Change search
ReferencesLink to record
Permanent link

Direct link
Synchrotron emission in GRBs observed with Fermi: Its limitations and the role of the photosphere
Stockholm University, Faculty of Science, Department of Physics.
(English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966Article in journal (Refereed) Submitted
National Category
Physical Sciences
Research subject
Theoretical Physics
URN: urn:nbn:se:su:diva-116735OAI: diva2:807906
Available from: 2015-04-26 Created: 2015-04-26 Last updated: 2015-04-27
In thesis
1. Photospheric emission in gamma ray bursts: Analysis and interpretation of observations made by the Fermi gamma ray space telescope
Open this publication in new window or tab >>Photospheric emission in gamma ray bursts: Analysis and interpretation of observations made by the Fermi gamma ray space telescope
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The large flashes of radiation that are observed in GRBs are generally believed to arise in a relativistic jetted outflow. This thesis addresses the question of how and where in the jet this radiation is produced. It further explores the jet properties that can be inferred from the observations made by the Fermi GST that regularly observes GRBs in the range 8 keV - 300 GeV.  In my analysis I focus on the observational effects of the emission from the jet photosphere. I show that the photosphere has an important role in shaping the observed radiation spectrum and that its manifestations can significantly vary between bursts. For bursts in which the photospheric  emission component can be identified, the dynamics of the flow can be explored by determining the  jet Lorentz factor and the position of the jet nozzle. I also develop the theory of how to derive the properties of the outflow for general cases. The spectral analysis of the strong burst GRB110721A reveals a two-peaked spectrum, with the peaks evolving differently. I conclude that three main flow quantities can describe the observed spectral behaviour in bursts:  the luminosity, the Lorentz factor, and the nozzle radius. While the photosphere can appear like a pure blackbody it can also be substantially broadened, due to dissipation of the jet energy below the photosphere. I show that Comptonisation of the blackbody can shape the observed spectra and describe its evolution. In particular this model can very well explain GRB110920A which has two prominent breaks in its spectra.  Alternative models including synchrotron emission leads to severe physical constraints, such as the need for very high electron Lorentz factors, which are not expected in internal shocks. Even though different manifestations of the photospheric emission can explain the data, and lead to ambiguous interpretations, I argue that dissipation below the photosphere is the most important process in shaping the observed spectral shapes and evolutions.

Place, publisher, year, edition, pages
Stockholm: Department of Physics, Stockholm University, 2015. 115 p.
gamma ray bursts, photosphere, radiation mechanism
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Theoretical Physics
urn:nbn:se:su:diva-116244 (URN)978-91-7649-185-0 (ISBN)
Public defence
2015-05-22, Lecture hall FB42, Albanova University Center, Roslagstullsbacken 21, Stockholm, 13:00 (English)

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 4: In press. Paper 5: Submitted.

Available from: 2015-04-29 Created: 2015-04-16 Last updated: 2015-06-24Bibliographically approved

Open Access in DiVA

No full text

Search in DiVA

By author/editor
Iyyani, Shabnam
By organisation
Department of Physics
In the same journal
Monthly notices of the Royal Astronomical Society
Physical Sciences

Search outside of DiVA

GoogleGoogle Scholar
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 205 hits
ReferencesLink to record
Permanent link

Direct link