Is magnetically dominated outflow required to explain GRBs?

TL;DR

This study analyzes GRB 080916C's spectrum, showing that a baryonic outflow can explain observed features without requiring magnetic dominance, challenging previous assumptions about GRB outflow composition.

Contribution

The paper demonstrates that the spectral components of GRB 080916C are consistent with a baryonic outflow, questioning the necessity of magnetically dominated models for GRBs.

Findings

Spectral analysis confirms a photospheric component in GRB 080916C.

Baryonic outflow models can explain the observed spectra.

Magnetic dominance is not required for interpreting this GRB.

Abstract

The composition of relativistic outflows producing gamma-ray bursts is a long standing open question. One of the main arguments in favor of magnetically dominated outflows is the absence of photospheric component in their broadband time resolved spectra, with such notable example as GRB 080916C. Here, we perform a time-resolved analysis of this burst and confirm the previous detection of an additional spectral component. We show that this subdominant component is consistent with the photosphere of ultrarelativistic baryonic outflow, deep in the coasting regime. We argue that, contrary to previous statements, the magnetic dominance of the outflow is not required for the interpretation of this GRB. Moreover, simultaneous detection of high energy emission in its prompt phase requires departure from a one-zone emission model.