Abstract
Context. The magnetized solar system planets are strong radio emitters and theoretical studies suggest that the radio emission from nearby exoplanets in close-in orbits could reach intensity levels 103–107 times higher than Jupiter’s decametric emission. Detection of exoplanets in the radio domain would open up a brand new field of research, however, currently there are no confirmed detections at radio frequencies. Aims. We investigate the radio emission from Jupiter, scaled such that it mimics emission coming from an exoplanet, with low-frequency beam-formed observations using LOFAR. The goals are to define a set of observables that can be used as a guideline in the search for exoplanetary radio emission and to measure effectively the sensitivity limit for LOFAR beam-formed observations. Methods. We observe “Jupiter as an exoplanet” by dividing a LOFAR observation of Jupiter by a down-scaling factor and adding this observation to beam-formed data of the “sky background”. Then we run this artificial dataset through our total intensity (Stokes-I) and circular polarization (Stokes-V) processing and post-processing pipelines and determine up to which down-scaling factor Jupiter is still detected in the dataset. Results. We find that exoplanetary radio bursts can be detected at 5 pc if the circularly polarized flux is 105 times stronger than the typical level of Jupiter’s radio bursts during active emission events (~4 × 105 Jy). Equivalently, circularly polarized radio bursts can be detected up to a distance of 20 pc (encompassing the known exoplanets 55 Cnc, Tau Boötis, and Upsilon Andromedae) assuming the level of emission is 105 times stronger than the peak flux of Jupiter’s decametric burst emission (~6 × 106 Jy).
Highlights
The detection and characterization of exoplanetary radio emission would constitute a new and important field of exoplanet science
In the pipeline (1) we divide the raw data into sections of 4000 spectra (42 s), (2) we apply the Radio Frequency Interference (RFI) mask to the raw data, (3) we create an integrated spectrum from the 10% quantile of the distribution of intensities at each frequency, (4) we correct the average of the 10% quantile such that it is equivalent to the mean using Eq (7), (5) we find a second order polynomial fit at each frequency over all time sections, and (6) we create and save the 2-d timefrequency response surface made from the polynomial fits
Our detection in Q4f consists of ∼30 data-points in the Nançay Decameter Array (NDA) calibration data exceeding 3 × 104 Jy with a threshold ≥2σ (Fig 8d). This limit corresponds to a flux density of ∼α × 4 × 104 Jy = 1.3 Jy using the value of Jupiter’s absolute flux density corresponding to 30 data-points from Fig. 2c. We find that this flux density is ∼1.3 times the theoretical sensitivity expected for Low-Frequency Array (LOFAR) beam-formed observations using Eq (19) when τ = 1 sec and b = 3 MHz
Summary
The detection and characterization of exoplanetary radio emission would constitute a new and important field of exoplanet science. Starting with Zarka et al (1997) and Farrell et al (1999), a number of articles have attempted to estimate the radio flux density that can be expected for different types of exoplanets. Such estimates have to be taken carefully. The uncertainties are even larger when different models are compared Still, such numbers can be used to determine whether the detection of exoplanetary auroral radio emission seems realistic with a given radio telescope and observational setup. Grießmeier (2017) find that the flux densities of 15 exoplanets are above the theoretical detection limit of LOFAR as given by Turner et al (2017)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
