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

Jake Turner, Philippe Zarka, Jean-Mathias Griessmeier, Joseph Lazio, Baptiste Cecconi, J. Emilio Enriquez, Julien Girard, Ray Jayawardhana, Laurent Lamy, Jonathan Nichols, et al.

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Jake Turner, Philippe Zarka, Jean-Mathias Griessmeier, Joseph Lazio, Baptiste Cecconi, et al. The search for radio emission from the exoplanetary systems 55 Cancri, Upsilon Andromedae, and Tau Bootis using LOFAR beam-formed observations. Europlanet Science Congress 2021, Sep 2021, Virtual Meeting, France. 14 pp., 10.5194/epsc2021-430. [hal-03536599](https://hal.science/hal-03536599)

HAL Id: hal-03536599

https://hal.science/hal-03536599

Submitted on 20 Jan 2022

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

Jake Turner<fnref n="1" />, Philippe Zarka<fnref n="2" />,<fnref n="3" />, Jean-Mathias Griessmeier<fnref n="2" />,<fnref n="4" />, Joseph Lazio<fnref n="5" />, Baptiste Cecconi<fnref n="2" />,<fnref n="3" />, J. Emilio Enriquez<fnref n="6" />,<fnref n="7" />, Julien Girard<fnref n="8" />,<fnref n="9" />, Ray Jayawardhana<fnref n="1" />, Laurent Lamy<fnref n="3" />, Jonathan Nichols<fnref n="10" />, and Imke de Pater<fnref n="11" />

Observing 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.

<footnote n="1">¹Cornell University, Department of Astronomy, Ithaca, United States of America (jt6an@virginia.edu)</footnote>

<footnote n="2">²Station de Radioastronomie de Nancay, Observatoire de Paris, PSL Research University, CNRS, Univ. Orleans, OSUC, 18330 Nancay, France</footnote>

<footnote n="3">³LESIA, Observatoire de Paris, CNRS, PSL, Meudon, France</footnote>

<footnote n="4">⁴Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E) Université d'Orléans/CNRS, Orleans, France</footnote>

<footnote n="5">⁵Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA</footnote>

<footnote n="6">⁶Department of Astronomy, University of California, Berkeley, 501 Campbell Hall 3411, Berkeley, CA, 94720, USA</footnote>

<footnote n="7">⁷Department of Astrophysics/IMAPP, Radboud University, P.O. Box 9010, NL-6500 GL Nijmegen, The Netherlands</footnote>

<footnote n="8">⁸Department of Physics and Electronics, Rhodes University, PO Box 94, Grahamstown 6140, South Africa</footnote>

<footnote n="9">⁹AIM, CEA, CNRS, Université Paris-Saclay, Université Paris Diderot, Sorbonne Paris Cite, F-91191 Gif-sur-Yvette, France</footnote>

<footnote n="10">¹⁰Department of Physics and Astronomy, University of Leicester, Leicester, UK</footnote>

<footnote n="11">¹¹Department of Astronomy, University of California at Berkeley, Berkeley, CA, USA</footnote>