Physical parameters of GRB 970508 from its afterglow synchrotron emission

Abstract

Abstract. For the case of an adiabatically expanding blast wave, which is applicable to observed gamma-ray burst (GRB) afterglows at late times, we give expressions to infer the physical properties of the afterglow from the measured spectral features.We show that enough data exist for GRB 970508 to compute unambiguously the ambient density, n = 0.03 cm −3 , and the blast wave energy per unit solid angle, E = 4 10 52 erg/4π sr. We also compute the energy density in electrons and magnetic field. We find that they are 12% and 9%, respectively, of the nucleon energy density.

Gamma-ray burst afterglow scaling coefficients for general density profiles

“…Also for comparison, we give some of the values obtained by other authors. Galama et al (1999) obtain for the ISM case: E 52 = 3.5, n 0 = 0.03, ε B = 0.09 and ε E = 0.12. Granot & Sari (2002) obtain for the ISM case: E 52 = 0.12, n 0 = 22, ε B = 0.012 and ε E = 0.57.…”

“…Various authors have used flux scaling equations to derive the physical properties of GRB 970508 from afterglow data (Galama et al 1999; Granot & Sari 2002; Yost et al 2003; van der Horst et al 2008). This provides us with a context to illustrate the scaling laws derived in .…”

“…Both van der Horst et al (2008) and Galama et al (1999) take for the hydrogen mass fraction of the circumburst medium X = 0.7, which in our flux equations is mathematically equivalent (though conceptually different) to setting ξ N = (1 + X)/2 = 0.85. Unfortunately, this still leaves us with four variables to determine ( B , E , E 52 and n 0 ) and only three constraints (peak flux, cooling and peak frequency).…”

From blast wave to observation

“…For comparison we give some of the values obtained by other authors. [5] obtain for the ISM case: E 52 = 3.5, n 0 = 0.03, ε B = 0.09, ε E = 0.12. [8] obtain for the ISM case: E 52 = 0.12, n 0 = 22, ε B = 0.012, ε E = 0.57.…”

“…Various authors have used flux scaling equations to derive the physical properties of GRB 970508 from afterglow data [5,8,28,11]. This provides us with a context to illustrate the scaling laws presented in this paper.…”