GRB 060714: No Clear Dividing Line between Prompt Emission and X‐Ray Flares

Abstract

The long gamma-ray burst GRB 060714 was observed to exhibit a series of five X-ray flares beginning $70 s after the burst trigger T 0 and continuing until $T 0 þ 200 s. The first two flares were detected by the Burst Alert Telescope (BAT) on the Swift satellite, before Swift had slewed to the burst location, while the last three flares were strongly detected by the X-Ray Telescope (XRT) but only weakly detected by the BAT. This burst provides an unusual opportunity to track a complete sequence of flares over a wide energy range. The flares were very similar in their light curve morphology, showing power-law rise and fall components, and in most cases significant substructure. The flares also showed strong evolution with time, both spectrally and temporally. The small timescale and large amplitude variability observed are incompatible with an external shock origin for the flares, and support instead late-time sporadic activity either of the central source or of localized dissipation events within the outflow. We show that the flares in GRB 060714 cannot be the result of internal shocks in which the contrast in the Lorentz factor of the colliding shells is very small, and that this mechanism faces serious difficulties in most Swift GRBs. The morphological similarity of the flares and the prompt emission and the gradual and continual evolution of the flares with time makes it difficult and arbitrary to draw a dividing line between the prompt emission and the flares.

Infrared/optical – X-ray simultaneous observations of X-ray flares in GRB 071112C and GRB 080506

“…The lack of optical variations is consistent with previously reported observations (e.g. Burrows et al 2005;Krimm et al 2007;Butler & Kocevski 2007). The optical spectral index also unchanged during the X-ray flares in both GRB 071112C and 080506.…”

“…No optical-infrared flare has been reported during the X-ray flares in previous observations, while a part of those observations were too sparse to investigate the detailed behavior of optical-infrared afterglows during the X-ray flares (Stanek et al 2007;Krimm et al 2007).…”

Discoveries enabled by multiwavelength afterglow observations of gamma-ray bursts

“…The flares are relatively sharp, with ∆t/t ∼ 0.1, and are spectrally different (harder) than the underlying afterglow emission. There is considerable spectral evolution during a flare with a hardening during the rise followed by softening during the decay Krimm et al, 2007;Godet et al, 2007). The first case where these flares were seen simultaneous in the optical/NIR was GRB 071031 (Krühler et al, 2009), which showed that the peak of the emission shifts at late times from the few keV band into the UV.…”

Photometry and spectroscopy of GRB 060526: a detailed study of the afterglow and host galaxy of az = 3.2 gamma-ray burst

“…Burrows et al 2005;Chincarini at al. 2007;Krimm et al 2007), and strong optical/NIR flaring contemporaneous with the GRB prompt emission may also occur (Vestrand et al 2005Blake et al 2005;Racusin et al 2008), thus making optical flares from late central engine activity an interesting prospect (Kann 2007;Malesani et al 2007). …”