Testing the Curvature Effect and Internal Origin of Gamma-Ray Burst Prompt Emissions and X-Ray Flares with Swift Data

By E. Liang, Bing Zhang, P. O’Brien, R. Willingale, L. Angelini, D. Burrows, S. Campana, G. Chincarini, A. Falcone, N. Gehrels and 8 more. 2006

187 citations recorded by the source corpus.

The X-ray light curves of many GRBs have a steep tail following the gamma-rays and have some erratic flares. We assume that these tails and flares are of ``internal'' origin and that their decline behaviors are dominated by the curvature effect. This effect suggests that the decay slope of the late steep decay part of the light curves is α = 2 + β, where β is the X-ray spectral index. We present a self-consistency test for this scenario with a sample of 36 prompt emission tails/flares in 22 light curves observed by the Swift XRT. We derive the zero time (t0) for each steep decay component by fitting the light curves with the constraint of α = 2 + β. Our results show that the t0values of the prompt emission tails and the tails of well-separated flares are self-consistent with the expectation of the internal dissipation models, indicating that each X-ray flare forms a distinct episode of the central engine activity and the central engine remains active after the prompt emission is over, sometimes up to ~1 day after the GRB trigger. This challenges the conventional models and calls for new ideas to restart the central engine. We further show that the onset time of the late central engine activity does not depend on the GRB duration. We also identify a minority group of GRBs whose combined BAT-XRT light curves are smoothly connected, without an abrupt transition between the prompt emission and the afterglow. These GRBs may have an external origin for both the prompt emission and the afterglow.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/b0c6be82d447942234164a7a0cd5ef3717f9fc5c

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In Astronomy and Astrophysics

1. Bing Zhang
2. E. Liang
3. Pawan Kumar
4. E. Berger
5. Binbin Zhang
6. D. Burrows
7. B. Metzger
8. N. Gehrels

In Instrumentation

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

Citations in the corpus

• 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).”
• JET BREAKS AND ENERGETICS OF Swift GAMMA-RAY BURST X-RAY AFTERGLOWS (2008, background): “This is further complicated by the choice of t0 for determining the slope of the temporal decay that affects segment I much more strongly than the other segments (Zhang et al. 2006; Liang et al. 2006).”
• Gamma-Ray Bursts in the Swift Era (2007, methodology): “Such a high event rate for LL-GRBs has been independently derived by several groups (e.g., Cobb et al. 2006a; Pian et al. 2006; Soderberg et al. 2006a; Liang et al. 2006c).”
• THE INTERNAL-COLLISION-INDUCED MAGNETIC RECONNECTION AND TURBULENCE (ICMART) MODEL OF GAMMA-RAY BURSTS (2010, methodology): “Attributing the observed variability to random motion of the relativistic “fundamental emitters” in the emission region (Lyutikov and Blandford 2003) would then require arguing that the “T0-reset” effect of the last pulse and X-ray flares (Liang et al. 2006) is purely due to a chance coincidence.”
• 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).”
• A Comprehensive Analysis of Swift XRT Data. I. Apparent Spectral Evolution of Gamma-Ray Burst X-Ray Tails (2006, methodology): “…et al. 2006), which could be generally interpreted as the so-called curvature effect due to the delay of propagation of photons from high latitudes with respect to the line of sight (Fenimore et al. 1996; Kumar & Panaitescu 2000; Qin et al. 2004; Dermer 2004; Zhang et al. 2006; Liang et al. 2006b).”
• 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).”
• Methods and results of an automatic analysis of a complete sample of Swift-XRT observations of GRBs (2008, result): “…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 unusual X-ray emission of the short Swift GRB 090515: evidence for the formation of a magnetar? (2010, methodology): “Using the method described by Liang et al. (2006), we shifted the t0 to the possible flare at the end of the plateau in GRB 090515.”
• Swift Observations of GRB 070110: An Extraordinary X-Ray Afterglow Powered by the Central Engine (2007, methodology): “The very steep decay component therefore strongly suggests that the plateau is of internal origin, since t0 is allowed to shift to much later epochs within the internal scenarios (Zhang et al. 2006a; Liang et al. 2006).”
• A Comprehensive Analysis of Swift XRT Data. II. Diverse Physical Origins of the Shallow Decay Segment (2007, background): “The XRT light curves generally begin with a rapidly decaying segment (Tagliaferri et al. 2005; O’Brien et al. 2006b), which is explained as the prompt emission tail due to the so-called “curvature effect” (Kumar & Panaitescu 2000b; Zhang et al. 2006; Liang et al. 2006; Yamazaki et al. 2006)4.”