Fine structures of radio bursts from flare star AD Leo with FAST observations

Radio bursts from nearby active M-dwarfs have been frequently reported and extensively studied in solar or planetary paradigms. Whereas, their sub-structures or fine structures remain rarely explored despite their potential significance in diagnosing the plasma and magnetic field properties of the star. Such studies in the past have been limited by the sensitivity of radio telescopes. Here we report the inspiring results from the high time-resolution observations of a known flare star AD Leo with the Five-hundred-meter Aperture Spherical radio Telescope (FAST). We detected many radio bursts in the two days of observations with fine structures in the form of numerous millisecond-scale sub-bursts. Sub-bursts on the first day display stripe-like shapes with nearly uniform frequency drift rates, which are possibly stellar analogs to Jovian S-bursts. Sub-bursts on the second day, however, reveal a different blob-like shape with random occurrence patterns and are akin to solar radio spikes. The new observational results suggest that the intense emission from AD Leo is driven by electron cyclotron maser instability which may be related to stellar flares or interactions with a planetary companion.Comment: 25 pages, 12 figures, accepted for publication in Ap

The Io, Europa and Ganymede auroral footprints at Jupiter in the ultraviolet: positions and equatorial lead angles

Jupiter's satellite auroral footprints are a consequence of the interaction between the Jovian magnetic field with co-rotating iogenic plasma and the Galilean moons. The disturbances created near the moons propagate as Alfv\'en waves along the magnetic field lines. The position of the moons is therefore "Alfv\'enically" connected to their respective auroral footprint. The angular separation from the instantaneous magnetic footprint can be estimated by the so-called lead angle. That lead angle varies periodically as a function of orbital longitude, since the time for the Alfv\'en waves to reach the Jovian ionosphere varies accordingly. Using spectral images of the Main Alfv\'en Wing auroral spots collected by Juno-UVS during the first forty-three orbits, this work provides the first empirical model of the Io, Europa and Ganymede equatorial lead angles for the northern and southern hemispheres. Alfv\'en travel times between the three innermost Galilean moons to Jupiter's northern and southern hemispheres are estimated from the lead angle measurements. We also demonstrate the accuracy of the mapping from the Juno magnetic field reference model (JRM33) at the completion of the prime mission for M-shells extending to at least 15RJ . Finally, we shows how the added knowledge of the lead angle can improve the interpretation of the moon-induced decametric emissions.Comment: 20 pages, 8 figures, Accepted for publication in Journal of Geophysical Research: Space Physics on 20 April 202

Search for muon neutrinos from gamma-ray bursts with the ANTARES neutrino telescope using 2008 to 2011 data

9 pages, 8 figures; added Fig. 1 with effective area, updated Fig. 8 (b) according to arXiv:1204.4219 ; Références publication Astron Astrophys 559 (2013) A9International audienceAims. We search for muon neutrinos in coincidence with GRBs with the ANTARES neutrino detector using data from the end of 2007 to 2011. Methods. Expected neutrino fluxes were calculated for each burst individually. The most recent numerical calculations of the spectra using the NeuCosmA code were employed, which include Monte Carlo simulations of the full underlying photohadronic interaction processes. The discovery probability for a selection of 296 GRBs in the given period was optimised using an extended maximum-likelihood strategy. Results. No significant excess over background is found in the data, and 90% confidence level upper limits are placed on the total expected flux according to the model

Comment on “Locating the source field lines of Jovian decametric radio emissions” by YuMing Wang et al.

International audienceIn this comment on the article "Locating the source field lines of Jovian decametric radio emissions" by Wang YM et al., 2020, we discuss the assumptions used by the authors to compute the beaming angle of Jupiter's decametric emissions induced by the moon Io. Their method, relying on multi-point radio observations, was applied to a single event observed on 14 th March 2014 by Wind and both STEREO A/B spacecraft from ~5 to ~16 MHz. They have erroneously identified the emission as a northern (Io-B type) instead of a southern one (Io-D type). We encourage the authors to update their results with the correct hemisphere of origin and to test their method on a larger sample of Jupiter-Io emissions

Jovian auroral radio source occultation modelling and application to the JUICE science mission planning

International audienceOccultations of the Jovian low frequency radio emissions by the Galilean moons have been observed by the PWS (Plasma Wave Science) instrument of the Galileo spacecraft. We show that the ExPRES (Exoplanetary and Planetary Radio Emission Simulator) code accurately models the temporal occurrence of the occultations in the whole spectral range observed by Galileo/PWS. This validates of the ExPRES code. In addition to supporting the analysis of the science observations, the method can be applied for preparing the JUICE moon flyby science operation planning

ExPRES: an Exoplanetary and Planetary Radio Emissions Simulator

International audienceContext. Earth and outer planets are known to produce intense non-thermal radio emissions through a mechanism known as cyclotron maser instability (CMI), requiring the presence of accelerated electrons generally arising from magnetospheric current systems. In return, radio emissions are a good probe of these current systems and acceleration processes. The CMI generates highly anisotropic emissions and leads to important visibility effects, which have to be taken into account when interpreting the data. Several studies have shown that modelling the radio source anisotropic beaming pattern can reveal a wealth of physical information about the planetary or exoplanetary magnetospheres that produce these emissions. Aims. We present a numerical tool, called ExPRES (Exoplanetary and Planetary Radio Emission Simulator), which is able to reproduce the occurrence in a time-frequency plane of R−X CMI-generated radio emissions from planetary magnetospheres, exoplanets, or star-planet interacting systems. Special attention is given to the computation of the radio emission beaming at and near its source. Methods. We explain what physical information about the system can be drawn from such radio observations, and how it is obtained. This information may include the location and dynamics of the radio sources, the type of current system leading to electron acceleration and their energy, and, for exoplanetary systems, the orbital period of the emitting body and the strength, rotation period, tilt, and the offset of the planetary magnetic field. Most of these parameters can only be remotely measured via radio observations. Results. The ExPRES code provides the proper framework of analysis and interpretation for past, current, and future observations of planetary radio emissions, as well as for future detection of radio emissions from exoplanetary systems (or magnetic, white dwarf-planet or white dwarf-brown dwarf systems). Our methodology can be easily adapted to simulate specific observations once effective detection is achieved

Probing Jovian broadband kilometric radio sources tied to the ultraviolet main auroral oval with Juno

International audienceObservations of Jovian broadband kilometric (bKOM) radiation and ultraviolet (UV) auroras were acquired with the Waves and Juno‐UVS instruments for ∼2 hours over the northern and southern polar regions during Juno's perijove 4, 5, and 6 passes (PJ4, PJ5, and PJ6). During all six time periods, Juno traversed auroral magnetic field lines connecting to the UV main auroral ovals, matching the estimates of bKOM radio source footprints. The localized bKOM radio sources for the PJ4 north pass map to magnetic field lines having distances of 10 to 12 Jovian radii (RJ) at the magnetic equator, whereas the extended bKOM radio sources for the other events map to field lines extending to 20–61 RJ. We found the peak bKOM intensities during Juno's potential radio source crossings show positive, negative, and no correlations with the UV main oval brightness and color ratio. Only the positive correlations suggest wave‐particle energy transport

Method to observe Jupiter's radio emissions at high resolution using multiple LOFAR stations: a first case study of the Io-decametric emission using the Irish IE613, French FR606, and German DE604 stations

International audienceThe Low Frequency Array (LOFAR) is an international radio telescope array, consisting of 38 stations in the Netherlands and 14 international stations spread over Europe. Here, we present an observation method to study the Jovian decametric radio emissions from several LOFAR stations (here Birr Castle in Ireland, Nançay in France, and Postdam in Germany), at high temporal and spectral resolution. This method is based on prediction tools, such as radio emission simulations and probability maps, and data processing. We report an observation of Io-induced decametric emission from 2021 June, and a first case study of the substructures that compose the macroscopic emissions (called millisecond bursts). The study of these bursts makes it possible to determine the electron populations at the origin of these emissions. We then present several possible future avenues for study based on these observations. The methodology and study perspectives described in this paper can be applied to new observations of Jovian radio emissions induced by Io, but also by Ganymede or Europa, or Jovian auroral radio emissions

High-frequency internal wave motions at the ANTARES site in the deep western mediterranean

[EN] High-frequency internal wave motions of periods down to 20 min have been observed in a yearlong record from the deep Western Mediterranean, mainly in vertical currents. The observations were made using the ANTARES neutrino telescope infrastructure. One line of the telescope is instrumented with environmental monitoring devices, and in particular with an Acoustic Doppler Current Profiler that was used to measure currents around 2,200 m. Such high-frequency internal waves are commonly observed much closer to the sea surface where the vertical density stratification is more stable than in the deep sea. In this paper, they are supported by the relatively large stratification following newly formed dense water. During the severe winters of 2005 and 2006, deep dense-water formation occurred in the Ligurian subbasin. Its collapse and spread over the sea floor across the basin remained detectable for at least 3 years as deduced from the present yearlong current record, which is from 2008. The observed high-frequency internal waves match the occasional density stratification observed in ¡«1-m-thin layers using previous shipborne conductivity¿C temperature¿C depth measurements. Such layers and waves are relatively unusual in the deep Mediterranean, where commonly several hundreds-ofmeters- thick near-homogeneous layers dominate. Such thick near-homogeneous layers provide about a half-decade narrow internal wave band around the inertial frequency (f). In contrast, the presently observed vertical currents occasionally show a ¡°small-scale¡± internal wave band that is on average 1.5 decades wide, associated with thin-layer stratification. In spite of its relatively largewidth, this band still shows variance peaking near f rather than near the large-scale buoyancy frequency N (= 2.3 4.5f) and this variance is found to increase with increasing N.The CTD observations were made in the framework of "Gyroscop" and "Gyroscop-2" for which we acknowledge Claude Millot and the Netherlands Organisation for the Advancement of Scientific Research, NWO, and Centre National de la Recherche Scientifique, CNRS, for support (French-Dutch collaboration). The authors acknowledge the financial support of the funding agencies: Centre National de la Recherche Scientifique (CNRS), Commissariat a l'energie atomique et aux energies alternatives (CEA), Commission Europeenne (FEDER fund and Marie Curie Program), Region Alsace (contrat CPER), Region Provence-Alpes-Cote d'Azur, Departement du Var and Ville de La Seyne-sur-Mer, France; Bundesministerium fur Bildung und Forschung (BMBF), Germany; Istituto Nazionale di Fisica Nucleare (INFN), Italy; Stichting voor Fundamenteel Onderzoek der Materie (FOM) and NWO, the Netherlands; Council of the President of the Russian Federation for young scientists and leading scientific schools supporting grants, Russia; National Authority for Scientific Research (ANCS - UEFISCDI), Romania; Ministerio de Ciencia e Innovacion (MICINN), Prometeo of Generalitat Valenciana and MultiDark, Spain; Agence de l'Oriental and CNRST, Morocco. We also acknowledge the technical support of Ifremer, AIM, and Foselev Marine for the sea operation and the CC-IN2P3 for the computing facilities.Van Haren, H.; Adrián Martínez, S.; Al Samarai, I.; Albert, A.; André, M.; Anghinolfi, M.; Anton, G.... (2014). High-frequency internal wave motions at the ANTARES site in the deep western mediterranean. Ocean Dynamics. 64(4):507-517. https://doi.org/10.1007/s10236-014-0702-0S507517644Ageron M, ANTARES collaboration et al (2011) ANTARES: the first neutrino telescope in the Mediterranean Sea. Nucl Inst Methods Phys Res A 656:11–38Aguilar JA, ANTARES collaboration et al (2007) The data acquisition for the ANTARES neutrino telescope. Nucl Inst Meth Phys Res A 570:107–116Albérola C, Millot C, Font J (1995) On the seasonal and mesoscale variabilities of the Northern Current during the PRIMO-0 experiment in the western Mediterranean Sea. Oceanol Acta 18:163–192Cairns JL, Williams GO (1976) Internal wave observations from a midwater float, 2. J Geophys Res 81:1943–1950Crépon M, Wald L, Monget JM (1982) Low-frequency waves in the Ligurian Sea during December 1977. J Geophys Res 87:595–600Crépon M, Boukhtir M, Barnier B, Aikman F III (1989) Horizontal ocean circulation forced by deep-water formation. Part I: an analytical study. J Phys Oceanogr 19:1781–1792Fofonoff NP (1969) Spectral characteristics of internal waves in the ocean. Deep-Sea Res 16:58–71Garrett CJR, Munk WH (1972) Space-time scales of internal waves. Geophys Fluid Dyn 3:225–264Gascard J-C (1973) Vertical motions in a region of deep water formation. Deep-Sea Res 20:1011–1027Gerkema T, Zimmerman JTF, Maas LRM, van Haren H (2008) Geophysical and astrophysical fluid dynamics beyond the traditional approximation. Rev Geophys 46:RG2004. doi: 10.1029/2006RG000220LeBlond PH, Mysak LA (1978) Waves in the ocean. Elsevier, AmsterdamMillot C (1999) Circulation in the Western Mediterranean Sea. J Mar Syst 20:423–442Munk WH (1980) Internal wave spectra at the buoyant and inertial frequencies. J Phys Oceanogr 10:1718–1728Pinkel R (1981) Observations of the near-surface internal wavefield. J Phys Oceanogr 11:1248–1257RDI (1992) A practical primer. RD-Instruments, San DiegoSchroeder K, Ribotti A, Borghini M, Sorgente R, Perilli A, Gasparini GP (2008) An extensive Western Mediterranean deep water renewal between 2004 and 2006. Geophys Res Lett 35:L18605. doi: 10.1029/2008GL035146Schroeder K, Gasparini GP, Borghini M, Ribotti A (2009) Experimental evidence of recent abrupt changes in the deep Western Mediterranean Sea. CIESM Workshop Monographs, n°38: Dynamics of Mediterranean deep waters, Malta, 27–30 May 2009:51–56Sheremet VA (2004) Laboratory experiments with tilted convective plumes on a centrifuge: a finite angle between the buoyancy and the axis of rotation. J Fluid Mech 506:217–244Straneo F, Kawase M, Riser SC (2002) Idealized models of slantwise convection in a baroclinic flow. J Phys Oceanogr 32:558–572Taupier-Letage I, Millot C (1986) General hydrodynamic features in the Ligurian Sea inferred from the DYOME experiment. Oceanol Acta 9:119–132Testor P, Gascard J-C (2006) Post-convection spreading phase in the Northwestern Mediterranean Sea. Deep-Sea Res I 53:869–893van Haren H (2008) A comparison between vertical motions measured by ADCP and inferred from temperature data. Ocean Sci 4:215–222van Haren H, Gostiaux L (2011) Large internal waves advection in very weakly stratified deep Mediterranean waters. Geophys Res Lett 38:L22603. doi: 10.1029/2011GL049707van Haren H, Millot C (2004) Rectilinear and circular inertial motions in the Western Mediterranean Sea. Deep-Sea Res I 51:1441–1455van Haren H, Millot C (2005) Gyroscopic waves in the Mediterranean Sea. Geophys Res Lett 32:L24614. doi: 10.1029/2005GL023915van Haren H, Millot C (2006) Determination of buoyancy frequency in weakly stable waters. J Geophys Res 111:C03014. doi: 10.1029/2005JC003065van Haren H, Millot C (2009) Slantwise convection: a candidate for homogenization of deep newly formed dense waters. Geophys Res Lett 36:L12604. doi: 10.1029/2009GL038736van Haren H, Millot C, Taupier-Letage I (2006) Fast deep sinking in Mediterranean eddies. Geophys Res Lett 33:L04606. doi: 10.1029/2005GL025367van Haren H, ANTARES-collaboration et al (2011) Acoustic and optical variations during rapid downward motion episodes in the deep north-western Mediterranean Sea. Deep-Sea Res I 58:875–88