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 Merging neutron stars Long bursts Hypernova

Current scenario GRB170817 From all wavelength observations of the prompt and afterglow observations The prompt γ -ray emission is suggested to be the photospheric emission of the cocoon as the jet breaks out of the ejecta Jet is there, but not directly seen! (Lazzati et al. 2017, Nakar et al. 2018) 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.

Light curve variability in the MeV energy range 2 July 1967 by the Vela 4A Counts/s Time [s] The variability time sets a constraint on the emission radius R max = 2 c Γ 2 Δ t min / (1 + z ) ∼ 3 × 10 14 cm

Light curve variability in the MeV energy range 2 July 1967 by the Vela 4A Counts/s Time [s] The variability time sets a constraint on the emission radius R max = 2 c Γ 2 Δ t min / (1 + z ) ∼ 3 × 10 14 cm MeV range energy spectrum Non-thermal spectrum Featureless With a MeV brak

Basic framework: the fireball model

Basic framework: the fireball model Goodman 1986 Blackbody from the jet photosphere 10 12 cm

Basic framework: the fireball model Goodman 1986 Problem: Blackbody from the jet photosphere 10 12 cm

Distribution of low-energy power-law index 𝛽 Typical gamma-ray spectrum N E = A E α E 2 N E Slow cooling Rayleigh- synchrotron Jeans Distribution of Current 𝛽 - distribution 2300 GRBs observed By Fermi/GBM Acuner, Ryde &Yu 2019

Distribution of low-energy power-law index 𝛽 Typical gamma-ray spectrum N E = A E α E 2 N E Slow cooling Rayleigh- synchrotron Jeans Distribution of Current 𝛽 - distribution 2300 GRBs observed By Fermi/GBM Acuner, Ryde &Yu 2019

Thermal spectra A few per cent of all spectra are quasi-Planckian CGRO/BATSE Fermi/GBM Fermi/GBM 100 keV 2 (Photons cm � 2 s � 1 keV � 1 ) 10 1 0.1 0.01 10 20 50 100 200 500 Energy (keV) Ryde 04 Ghirlanda+10 Larsson+15

Thermal spectra A few per cent of all spectra are quasi-Planckian CGRO/BATSE Fermi/GBM Fermi/GBM 100 keV 2 (Photons cm � 2 s � 1 keV � 1 ) 10 1 0.1 0.01 10 20 50 100 200 500 Energy (keV) Ryde 04 Ghirlanda+10 Larsson+15 Physical interpretation and derivation of flow parameters becomes easy: Pe’er, Ryde, Wijers, & Rees 2007

Basic framework: the fireball model Rees & Mészáros 1992 External Forward and reverse shock Synchrotron emission 10 16 cm

Basic framework: the fireball model Problem: Rees & Mészáros 1992 Variability time scale External Forward and reverse shock Synchrotron emission Δ t min = R ES 2 c Γ 2 ∼ 10 s 10 16 cm

Basic framework: the fireball model Rees & Mészáros 1994 Internal shocks: Synchrotron emission and high variability 10 13 cm

Basic framework: the fireball model Rees & Mészáros 1994 Problem: Internal shocks: Synchrotron emission and high variability E ffi ciency typically low! 10 13 cm

Basic framework: the fireball model Rees & Mészáros 2005 Dissipation below the photosphere 10 9 cm

Basic framework: the fireball model Björn Ahlgren PhD Thesis 2019 Rees & Mészáros 2005 Dissipation below the photosphere 10 9 cm Pe’er+06, Giannos+06, Ioka+07, Beloborodov+10, Lazzati+11, Ahlgren+15, Vianello+17, Ahlgren+19

Basic framework: the fireball model Beloborodov 2011 Lundman, Pe’er & Ryde 2013 Vurm+2016 Photospheres in a relativistic expanding plasma 10 12 cm

Relativistic jet photosphere without any energy dissipation Planck function Beloborodov 11 Lundman, Pe’er, Ryde13

What fraction of bursts can be fitted by a relativistic photopshere? Generate synthetic Fermi/GBM data from theoretical model Relativistic photosphere Best fit to generated data n o i t Data generating model c n u f k c n a l P Acuner, Ryde & Yu 2019

What fraction of bursts can be fitted by a relativistic photopshere? Generate synthetic Fermi/GBM data from theoretical model Large discrepancy! Relativistic photosphere Best fit to generated data n o i t Data generating model c n u f k c n a l P Acuner, Ryde & Yu 2019

Distribution of low-energy power-law index 𝛽 Current 𝛽 - distribution 2300 GRBs observed By Fermi/GBM Slow cooling Non dissipative Rayleigh- synchrotron photosphere Jeans Distribution of 𝛽 Acuner, Ryde &Yu 2019 Acuner, Ryde &Yu 2019

Distribution of low-energy power-law index 𝛽 Current 𝛽 - distribution 2300 GRBs observed By Fermi/GBM Slow cooling Non dissipative Rayleigh- synchrotron photosphere Jeans Distribution of 𝛽 Acuner, Ryde &Yu 2019 Acuner, Ryde &Yu 2019

Distribution of low-energy power-law index 𝛽 Current 𝛽 - distribution 2300 GRBs observed By Fermi/GBM Slow cooling Non dissipative Rayleigh- synchrotron photosphere Jeans Distribution of 𝛽 Acuner, Ryde &Yu 2019 Acuner, Ryde &Yu 2019 1/4 of all burst have non-dissipative photospheres

Distribution of low-energy power-law index 𝛽 Current 𝛽 - distribution 2300 GRBs observed By Fermi/GBM Slow cooling Non dissipative Rayleigh- synchrotron photosphere Jeans Distribution of 𝛽 Acuner, Ryde &Yu 2019 Acuner, Ryde &Yu 2019 For short GRBs: 1/3 of all burst have 1/4 of all burst have non-dissipative photospheres non-dissipative photospheres Dereli, Pe’er & Ryde 2020

Comparison of Bayesian Evidences between the NDP and empirical models Spectra inconsistent with synchrotron emission NDP preferred CPL preferred Acuner, Ryde+2020 Zeynep Acuner PhD thesis 2020

Comparison of Bayesian Evidences between the NDP and empirical models Spectra inconsistent with synchrotron emission NDP preferred CPL preferred Acuner, Ryde+2020 Subphotospheric dissipation Zeynep Acuner PhD thesis 2020 Ahlgren+19 Vurm+16

Conclusions Current paradigm of GRBs emission: an e ffi cient photosphere and an e ffi cient external shock Mészáros 2019 Slow cooling Non dissipative Rayleigh- synchrotron photosphere Jeans Distribution of 𝛽 Prompt emission < 10s: Acuner, Ryde &Yu 2019 Acuner, Ryde &Yu 2019

Conclusions Current paradigm of GRBs emission: an e ffi cient photosphere and an e ffi cient external shock Mészáros 2019 Slow cooling Non dissipative Rayleigh- synchrotron photosphere Jeans Distribution of 𝛽 Prompt emission < 10s: Acuner, Ryde &Yu 2019 Acuner, Ryde &Yu 2019 1/4 of all burst have non-dissipative photospheres Acuner+19

Conclusions Current paradigm of GRBs emission: an e ffi cient photosphere and an e ffi cient external shock Mészáros 2019 Slow cooling Non dissipative Rayleigh- synchrotron photosphere Jeans Distribution of 𝛽 Prompt emission < 10s: Acuner, Ryde &Yu 2019 Acuner, Ryde &Yu 2019 1/4 of all burst have Dissipative photospheres non-dissipative photospheres Vurm+16, Ahlgren+19 Acuner+19

Conclusions Current paradigm of GRBs emission: an e ffi cient photosphere and an e ffi cient external shock Mészáros 2019 Slow cooling Non dissipative Rayleigh- synchrotron photosphere Jeans Distribution of 𝛽 Prompt emission < 10s: Acuner, Ryde &Yu 2019 Acuner, Ryde &Yu 2019 External shock emission. Alone 1/4 of all burst have Dissipative photospheres or in combination with a non-dissipative photospheres Vurm+16, Ahlgren+19 photosphere (Abdo+19) Acuner+19