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Analysis of GRBs KONUS/Wind Spectra from 2002 to 2004 : The correlation R-H ?

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Analysis of GRBs KONUS/Wind Spectra from 2002 to 2004 :

The correlation R-H ?

Gamma Ray Bursts & Neutron Stars

March 30 - April 4, 2009

Cairo & Alexandria, Egypt

Mourad FOUKA

CRAAG, Algiers Observatory, Algeria

► Results and discussion:

● Distribution of spectral parameters

● Correlations:

□Epeak -H

□Ftotal - H

□ Correlation R – H ? how to interpret it ?

► SSC model and the high energy range ?

► Unified model for Konus spectra: SSC (internal)+IC (external)

First question: why this increasing shape in Konus spectra, in terms of E2N(E)for high energy range ?

PLE

PL

Pure Inverse Compton model

For external monoenergetic soft photons

Both pure Synchrotron and Inverse Compton models can’t explain the increasing part in E2N(E) of Konus-Wind spectra, even with two components for electron distribution ne(E) = NT+TH.

354 GRBs KONUS-Wind spectra for the years 2002, 2003 and 2004 are analyzed.

Model of fits

The sum of two components

i) PLE component, dominant at low energies

ii) a PL component, dominant at high energies

The spectra are presented and fitted in terms of S(E):

We put

1st Step

► It becomes very easy to fit the data in term of

to have a linear problem.

► In first time we consider a limit energy EL for the low energy range to fit only by using the PLE component. We can write:

where is the weight of the ith point, given by

We finally obtain the linear system

2nd Step

►After having the parameters we introduce the PL component:

►We consider the data:

As for the 1st step we can have

Where

and

3rd Step

► For this step we refine our parameters to minimize the . We define:

► We omit the points whose .

► We continue as for the 1st step

♦ The final result depend on the value of the energy EL.

♦ we repeat this procedure for many values of the energy ELin some range of low energies

Results and discussion

For a sample of 354 GRB we find:

►6 XRFs (1.7%)(bad statistics)

►214 XRRs (60.5%) 26.1% with

►134 GRBs (37.8%) 36.1% with

?

Why not all GRBs with

(Epeak of E2N(E))

Lac because of the range of Konus spectrometers: 13.12 keV – 9.17 MeV

(Hardness)

It’s interesting to present the parameter distributions for each class of gamma-ray bursts to more investigate results and to show if they exist important differences between the three classes.

For

▶ GRBs: 26.1%

▶ XRRs: 36.1%

▶ XRFs: (bad statistics)

Two remarks:

1. GRB% < XRR% for:

2. Values of alpha around zero

Now, Lets focusing on bursts whose

For Konus spectra 13.12 keV < EKONUS < 9.17 MeV

Lac of data

Two suggested interpretations:

1. Determinations of slop alpha depends on the range 13.12 keV < E < Epeak,

i.e. when Ep is close to 13.12 keV, the value of index-alpha is more uncertain.

2. Contribution of Inverse Compton for external soft photons ( ):

around zero for low Epeak values

Need of soft GRBs

Lac of data

Final GRB spectrum

=

Inverse Compton for soft external photons

+

GRBs internal photons

It’s interesting to remark and evaluate the dispersion for data:

Is this dispersion a property of Konus spectra or a property of GRBs ?

Correlation Log(Ftotal)-Log(H)

But a true correlation may be between Esource (intrinsic energy of the source) and hardness H.

But : 3 problems:

1. Redshift z not measured for all GRBs !

2. Need of true cosmological model to calculate DL(z)

3. Need of jet angle

►Apparent correlation Log(Ftotal)-Log(H)

We defined the parameter R as the ratio of the PLE fluency FPLE (the low energy range) to the PL fluency FPL(high energy range):

► The Figure show an apparent correlation between the ratio R ( defined here) and the hardness H.

►This apparent correlation can be easily explained:

In fact,In the commoving frame of GRB jet, as the initial flash is rich on soft synchrotron photons (low H=Fgamma /FX), the inverse Compton scattering is efficient (large SigmaIC). So that, as the jet is reach on hard synchrotron photons (large H=Fgamma /FX), the inverse Compton fluency FIC is much lower than the synchrotron fluency FSy R=FSy /FIC large. As a consequence the more hard GRBs (large H) are more reach on synchrotron photons than inverse Compton ones (large R) .

Finally

We can conclude that correlation R-H, revealed here, give a direct proof of contribution of Inverse Compton mechanism in GRB’s jets this favorite the SSC (Synchrotron-Self Compton) mechanism ?

SSC with NT + TH electrons

The high energy part can be interpreted by an SSC Thermal term

Unified model for all Konus wind spectra may be:

Final GRB spectrum

=

Inverse Compton for soft external photons

+

GRBs internal photons in the SSC model with NT+TH electrons

And, Synchrotron self-absorption can also be involved for low energy photon energies if data are available.

CRAAG, Algiers Observatory, Algeria

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