Quasi-universal gaussian jets: a unified picture for gamma-ray bursts and X-ray flashes.
ZHANG B., DAI X., LLOYD-RONNING N.M. and MESZAROS P.
Abstract (from CDS):
An observed correlation Ep∝(Eiso)1/2 extending from gamma-ray bursts (GRBs) to X-ray flashes (XRFs) poses problems both for a power-law universal jet model, in which the energy per solid angle decreases as the inverse square of the angle with respect to the jet axis, and for a conical jet model with a uniform energy density within the jet beam and a sharp energy cutoff at the jet edge. Here we show that the current GRB-XRF prompt emission/afterglow data can be understood in terms of a picture in which the GRB-XRF jets are quasi-universal and structured, with a Gaussian-like or similar structure, i.e., one where the jet has a characteristic angle, with a mild variation of energy inside and a rapid (e.g., exponential) decrease of energy outside of it. A Monte Carlo simulation shows that the current data is compatible with such a quasi-universal Gaussian jet with a typical opening angle of 5.7+3.4–2.1deg and with a standard jet energy of about log(Ej/1 erg)=51.1±0.3. According to this model, the true-to-observed number ratio of the whole GRB-XRF population is about 14 with the current instrumental sensitivity.