A theory of photospheric emission from relativistic, collimated outflows
2013 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 428, no 3, 2430-2442 p.Article in journal (Refereed) Published
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 / Eα), 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.
Place, publisher, year, edition, pages
2013. Vol. 428, no 3, 2430-2442 p.
Gamma-ray burst: general., Plasmas, Radiation mechanisms: thermal, Radiative transfer, Scattering
IdentifiersURN: urn:nbn:se:kth:diva-119684DOI: 10.1093/mnras/sts219ISI: 000318230700043ScopusID: 2-s2.0-84873463810OAI: oai:DiVA.org:kth-119684DiVA: diva2:612110
QC 201303202013-03-202013-03-202013-06-18Bibliographically approved