A. Mastichiadis, DK 2009A. Mastichiadis, DK 2009DK, A. Mastichiadis, M. DK, A. Mastichiadis, M.

Georaganopoulos 2007 A. Georaganopoulos 2007 A. Mastichiadis, DK 2006Mastichiadis, DK 2006

DK, M. Georganopoulos, A. DK, M. Georganopoulos, A. Mastichiadis 2002 Mastichiadis 2002

Bulk Comptonization GRB Model and itsRelation to the Fermi GRB Spectra

Major GRB Facts/IssuesMajor GRB Facts/Issues

GRB involve relativistic blast waves (GRB involve relativistic blast waves (Ress & Ress &

MeszarosMeszaros)) This guarantees that most of the energy of This guarantees that most of the energy of

the swept-up matter is stored in the swept-up matter is stored in relativistic protons (accelerated or not; relativistic protons (accelerated or not; electrons carry ~1/2000 of available electrons carry ~1/2000 of available energy). energy).

PROBLEMS:PROBLEMS: Protons do not lose energy to radiation Protons do not lose energy to radiation

easily.easily. The observed luminosity peaks at E~1 The observed luminosity peaks at E~1

MeV in the lab frame! (Despite the blast MeV in the lab frame! (Despite the blast wave LF of order 100-1000).wave LF of order 100-1000).

There are (at least) two outstanding issues There are (at least) two outstanding issues with the prompt GRB emission (Piran with the prompt GRB emission (Piran 2004):2004): AA. . DissipationDissipation of the RBW free energy. of the RBW free energy.

Energy stored in relativistic p’s or B-field. Energy stored in relativistic p’s or B-field. Sweeping of ambient protons stores significant Sweeping of ambient protons stores significant amount of energy in p’s anyway. Necessary to amount of energy in p’s anyway. Necessary to store energy in non-radiant form, but hard to store energy in non-radiant form, but hard to extract when needed.extract when needed.

BB. . The presence of EThe presence of Epeakpeak ~0.1 – 1.0 ~0.1 – 1.0 MeV. MeV. If prompt emission is synchrotron by If prompt emission is synchrotron by relativistic electrons of Loretnz factor (LF) relativistic electrons of Loretnz factor (LF) same as shock Esame as shock Epp ~ ~, much too strong to , much too strong to account for the observations.account for the observations.

We have proposed a model that can We have proposed a model that can resolve both these issues simultaneously. resolve both these issues simultaneously. The model relies:The model relies: 1. On a 1. On a radiative instabilityradiative instability of a of a

relativistic proton plasma with B-fields relativistic proton plasma with B-fields due to the internally produced due to the internally produced sychrotron radiation (sychrotron radiation (Kirk & Mastichiadis 1992 Kirk & Mastichiadis 1992 ).).

2. On the 2. On the amplificationamplification of the of the

instability instability by relativistic motionby relativistic motion

and and scatteringscattering of the internally of the internally produced radiation by upstream located produced radiation by upstream located matter, a ‘mirror’ (matter, a ‘mirror’ (Kazanas & Mastichiadis 1999Kazanas & Mastichiadis 1999).).

p e+e-

eB B In the blast frame the

width of the shock ~R/ is comparable to its observed lateral widththereby considering all processes taking place in a spherical volume of radius

The instability involves 2 thresholds: The instability involves 2 thresholds: 1. A kinematic one1. A kinematic one for the reaction for the reaction p p e e-- e e++

b b 55 > 2 m > 2 mee c c22 (the prompt phase ends when this condition is not satisfied)(the prompt phase ends when this condition is not satisfied)

2. A dynamic one:2. A dynamic one: At least one of the At least one of the synchrotron photons must be able to synchrotron photons must be able to reproduce before escaping the plasma reproduce before escaping the plasma volume. This leads to the following volume. This leads to the following condition for the plasma condition for the plasma column densitycolumn density (note similarity with atomic bombs!)(note similarity with atomic bombs!)

to

¾p° R n >» b¡ or ¾p° R n¡ 4 >» 2

Similarity of GRB/Nuclear Piles-Similarity of GRB/Nuclear Piles-BombsBombs

The similarity of GRB to a “Nuclear Pile” is The similarity of GRB to a “Nuclear Pile” is more than incidental:more than incidental:

1. They both contain lots of free energy 1. They both contain lots of free energy stored in:stored in: Nuclear Binding Energy (nuclear pile)Nuclear Binding Energy (nuclear pile) Relativistic Protons or Magnetic Field (GRB)Relativistic Protons or Magnetic Field (GRB)

2. The energy can be released explosively 2. The energy can be released explosively once certain condition on the fuel column once certain condition on the fuel column density (and not mass) is fulfilled (density (and not mass) is fulfilled (Note: no particle Note: no particle

acceleration required!!acceleration required!!).).

No accelerated population is invoked !!

RBW Mirror

Min(mec2 , b6+1GeV photons

b MeV photons (GBM photons are due to BC)

beV O-UV photons

R

Syn.

BC RS

BC SSC

We have modeled this process We have modeled this process numerically. We assume the presence of numerically. We assume the presence of scattering medium at scattering medium at R ~10R ~101616 cm cm and of and of finite radial extent. finite radial extent.

We follow the evolution of the We follow the evolution of the protonproton, , electronelectron and and photonphoton distribution by solving distribution by solving the corresponding kinetic equations.the corresponding kinetic equations.

We obtain the spectra as a function of time We obtain the spectra as a function of time for the prompt GRB emission.for the prompt GRB emission.

The The time scalestime scales are given in units of the are given in units of the comoving blob crossing time comoving blob crossing time coco/c ~ R /c ~ R c c ~ 2 R~ 2 R16162.62.6 sec sec

Prompt GRB Spectra (Mastichiadis & Kazanas 2006)Prompt GRB Spectra (Mastichiadis & Kazanas 2006)

We have also modeled the propagation of We have also modeled the propagation of a relativistic blast wave through the wind a relativistic blast wave through the wind of a WR star (that presumably collapses to of a WR star (that presumably collapses to produce the relativistic outflow that produce the relativistic outflow that produces the GRB).produces the GRB).

In this case we also follow the In this case we also follow the development of the blast wave LF and the development of the blast wave LF and the radiative feedback on it. radiative feedback on it.

In this scenario the “mirror” necessary for In this scenario the “mirror” necessary for the model to work is provided by the pre-the model to work is provided by the pre-supernova star wind, the length scales supernova star wind, the length scales smaller, smaller, RR00~10~101313 cm cm and the GRB is a and the GRB is a “short GRB”“short GRB”. .

Evolution of the LF and the Evolution of the LF and the luminosityluminosity

Evolution of Spectra with Time Evolution of Spectra with Time ((BB~1)~1)

Evolution of Luminosity with Time Evolution of Luminosity with Time ((BB~1)~1)

Evolution of Luminosity with Time Evolution of Luminosity with Time ((BB~0.01)~0.01)

Ep decreaseswith decreasingluminosity

ConclusionsConclusions The “nuclear pile” GRB model provides an over all The “nuclear pile” GRB model provides an over all

satisfactory description of several GRB features, satisfactory description of several GRB features, including the dissipation process, Ep and the Fermi including the dissipation process, Ep and the Fermi observations.observations.

Provides an operational definition of the GRB prompt Provides an operational definition of the GRB prompt phase.phase.

No particle acceleration necessary to account for most No particle acceleration necessary to account for most of prompt observations (but it is not forbidden!).of prompt observations (but it is not forbidden!).

GBM photons due to bulk Comptonization ( => GBM photons due to bulk Comptonization ( => possibility of high polarization ~100%).possibility of high polarization ~100%).

It can produce “short GRB” even in situations that do It can produce “short GRB” even in situations that do not involve neutron star mergers.not involve neutron star mergers.

Exploration of the parameter space and attempt to Exploration of the parameter space and attempt to systematize GRB phenomenology within this model is systematize GRB phenomenology within this model is

currently at work.currently at work.

Distribution of LE Distribution of LE indicesindices

The spectra of doubly scattered component The spectra of doubly scattered component (Mastichiadis & DK (2005))(Mastichiadis & DK (2005))

S=1/2,

S=1,

S=2,

Fig. 6.| Plot of thephoton luminosity evolution as this ismeasured in thecomoving framein theEE casewherenp = ne = 104 cm¡ 3 whileB varies (bottomto top) from0.12G to 120G by incrementsof a factor of 10. Therest of theparametersareasstated in thetext. Timeis measured in blob crossing times and thevaluet = 0 has been set at theinstant when theRBW enters there°ection zone.

G

G

G

G

EEisoiso of the three different spectral components as a function of the three different spectral components as a function of B for of B for =400 and n=400 and npp=10=1055 cm cm-3-3. x 10. x 1033 denotes the relative denotes the relative --ray – O-UV normalization of GRB 990123, 041219a. ray – O-UV normalization of GRB 990123, 041219a.

O-UV

100 GeV

1 MeV

X 103

EEpeakpeak as a function of the magnetic field B as a function of the magnetic field B

VariationsVariations If the “mirror” is in relative motion to the RBW then If the “mirror” is in relative motion to the RBW then

the kinematic threshold is modified to the kinematic threshold is modified to b b relrel ~ 2 ~ 2; ;

rel rel is the relative LF between the RBW and the is the relative LF between the RBW and the “mirror”.“mirror”.

The value of The value of EEpeakpeak is again ~ is again ~ 1 MeV1 MeV, however the , however the synchrotron and IC peaks are higher and lower by synchrotron and IC peaks are higher and lower by

relrel than than

In the presence of In the presence of accelerated particlesaccelerated particles the the threshold condition is satisfied even for threshold condition is satisfied even for (2/b) (2/b)1/51/5. . This may explain the time evolution of This may explain the time evolution of GRB941017GRB941017 (Gonzalez et al. 04)(Gonzalez et al. 04)

GRB flux is likely to be highly polarized (GRB GRB flux is likely to be highly polarized (GRB 031206, Coburn & Boggs 03).031206, Coburn & Boggs 03).

This model applicable to internal shock model This model applicable to internal shock model (photons from downstream shell instead of (photons from downstream shell instead of “mirror”).“mirror”).

{ 23 {

Fig. 6.| Plot of thephoton luminosity evolution as this is measured in thecomoving framein theEE casewherenp = ne = 104 cm¡ 3 whileB varies (bottomto top) from0.12G to 120G by incrementsof a factor of 10. Therest of theparametersareasstated in thetext. Timeis measured in blob crossing times and thevalue t = 0 has been set at theinstant when theRBW enters there°ection zone.

Then ....Then ....

to

¾p° R n >» b¡ or ¾p° R n¡ 4 >» 2the source. Hence, thee p° ! e¡ e+ reactionre N ' °c=b°2

c = 1=b°ctron photons produced

Shock – Mirror GeometryShock – Mirror Geometry

formation region, generally not much different than the formation region, generally not much different than the

reshold condition

¡ 5b>» 2 or ¡ >»

µ2b

¶1=5

: