GeV emission from gamma‐ray bursts: a radiative fireball?

By G. Ghisellini, G. Ghirlanda, L. Nava, A. Celotti. 2009

227 citations recorded by the source corpus.

We study the emission observed at energies > 100 MeV of 11 gamma-ray bursts (GRBs) detected by the Fermi-Large Area Telescope (LAT) until 2009 October. The GeV emission has three main properties: (i) its duration is often longer than the duration of the softer emission detected by the Gamma Burst Monitor onboard Fermi (this confirms earlier results from the Energetic Gamma-Ray Experiment Telescope); (ii) its spectrum is consistent with F ν ∝ ν ―1 and does not show strong spectral evolution; and (iii) for the brightest bursts the flux detected by the LAT decays as a power law with a typical slope t ―1.5 . We argue that the observed >0.1 GeV flux can be interpreted as afterglow emission shortly following the start of the prompt phase emission as seen at smaller frequencies. The decay slope is what is expected if the fireball emission is produced in the radiative regime, i.e. all dissipated energy is radiated away. We also argue that the detectability in the GeV energy range depends on the bulk Lorentz factor Γ of the bursts, being strongly favoured in the case of large Γ. This implies that the fraction of bursts detected at high energies corresponds to the fraction of bursts having the largest r. The radiative interpretation can help to explain why the observed X-ray and optical afterglow energetics are much smaller than the energetics emitted during the prompt phase, despite the fact that the collision with the external medium should be more efficient than internal shocks in producing the radiation that we see.

Subfields: Astronomy and Astrophysics, Nuclear and High Energy Physics

View Paper: https://www.semanticscholar.org/paper/c2a98cd1ed8bf7c7b046178a2c3cc2c2df5627d9

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In Astronomy and Astrophysics

1. Bing Zhang
2. Pawan Kumar
3. E. Berger
4. B. Metzger
5. E. Liang
6. A. Pe’er
7. L. Sironi
8. Binbin Zhang

In Nuclear and High Energy Physics

1. Bing Zhang
2. L. Sironi
3. Pawan Kumar
4. A. Spitkovsky
5. J. Arons
6. E. Berger
7. U. Keshet
8. M. Lemoine

Citations in the corpus

• The physics of gamma-ray bursts & relativistic jets (2014, background): “There are several different lines of strong evidence suggesting that the high energy photons (>102MeV) we observe after the prompt phase (t >∼ 10s) are produced in the external forward shock via the synchrotron process (Kumar and Barniol Duran, 2009; Ghisellini et al., 2010).”
• Relativistic Shocks: Particle Acceleration and Magnetization (2015, background): “The synchrotron radiation of electrons accelerated at the external ultra-relativistic shock of GRBs can thus produce the bulk of the long-lasting > 100 MeV emission detected by the Fermi satellite (e.g. Kumar and Barniol Duran 2009; Ackermann 2010; De Pasquale 2010; Ghisellini et al. 2010).”
• THE MAXIMUM ENERGY OF ACCELERATED PARTICLES IN RELATIVISTIC COLLISIONLESS SHOCKS (2013, background): “Synchrotron emission from the shock-accelerated electrons powers the GRB afterglow emission, which is usually detected in the X–ray, optical and sometimes radio bands, and recently up to sub-GeV energies by the Fermi telescope (e.g., Ackermann 2010; De Pasquale 2010; Ghisellini et al. 2010).”
• Gamma-ray bursts in the comoving frame (2011, background): “If the GeV emission is interpreted as afterglow (Barniol–Duran & Kumar 2009; Ghirlanda et al. 2010; Ghisellini et al. 2010) the measure oftp,z at early times in the GeV range allows us to estimate theirΓ0, that are consistent with the correlations found using only the bursts withp,z observed in the…”
• A complete reference of the analytical synchrotron external shock models of gamma-ray bursts (2013, background): “Recent Fermi observations suggest that the GeV afterglow after the prompt emission phase is also dominated by the emission from the external shock (Kumar and Barniol Duran, 2009, 2010; Ghisellini et al., 2010; He et al., 2011; Liu and Wang, 2011; Maxham et al., 2011).”
• THE INTERNAL-COLLISION-INDUCED MAGNETIC RECONNECTION AND TURBULENCE (ICMART) MODEL OF GAMMA-RAY BURSTS (2010, background): “The neutron-heating photosphere model developed by Beloborodov (2010) needs to attribute the very high energy emission to a different component (e.g. from the external shock, Kumar and Barniol Duran 2009; Ghisellini et al. 2010).”
• Collisional mechanism for gamma‐ray burst emission (2009, background): “…source is visible in several GeV-emitting bursts (e.g. Abdoet al. 2009b; Ryde et al. 2010) and likely present in all of them, obscuring the behavior of the prompt Band spectrum at high energies (cf. the debate over GRB 080916C: Abdo et al. 2009a; Kumar & Barniol Duran 2009; Ghisellini et al. 2009).”
• AFTERGLOW OBSERVATIONS OF FERMI LARGE AREA TELESCOPE GAMMA-RAY BURSTS AND THE EMERGING CLASS OF HYPER-ENERGETIC EVENTS (2010, background): “…component observed from several LAT events is in fact due to the same source as the late-time afterglow emission: synchrotron radiation from accelerated electrons in the circumburst medium shock-heated by the outgoing blast wave (i.e., external shock emission; see also Ghisellini et al. 2010).”
• Detection of a Spectral Break in the Extra Hard Component of GRB 090926A (2011, background): “The delay timescale of the extra spectral component would correspond to the time needed for the forward shock to sweep up material and brighten (Kumar & Barniol Duran 2009; Ghisellini et al. 2010; Razzaque 2010).”
• A COMPREHENSIVE ANALYSIS OF FERMI GAMMA-RAY BURST DATA. I. SPECTRAL COMPONENTS AND THE POSSIBLE PHYSICAL ORIGINS OF LAT/GBM GRBs (2010, background): “It has been suggested that the entire GeV emission originates from the external shock (e.g. Kumar & Barniol Duran 2009a, 2009b; Ghisellini et al. 2010; Corsi et al. 2009).”
• A Decade of Gamma-Ray Bursts Observed by Fermi-LAT: The Second GRB Catalog (2019, background): “…smooth light curve and temporally extended emission & 100 MeV have led to the development of an early afterglow interpretation of high-energy radiation from the external forward shock (Kumar & Barniol Duran 2009; Ghisellini et al. 2010; Ackermann et al. 2010b; Razzaque 2010; Corsi et al. 2010).”