http://arxiv.org/abs/2007.00020
The prompt emission of short gamma ray bursts (sGRBs) with known redshifts are analyzed using the model of multi-color blackbody which is interpreted as the emission from a non-dissipative photosphere taking into account the structure and the viewing geometry of the jet. We find nearly $69\%$ and $26\%$ of the sample are consistent with multi-color blackbody and a pure blackbody model, respectively. We find that nearly $57\% \, (18\%)$ of the sGRBs in our sample are observed within (or along the edge of) the jet cone. The sGRB jets are found to be very narrow with the most probable value of the jet opening angle, $\theta_j = 2^{\circ} \pm 1^{\circ}$. This gives the rate of sGRBs that would be viewed within the jet cone to be $0.2 – 4.4 \, \rm Gpc^{-3} \, yr^{-1}$. The intrinsic luminosity are found to range between $10^{48} – 10^{53}\, \rm erg/s$. The average values of Lorentz factor and nozzle radius of the sGRB jets are found to be $210\, (85)$ and $10^{7.7} \, (10^{9.6}) \, \rm cm$ for the cases when the photosphere forms in the coasting (accelerating) phase respectively. No significant correlation is found between the peak multi-color blackbody temperature and isotropic burst energies. The power law index of the decreasing Lorentz factor profile of the jet structure is found to be $1.3 – 2.2$. The consistency of the spectral fits from a non-dissipative photosphere accounting for the geometrical effects and the limitations of the non-thermal emissions like synchrotron strongly suggests that the outflow is not Poynting flux dominated and thereby the remnant of the merger of the binary neutron stars is likely to be a black hole rather than a magnetar.
S. Iyyani and V. Sharma
Thu, 2 Jul 20
58/64
Comments: 40 pages, 20 figures, 7 tables, submitted to ApJS
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