Testing the Standard Fireball Model of Gamma-Ray Bursts Using Late X-Ray Afterglows Measured by Swift

By R. Willingale, P. O’Brien, J. Osborne, O. Godet, K. Page, M. Goad, D. Burrows, Bing Zhang, E. Rol, N. Gehrels and 1 more. 2006

234 citations recorded by the source corpus.

We show that all X-ray decay curves of γ-ray bursts (GRBs) measured by Swift can be fitted using one or two components, both of which have exactly the same functional form comprised of an early falling exponential phase followed by a power-law decay. The first component contains the prompt γ-ray emission and the initial X-ray decay. The second component appears later, has a much longer duration, and is present for ≈80% of GRBs. It most likely arises from the external shock that eventually develops into the X-ray afterglow. In the remaining ≈20% of GRBs the initial X-ray decay of the first component fades more slowly than the second and dominates at late times to form an afterglow. The temporal decay parameters and γ/X-ray spectral indices derived for 107 GRBs are compared to the expectations of the standard fireball model including a search for possible "jet breaks." For ~50% of GRBs the observed afterglow is in accord with the model, but for the rest the temporal and spectral indices do not conform to the expected closure relations and are suggestive of continued, late, energy injection. We identify a few possible jet breaks, but there are many examples where such breaks are predicted but are absent. The time Ta at which the exponential phase of the second component changes to a final power-law decay afterglow is correlated with the peak of the γ-ray spectrum, Epeak. This is analogous to the Ghirlanda relation, indicating that this time is in some way related to optically observed break times measured for pre-Swift bursts.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/259bed9dbb9df9b5b1649b9a58bd1d4d5aa26937

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In Astronomy and Astrophysics

1. Bing Zhang
2. E. Berger
3. B. Metzger
4. Pawan Kumar
5. E. Liang
6. E. Quataert
7. Binbin Zhang
8. T. Thompson

In Instrumentation

1. Bing Zhang
2. E. Liang
3. E. Berger
4. Binbin Zhang
5. E. Quataert
6. B. Metzger
7. Pawan Kumar
8. P. Hopkins

Citations in the corpus

• Signatures of magnetar central engines in short GRB light curves (2013, methodology): “However, it is very rare for XRT to not observe thesteep decay phase for LGRBs so the inclusion of BAT data does not affect the plateau fits (e.g. O’Brien et al. 2006; Willingale et al. 2007).”
• Methods and results of an automatic analysis of a complete sample of Swift-XRT observations of GRBs (2008, methodology): “…however many other authors have confirmed that the steep decay phase is consistent with the expectation for high latitude emission (e.g. Tagliaferri et al. 2005; Barthelmy et al. 2005b; O’Brien et al. 2006; Goad et al. 2006; Liang et al. 2006; Willingale et al. 2007; Butler & Kocevski 2007b).”
• The prompt-afterglow connection in gamma-ray bursts: a comprehensive statistical analysis of Swift X-ray light curves (2012, background): “…EFLX : for z > 2 we are not sensitive to E FL X < 10 50 erg. Observations suggest that the GRB X-ray LCs consist of two distinct phases (see e.g. Willingale et al. 2007): a first steep decay phase tightly connected to the prompt γ-ray emission (Tagliaferri et al. 2005; Goad et al. 2006); and a…”
• A Comprehensive Analysis of Swift XRT Data. II. Diverse Physical Origins of the Shallow Decay Segment (2007, methodology): “Empirically, O’Brien et al. (2006a,b) and Willingale et al. (2007) show that the data can be fitted by the superposition of a prompt emission component and an afterglow component.”
• AFTERGLOW OBSERVATIONS OF FERMI LARGE AREA TELESCOPE GAMMA-RAY BURSTS AND THE EMERGING CLASS OF HYPER-ENERGETIC EVENTS (2010, background): “…well tested (Meszaros & Rees 1997; Sari et al. 1998, 1999; Wijers & Galama 1999; Chevalier & Li 2000; Panaitescu & Kumar 2000; Yost et al. 2003; Willingale et al. 2007), it still must make several simplifying assumptions about the shock dynamics, magnetic field generation, particle…”
• A time - luminosity correlation for Gamma - Ray Bursts in the X - rays (2008, methodology): “To this aim, we use the data in Willingale et al. (2007) to look for a possible correlation between the X - ray luminosity at the break time Ta and the Ta itself.”
• A Reconnection Switch to Trigger gamma-Ray Burst Jet Dissipation (2010, background): “…away instead of accelerating the jet, it allows the electromagnetic dissipation to produce a prompt GRB luminosity that is equal to (or even exceeds) the associated afterglow emission, which could be what is observed but is difficult to obtain in the internal shock model (Willingale et al. 2007).”
• JET BREAKS AND ENERGETICS OF Swift GAMMA-RAY BURST X-RAY AFTERGLOWS (2008, background): “Comparing this work to other recent studies of jet breaks in X-ray afterglows (Burrows & Racusin 2007; Willingale et al. 2007; Panaitescu 2007; Kocevski & Butler 2008; Liang et al. 2008; Evans et al. 2008), we find significant overlap with our jet break candidates.”
• The physics of gamma-ray bursts & relativistic jets (2014, methodology): “An alternative way to describe the X-ray afterglow is a two-component phenomenological model (O’Brien et al., 2006; Willingale et al., 2007; Ghisellini et al., 2009).”
• GeV emission from gamma‐ray bursts: a radiative fireball? (2009, unknown): “These estimates w re based on the observed X–ray afterglow energetics (see e.g. Willingale et al. 2007; Ghisellini et al. 2009), and we can now revise them including the much more powerful high energyγ–ray emission, bringing the total afterglow energetics to be roughlyequal to the prompt phase one.”
• Swift Observations of GRB 070110: An Extraordinary X-Ray Afterglow Powered by the Central Engine (2007, methodology): “The best fit models of the three UVOT light curves (U, B, and V) with the Willingale et al. (2007) function are shown by solid lines in Fig.”
• CONSTRAINING GAMMA-RAY BURST INITIAL LORENTZ FACTOR WITH THE AFTERGLOW ONSET FEATURE AND DISCOVERY OF A TIGHT Γ0–Eγ,iso CORRELATION (2009, background): “…analyses suggest that the normal decay segment following the shallow decay one in the canonical XRT lightcurves are roughly consistent with the forward shock models (Willingale et al. 2007; Liang et al. 2007), favoring the long lasting energy injection models for the shallow-decay segment.”
• THE MILLISECOND MAGNETAR CENTRAL ENGINE IN SHORT GRBs (2015, methodology): “We extrapolate the BAT (15-150 keV) data to the XRT band (0.3-10 KeV) by assuming a single power law spectrum (see also O’Brien et al. 2006; Willingale et al. 2007; Evans et al. 2009).”
• A Comprehensive Analysis of Swift XRT Data. III. Jet Break Candidates in X-Ray and Optical Afterglow Light Curves (2007, background): “The GRB tail and the shallow decay segments are usually seen in the XRT light curves (O’Brien et al. 2006b; Liang et al. 2006; Willingale et al. 2007; Zhang et al. 2007c, hereafter Paper I; Liang et al. 2007, hereafter Paper II).”
• The Proto-Magnetar Model for Gamma-Ray Bursts (2010, background): “The X-ray afterglow in particular shows a complex evolution, including a ‘plateau’ phase in the light curve which is not predicted by the standard forward shock model (Nousek 2006; Willingale et al. 2007).”