Ground-based study of solar system planetary lightning

Contains fulltext : 83426.pdf (publisher's version ) (Open Access)ISKAF 2010, 10 juni 201

PALANTIR: An updated prediction tool for exoplanetary radio emissions

In the past two decades, it has been convincingly argued that magnetospheric radio emissions, of cyclotron maser origin, can occur for exoplanetary systems, similarly as solar planets, with the same periodicity as the planetary orbit. These emissions are primarily expected at low frequencies (usually below 100 MHz, c.f. Farrell et al., 1999; Zarka, 2007). The radio detection of exoplanets will considerably expand the field of comparative magnetospheric physics and star-planet plasma interactions (Hess & Zarka, 2011). We have developped a prediction code for exoplanetary radio emissions, PALANTIR: "Prediction Algorithm for star-pLANeT Interactions in Radio". This code has been developed for the construction of an up-to-date and evolutive target catalog, based on observed exoplanet physical parameters, radio emission theory, and magnetospheric physics embedded in scaling laws. It is based on, and extends, previous work by Grießmeier et al. (2007b). Using PALANTIR, we prepared an updated list of targets of interest for radio emissions. Additionally, we compare our results with previous studies conducted with similar models (Griessmeier, 2017). For the next steps, we aim at improving this code by adding new models and updating those already used

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

International audienceDetection 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

Probing Jupiter-satellite interactions from the beaming of their decametric emissions: the case of Europa and Ganymede

In a recent study, we accurately measured the beaming of Io-Jupiter decametric emissions, whose uncertainty is controlled by that on the position of the active Io ux tube (IFT) hosting the radiosources. The active IFT was positioned by 3 different methods using either simultaneous radio/UV measurements, either bi-point radio measurements, or independent models of equatorial lead angle. We found largely oblique beaming angles θ within 70 - 80° from the local magnetic field vector, decreasing with increasing frequency. Assuming that Io-Jupiter radio emissions are driven by the electron cyclotron maser from loss cone electron distribution functions, we then derived the kinetic energy of unstable electrons E_e- associated to each time-frequency measurement of Io-Jupiter decametric arcs, ranging from 3 to 16 keV. Both θ and E_e- were found to significantly vary as a function of the altitude along the field line and, independently, as a function of time. In this follow-up study, we employ the same approach to study a sample of the recently discovered Europa- and Ganymede-Jupiter decametric emissions, as observed from the Nançay Decameter Array (NDA) and NenuFAR in Nançay. Interestingly, we measure θ and E_e- which strikingly compare to those obtained for the Io-Jupiter decametric events, promoting common acceleration and radio emission processes for the three planet-moon interactions

The search for radio emission from the exoplanetary systems 55 Cancri, Upsilon Andromedae, and Tau Bootis using LOFAR beam-formed observations

International audienceObserving planetary auroral radio emission is the most promising method to detect exoplanetary magnetic fields, the knowledge of which will provide valuable insights into the planet's interior structure, atmospheric escape, and habitability. We present LOFAR-LBA circularly polarized beamformed observations of the exoplanetary systems 55 Cancri, υ Andromedae, and τ Boötis. We tentatively detect circularly polarized bursty emission from the τ Boötis system in the range 14-21 MHz with a flux density of ∼890 mJy and with a significance of ∼3σ. For this detection, no signal is seen in the OFF-beams, and we do not find any potential causes which might cause false positives. We also tentatively detect slowly variable circularly polarized emission from τ Boötis in the range 21-30 MHz with a flux density of ∼400 mJy and with a statistical significance of >8σ. The slow emission is structured in the time-frequency plane and shows an excess in the ON-beam with respect to the two simultaneous OFF-beams. Close examination casts some doubts on the reality of the slowly varying signal. We discuss in detail all the arguments for and against an actual detection. Furthermore, a ∼2σ marginal signal is found from the υ Andromedae system and no signal is detected from the 55 Cancri system. Assuming the detected signals are real, we discuss their potential origin. Their source probably is the τ Bootis planetary system, and a possible explanation is radio emission from the exoplanet τ Bootis b via the cyclotron maser mechanism. Assuming a planetary origin, we derived limits for the planetary polar surface magnetic field strength, finding values compatible with theoretical predictions. Further low-frequency observations are required to confirm this possible first detection of an exoplanetary radio signal

The LOFAR Tied-Array All-Sky Survey (LOTAAS): Characterization of 20 pulsar discoveries and their single-pulse behavior

International audienceWe are using the LOw-Frequency ARray (LOFAR) to perform the LOFAR Tied-Array All-Sky (LOTAAS) survey for pulsars and fast transients. Here, we present the astrometric and rotational parameters of 20 pulsars discovered as part of LOTAAS. These pulsars have regularly been observed with LOFAR at 149 MHz and the Lovell telescope at 1532 MHz, supplemented by some observations with the Lovell telescope at 334 MHz and the Nançay Radio Telescope at 1484 MHz. Timing models are calculated for the 20 pulsars, some of which are among the slowest spinning pulsars known. PSR J1236 − 0159 rotates with a period P ∼ 3.6 s, while five additional pulsars show P > 2 s. Also, the spin-down rates P˙ are, on average, low, with PSR J0815 + 4611 showing P˙∼4×10−18⁠. Some of the pulse profiles, generically single-peaked, present complex shapes evolving with frequency. Multifrequency flux measurements show that these pulsars have generically relatively steep spectra but exceptions are present, with values ranging between ∼−4 and −1. Among the pulsar sample, a large fraction shows large single-pulse variability, with four pulsars being undetectable more than 15 per cent of the time and one tentatively classified as a Rotating Radio Transient. Two single-peaked pulsars show drifting sub-pulses

Radio Astronomy from the Moon

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