Abstract
Previously detected in only a few gamma-ray bursts (GRBs), X-ray flares are now observed in ~50% of Swift GRBs, though their origins remain unclear. Most flares are seen early on in the afterglow decay, while some bursts exhibit flares at late times of 10^4 to 10^5 seconds, which may have implications for flare models.We investigate whether a sample of late time (> 10^4s) flares are different from previous samples of early time flares, or whether they are merely examples on the tail of the early flare distribution. We examine the X-ray light curves of Swift bursts for late flares and compare the flare and underlying temporal power-law properties with those of early flares, and the values of these properties predicted by the blast wave model. The burst sample shows late flare properties consistent with those of early flares, where the majority of the flares can be explained by either internal or external shock, though in a few cases one origin is favoured over the other. The underlying power laws are mainly consistent with the normal decay phases of the afterglow. If confirmed by the ever growing sample of late time flares, this would imply that, in some cases, prolonged activity out to a day or a restarting of the central engine is required.
Highlights
The majority of gamma-ray bursts (GRBs) are well described by the blast wave model (Rees & Mészáros 1992; Mészáros et al 1998), which details their temporal and spectral behaviour. In this model GRB prompt emission is caused by internal shocks within a collimated ultrarelativistic jet while afterglow emission is created by external shocks when the jet ploughs into the circumburst medium, causing a blast wave
Prior to Swift, X-ray coverage typically began at ∼0.5–1.5 days after the GRB event, and X-ray flares were detected in only a few bursts (e.g., GRB 970508, Piro et al 1998; GRB 011121 & GRB 011211; Piro et al 2005)
The underlying temporal indices of the bursts range from α ∼ 0.4 to α ∼ 1.2, which are quite shallow, suggesting that these flares might occur during plateau phases (e.g., Nousek et al 2006; O’Brien et al 2006)
Summary
The majority of gamma-ray bursts (GRBs) are well described by the blast wave model (Rees & Mészáros 1992; Mészáros et al 1998), which details their temporal and spectral behaviour In this model GRB prompt emission is caused by internal shocks within a collimated ultrarelativistic jet while afterglow emission is created by external shocks when the jet ploughs into the circumburst medium, causing a blast wave. A very small number of GRBs have exhibited flares on much later timescales of 104 to 105 s, or approximately one day after the prompt event (including, in the optical, pre-Swift GRB 000301C, Sagar et al 2000) These late flares, like the early flares, are difficult to accommodate within the external shock model if the width, Δt, is smaller than the observing timescale, t, as is often the case (Lazzati et al 2002; Lazzati & Perna 2007).
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
