RFI Flagging Implications for Short-Duration Transients

TL;DR

This paper examines how radio frequency interference flagging impacts the detection of short-duration astrophysical transients in radio survey data, proposing strategies to mitigate signal loss and improve transient identification.

Contribution

It analyzes the effects of standard RFI flagging on transient detectability and introduces a modified flagging strategy and a notification script to better preserve transient signals.

Findings

Short transients are often completely flagged and lost.

Longer transients experience partial signal loss due to flagging.

A modified flagging approach reduces transient signal suppression.

Abstract

With their wide fields of view and often relatively long coverage of any position in the sky in imaging survey mode, modern radio telescopes provide a data stream that is naturally suited to searching for rare transients. However, Radio Frequency Interference (RFI) can show up in the data stream in similar ways to such transients, and thus the normal pre-treatment of filtering RFI (flagging) may also remove astrophysical transients from the data stream before imaging. In this paper we investigate how standard flagging affects the detectability of such transients by examining the case of transient detection in an observing mode used for Low Frequency Array (LOFAR; \citep{LOFAR}) surveys. We quantify the fluence range of transients that would be detected, and the reduction of their SNR due to partial flagging. We find that transients with a duration close to the integration sampling time, as well as bright transients with durations on the order of tens of seconds, are completely flagged. For longer transients on the order of several tens of seconds to minutes, the flagging effects are not as severe, although part of the signal is lost. For these transients, we present a modified flagging strategy which mitigates the effect of flagging on transient signals. We also present a script which uses the differences between the two strategies, and known differences between transient RFI and astrophysical transients, to notify the observer when a potential transient is in the data stream.