| Abstract : | The emission mechanism of Fast Radio Bursts (FRBs) is yet unknown though many different models have been proposed. Many FRB emission mechanisms predict that the relativistic plasma, after FRB emission, may continue to emit fainter radiation, not unlike afterglows observed from gamma-ray bursts and magnetar giant flares. This motivates us to constrain any faint afterglows or longer timescale emissions from FRB sources. Previously, Bhandari et al. (2020) have put limits on the long time-scale emission before and after a burst from observations of FRB 20191001. In this project, we have put constraints on any faint afterglow or precursor emission over a timescale between 200 ms to 10 seconds by stacking 365 FRBs from CHIME/FRB Catalog 1. We also separately stacked 86 bursts from the repeating FRB 20180916B and 36 bursts from FRB 20201124A. We aligned dynamic spectra of all FRBs by peak and normalized by peak flux. We generated a control sample with the same noise signature to compare our final results by shuffling our data in time and treating it identically to the dynamic spectra of FRBs. After stacking, we fitted Gaussian and exponential decay models to the data with timescales from 200ms to 10s. Our new stacked limits are 2 orders of magnitude lower than the previous limits. At a 5-sigma confidence, we constrain the emission to be ~ 4×10-3 to 2×10-2 times fainter relative to the peak FRB flux.
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