Evidence for a Canonical Gamma-Ray Burst Afterglow Light Curve in the Swift XRT Data

By J. Nousek, C. Kouveliotou, D. Grupe, K. Page, J. Granot, E. Ramirez-Ruiz, S. Patel, D. Burrows, V. Mangano, S. Barthelmy and 18 more. 2005

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We present new observations of the early X-ray afterglows of the first 27 gamma-ray bursts (GRBs) well observed by the Swift X-Ray Telescope (XRT). The early X-ray afterglows show a canonical behavior, where the light curve broadly consists of three distinct power-law segments: (1) an initial very steep decay (∝t-α with 3 ≲ α1 ≲ 5), followed by (2) a very shallow decay (0.5 ≲ α2 ≲ 1.0), and finally (3) a somewhat steeper decay (1 ≲ α3 ≲ 1.5). These power-law segments are separated by two corresponding break times, tbreak,1 ≲ 500 s and 103 s ≲ tbreak,2 ≲ 104 s. On top of this canonical behavior, many events have superimposed X-ray flares, which are most likely caused by internal shocks due to long-lasting sporadic activity of the central engine, up to several hours after the GRB. We find that the initial steep decay is consistent with it being the tail of the prompt emission, from photons that are radiated at large angles relative to our line of sight. The first break in the light curve (tbreak,1) takes place when the forward shock emission becomes dominant, with the intermediate shallow flux decay (α2) likely caused by the continuous energy injection into the external shock. When this energy injection stops, a second break is then observed in the light curve (tbreak,2). This energy injection increases the energy of the afterglow shock by at least a factor of f ≳ 4 and augments the already severe requirements for the efficiency of the prompt gamma-ray emission.

Subfields: Astronomy and Astrophysics

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Citations in the corpus

Making a Short Gamma-Ray Burst from a Long One: Implications for the Nature of GRB 060614 (2006, methodology): “We adjust the XRT lightcurve to match the tail of the pseudo burst (blue lightcurve in Fig.3), as has been the case for the majority of Swift bursts (e.g. Tagliaferri et al. 2005; Barthelmy et al. 2005b; Nousek et al. 2006; Zhang et al. 2006; O’Brien et al. 2006; Liang et al. 2006).”
Gamma-Ray Bursts in the Swift Era (2009, background): “This is consistent with an interpretation (Nousek et al. 2006, Zhang et al. 2006) in which the first break occurs when the slowly decaying emission from the forward shock becomes dominant over the steeply decaying tail emission of the prompt γ-rays as seen from large angles (Kumar and Panaitescu…”
Swift J1112.2−8238: a candidate relativistic tidal disruption flare (2015, background): “…are also apparently distinct, since the inferred isotropic X-ray luminosity lies an order of magnitude above GRBs at a similar epoch (see e.g. Nousek et al. 2006; Levan et al. 2014), and GRB afterglows at such late times seldom show such pronounced variability (likely due to the lack of…”
A DECADE OF SHORT-DURATION GAMMA-RAY BURST BROADBAND AFTERGLOWS: ENERGETICS, CIRCUMBURST DENSITIES, AND JET OPENING ANGLES (2015, positive): “Since early-time Xray afterglow light curves are often subject to steep decays, plateaus, or flares which may contaminate the afterglow emission (Nousek et al. 2006; Zhang et al. 2006; Margutti et al. 2011, 2013), we only utilize X-ray data atδt & 1000 s, when bursts have typically settled into the…”
Fallback accretion in the aftermath of a compact binary merger (2006, background): “The observations, however, have also revealed long-lasting X-ray activity after the main gamma-ray emission phase for about half of the bursts (Burrows et al. 2005; Nousek et al. 2006; O’Brien et al. 2006).”
JET BREAKS AND ENERGETICS OF Swift GAMMA-RAY BURST X-RAY AFTERGLOWS (2008, background): “We assume that all X-ray light curves in our sample inherently follow the canonical form (Figure 1) described by Zhang et al. (2006) and Nousek et al. (2006).”
Testing the Standard Fireball Model of Gamma-Ray Bursts Using Late X-Ray Afterglows Measured by Swift (2006, methodology): “The time Ta for these GRBs is not a pure jet break time since in all cases the Ta marks the end of the plateau phase which does not behave as a pre-jet afterglow (e.g. Nousek et al. 2006).”
Swift Observations of GRB 070110: An Extraordinary X-Ray Afterglow Powered by the Central Engine (2007, background): “Such behavior has been seen in other GRBs detected by Swift and, as reported by Zhang et al. (2006b), spectral evolution seems a common feature in early, bright GRB tails (e.g. GRB 060614, Mangano et al. 2007a).”
The Early X-Ray Emission from GRBs (2006, methodology): “Alternatives such as structured jets (e.g. Zhang & Mészáros 2002), multiple jets or patchy jets (e.g. Burrows et al. 2005c) in which we see varying emission as our light cone expands are also possibilities.”
Unveiling the origin of X-ray flares in gamma-ray bursts (2010, background): “It was realized rather soon by the Swift team that the light curve of many GRBs was characterized by a more complex temporal behaviour (Nousek et al. 2006; O’Brien et al. 2006; Zhang et al. 2006): a steep early decay, a “plateau” and a late decay where the slope observed by Beppo-SAX is essentially…”
A RADIO-SELECTED SAMPLE OF GAMMA-RAY BURST AFTERGLOWS (2011, background): “Compilations of X-ray and optical light curves from the Swift satellite have revealed complex but canonical light curve behaviors (Nousek et al. 2006; Zhang et al. 2006; Melandri et al. 2008; Roming et al. 2009; Evans et al. 2009).”
A time - luminosity correlation for Gamma - Ray Bursts in the X - rays (2008, background): “Most of the observed GRB afterglows belong to the first group, showing what has been called a canonical behavior (Nousek et al. 2006) described by a broken power - law.”
A Comprehensive Analysis of Swift XRT Data. I. Apparent Spectral Evolution of Gamma-Ray Burst X-Ray Tails (2006, background): “This component provides one possible reason to refresh the forward shock to sustain a shallow decay plateau in early X-ray afterglows (Zhang et al. 2006; Nousek et al. 2006), and it has been invoked to interpret the peculiar X-ray plateau afterglow of GRB 070110 (Troja et al. 2007).”
The physics of gamma-ray bursts & relativistic jets (2014, background): “…simply the high latitude emission (described in §2.1) associated with the prompt γ-ray source at R >∼ 1015cm when the central engine turns off faster than the decline of the X-ray lightcurve (Kumar and Panaitescu, 2000a; Dermer, 2004; Zhang et al., 2006; Nousek et al., 2006; Liang et al., 2006a).”
Testing the Curvature Effect and Internal Origin of Gamma-Ray Burst Prompt Emissions and X-Ray Flares with Swift Data (2006, methodology): “Combined analyses of the early data from the Burst Alert Telescope (BAT) and the X-Ray Telescope (XRT) for a large sample of bursts (Nousek et al. 2006; O’Brien et al. 2006) reveal a canonical X-ray afterglow lightcurve characterized by 5 components (Zhang et al. 2006a, see also Nousek et al.…”
The unusual X-ray emission of the short Swift GRB 090515: evidence for the formation of a magnetar? (2010, background): “Nousek et al. (2006) and Zhang et al. (2006) described the ‘canonical GRB light curve’ as three stages comprising a steep decline followed by a shallower decay and then a final decay phase.”
The multimessenger picture of compact object encounters: binary mergers versus dynamical collisions (2012, background): “Swift observations have revealed that both short and long bursts can show late time X-ray flaring activity (Burrows et al. 2005; Nousek et al. 2006).”
Methods and results of an automatic analysis of a complete sample of Swift-XRT observations of GRBs (2008, background): “The usual explanation of the phases (e.g. Nousek et al. 2006; Zhang et al. 2006, O’Brien et al. 2006) is as follows: • Steep decay – high latitude prompt emission (internal shocks).”