Modeling GRB 080319B

Xuefeng Wu (X. F. Wu, 吴雪峰 )Penn State University

Purple Mountain Observatory

2008 Nanjing GRB Workshop, Nanjing, China, June 23-27

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/0805.1557, J. Bloom et al., astro-ph/0803.3215, S. Dado et al., astro-ph/0804.0621, V. D’Elia et al., astro-ph/0804.2141 P. Kumar & A. Panaitescu, astro-ph/0805.0144, Y. Yu et al., astro-ph/0806.2010

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

Prompt Emission

• T90 ~ 57 s

• Epeak = 651 ± 15 keV

• Peak flux: 2.3 x 10-4 erg/cm2/s• Fluence: ~6x10-3 erg/cm2

• Eγ,iso ~ 1.3 x 1054 ergs (DL=1.88 x 1028 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

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 EmissionConstraining the possible models:

the extremely bright prompt optical emission must be emitted at a large radius (optical thin region, ~1016 cm), compared with typical internal shocks radii (1013-14 cm)

For afterglow theory, cf. B. Zhang’s review talk

Prompt EmissionModels• 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 EmissionConstraining the prompt optical emission radius

Black body (Rayleigh-Jeans limit) assumption specific intensity: flux density:

: a constant ~1, tobs ~ variability time tv (internal shocks model) : (1010K – 1012K), comoving electron temperature

Prompt EmissionConstraining the prompt optical emission radius

tv~3 s (assuming), flux density ~ 25 Jansky

Г~103

R~ 1016 cm a shorter variability time will result in larger Г and R

Prompt EmissionSyn.+ SSC Internal Shocks Model

Predictions

Esyn~20 eVESSC

1st ~650 keVESSC

2st ~25 GeVE

E2

N(E

)

Klein-Nishina cut-off Y ~ 10

Y ~ 10

Y2 ~100

obs., Y = ratio of E2N(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 EmissionSyn.+ SSC Internal Shocks Model

Predictions

Esyn~20 eVESSC

1st ~650 keVESSC

2st ~25 GeVE

E2

N(E

)

Klein-Nishina cut-off Y ~ 10

Y ~ 10

Y2 ~100

magnetic energy ~ 10-3 electron energyGRB ejecta unmagnetized

Optical depth due to IBL >1 for >30 GeV photons from z~1 GRB

Prompt EmissionSyn.+ SSC Internal Shocks Model

Predictions

Esyn~20 eVESSC

1st ~650 keVESSC

2st ~25 GeVE

E2

N(E

)

Klein-Nishina cut-off Y ~ 10

Y ~ 10

Y2 ~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/cm2/s (1.5x10-1 MeV/cm2/s), peak photon flux: ~10-5 photons/cm2/s, total fluence of ~6x10-3 erg/cm2.

GLAST/LAT sensitivities @ 20GeV :1.3x10-6 MeV/cm2/s, 3x10-10 photons/cm2/s, 2x10-5 erg/cm2.

This model could be easy to be tested by GLAST

Total energy released in gamma-rays is ~ a few 1055 erg(see also Kumar & Panaitescu08)

Afterglow

Optical light curve is normalized to UVOT v-bandX-ray and γ-ray arbitrarily scaled

Very Early Afterglow

high latitude emission

Very Early Afterglow

external reverse shock at the crossing time

t0

t1

t2

t1

t2

schematic for high latitude emission (cooling frequency < typical syn. frequency)

R

Very Early Afterglow

external reverse shock at the crossing time

t0

t1

t2

t1

t2

schematic for high latitude emission (cooling frequency < typical syn. frequency)

R

(Zou et al. 2005; Wu et al. 2003)

A relatively low Eiso (~1053 erg) and a relatively large B (~0.1) are required

AfterglowEvidence for a stellar wind environment: XRT LC

wind model:

Afterglow Evidence for a stellar wind environment: UVOT LC

wind model:

AfterglowX-ray Light Curve

Jet break without sideways expansion:

Afterglow ModelsTwo-Component Jet

Afterglow ModelsTwo-Component Jet

Afterglow ModelsTwo-Component Jet

Analytical Constrainments for Model Parameters

Narrow Jet:

Wide Jet:

Afterglow

Tail of Prompt Emission WJRS

WJFS

NJFS

WJFS

Afterglow ModelsNumerical 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 (Cs=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