The search for radio emission from exoplanets using LOFAR low-frequency beam-formed observations: Data pipeline and preliminary results for the 55 Cnc system

Abstract

Detection of radio emission from exoplanets can provide information on the star-planet system that is difficult to study otherwise, such as the planetary magnetic field, magnetosphere, rotation period, interior structure, atmospheric dynamics and escape, and any star-planet interactions. Such a detection in the radio domain would open up a whole new field in the study of exoplanets. However, currently there are no confirmed detections of an exoplanet at radio frequencies. In this study, we search for non-thermal radio emission from the 55 Cnc system which has 5 known exoplanets. According to theoretical predictions 55 Cnc e, the innermost planet, is among the best targets for this search. We observed for 18 hours with the Low-Frequency Array (LOFAR) Low Band Antenna in the frequency range 26-73 MHz with full-polarization and covered 85% of the orbital phase of 55 Cnc e. During the observations four digital beams within the station beam were recorded simultaneously on 55 Cnc, nearby "empty" sky, a bright radio source, and a pulsar. A pipeline was created to automatically find and mask radio frequency interference, calibrate the time-frequency response of the telescope, and to search for bursty planetary radio signals in our data. Extensive tests and verifications were carried out on the pipeline. Analysis of the first 4 hours of these observations do not contain any exoplanet signal from 55 Cnc but we can confirm that our setup is adequate to detect faint astrophysical signals. We find a 3$\sigma$ upper limit for 55 Cnc of 230 mJy using the pulsar to estimate the sensitivity of the observations and 2.6 Jy using the time-series difference between the target and sky beam. The full data set is still under-going analysis. In the near future we will apply our observational technique and pipeline to the most promising exoplanet candidates for which LOFAR observations have already been obtained.