Abstract
Abstract Gamma-ray Bursts (GRBs) are the most explosive phenomena in the universe after the big bang. A large fraction of GRB lightcurves (LCs) shows X-ray plateaus. We perform the most comprehensive analysis of all GRBs (with known and unknown redshifts) with plateau emission observed by The Neil Gehrels Swift Observatory from its launch until 2019 August. We fit 455 LCs showing a plateau and explore whether these LCs follow closure relations, relations between the temporal and spectral indices of the afterglow, corresponding to two distinct astrophysical environments and cooling regimes within the external forward shock (ES) model, and find that the ES model works for the majority of cases. The most favored environments are a constant-density interstellar or wind medium with slow cooling. We also confirm the existence of the fundamental plane relation between the rest-frame time and luminosity at the end of the plateau emission and the peak prompt luminosity for this enlarged sample, and test this relation on groups corresponding to the astrophysical environments of our known redshift sample. The plane becomes a crucial discriminant corresponding to these environments in terms of the best-fitting parameters and dispersions. Most GRBs for which the closure relations are fulfilled with respect to astrophysical environments have an intrinsic scatter σ compatible within 1σ of that of the “Gold” GRBs, a subset of long GRBs with relatively flat plateaus. We also find that GRBs satisfying closure relations indicating a fast cooling regime have a lower σ than ever previously found in literature.
Highlights
Gamma-ray bursts (GRBs) are short-lived bursts of γ-ray photons originating from high-energy astrophysical phenomena, and are spectacular events due to their energy emission mechanism
The paper has the following structure: in Section 2 we present the sample selection for the Swift Gamma-ray Bursts (GRBs), in Section 3 we explain the details of the fitting with the Willingale et al (2007) model (W07 model) and the spectral data analysis, along with the computation of the luminosity in X-rays, in Section 4 we present the X-ray closure relations, in Section 5 their interpretations, in Section 6 we show the 3D correlation, compare and contrast it with a new definition of the “Gold” sample, and test the 3D correlation for groups with respect to their astrophysical environments and cooling regimes, and in Section 7 we summarize the analysis and the results
The “Gold 2” has a R2adj = 0.73, which is 9.9% lower than that of the “Gold” in Dainotti et al (2017b) (Ra2dj = 0.81). The reasons for this decrease can be due to several factors: (1) the decreased number of data points in the beginning of the plateau emission may give rise to less precise fitting, (2) the different calculation of spectral parameters for the afterglow when compared to previous analysis, (3) the use of a cutoff power law (CPL) functional form in the prompt emission for GRBs where the necessary parameters are available
Summary
Gamma-ray bursts (GRBs) are short-lived bursts of γ-ray photons originating from high-energy astrophysical phenomena, and are spectacular events due to their energy emission mechanism. The paper has the following structure: in Section 2 we present the sample selection for the Swift GRBs, in Section 3 we explain the details of the fitting with the Willingale et al (2007) model (W07 model) and the spectral data analysis, along with the computation of the luminosity in X-rays, in Section 4 we present the X-ray closure relations, in Section 5 their interpretations, in Section 6 we show the 3D correlation, compare and contrast it with a new definition of the “Gold” sample, and test the 3D correlation for groups with respect to their astrophysical environments and cooling regimes, and in Section 7 we summarize the analysis and the results. All GRBs with T90 > 2 s that do not fall into any of the other classes are categorized as purely lGRBs, with the aims of creating a single observationally homogeneous class
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