X-ray flares, plateaus, and chromatic breaks of GRB afterglows from up-scattered forward-shock emission - AstrophysicsReport as inadecuate

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Abstract: Scattering of the forward-shock synchrotron emission by a relativisticoutflow located behind the leading blast-wave may produce an X-ray emissionbrighter than that coming directly from the forward-shock and may explain fourfeatures displayed by Swift X-ray afterglows: flares, plateaus slow decays,chromatic light-curve breaks, and fast post-plateau decays. For a coldscattering outflow, the reflected flux overshines the primary one if thescattering outflow is nearly baryon-free and highly relativistic. These tworequirements can be relaxed if the scattering outflow is energized by weakinternal shocks, so that the incident forward-shock photons are alsoinverse-Compton scattered, in addition to bulk-scattering. Sweeping-up of thephotons left behind by the forward shock naturally yields short X-ray flares.Owing to the boost in photon energy produced by bulk-scattering scattering, thereflected emission is more likely to overshine that coming directly from theforward shock at higher photon energies, yielding light-curve plateaus andbreaks that appear only in the X-ray. The brightness, shape, and decay of theX-ray light-curve plateau depend on the radial distribution of the scatterer-sLorentz factor and mass-flux. Chromatic X-ray light-curve breaks and sharppost-plateau decays cannot be accommodated by the direct forward-shock emissionand argue in favour of the scattering-outflow model proposed here. On the otherhand, the X-ray afterglows without plateaus, those with achromatic breaks, andthose with very long-lived power-law decays are more naturally accommodated bythe standard forward-shock model. Thus the diversity of X-ray light-curvesarises from the interplay of the scattered and direct forward-shock emissions.

Author: A. Panaitescu

Source: https://arxiv.org/

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