and External shocks Credit P. Meszaros Rees & Meszaros 92; Meszaros & Rees 1994

10. Xiang-Yu Wang TeVPA08 Electrons- Shock acceleration: ~10 TeV Protons (or nuclei)- 1) Shock acceleration (e.g. Waxman 1995; Vietri 1995) Candidate source of ultra-high energy cosmic rays (UHECRs) 2) Neutrinos from photo-meson and pp processes (e.g. Waxman & Bahcall 1997; Bottcher & Dermer 1998) Particle acceleration in GRB shocks X-ray afterglows modeling e.g. Li & Waxman 2006

11. Xiang-Yu Wang TeVPA08 Two basic processes for high-energy gamma-ray emission 1. Leptonic inverse-Compton scattering 2. Hadronic processes: 1)proton synchrotron; 2) p-γneutral pion decay; 3)secondary electrons synchrotron & IC Prompt phase Internal shock, leptonic: electron synchrotron & SSC Internal shock, hadronic: proton synchrotron & p-γ interaction Early afterglow phase External, leptonic: forward, reverse and cross shock SSC External, hadronic: proton synchrotron & p-γ interaction

12. Xiang-Yu Wang TeVPA08 Efficiency comparison for the two processes (I) Prompt gamma-ray emission (Gupta & Zhang 2007) -- Proton syn. -- synchrotron radiation produced by secondary positrons **high energy emission is dominated by the leptonic component if є_e>0.01** neutral pion decay

13. Xiang-Yu Wang TeVPA08 Efficiency comparison for the two processes (II)-mildly relativistic outflow Ando & Meszaros 08

14. Xiang-Yu Wang TeVPA08 GRB high energy emission: IC processes central internal external shocks engine (shocks) (reverse) (forward) Internal shock IC: e.g. Pilla & Loeb 1998; Razzaque et al. 2004; Gupta & Zhang 2007 External shock IC reverse shock IC: e.g. Meszaros, et al. 94; Wang et al. 01; Granot & Guetta 03 forward shock IC: e.g.Meszaros & Rees 94; Dermer et al. 00; Zhang & Meszaros 01

15. Xiang-Yu Wang TeVPA08 Typical energies of SSC emission

16. Xiang-Yu Wang TeVPA08 (1) IC emission from very early external shocks Shocked shell Shocked ISM Cold ISM Cold shell pressure FS RS CD 1)(rr) 2)(ff) 3)(fr) 4)(rf) Four IC processes (Wang, Dai & Lu 2001 ApJ,556, 1010) At deceleration radius, T_obs~10-100 s Forward shock---Reverse shock structure is developed

17. Xiang-Yu Wang TeVPA08 Energy spectra--- At sub-GeV to GeV energies, the SSC of reverse shock is dominant; at higher energies, the Combined IC or SSC of forward shock becomes increasingly dominated Reverse shock SSC (r,f) IC (f,r) IC Forward shock SSC Log(E/keV) GLAST 5 photons sensitivity (Wang, Dai & Lu 2001 ApJ,556, 1010)

18. Xiang-Yu Wang TeVPA08 One GeV burst with very hard spectrum- leptonic or hadronic process? − 18 s – 14 s 14 s – 47 s 47 s – 80 s 80 s – 113 s 113 s – 211 s Gonzalez et al. 03: Hadronic model Leptonic IC model: Granot & Guetta 03 Pe’er & Waxman 04 Wang X Y et al. 05 GRB941017 Wang X Y et al. 05, A&A, 439,957 Reverse shock SSC ISM medium environment

19. Xiang-Yu Wang TeVPA08 (2) afterglow IC emission Zhang & Meszaros 01 May explain delayed GeV emission

20. Xiang-Yu Wang TeVPA08 Swift/GLAST synergy 1) X-ray flares 2) early shallow decay 3)low-luminosity GRBs 4)prompt emission

21. Xiang-Yu Wang TeVPA08 Swift: A Canonical X-ray Lightcurve (Zhang et al. 2006; Nousek et al. 2006; O ’ Brien et al. 2006) ~ -3 ~ -0.5 ~ - 1.2 ~ -2 10^2 – 10^3 s 10^4 – 10^5 s prompt emission

22. Xiang-Yu Wang TeVPA08 ~30%-50% early afterglow have x-ray flares, Swift discovery Flare light curves: rapid rise and decay <<1 Afterglow decay consistent with a single power-law before and after the flare (1) High-energy photons from X-ray flares Burrows et al. 2005 Falcone et al. 2006 amplitude: ~500 times above the underlying afterglow GRB050502B X-ray flares occur inside the deceleration radius of the afterglow shock X-ray flares: late-time central engine activity

23. Xiang-Yu Wang TeVPA08 IC between X-ray flare photons and afterglow electrons (Wang, Li & Meszaros 2006) Cnetral engine X-ray flare photons Forward shock region Cartoon X-ray flare photons illuminate the afterglow shock electrons from inside also see Fan & Piran 2006: unseen UV photons

24. Xiang-Yu Wang TeVPA08 IC GeV flare fluence-An estimate So most energy of the newly shock electrons will be lost into IC emission X-ray flare peak energy

25. Xiang-Yu Wang TeVPA08 Temporal behavior of the IC emission Not exactly correlated with the X-ray flare light curves. IC emission will be lengthened by the afterglow shock angular spreading time and the anisotropic IC effect Self-IC of flares, peak at lower energies Wang, Li & Meszaros 2006 In external shock model for x-ray flares

26. Xiang-Yu Wang TeVPA08 IC emission from X-ray flares at VHE

27. Xiang-Yu Wang TeVPA08 (2)High-energy emission during shallow decay phase-energy injection model (Fan et al. 2008)

28. Xiang-Yu Wang TeVPA08 (3)High-energy emission from low- luminosity GRBs

29. Xiang-Yu Wang TeVPA08 GRB980425: first low-luminosity GRB identified sub-energetic GRB—GRB980425: E~1e48 erg, at d=38 Mpc Radio afterglow modeling: E>1e49 erg, \Gamma~1-2 X-ray afterglow: E~5e49 erg, \beta=0.8 (Waxman 2004) Mildly relativistic ejecta component In the error box of GRB980425

30. Xiang-Yu Wang TeVPA08 GRB060218/SN2006aj – Swift discovery An unusually long, smooth burst Low luminosity, low energy z=0.033, second nearest GRB Campana et al. 2006

31. Xiang-Yu Wang TeVPA08 Thermal x-ray emission from low-luminosity GRBs SN2006aj/GRB060218  prompt thermal x-ray emission— mildly relativistic SN shock breakout from stellar wind Campana et al. 06 Waxman, Meszaros, Campana 07

32. Xiang-Yu Wang TeVPA08 Three low-luminosity supernova-GRBs 1) Low-luminosity 2) Smooth light curves 3) Spectrum: a simple power-law with a high energy cutoff So why they are so unusual? Mildly relativistic hypernova?

33. Xiang-Yu Wang TeVPA08 High-energy emission from mildly- relativistic hypernova ejecta Ando & Meszaros 08 at deceleration time ~1d

34. Xiang-Yu Wang TeVPA08 High-energy emission from mildly- relativistic hypernova ejecta He & Wang, in preparation

35. Xiang-Yu Wang TeVPA08 Compared with relativistic jet case

36. Xiang-Yu Wang TeVPA08 (4)Prompt multi-band study by Swift/GLAST Swift can detect optical to KeV-MeV emission GLAST can detected GeV-TeV emission One natural scenario: optical from syn, MeV from IC, Y>=10 2nd IC at GeV-TeV? Naked eye burst GRB080319B

37. Xiang-Yu Wang TeVPA08 IR, opt, UV~500keV~500GeV YLYL Y H =Y L

38. Xiang-Yu Wang TeVPA08 Swift/GLAST can distinguish … SSC model or double syn. model for prompt optical and MeV emission

39. Xiang-Yu Wang TeVPA08 Summary Leptonic vs. Hadronic  Leptonic component dominate at GeV-TeV for typical parameters  Only for very inefficient bursts (may be diagnosed by coordinated GLAST/Swift observations), would one expects a significant hadronic contribution in the high energy spectrum Prompt emission: SSC or double synchrotron model fro prompt optical and MeV emission Forward shock SSC would give extended GeV-TeV emission  Fluence peaks at hours GeV-TeV flares will accompany X-ray flares  Broader  Delayed in time Low-luminosity GRB afterglow  Detectable at 30MeV-10 GeV at the peak time for e_e>0.1  Can be used to distinguish high \Gamma or low \Gamma with GLAST observations of the light curves