Abstract We have analysed a sample of 328 time-integrated GRB prompt emission spectra taken via the Konus instrument on board the US GGS-Wind spacecraft between 2002 and 2004 using a couple of two-components models, Cut-off Power Law (CPL)+Power Law (PL) and blackbody (BB)+PL. The spectra show clear deviation from the Band function. The PL term is interpreted as the low energy tail of a nonthermal emission mechanism. The distributions of corresponding index β give values β <−2/3 consistent with synchrotron and synchrotron self-Compton mechanisms. The distribution of low energy index α associated with the CPL term shows clear discordance with synchrotron models for 31.4% of the analysed GRBs with values exceeding that for the line of death, α =−2/3. Then, a set of nonthermal radiation mechanisms producing harder slopes, i.e., α >−2/3, are presented and discussed. For the remaining majority (68.6%) of GRBs with CPL index α <−2/3, we show that optically thin synchrotron produced by a power law electron distribution of type, N(γ)∼ γ −p, γ 1 < γ < γ 2, for finite energy range (γ 2 ≠∞) is a likely emission mechanism with α ∼−(p +1)/2 in the frequency range ν 1 ≪ ν ≪ ν 2 (where ν 2 = η 2 ν 1 with η = γ 2/γ 1), such that for p >1/3, one gets α <−2/3. We also show that corresponding spectra in terms of F ν and νF ν functions are peaked around frequency ν 2 instead of ν 1, respectively for p <1 and p <3. Besides, thermal emission is examined taking a single Planck function for fitting the low energy range. It can be interpreted as an early emission from the GRB fireball photosphere with observed mean temperature, kT′∼16.8keV. Furthermore, we have performed a statistical comparison between the CPL+PL and BB+PL models finding comparable χ 2-values for an important fraction of GRBs, which makes it difficult to distinguish which model and specific radiation mechanism (possible thermal or nonthermal γ-ray emissions) are best suitable for describing the reported data. Therefore, additional information for those bursts, such as γ-ray polarization, would be highly desirable in future determinations of GRBs observational data.


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    Title :

    Spectral analysis of time-integrated Konus–Wind GRBs: Implication on radiative mechanisms


    Contributors:
    Fouka, M. (author) / Ouichaoui, S. (author)

    Published in:

    Advances in Space Research ; 47 , 8 ; 1387-1403


    Publication date :

    2010-08-03


    Size :

    17 pages




    Type of media :

    Article (Journal)


    Type of material :

    Electronic Resource


    Language :

    English





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