RFI Flagging Implications for Short-Duration Transients

With their wide fields of view and often relatively long coverage of any position in the sky in imaging survey mode, modern radio telescopesprovide a data streamthat is naturally suited to searching for rare transients. However, Radio Frequency Interference (RFI) can show up in the data streamin similar ways to such transients, and thus the normal pre-treatment of filtering RFI ( flagging) may also remove astrophysical transients from the data streambefore imaging. In this paper we investigate how standard flaggingaffects 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 flaggingeffects are not as severe, although part of the signal is lost. For these transients, we present a modified flaggingstrategy which mitigates the effect of flaggingon 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.