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What does FRB light-curve variability tell us about the emission mechanism?

Beniamini, Paz and Kumar, Pawan (2020) What does FRB light-curve variability tell us about the emission mechanism? . (Unpublished)

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A few fast radio bursts' (FRBs) light-curves have exhibited large intrinsic modulations of their flux on extremely short (t_r ∼ 10μs) time scales, compared to pulse durations (t_(FRB) ∼ 1ms). Light-curve variability timescales, the small ratio of rise time of the flux to pulse duration, and the spectro-temporal correlations in the data constrain the compactness of the source and the mechanism responsible for the powerful radio emission. The constraints are strongest when radiation is produced far (≳ 10¹⁰cm) from the compact object. We describe different physical set-ups that can account for the observed t_r/t_(FRB) ≪ 1 despite having large emission radii. The result is either a significant reduction in the radio production efficiency or distinct light-curves features that could be searched for in observed data. For the same class of models, we also show that due to high-latitude emission, if a flux f₁ (ν₁) is observed at t₁ then at a lower frequency ν₂ < ν₁ the flux should be at least (ν₂/ν₁)²f₁ at a slightly later time (t₂ = t₁ν₁/ν₂) independent of the duration and spectrum of the emission in the comoving frame. These features can be tested, once light-curve modulations due to scintillation are accounted for. We provide the timescales and coherence bandwidths of the latter for a range of possibilities regarding the physical screens and the scintillation regime. Finally, if future highly resolved FRB light-curves are shown to have intrinsic variability extending down to ∼μs timescales, this will provide strong evidence in favor of magnetospheric models.

Item Type:Report or Paper (Discussion Paper)
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URLURL TypeDescription Paper
Beniamini, Paz0000-0001-7833-1043
Additional Information:PB thanks Wenbin Lu and Ben Margalit for helpful discussions. The research of PB was funded by the Gordon and Betty Moore Foundation through Grant GBMF5076. This work has been funded in part by an NSF grant AST-2009619. Data availability: The data produced in this study will be shared on reasonable request to the authors.
Funding AgencyGrant Number
Gordon and Betty Moore FoundationGBMF5076
Subject Keywords:Radiation mechanisms: non-thermal - methods: analytical - stars: magnetars - radio continuum: transients - masers
Record Number:CaltechAUTHORS:20200901-104243241
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:105201
Deposited By: Tony Diaz
Deposited On:08 Sep 2020 19:53
Last Modified:08 Sep 2020 19:53

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