Physical Processes Shaping Gamma-Ray Burst X-Ray Afterglow Light Curves: Theoretical Implications from the Swift X-Ray Telescope Observations

By Bing Zhang, Yizhong Fan, J. Dyks, S. Kobayashi, P. Mészáros, D. Burrows, J. Nousek, N. Gehrels. 2005

887 citations recorded by the source corpus.

With the successful launch of the Swift Gamma-Ray Burst Explorer, a rich trove of early X-ray afterglow data has been collected by its onboard X-Ray Telescope (XRT). Some interesting features are emerging, including a distinct rapidly decaying component preceding the conventional afterglow component in many sources, a shallow decay component before the more "normal" decay component observed in a good fraction of GRBs, and X-ray flares in nearly half of the afterglows. In this paper we systematically analyze the possible physical processes that shape the properties of the early X-ray afterglow light curves and use the data to constrain various models. We suggest that the steep decay component is consistent with the tail emission of the prompt gamma-ray bursts and/or the X-ray flares. This provides strong evidence that the prompt emission and afterglow emission are likely two distinct components, supporting the internal origin of the GRB prompt emission. The shallow decay segment observed in a group of GRBs suggests that very likely the forward shock keeps being refreshed for some time. This might be caused by either a long-lived central engine, or a wide distribution of the shell Lorentz factors, or else possibly the deceleration of a Poynting flux-dominated flow. X-ray flares suggest that the GRB central engine is very likely still active after the prompt gamma-ray emission is over, but with a reduced activity at later times. In some cases, the central engine activity even extends to days after the burst triggers. Analyses of early X-ray afterglow data reveal that GRBs are indeed highly relativistic events and that early afterglow data of many bursts, starting from the beginning of the XRT observations, are consistent with the afterglow emission from an ISM environment.

Subfields: Astronomy and Astrophysics

View Paper: https://www.semanticscholar.org/paper/6425de15e74aa8026c32ec9c94aa0ba8376cd888

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In Astronomy and Astrophysics

1. Bing Zhang
2. E. Berger
3. Pawan Kumar
4. D. Schneider
5. E. Liang
6. B. Metzger
7. P. Hopkins
8. L. Hernquist

Citations in the corpus

• A NEW POPULATION OF ULTRA-LONG DURATION GAMMA-RAY BURSTS (2013, background): “In this model the rapid variability is not uncommon in GRB prompt emission, and the steep decay can be naturally interpreted as emission from high latitudes (Zhang et al. 2006).”
• A Comprehensive Analysis of Swift XRT Data. I. Apparent Spectral Evolution of Gamma-Ray Burst X-Ray Tails (2006, background): “In this scenario, the decay is strictly a power law with a slope ¼ (2þ ) if the time zero point is set to the beginning of the rising segment of the light curve (Zhang et al. 2006; see Huang et al. [2002] for the discussion of time zero point in a different context).”
• Short Gamma-Ray Bursts with Extended Emission (2006, background): “Instead, these pulses might be analogous to the X-ray flares observed accompanying the prompt portions of afterglows as revealed by Swift’s XRT, and attributed to central engine activity (Zhang et al. 2005).”
• 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).”
• Gamma-ray burst afterglows (2006, background): “This is in contradiction with the Swift finding that prompt emission and X-ray flares are of the internal origin while afterglows are of external origin (e.g. Zhang et al. 2006).”