Gamma‐ray burst efficiency and possible physical processes shaping the early afterglow

By Yizhong Fan, T. Piran. 2006

183 citations recorded by the source corpus.

The discovery by Swift that a good fraction of gamma-ray bursts (GRBs) have a slowly decaying X-ray afterglow phase led to the suggestion that energy injection into the blast wave takes place several hundred seconds after the burst. This implies that right after the burst the kinetic energy of the blast wave was very low and in turn the efficiency of production of gamma-rays during the burst was extremely high, rendering the internal shocks model unlikely. We re-examine the estimates of kinetic energy in GRB afterglows and show that the efficiency of converting the kinetic energy into gamma-rays is moderate and does not challenge the standard internal shock model. We also examine several models, including in particular energy injection, suggested to interpret this slow decay phase. We show that with proper parameters, all these models give rise to a slow decline lasting several hours. However, even those models that fit all X-ray observations, and in particular the energy injection model, cannot account self-consistently for both the X-ray and the optical afterglows of well-monitored GRBs such as GRB 050319 and GRB 050401. We speculate about a possible alternative resolution of this puzzle.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/42a0d7438dee2c5133bb5981b4573ccc389332eb

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In Astronomy and Astrophysics

1. Bing Zhang
2. Pawan Kumar
3. E. Liang
4. A. Pe’er
5. Binbin Zhang
6. Xuefeng Wu
7. E. Nakar
8. P. Mészáros

Citations in the corpus

• A New Method of Determining the Initial Size and Lorentz Factor of Gamma-Ray Burst Fireballs Using a Thermal Emission Component (2007, background): “Theoretical arguments based on fitting the flux of ultra-high energy cosmic rays (UHECR; Wick et al. 2004), under the assumption that UHECRs originate from GRBs (Waxman 1995; Vietri 1995), as well as efficiency considerations (Fan & Piran 2006) suggest larger value, Y & 10.”
• Gamma-Ray Bursts in the Swift Era (2007, methodology): “However, in some cases, clear chromatic features have been revealed (e.g., Fan & Piran 2006a; Panaitescu et al. 2006b; Huang et al. 2007), which rejects the interpretation at least for those cases.”
• CONSTRAINING GAMMA-RAY BURST INITIAL LORENTZ FACTOR WITH THE AFTERGLOW ONSET FEATURE AND DISCOVERY OF A TIGHT Γ0–Eγ,iso CORRELATION (2009, background): “However, the optical/X-ray chromatic behavior around the shallow and normal decay transition time (Panaitescu et al. 2006; Fan & Piran 2006; Liang et al. GRB initial Lorentz factor and Γ0 − Eγ,iso relation 5 2007) suggests that the X-ray and optical emissions are two independent components.”
• Gamma-ray burst afterglows (2006, background): “However, numerical calculations suggest that a pulsar model can fit some of the XRT lightcurves (Fan & Xu 2006; De Pasquale et al. 2006; Yu & Dai 2006).”
• A complete reference of the analytical synchrotron external shock models of gamma-ray bursts (2013, background): “In principle, these parameters may evolve with time also, and some authors have considered such more complicated models (e.g. Ioka et al., 2006; Fan and Piran, 2006).”
• The physics of gamma-ray bursts & relativistic jets (2014, background): “By contrast, the observed efficiency for prompt γ-ray emission is reported to be much higher — approaching, or possibly exceeding 50% (Zhang et al., 2007a; Fan and Piran, 2006a).”
• Extending the Search for Muon Neutrinos Coincident with Gamma-Ray Bursts in IceCube Data (2017, background): “…altogether surprising, as the radiative efficiency of these models has long been suggested to be insufficient to yield the observed γ-ray spectra (Fan & Piran 2006; Zhang et al. 2007; Kumar & Zhang 2015)unless the distribution of shell Γfactors within the fireball is unrealistically…”
• A Comprehensive Analysis of Swift XRT Data. II. Diverse Physical Origins of the Shallow Decay Segment (2007, background): “For example, simultaneous X-ray/optical observations suggest that the break between the shallow and the normal decay segments in the X-ray band for some GRBs is chromatic (Panaitescu et al. 2006b; Fan & Piran 2006).”
• The X-ray afterglow flat segment in short GRB 051221A: Energy injection from a millisecond magnetar? (2006, methodology): “One modification is that now we have taken into account the energy injection (for instance see equation (12) of Fan & Piran (2006); see also Wei, Yan & Fan 2006).”
• Short-hard gamma-ray bursts (2007, background): “…the prompt emission in long and short GRBs are similar, we expect similar efficiency, implying that the γ-ray isotropic equivalent energy output is a reasonable estimator of E (Freedman & Waxman, 2001; Granot, Königl & Piran, 2006; Fan & Piran, 2006), and therefore E ∼ 1050 erg (see Table 2).”