The prompt emission & peculiar break of GRB 060124

— Our multi-wavelength analysis of GRB 060124 shows the unusual behaviour of the decaying lightcurve as well as supporting the recently proposed phenomenon of long-lasting central engine activity. The prompt X-ray emission displays uncommonly well resolved flaring behaviour, with spectral evolution – indicative of central engine activity – which allows us to estimate the energy injection time for each flare. The otherwise smooth X-ray & optical afterglows demonstrate achromatic breaks at about 1 day which differ significantly from the usual jet break in the blastwave model of afterglows. On 2006 January 24 the bright gamma-ray burst, GRB 060124, triggered instruments on multiple satellites, including Swift and Konus-Wind. Swift immediately slewed to the burst and started observing in X-rays, ∼ 350s before the main period of activity. The discovery of the bright optical counterpart only 1 hour after the burst allowed for well-sampled follow-up. The brightness of the burst permitted observations in X-rays for nearly a month despite a redshift of z = 2.3. We analysed the previously observed high-energy flaring from the Swift BAT & XRT instruments and Konus-Wind[1],[2]. This exhibits spectral evolution, supporting the theory of a central engine which is active for extended periods. A joint spectral fit of Fig. 1. – The X-ray (dashed) and optical (solid) lightcurves of GRB 060124. the data gives an average spectral decay index over the entire energy range (0.2keV – 1160keV) of β = 0.5 after a break at 1.2keV. There is negligible Hydrogen column density above that of the Galactic value. We also fit the XRT data to the curvature effect model[3], and estimate the times at which the central engine ejects the energy required to power the two main flares. Our results are consistent with similar fits to other GRBs[4], in that the ejection time of flares is during the rising period of the flare, though ours is a most striking example. The fading optical & X-ray lightcurves ([1]; Fig. 1) display simultaneous achromatic breaks. Before the break the temporal decay indices, and spectral decay indices, are consistent with the blastwave model of GRB afterglows in a homogeneous circumburst medium, with a power law index of the electron energy distribution, p ≈ 2. The achro-matic nature of the break points to a change in the dynamics of the blastwave. After the break there is a deviation from the behaviour expected from a laterally spreading jet. As observed in the …