Amsterdam–ASTRON radio transient facility and analysis centre: towards a 24× 7, all-sky monitor for the low-frequency array (LOFAR)

The Amsterdam–ASTRON Radio Transient Facility And Analysis Centre (AARTFAAC) project aims to implement an all-sky monitor (ASM), using the lowfrequency array (LOFAR) telescope. It will enable real-time, 24 × 7 monitoring for low-frequency radio transients over most of the sky locally visible to the LOFAR at time scales ranging from seconds to several days, and rapid triggering of follow-up observations with the full LOFAR on detection of potential transient candidates. These requirements pose several implementation challenges: imaging of an all-sky field of view, low latencies of processing, continuous availability and autonomous operation of the ASM. The first of these has already resulted in the correlator for the ASM being the largest in the world in terms of the number of input data streams. We have carried out test observations using existing LOFAR infrastructure, in order to quantify and constrain crucial instrumental design criteria for the ASM. In this study, we present an overview of the AARTFAAC data-processing pipeline and illustrate some of the aforementioned challenges by showing all-sky images obtained from one of the test observations. These results provide quantitative estimates of the capabilities of the instrument.