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Published June 2022 | Published + Accepted Version
Journal Article Open

Flares in gamma-ray burst X-ray afterglows as prompt emission from slightly misaligned structured jets

Abstract

We develop a model to explain the flaring activity in gamma-ray burst X-ray afterglows within the framework of slightly misaligned observers to structured jets. We suggest that flares could be the manifestation of prompt dissipation within the core of the jet, appearing to a misaligned observer in the X-ray band because of less favourable Doppler boosting. These flares appear during the afterglow phase because of core–observer light travel delays. In this picture, the prompt emission recorded by this observer comes from material along their line of sight, in the lateral structure of the jet, outside the jet's core. We start by laying down the basic analytical framework to determine the flares characteristics as a function of those of the gamma-ray pulse an aligned observer would see. We show that there is viable parameter space to explain flares with typical observing times and luminosities. We then analytically explore this model, showing that it naturally produces flares with small aspect ratios, as observed. We perform fits of our model to two Swift/XRT flares representing two different types of morphology, to show that our model can capture both. The ejection time of the core jet material responsible of the flare is a critical parameter. While it always remains small compared to the observed time of the flare, confirming that our model does not require very late central engine activity, late ejection times are strongly favoured, sometimes larger than the observed duration of the parent gamma-ray burst's prompt emission as measured by T90.

Additional Information

© 2022 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model). Accepted 2022 April 1. Received 2022 April 1; in original form 2021 December 7. We thank T. Matsumoto, R. Sari, and O. S. Salafia for useful discussion. RD is supported by the European Research Council Advanced Grant 'JETSET: Launching, propagation and emission of relativistic jets from binary mergers and across mass scales' (grant no. 884631). PB was supported by the Gordon and Betty Moore Foundation, grant GBMF5076 and by grant (no. 2020747) from the United States-Israel Binational Science Foundation (BSF), Jerusalem, Israel. DATA AVAILABILITY. The data and software underlying this article will be shared on reasonable request to the corresponding author.

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Published - stac938.pdf

Accepted Version - 2112.02917.pdf

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Additional details

Created:
August 22, 2023
Modified:
October 24, 2023