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Investigating subphotospheric dissipation in gamma-ray bursts by fitting a physical model
KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics.ORCID iD: 0000-0003-4000-8341
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. , p. 76
Series
TRITA-SCI-FOU ; 2019:14
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-245241ISBN: 978-91-7873-140-4 (print)OAI: oai:DiVA.org:kth-245241DiVA, id: diva2:1294579
Public defence
2019-03-29, FA31, Roslagstullsbacken 21, Stockholm, 13:00 (English)
Supervisors
Note

QC 20190308

Available from: 2019-03-08 Created: 2019-03-07 Last updated: 2019-03-08Bibliographically approved
List of papers
1. Confronting GRB prompt emission with a model for subphotospheric dissipation
Open this publication in new window or tab >>Confronting GRB prompt emission with a model for subphotospheric dissipation
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2015 (English)In: Monthly Notices of the Royal Astronomical Society: Letters, ISSN 1745-3925, Vol. 454, no 1, p. L31-L35Article in journal (Refereed) Published
Abstract [en]

The origin of the prompt emission in gamma-ray bursts (GRBs) is still an unsolved problem and several different mechanisms have been suggested. Here, we fit Fermi GRB data with a photospheric emission model which includes dissipation of the jet kinetic energy below the photosphere. The resulting spectra are dominated by Comptonization and contain no significant contribution from synchrotron radiation. In order to fit to the data, we span a physically motivated part of the model's parameter space and create DREAM (Dissipation with Radiative Emission as A table Model), a table model for XSPEC. We show that this model can describe different kinds of GRB spectra, including GRB 090618, representing a typical Band function spectrum, and GRB 100724B, illustrating a double peaked spectrum, previously fitted with a Band+blackbody model, suggesting they originate from a similar scenario. We suggest that the main difference between these two types of bursts is the optical depth at the dissipation site.

Place, publisher, year, edition, pages
Oxford University Press, 2015
Keywords
Gamma-ray burst: general, Gamma-ray burst: individual: GRB 090618, Gamma-ray burst: individual: GRB 100724B, Radiation mechanisms: thermal
National Category
Physical Sciences
Identifiers
urn:nbn:se:kth:diva-181222 (URN)10.1093/mnrasl/slv114 (DOI)000378922200006 ()2-s2.0-84944884952 (Scopus ID)
Note

QC 20160203

Available from: 2016-02-03 Created: 2016-01-29 Last updated: 2019-03-07Bibliographically approved
2. Testing a model for subphotospheric dissipation in GRBs: fits to Fermi data constrain the dissipation scenario
Open this publication in new window or tab >>Testing a model for subphotospheric dissipation in GRBs: fits to Fermi data constrain the dissipation scenario
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2019 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 485, p. 474-497Article in journal (Refereed) Published
Abstract [en]

It has been suggested that the prompt emission in gamma-ray bursts (GRBs) could be described by radiation from the photosphere in a hot fireball. Such models must be tested by directly fitting them to data. In this work we use data from the Fermi Gamma-ray Space Telescope and consider a specific photospheric model, in which the kinetic energy of a low-magnetization outflow is dissipated locally by internal shocks below the photosphere. We construct a table model with a physically motivated parameter space and fit it to time-resolved spectra of the 36 brightest Fermi GRBs with a known redshift. We find that about two-thirds of the examined spectra cannot be described by the model, as it typically underpredicts the observed flux. However, since the sample is strongly biased towards bright GRBs, we argue that this fraction will be significantly lowered when considering the full population. From the successful fits we find that the model can reproduce the full range of spectral slopes present in the sample. For these cases we also find that the dissipation consistently occurs at a radius of ∼1012 cm and that only a few per cent efficiency is required. Furthermore, we find a positive correlation between the fireball luminosity and the Lorentz factor. Such a correlation has been previously reported by independent methods. We conclude that if GRB spectra are due to photospheric emission, the dissipation cannot only be the specific scenario we consider here.

Keywords
gamma-ray burst
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-245227 (URN)10.1093/mnras/stz110 (DOI)000466786400034 ()
Note

QC 20190308

Available from: 2019-03-07 Created: 2019-03-07 Last updated: 2019-05-29Bibliographically approved
3. Constraining subphotospheric dissipation in Gamma-ray Bursts using joint Fermi-Swift observations
Open this publication in new window or tab >>Constraining subphotospheric dissipation in Gamma-ray Bursts using joint Fermi-Swift observations
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(English)Manuscript (preprint) (Other academic)
National Category
Astronomy, Astrophysics and Cosmology
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-245240 (URN)
Note

QC 20190312

Available from: 2019-03-07 Created: 2019-03-07 Last updated: 2019-03-12Bibliographically approved

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