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Emission from accelerating jets in gamma-ray bursts: radiation-dominated flows with increasing mass outflow rates
KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. Columbia University, USA.
KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.
2017 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 472, no 2, p. 1897-1906Article in journal (Refereed) Published
Abstract [en]

We study the narrowest spectra expected from gamma-ray bursts. We present an analytical function for the spectrum that is emitted from the photosphere of a radiation-dominated flow that is under acceleration. This is the narrowest possible spectrum and it differs from a Planck function. We also present numerical spectra from photospheres occurring during the transition into the coasting phase of the flow. Using these spectral models, we reanalyse Fermi observations of GRB 100507 and GRB 101219, which both have been reported to have very narrow spectra. The bursts can be fitted by the spectral models: for GRB 101219 the spectrum is consistent with the photosphere occurring below or close to the saturation radius, while for GRB 100507 the photosphere position relative to the saturation radius can be determined as a function of time. In the latter case, we find that the photosphere initially occurs in the acceleration phase and thereafter transitions into the coasting phase. We also find that this transition occurs at the same time as the change in observed cooling behaviour: the temperature is close to constant before the break and decays after. We argue that such a transition can be explained by an increasing mass outflow rate. Both analysed bursts thus give strong evidence that the jets are (initially) radiation dominated.

Place, publisher, year, edition, pages
Oxford University Press, 2017. Vol. 472, no 2, p. 1897-1906
Keywords [en]
radiation mechanisms: thermal, gamma-ray burst: general
National Category
Astronomy, Astrophysics and Cosmology
Identifiers
URN: urn:nbn:se:kth:diva-217167DOI: 10.1093/mnras/stx2019ISI: 000413082900050OAI: oai:DiVA.org:kth-217167DiVA, id: diva2:1155007
Funder
Swedish National Space BoardSwedish Research CouncilGöran Gustafsson Foundation for Research in Natural Sciences and Medicine
Note

QC 20171106

Available from: 2017-11-06 Created: 2017-11-06 Last updated: 2017-11-06Bibliographically approved

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