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Prompt emission in gamma-ray bursts
Felix Ryde
KTH Royal Institute of Technology Stockholm
Lund, February 2020
Prompt emission in gamma-ray bursts Felix Ryde KTH Royal Institute - - PowerPoint PPT Presentation
Prompt emission in gamma-ray bursts Felix Ryde KTH Royal Institute - - PowerPoint PPT Presentation
Prompt emission in gamma-ray bursts Felix Ryde KTH Royal Institute of Technology Stockholm Lund, February 2020 Gamma-ray burst progenitors Short bursts Merging neutron stars Long bursts Hypernova Gamma-ray burst progenitors Short bursts
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Long bursts Hypernova Short bursts Merging neutron stars
Gamma-ray burst progenitors
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Current scenario GRB170817
From all wavelength observations
- f the prompt and afterglow
- bservations
Jet is there, but not directly seen! Late-time X-ray/optical/radio afterglow hints at the existence of a significant lateral energy injection from a structured jet (Mooley et al. 2018) The Fermi GBM and LAT and LIGO/Virgo teams have an automated multimessenger association and reporting pipeline to facilitate success in follow-up observations.
The prompt γ-ray emission is suggested to be the photospheric emission of the cocoon as the jet breaks out of the ejecta (Lazzati et al. 2017, Nakar et al. 2018)
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2 July 1967 by the Vela 4A
Rmax = 2c Γ2 Δtmin/(1 + z) ∼ 3 × 1014 cm
The variability time sets a constraint on the emission radius
Light curve variability in the MeV energy range
Time [s] Counts/s
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2 July 1967 by the Vela 4A
Rmax = 2c Γ2 Δtmin/(1 + z) ∼ 3 × 1014 cm
The variability time sets a constraint on the emission radius
MeV range energy spectrum
Non-thermal spectrum Featureless With a MeV brak
Light curve variability in the MeV energy range
Time [s] Counts/s
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Basic framework: the fireball model
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Basic framework: the fireball model
Goodman 1986
Blackbody from the jet photosphere
1012 cm
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Basic framework: the fireball model
Goodman 1986
Problem: Blackbody from the jet photosphere
1012 cm
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NE = A Eα E2 NE
Distribution of low-energy power-law index 𝛽
Typical gamma-ray spectrum
Acuner, Ryde &Yu 2019 Distribution of
Current 𝛽-distribution 2300 GRBs observed By Fermi/GBM
Slow cooling synchrotron Rayleigh- Jeans
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NE = A Eα E2 NE
Distribution of low-energy power-law index 𝛽
Typical gamma-ray spectrum
Acuner, Ryde &Yu 2019 Distribution of
Current 𝛽-distribution 2300 GRBs observed By Fermi/GBM
Slow cooling synchrotron Rayleigh- Jeans
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Thermal spectra
10 100 20 50 200 500 0.01 0.1 1 10 100 keV2 (Photons cm2 s1 keV1) Energy (keV)
A few per cent of all spectra are quasi-Planckian Ryde 04 Ghirlanda+10 Larsson+15 CGRO/BATSE Fermi/GBM Fermi/GBM
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Thermal spectra
10 100 20 50 200 500 0.01 0.1 1 10 100 keV2 (Photons cm2 s1 keV1) Energy (keV)
A few per cent of all spectra are quasi-Planckian Ryde 04 Ghirlanda+10 Larsson+15 CGRO/BATSE Fermi/GBM Fermi/GBM Physical interpretation and derivation of flow parameters becomes easy: Pe’er, Ryde, Wijers, & Rees 2007
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Basic framework: the fireball model
Rees & Mészáros 1992
External Forward and reverse shock Synchrotron emission
1016 cm
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Basic framework: the fireball model
Rees & Mészáros 1992
External Forward and reverse shock Synchrotron emission Variability time scale
Δtmin = RES 2c Γ2 ∼ 10 s
Problem:
1016 cm
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Basic framework: the fireball model
Rees & Mészáros 1994
Internal shocks: Synchrotron emission and high variability
1013 cm
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Basic framework: the fireball model
Rees & Mészáros 1994
Internal shocks: Synchrotron emission and high variability Problem: Efficiency typically low!
1013 cm
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Basic framework: the fireball model
Rees & Mészáros 2005
Dissipation below the photosphere
109 cm
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Basic framework: the fireball model
Rees & Mészáros 2005
Dissipation below the photosphere
109 cm
Björn Ahlgren PhD Thesis 2019
Pe’er+06, Giannos+06, Ioka+07, Beloborodov+10, Lazzati+11, Ahlgren+15, Vianello+17, Ahlgren+19
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Basic framework: the fireball model
Beloborodov 2011 Lundman, Pe’er & Ryde 2013 Vurm+2016
1012 cm
Photospheres in a relativistic expanding plasma
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Relativistic jet photosphere without any energy dissipation
Beloborodov 11 Lundman, Pe’er, Ryde13
Planck function
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Generate synthetic Fermi/GBM data from theoretical model
Acuner, Ryde & Yu 2019
P l a n c k f u n c t i
- n
Relativistic photosphere Data generating model Best fit to generated data
What fraction of bursts can be fitted by a relativistic photopshere?
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Generate synthetic Fermi/GBM data from theoretical model
Acuner, Ryde & Yu 2019
P l a n c k f u n c t i
- n
Relativistic photosphere Data generating model Best fit to generated data
Large discrepancy!
What fraction of bursts can be fitted by a relativistic photopshere?
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Distribution of low-energy power-law index 𝛽
Acuner, Ryde &Yu 2019 Distribution of 𝛽
Current 𝛽-distribution 2300 GRBs observed By Fermi/GBM
Acuner, Ryde &Yu 2019
Slow cooling synchrotron Non dissipative photosphere Rayleigh- Jeans
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Distribution of low-energy power-law index 𝛽
Acuner, Ryde &Yu 2019 Distribution of 𝛽
Current 𝛽-distribution 2300 GRBs observed By Fermi/GBM
Acuner, Ryde &Yu 2019
Slow cooling synchrotron Non dissipative photosphere Rayleigh- Jeans
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Distribution of low-energy power-law index 𝛽
Acuner, Ryde &Yu 2019 Distribution of 𝛽
Current 𝛽-distribution 2300 GRBs observed By Fermi/GBM
Acuner, Ryde &Yu 2019
Slow cooling synchrotron Non dissipative photosphere Rayleigh- Jeans
1/4 of all burst have non-dissipative photospheres
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Distribution of low-energy power-law index 𝛽
Acuner, Ryde &Yu 2019 Distribution of 𝛽
Current 𝛽-distribution 2300 GRBs observed By Fermi/GBM
Acuner, Ryde &Yu 2019
Slow cooling synchrotron Non dissipative photosphere Rayleigh- Jeans
1/4 of all burst have non-dissipative photospheres For short GRBs: 1/3 of all burst have non-dissipative photospheres Dereli, Pe’er & Ryde 2020
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Comparison of Bayesian Evidences between the NDP and empirical models Acuner, Ryde+2020
NDP preferred CPL preferred
Spectra inconsistent with synchrotron emission
Zeynep Acuner PhD thesis 2020
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Comparison of Bayesian Evidences between the NDP and empirical models Acuner, Ryde+2020
NDP preferred CPL preferred
Subphotospheric dissipation
Ahlgren+19 Vurm+16
Spectra inconsistent with synchrotron emission
Zeynep Acuner PhD thesis 2020
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Conclusions
Acuner, Ryde &Yu 2019 Distribution of 𝛽 Acuner, Ryde &Yu 2019
Slow cooling synchrotron Non dissipative photosphere Rayleigh- Jeans
Current paradigm of GRBs emission: an efficient photosphere and an efficient external shock Mészáros 2019 Prompt emission < 10s:
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Conclusions
Acuner, Ryde &Yu 2019 Distribution of 𝛽 Acuner, Ryde &Yu 2019
Slow cooling synchrotron Non dissipative photosphere Rayleigh- Jeans
1/4 of all burst have non-dissipative photospheres Acuner+19
Current paradigm of GRBs emission: an efficient photosphere and an efficient external shock Mészáros 2019 Prompt emission < 10s:
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Conclusions
Acuner, Ryde &Yu 2019 Distribution of 𝛽 Acuner, Ryde &Yu 2019
Slow cooling synchrotron Non dissipative photosphere Rayleigh- Jeans
1/4 of all burst have non-dissipative photospheres Acuner+19
Dissipative photospheres Vurm+16, Ahlgren+19 Current paradigm of GRBs emission: an efficient photosphere and an efficient external shock Mészáros 2019 Prompt emission < 10s:
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Conclusions
Acuner, Ryde &Yu 2019 Distribution of 𝛽 Acuner, Ryde &Yu 2019
Slow cooling synchrotron Non dissipative photosphere Rayleigh- Jeans
1/4 of all burst have non-dissipative photospheres Acuner+19
Dissipative photospheres Vurm+16, Ahlgren+19 External shock emission. Alone
- r in combination with a
photosphere (Abdo+19) Current paradigm of GRBs emission: an efficient photosphere and an efficient external shock Mészáros 2019 Prompt emission < 10s: