Details

Autor(en) / Beteiligte

• Lundman, C
• Pe'er, A
• Ryde, F

Titel

A theory of photospheric emission from relativistic, collimated outflows

Ist Teil von

• Monthly notices of the Royal Astronomical Society, 2013-01, Vol.428 (3), p.2430-2442

Ort / Verlag

London: Oxford University Press

Erscheinungsjahr

2013

Link zum Volltext

Quelle

EZB-FREE-00999 freely available EZB journals

Beschreibungen/Notizen

• Relativistic outflows in the form of jets are common in many astrophysical objects. By their very nature, jets have angle-dependent velocity profiles, Γ = Γ(r, θ, φ), where Γ is the outflow Lorentz factor. In this work we consider photospheric emission from non-dissipative jets with various Lorentz factor profiles, of the approximate form Γ Γ0/[(θ/θj) p + 1], where θj is the characteristic jet opening angle. In collimated jets, the observed spectrum depends on the viewing angle, θv. We show that for narrow jets (θjΓ0 few), the obtained low-energy photon index is α −1 (dN/dE ∝ E α), independent of viewing angle, and weakly dependent on the Lorentz factor gradient (p). A similar result is obtained for wider jets observed at θv θj. This result is surprisingly similar to the average low-energy photon index seen in gamma-ray bursts. For wide jets (θjΓ0 few) observed at θv < θj, a multicolour blackbody spectrum is obtained. We discuss the consequences of this theory on our understanding of the prompt emission in gamma-ray bursts.