A Comprehensive Analysis of Swift XRT Data. I. Apparent Spectral Evolution of Gamma-Ray Burst X-Ray Tails

By Bin-Bin Zhang, E. Liang, Bing Zhang. 2006

148 citations recorded by the source corpus.

An early steep decay component following the prompt GRBs is commonly observed in Swift XRT light curves, which is regarded as the tail emission of the prompt gamma rays. Prompted by the observed strong spectral evolution in the tails of GRBs 060218 and 060614, we present a systematic time-resolved spectral analysis for the Swift GRB tails detected between 2005 February and 2007 January. We select a sample of 44 tails that are bright enough to perform time-resolved spectral analyses. Among them 11 tails are smooth and without superimposing significant flares, and their spectra have no significant temporal evolution. We suggest that these tails are dominated by the curvature effect of the prompt gamma rays due to delay of propagation of photons from large angles with respect to the line of sight. More interestingly, 33 tails show clear hard-to-soft spectral evolution, with 16 of them being smooth tails directly following the prompt GRBs, and the others being superimposed with large flares. We focus on the 16 clean, smooth tails and consider three toy models to interpret the spectral evolution. The curvature effect of a structured jet and a model invoking superposition of the curvature effect tail and a putative underlying soft emission component cannot explain all the data. The third model, which invokes an evolving exponential spectrum, seems to reproduce both the light curve and the spectral evolution of all the bursts, including GRBs 060218 and 060614. More detailed physical models are called for to understand the apparent evolution effect.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/f02a260042152dc287a4bdf3b20f9efd25ae098f

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In Astronomy and Astrophysics

1. Bing Zhang
2. Pawan Kumar
3. E. Liang
4. Binbin Zhang
5. W. Lei
6. Xuefeng Wu
7. D. Burrows
8. Houjun Lü

In Instrumentation

1. Bing Zhang
2. E. Liang
3. Pawan Kumar
4. Binbin Zhang
5. Huirong Yan
6. P. Lasky
7. D. Burrows
8. C. Guidorzi

Citations in the corpus

• A Comprehensive Analysis of Swift XRT Data. III. Jet Break Candidates in X-Ray and Optical Afterglow Light Curves (2007, background): “…(e.g., GRB 060729; Grupe et al. 2006), past the GRB triggers and revealed a canonical X-ray light curve that is composed of four successive segments that exhibit power-law decay (Zhang et al. 2006; Nousek et al. 2006; O’Brien et al. 2006b) with superposed erratic flares (Burrows et al. 2005a).”
• CONSTRAINING GAMMA-RAY BURST INITIAL LORENTZ FACTOR WITH THE AFTERGLOW ONSET FEATURE AND DISCOVERY OF A TIGHT Γ0–Eγ,iso CORRELATION (2009, background): “The majority is the so-called canonical XRT lightcurves characterized by a steep-shallownormal-steep decay pattern (Zhang et al. 2006; Nousek et al. 2006; O’Brien et al. 2006), although not all the segments show up in every burst (Evans et al. 2009).”
• JET BREAKS AND ENERGETICS OF Swift GAMMA-RAY BURST X-RAY AFTERGLOWS (2008, background): “The distributions are not nearly as narrow as those suggested by the canonical light curve form (Nousek et al. 2006; Zhang et al. 2006), but do suggest a spread to larger break times in the contaminated ambiguous II-III/III-IV sample and the segments I-II-III sample.”
• THE MILLISECOND MAGNETAR CENTRAL ENGINE IN SHORT GRBs (2015, methodology): “The derived EK,iso is a constant during the normal decay phase, but depends on time during the shallow decay phase (Zhang et al. 2007a).”
• A complete reference of the analytical synchrotron external shock models of gamma-ray bursts (2013, methodology): “After the cessation of the prompt emission, the lightcurve usually transits to the afterglow emission through a “steep decay” likely due to the high-latitude emission (e.g. as observed in the early X-ray afterglow detected with Swift, Tagliaferri et al., 2005; Zhang et al., 2006, 2007).”
• THE INTERNAL-COLLISION-INDUCED MAGNETIC RECONNECTION AND TURBULENCE (ICMART) MODEL OF GAMMA-RAY BURSTS (2010, background): “…ways to constrain RGRB. (1) Swift observations suggest that the early Xray afterglow light curves are dominated by a steep decay component (Tagliaferri et al. 2005), which is best interpreted as the the high-latitude emission of the prompt GRB as the emission is abruptly ceased (Zhang et al. 2006).”
• Gamma-ray burst afterglows (2006, methodology): “They are interpreted as internal shock afterglows by Zhang et al. (2007c).”
• Swift Observations of GRB 070110: An Extraordinary X-Ray Afterglow Powered by the Central Engine (2007, background): “Phenomenological models involving an underlying central engine afterglow with a steep spectral index or an internal shock afterglow with a cooling frequency passing through the XRT window may be candidates to interpret these spectral evolutions (Zhang et al. 2006b).”
• The physics of gamma-ray bursts & relativistic jets (2014, background): “behavior (X.-G. Wang et al. 2014, in preparation). decay phase (Zhang et al., 2007c).”
• THE THIRD SWIFT BURST ALERT TELESCOPE GAMMA-RAY BURST CATALOG (2015, background): “Several studies have shown that it is not uncommon that the spectral evolution follows the shape of the light curve (e.g., Zhang et al. 2007, 2011).”
• A Comprehensive Analysis of Swift XRT Data. II. Diverse Physical Origins of the Shallow Decay Segment (2007, methodology): “We have presented a comprehensive analysis of the Swift XRT light curves of long GRBs, focusing on the properties of the shallow decay phase and its relation with the follow-up decay phase.”