Change search
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Non-dissipative photospheres in GRBs: spectral appearance in the Fermi/GBM catalogue
KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. AlbaNova, Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden..
KTH, School of Engineering Sciences (SCI), Physics, Particle and Astroparticle Physics. AlbaNova, Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden..ORCID iD: 0000-0002-9769-8016
KTH, School of Engineering Sciences (SCI), Physics. AlbaNova, Oskar Klein Ctr Cosmoparticle Phys, SE-10691 Stockholm, Sweden.;Univ Hong Kong, Fac Sci, Pokfulam, Hong Kong, Peoples R China..
2019 (English)In: Monthly notices of the Royal Astronomical Society, ISSN 0035-8711, E-ISSN 1365-2966, Vol. 487, no 4, p. 5508-5519Article in journal (Refereed) Published
Abstract [en]

A large fraction of gamma-ray burst (GRB) spectra are very hard below the peak. Indeed, the observed distribution of sub-peak power-law indices, alpha, has been used as an argument for a photospheric origin of GRB spectra. Here, we investigate what fraction of GRBs have spectra that are consistent with emission from a photopshere in a non-dissipative outflow. This is the simplest possible photospheric emission scenario. We create synthetic spectra, with a range of peak energies, by folding the theoretical predictions through the detector response of the FERMI/GBM detector. These simulated spectral data are fitted with typically employed empirical models. We find that the low-energy photon indices obtain values ranging -0.4 < alpha < 0.0, peaking at around -0.1, thus covering a non-negligible fraction of observed values. These values are significantly softer than the asymptotic value of the theoretical spectrum of alpha similar to 0.4. The reason for the alpha values to be much softer than expected, is the limitation of the empirical functions to capture the true curvature of the theoretical spectrum. We conclude that more than a quarter of the bursts in the GBM catalogue have at least one time-resolved spectrum, whose alpha values are consistent with spectra from a non-dissipative outflow, releasing its thermal energy at the photosphere. The fraction of spectra consistent with emission from the photosphere will increase even more if dissipation of kinetic energy in the flow occurs below the photosphere.

Place, publisher, year, edition, pages
Oxford University Press, 2019. Vol. 487, no 4, p. 5508-5519
Keywords [en]
radiation mechanisms: thermal, methods: data analysis, methods: numerical, gamma-ray burst: general
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-255552DOI: 10.1093/mnras/stz1356ISI: 000475888500077Scopus ID: 2-s2.0-85070069004OAI: oai:DiVA.org:kth-255552DiVA, id: diva2:1340329
Note

QC 20190805

Available from: 2019-08-05 Created: 2019-08-05 Last updated: 2020-03-09Bibliographically approved
In thesis
1. Statistical Investigations ofthe Emission Processes in Gamma-ray Bursts
Open this publication in new window or tab >>Statistical Investigations ofthe Emission Processes in Gamma-ray Bursts
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Physical emission mechanisms responsible for gamma-ray bursts (GRBs) remain elusive to this day, 50 years after their discovery. Although there are well studied physical models, their power to explain the observed data is a matter of debate. In this thesis, the main focus is the statistical studies of the dierent physical models given the available data from the Fermi Gamma-Ray Space Observatory to make better comparisons between these models as well as ascertaining how well they can explain the available observations so far. To this end, theoretically predicted thermal and non-thermal GRB spectra are investigated. This investigation entails both ending groupings in the catalog data (clustering) and then simulating the expected physical emission processes to test how they would look like in the current data acquiry, processing and tting procedures. Finally, a Bayesian model comparison is performed in a sub-sample of these bursts to quantify the preference of different models by the data. In conclusion, it is found that around one third of all bursts include intervals where the emission is from a photosphere which is non-dissipative.

This means that during these intervals, the emission is either emitted close to the saturation radius or in a flow which is laminar. The results further indicate that dissipation below the photosphere is responsible for the spectral shape in a majority of GRB spectra. It is consequently argued that the dominant emission mechanism during the prompt emission phase in GRBs is thermal emission from the jet photosphere at distance of around 1012 cm from the central engine. A small percentage of the bursts are better explained with a non-thermal generating process such as the synchrotron emission.

Abstract [sv]

Stralningsprocessen som ligger till grund for gamma-blixtarnas initiala hogenergetiskautbrott av gamma-stralning ar fortfarande okand trots att de har observeratsi over 50ar. Aven om det nns valformulerade fysikaliska modeller sa debatterasdet huruvida de olika modellerna kan forklara observationerna. Huvudinriktningen iforeliggande avhandling ar statistiska studier av olika fysikaliska stralningsmodellersom testas mot data fran Fermi Gamma-Ray Space Observatory. Syftet ar attuppna forbattrade jamforelser mellan modellanpassningarna och att utrona hur valmodellerna kan beskriva de tillgangliga observationerna. De modeller som studerasar teoretiska beskrivningar av en termisk och en icke-termisk stralningsprocess. Destatistiska studierna innefattar saval klassicering genom klusteranalys av datakatalogersom dataanalys av simulerad data som ar baserade pa de fysikalisk modellerna.Slutligen gors aven en Bayesiansk modelljamforelseanalys av en delmangd av allaobserverade gammablixtar. Syftet ar att undersoka vilken av modellerna som foredrasav datan. Slutsatsen jag drar av mina undersokningar ar att ungefar en tredjedelav gammablixtarna har perioder da den observerade stralningen kommer franfotosfaren i ett utode dar ingen energidissipering sker. Detta innebar att underdessa perioder kommer stralningen antingen fran omraden nara satureringsradieneller fran ett laminart utode. Mina resultat visar vidare att fotonspektrumen franen en majoritet av blixtarna formas av just energidissipering under fotosfaren. Jagargumenterar darfor for att den dominerande stralningsprocessen under den initiala(eng. prompt) fasen hos gammablixtarna ar termisk stralning fran fotosfareni det relativistiska utodet. Enbart en liten del kan ges en battre forklaring med enicke-termisk model som t.ex. synkrotronstralning.v

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2019. p. 66
Series
TRITA-SCI-FOU ; 2019:61
Keywords
gamma-ray bursts
National Category
Physical Sciences
Research subject
Physics, Atomic, Subatomic and Astrophysics
Identifiers
urn:nbn:se:kth:diva-265527 (URN)978-91-7873-409-2 (ISBN)
Public defence
2020-01-28, FB42, Roslagstullsbacken 21, Stockholm, Stockholm, 13:00 (English)
Opponent
Supervisors
Note

QC 2020-01-15

Available from: 2020-01-15 Created: 2019-12-12 Last updated: 2020-01-22Bibliographically approved

Open Access in DiVA

fulltext(698 kB)62 downloads
File information
File name FULLTEXT01.pdfFile size 698 kBChecksum SHA-512
1aef1d3686657e579bbc93fbed6a890ff0df6f6f8613b4f34a9686aac37a72e9ee2f711f1230fa2f41946b6a1c3225c286c44ac4aebcc7f56ce0989eea5c3a68
Type fulltextMimetype application/pdf

Other links

Publisher's full textScopus

Authority records BETA

Acuner, ZeynepRyde, Felix

Search in DiVA

By author/editor
Acuner, ZeynepRyde, FelixYu, Hoi-Fung
By organisation
Particle and Astroparticle PhysicsPhysics
In the same journal
Monthly notices of the Royal Astronomical Society
Physical Sciences

Search outside of DiVA

GoogleGoogle Scholar
Total: 62 downloads
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

doi
urn-nbn

Altmetric score

doi
urn-nbn
Total: 75 hits
CiteExportLink to record
Permanent link

Direct link
Cite
Citation style
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf