Modeling GRB B Xuefeng Wu (X. F. Wu, 吴雪峰 ) Penn State University Purple Mountain Observatory 2008 Nanjing GRB Workshop, Nanjing, China, June Collaborators: J. Racusin, D. Burrows, P. Meszaros (PSU) B. Zhang (UNLV)

For more details about observations J. Racusin’s talk (broad-band) G. Beskin’s talk (TORTORA prompt optical) V. D’Elia’s talk (spectroscopy) Papers on this GRB on astro-ph: J. Racusin et al., astro-ph/ , J. Bloom et al., astro-ph/ , S. Dado et al., astro-ph/ , V. D’Elia et al., astro-ph/ P. Kumar & A. Panaitescu, astro-ph/ , Y. Yu et al., astro-ph/

Outline  Interpreting the prompt emission;  Interpreting the very early afterglow;  Modeling the broad-band afterglow;

Prompt Emission T 90 ~ 57 s E peak = 651 ± 15 keV Peak flux: 2.3 x erg/cm 2 /s Fluence: ~6x10 -3 erg/cm 2 E γ,iso ~ 1.3 x ergs (D L =1.88 x cm) Konus-Wind T0+11.4s – T0+21.3s

Prompt Emission See Guidorzi talk for details of correlation tests, and Beskin talk for TORTORA details

Prompt Emission

Temporal coincidence and similar shape of prompt optical and γ-rays light curves indicate that they may originate from the same physical region Optical flux ~4 orders of magnitude above extrapolation of γ-rays requires that the optical andγ-rays must come from different emission components

Prompt Emission Constraining the possible models: the extremely bright prompt optical emission must be emitted at a large radius (optical thin region, ~10 16 cm), compared with typical internal shocks radii ( cm) For afterglow theory, cf. B. Zhang’s review talk

Prompt Emission Models Synchrotron for optical and Syn. Self-Compton (SSC) for MeV gamma-rays (Racusin et al. 2008; Kumar & Panaitescu 2008); Optical from the forward shock and MeV gamma-rays from the reverse shock within the synchrotron internal shocks model (Yu’s talk); Neutron-rich model (Fan, Wei, Zhang 2008) Residual internal shock model (Zhuo Li’s talk) External reverse shock propagating into a stratified-density- profile GRB ejecta?

Prompt Emission Constraining the prompt optical emission radius Black body (Rayleigh-Jeans limit) assumption specific intensity: flux density: : a constant ~1, t obs ~ variability time t v (internal shocks model) : (10 10 K – K), comoving electron temperature

Prompt Emission Constraining the prompt optical emission radius t v ~3 s (assuming), flux density ~ 25 Jansky Г~10 3 R~ cm a shorter variability time will result in larger Г and R

Prompt Emission Syn.+ SSC Internal Shocks Model Predictions E syn ~20 eV E SSC 1st ~650 keV E SSC 2st ~25 GeV E E 2 N(E) Klein-Nishina cut-off Y ~ 10 Y 2 ~100 obs., Y = ratio of E 2 N(E) between the Ist SSC and the syn. emission components. theo., Y = (magnetic energy fraction / electron energy fraction) 1/3 (Kobayashi et al. 2007) Optical depth due to IBL >1 for >30 GeV photons from z~1 GRB

Prompt Emission Syn.+ SSC Internal Shocks Model Predictions E syn ~20 eV E SSC 1st ~650 keV E SSC 2st ~25 GeV E E 2 N(E) Klein-Nishina cut-off Y ~ 10 Y 2 ~100 magnetic energy ~ electron energy GRB ejecta unmagnetized Optical depth due to IBL >1 for >30 GeV photons from z~1 GRB

Prompt Emission Syn.+ SSC Internal Shocks Model Predictions E syn ~20 eV E SSC 1st ~650 keV E SSC 2st ~25 GeV E E 2 N(E) Klein-Nishina cut-off Y ~ 10 Y 2 ~100 Optical depth due to IBL >1 for >30 GeV photons from z~1 GRB 2rd SSC photons ( ~ 20 GeV) peak flux: 2.3x10 -4 erg/cm 2 /s (1.5x10 -1 MeV/cm 2 /s), peak photon flux: ~10 -5 photons/cm 2 /s, total fluence of ~6x10 -3 erg/cm 2. GLAST/LAT 20GeV : 1.3x10 -6 MeV/cm 2 /s, 3x photons/cm 2 /s, 2x10 -5 erg/cm 2. This model could be easy to be tested by GLAST Total energy released in gamma-rays is ~ a few erg (see also Kumar & Panaitescu08)

Afterglow Optical light curve is normalized to UVOT v-band X-ray and γ-ray arbitrarily scaled

Very Early Afterglow high latitude emission

Very Early Afterglow external reverse shock at the crossing time t0t0 t1t1 t2t2 t1t1 t2t2 schematic for high latitude emission (cooling frequency < typical syn. frequency) R 

Very Early Afterglow external reverse shock at the crossing time t0t0 t1t1 t2t2 t1t1 t2t2 schematic for high latitude emission (cooling frequency < typical syn. frequency) R  (Zou et al. 2005; Wu et al. 2003) A relatively low E iso (~10 53 erg) and a relatively large  B (~0.1) are required

Afterglow Evidence for a stellar wind environment: XRT LC wind model:

Afterglow Evidence for a stellar wind environment: UVOT LC wind model:

Afterglow X-ray Light Curve Jet break without sideways expansion:

Afterglow Models Two-Component Jet

Analytical Constrainments for Model Parameters Narrow Jet: Wide Jet:

Afterglow Tail of Prompt Emission WJRS WJFS NJFS WJFS

Afterglow Models Numerical Calculation of the LC Generic Hydrodynamic Model for Relativistic Shocks (Huang, Dai, Gou, & Lu 2000) Synchrotron Self-Absorption; Synchrotron Self-Compton; Adiabatic hydrodynamics (  =0); No sideways expansion (C s =0);

Summary Prompt emission mechanisms are still in debate, but will be solve in the GLAST era; Afterglow has been modeled well in the two- component jet model