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Spectroscopic multiplicity surveys of O stars in young clusters and OB associations have revealed that a large portion ($\sim$ 70%) of these massive stars (M$_{i}$ $\gt$ 15 $M_{\odot}$) belong to close and short-period binaries (physical separation d $\lt$few au). Despite the recent and significant progress, the formation mechanisms leading to such close massive multiple systems remain to be elucidated. As a result, young massive close binaries (or higher-order multiple systems) are unique laboratories to figure out the pairing mechanism of high-mass stars. We present the first VLTI/GRAVITY observations of six young O stars in the M17 star-forming region ($\lesssim$ 1 Myr) and two additional foreground stars. From the interferometric model fitting of visibility amplitudes and closure phases, we search for companions and measure their positions and flux ratios. Combining the resulting magnitude difference with atmosphere models and evolutionary tracks, we further constrain the masses of the individual components. All of the six high-mass stars are in multiple systems, leading to a multiplicity fraction (MF) of 100%, yielding a 68% confidence interval of 94-100%. We detect a total number of 9 companions with separations up to 120 au. Including previously identified spectroscopic companions, the companion fraction of the young O stars in our sample reaches 2.3$\pm$0.6. The derived masses span a wide range from 2.5 to 50 $M_{\odot}$, with a great tendency towards high-mass companions. While based on a modest sample, our results clearly indicate that the origin of the high degree of multiplicity is rooted in their star formation mechanism. No clear evidence for one of the competing concepts of massive star formation (core accretion or competitive accretion) could be found. However, our results are compatible with migration as a scenario for the formation of close massive binaries., Comment: 20 pages, 14 figures, 4 tables, 3 appendices

Multiplicity is a ubiquitous characteristic of massive stars. Multiple systems offer us a unique observational constraint on the formation of high-mass systems. Herschel 36 A is a massive triple system composed of a close binary (Ab1-Ab2) and an outer component (Aa). We measured the orbital motion of the outer component of Herschel 36 A using infrared interferometry with the AMBER and PIONIER instruments of ESO’s Very Large Telescope Interferometer. Our immediate aims are to constrain the masses of all components of this system and to determine if the outer orbit is co-planar with the inner one. Reported spectroscopic data for all two components of this system and our interferometric data allow us to derive full orbital solutions for the outer orbit Aa-Ab and the inner orbit Ab1-Ab2. For the first time, we derive the absolute masses of mAa = 22.3 ± 1.7, mAb1 = 20.5 ± 1.5, and mAb2 = 12.5 ± 0.9 M⊙. Despite not being able to resolve the close binary components, we infer the inclination of their orbit by imposing the same parallax as the outer orbit. Inclinations derived from the inner and outer orbits imply a modest difference of about 22° between the orbital planes. We discuss this result and the formation of Herschel 36 A in the context of Core Accretion and Competitive Accretion models, which make different predictions regarding the statistic of the relative orbital inclinations. © 2022 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society., RS and AA acknowledge financial support from the State Agency for Research of the Spanish MCIU through the ‘Center of Excellence Severo Ochoa’ award for the Instituto de Astrofísica de Andalucía (SEV-2017-0709). RS acknowledges financial support from national project PGC2018-095049-B-C21 (MCIU/AEI/FEDER, UE). AA acknowledges financial support from national project PID2020-117404GB-C21 (MCIU/AEI/FEDER, UE). JSB acknowledges the financial support from the ‘Visitor Scientist Program’ of the ‘Center of Excellence Severo Ochoa’ provided by the IAA-CSIC; and to the ‘ESO-Garching Visitor Program’ of the European Southern Observatory. This work presents results from the European Space Agency (ESA) space mission Gaia. Gaia data are being processed by the Gaia Data Processing and Analysis Consortium (DPAC). Funding for the DPAC is provided by national institutions, in particular the institutions participating in the Gaia MultiLateral Agreement (MLA).

Context. The fate of a massive star during the latest stages of its evolution is highly dependent on its mass-loss rate/geometry and therefore knowing the geometry of the circumstellar material close to the star and its surroundings is crucial. Aims. We aim to study the nature (i.e. geometry, rates) of mass-loss episodes. In this context, yellow hypergiants are great targets. Methods. We analyse a large set of optical/near-infrared data, in spectroscopic and photometric (X-shooter/VLT), spectropolarimetric (ISIS/WHT), and interferometric GRAVITY-AMBER/VLTI) modes, toward the yellow hypergiant IRAS 17163-3907. We present the first model-independent reconstructed images of IRAS 17163-3907 at these wavelengths at milli-arcsecond scales. Lastly, we apply a 2D radiative transfer model to fit the dereddened photometry and the radial profiles of published VISIR images at 8.59 {\mu}m, 11.85 {\mu}m and 12.81 {\mu}m simultaneously, adopting the revised Gaia distance (DR2). Results. The interferometric observables around 2 {\mu}m show that the Br{\gamma} emission is more extended and asymmetric than the Na i and the continuum emission. In addition to the two known shells surrounding IRAS 17163-3907 we report on the existence of a third hot inner shell with a maximum dynamical age of only 30 yr. Conclusions. The interpretation of the presence of Na i emission at closer distances to the star compared to Br{\gamma} has been a challenge in various studies. We argue that the presence of a pseudophotosphere is not needed, but it is rather an optical depth effect. The three observed distinct mass-loss episodes are characterised by different mass-loss rates and can inform the theories on mass-loss mechanisms, which is a topic still under debate. We discuss these in the context of photospheric pulsations and wind bi-stability mechanisms., Comment: 26 pages, 22 Figures, 6 tables, accepted for publication in A&A. Original abstract will be available after publication

Two scenarios have been proposed to match the existing observational constraints of the object HR 6819. The system could consist of a close inner B-type giant plus a black hole (BH) binary with an additional Be companion in a wide orbit. Alternatively, it could be a binary composed of a stripped B star and a Be star in a close orbit. Either scenario makes HR 6819 a cornerstone object as the stellar BH closest to Earth, or as an example of an important transitional, non-equilibrium phase for Be stars with solid evidence for its nature. We aimed to distinguish between the two scenarios for HR 6819. Both models predict two luminous stars but with very different angular separations and orbital motions. Therefore, the presence of bright sources in the 1-100 milliarcsec (mas) regime is a key diagnostic for determining the nature of the HR 6819 system. We obtained new high-angular resolution data with VLT/MUSE and VLTI/GRAVITY of HR 6819. The MUSE data are sensitive to bright companions at large scales, whilst the interferometric GRAVITY data are sensitive down to separations on mas scales and large magnitude differences. The MUSE observations reveal no bright companion at large separations and the GRAVITY observations indicate the presence of a stellar companion at an angular separation of ~1.2 mas that moves on the plane of the sky over a timescale compatible with the known spectroscopic 40-day period. We conclude that HR 6819 is a binary system and that no BH is present in the system. The unique nature of HR 6819, and its proximity to Earth make it an ideal system for quantitatively characterising the immediate outcome of binary interaction and probing how Be stars form., 16 pages, 11 figures, subject of ESO press release eso2204

Relatively little information is available about the Universe at ultra-low radio frequencies (ULF; i.e., below 50 MHz), although the ULF spectral window contains a wealth of unique diagnostics for studying galactic and extragalactic phenomena. Subarcsecond resolution imaging at these frequencies is extremely difficult, due to the long baselines (>1000 km) required and large ionospheric perturbations. We have conducted a pilot project to investigate the ULF performance and potential of the International LOFAR Telescope (ILT), a trans-European interferometric array with baselines up to ~2000 km and observing frequencies down to 10 MHz. We have successfully produced images with subarcsecond resolution for six radio sources at frequencies down to 30 MHz. This resolution is more than an order of magnitude better than pre-ILT observations at similar frequencies. The six targets that we imaged (3C 196, 3C 225, 3C 273, 3C 295, 3C 298, and 3C 380) are bright radio sources with compact structures. By comparing our data of 3C 196 and 3C 273 with observations at higher frequencies, we investigate their spatially resolved radio spectral properties. Our success shows that at frequencies down to 30 MHz, subarcsecond imaging with the ILT is possible. Further analysis is needed to determine the feasibility of observations of fainter sources or sources with less compact emission. © ESO 2022., We kindly thank the anonymous referee for the valuable and instructive comments. C.G. and R.J.v.W. acknowledge support from the ERC Starting Grant ClusterWeb 804 208. L.K.M. is grateful for support from the UKRI Future Leaders Fellowship (grant MR/T042842/1). A.B. acknowledges support from the VIDI research programme with project number 639.042.729, which is financed by the Netherlands Organisation for Scientific Research (NWO). J.M. acknowledges financial support from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709) and from the grant RTI2018-096228-B-C31 (MICIU/FEDER, EU) LOFAR is the LOw Frequency ARray designed and constructed by ASTRON. It has observing, data processing, and data storage facilities in several countries, which are owned by various parties (each with their own funding sources), and are collectively operated by the ILT foundation under a joint scientific policy. The ILT resources have benefitted from the following recent major funding sources: CNRS-INSU, Observatoire de Paris and Université d’Orléans, France; BMBF, MIWF-NRW, MPG, Germany; Science Foundation Ireland (SFI), Department of Business, Enterprise and Innovation (DBEI), Ireland; NWO, The Netherlands; The Science and Technology Facilities Council, UK; Ministry of Science and Higher Education, Poland; Istituto Nazionale di Astrofisica (INAF), Italy. This research made use of Astropy, http://www.astropy.org a community-developed core Python package for Astronomy (Astropy Collaboration 2013, 2018).

No statistical study of COMs toward a large sample of high-mass protostars with ALMA has been carried out so far. We aim to study six N-bearing species: CH$_3$CN, HNCO, NH$_2$CHO, C$_2$H$_5$CN, C$_2$H$_3$CN and CH$_3$NH$_2$ in a large sample of high-mass protostars. From the ALMAGAL survey, 37 of the most line-rich hot molecular cores are selected. Next, we fit their spectra and find column densities and excitation temperatures of the above N-bearing species, in addition to CH$_3$OH. We (tentatively) detect CH$_3$NH$_2$ in $\sim32%$ of the sources. We find three groups of species when comparing their excitation temperatures: hot (NH$_2$CHO; Tex > 250 K), warm (C$_2$H$_3$CN, HN$^{13}$CO and CH$_{3}^{13}$CN; 100 K < Tex < 250 K) and cold species (CH$_3$OH and CH$_3$NH$_2$; Tex < 100 K). This temperature segregation reflects the trend seen in their sublimation temperatures and validates the idea of onion-like structure of COMs around protostars. Moreover, the molecules studied here show constant column density ratios across low- and high-mass protostars with scatter less than a factor $\sim3$ around the mean. The constant column density ratios point to a common formation environment of COMs or their precursors, most likely in the pre-stellar ices. The scatter around the mean of the ratios, although small, varies depending on the species considered. This spread can either have a physical origin (source structure, line or dust optical depth) or a chemical one. Formamide is most prone to the physical effects as it is tracing the closest regions to the protostars, whereas such effects are small for other species. Assuming that all molecules form in the pre-stellar ices, the scatter variations could be explained by differences in lifetimes or physical conditions of the pre-stellar clouds. If the pre-stellar lifetimes are the main factor, they should be similar for low- and high-mass protostars., 49 pages, 46 figures, Accepted for publication in A&A

Full list of authors: Jackson, N.; Badole, S.; Morgan, J.; Chhetri, R.; Prūsis, K.; Nikolajevs, A.; Morabito, L.; Brentjens, M.; Sweijen, F.; Iacobelli, M.; Orrù, E.; Sluman, J.; Blaauw, R.; Mulder, H.; van Dijk, P.; Mooney, S.; Deller, A.; Moldon, J.; Callingham, J. R.; Harwood, J.; Hardcastle, M.; Heald, G.; Drabent, A.; McKean, J. P.; Asgekar, A.; Avruch, I. M.; Bentum, M. J.; Bonafede, A.; Brouw, W. N.; Brüggen, M.; Butcher, H. R.; Ciardi, B.; Coolen, A.; Corstanje, A.; Damstra, S.; Duscha, S.; Eislöffel, J.; Falcke, H.; Garrett, M.; de Gasperin, F.; Griessmeier, J. -M.; Gunst, A. W.; van Haarlem, M. P.; Hoeft, M.; van der Horst, A. J.; Jütte, E.; Koopmans, L. V. E.; Krankowski, A.; Maat, P.; Mann, G.; Miley, G. K.; Nelles, A.; Norden, M.; Paas, M.; Pandey, V. N.; Pandey-Pommier, M.; Pizzo, R. F.; Reich, W.; Rothkaehl, H.; Rowlinson, A.; Ruiter, M.; Shulevski, A.; Schwarz, D. J.; Smirnov, O.; Tagger, M.; Vocks, C.; van Weeren, R. J.; Wijers, R.; Wucknitz, O.; Zarka, P.; Zensus, J. A.; Zucca, P., The Low-Frequency Array (LOFAR) Long-Baseline Calibrator Survey (LBCS) was conducted between 2014 and 2019 in order to obtain a set of suitable calibrators for the LOFAR array. In this paper, we present the complete survey, building on the preliminary analysis published in 2016 which covered approximately half the survey area. The final catalogue consists of 30 006 observations of 24 713 sources in the northern sky, selected for a combination of high low-frequency radio flux density and flat spectral index using existing surveys (WENSS, NVSS, VLSS, and MSSS). Approximately one calibrator per square degree, suitable for calibration of ≥200 km baselines is identified by the detection of compact flux density, for declinations north of 30° and away from the Galactic plane, with a considerably lower density south of this point due to relative difficulty in selecting flat-spectrum candidate sources in this area of the sky. The catalogue contains indicators of degree of correlated flux on baselines between the Dutch core and each of the international stations, involving a maximum baseline length of nearly 2000 km, for all of the observations. Use of the VLBA calibrator list, together with statistical arguments by comparison with flux densities from lower-resolution catalogues, allow us to establish a rough flux density scale for the LBCS observations, so that LBCS statistics can be used to estimate compact flux densities on scales between 300 mas and 2′′, for sources observed in the survey. The survey is used to estimate the phase coherence time of the ionosphere for the LOFAR international baselines, with median phase coherence times of about 2 min varying by a few tens of percent between theshortest and longest baselines. The LBCS can be used to assess the structures of point sources in lower-resolution surveys, with significant reductions in the degree of coherence in these sources on scales between 2′′ and 300 mas. The LBCS survey sources show a greater incidence of compact flux density in quasars than in radio galaxies, consistent with unified schemes of radio sources. Comparison with samples of sources from interplanetary scintillation (IPS) studies with the Murchison Widefield Array shows consistent patterns of detection of compact structure in sources observed both interferometrically with LOFAR and using IPS. © ESO 2022., Support for the operation of the MWA is provided by the Australian Government (NCRIS), under a contract to Curtin University administered by Astronomy Australia Limited. We acknowledge the Pawsey Supercomputing Centre which is supported by the Western Australian and Australian Governments. A.D. acknowledges support by the BMBF Verbundforschung under the grant 052020. L.K.M. is grateful for support from the UKRI Future Leaders Fellowship (grant MR/T042842/1). J. Moldón acknowledges financial support from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709) and from the grant RTI2018-096228-B-C31 (MICIU/FEDER, EU). J.P.M. acknowledges support from the Netherlands Organization for Scientific Research (NWO, project number 629.001.023) and the Chinese Academy of Sciences (CAS, project number 114A11KYSB20170054).

C. Vastel et al., [Aims] Methanol is a ubiquitous species commonly found in the molecular interstellar medium. It is also a crucial seed species for the build-up of chemical complexity in star forming regions. Thus, understanding how its abundance evolves during the star formation process and whether it enriches the emerging planetary system is of paramount importance., [Methods] We used new data from the ALMA Large Program FAUST (Fifty AU STudy of the chemistry in the disc/envelope system of solar protostars) to study the methanol line emission towards the [BHB2007] 11 protobinary system (sources A and B), where a complex structure of filaments connecting the two sources with a larger circumbinary disc has previously been detected., [Results] Twelve methanol lines have been detected with upper energies in the [45–537] K range along with one 13CH3OH transition and one methyl formate (CH3OCHO) line blended with one of the methanol transitions. The methanol emission is compact (FWHM ~ 0.5″) and encompasses both protostars, which are separated by only 0.2″ (28 au). In addition, the overall methanol line emission presents three velocity components, which are not spatially resolved by our observations. Nonetheless, a detailed analysis of the spatial origin of these three components suggests that they are associated with three different spatial regions, with two of them close to 11B and the third one associated with 11A. A radiative transfer analysis of the methanol lines gives a kinetic temperature of [100–140] K, an H2 volume density of 106–107 cm−3 and column density of a few 1018 cm−2 in all three components with a source size of ~0.15″. Thus, this hot and dense gas is highly enriched in methanol with an abundance as high as 10−5. Using previous continuum data, we show that dust opacity can potentially completely absorb the methanol line emission from the two binary objects., [Conclusions] Although we cannot firmly exclude other possibilities, we suggest that the detected hot methanol is resulting from the shocked gas from the incoming filaments streaming towards [BHB2007] 11A and B, respectively. Higher spatial resolution observations are necessary to confirm this hypothesis., This project has received funding within the European Union’s Horizon 2020 research and innovation program from the European Research Council (ERC) for the project The Dawn of Organic Chemistry (DOC), grant agreement no. 741002, and from the Marie Sklodowska-Curie for the project Astro-Chemical Origins (ACO), grant agreement no. 811312. I.J.-S. has received partial support from the Spanish State Research Agency (project number PID2019-105552RB-C41). D.J. is supported by NRC Canada and by an NSERC Discovery Grant. S.Y. thanks the support by Grant-in-Aids from Ministry of Education, Culture, Sports, Science, and Technologies of Japan (18H05222). This paper makes use of the following ALMA data: ADS/JAO.ALMA#2018.1.01205.L. ALMA is a partnership of ESO (representing its member states), NSF (USA) and NINS (Japan), together with NRC (Canada), MOST and ASIAA (Taiwan), and KASI (Republic of Korea), in cooperation with the Republic of Chile. The Joint ALMA Observatory is operated by ESO, AUI/NRAO and NAOJ. The National Radio Astronomy Observatory is a facility of the National Science Foundation operated under cooperative agreement by Associated Universities, Inc.

Context. The substellar triple system VHS J125601.92−125723.9 (hereafter VHS 1256−1257) is composed of an equal-mass M7.5 brown dwarf binary and an L7 low-mass substellar object. In Guirado et al. (2018, A&A, 610, A23) we published the detection of radio emission at 8.4 GHz coming from the central binary and making it an excellent target for further observations. Aims. We aim to identify the origin of the radio emission occurring in the central binary of VHS 1256−1257 while discussing the expected mechanisms involved in the radio emission of ultra-cool dwarfs. Methods. We observed this system with the Karl G. Jansky Very Large Array, the European very-long-baseline interferometry (VLBI) Network, the enhanced Multi-Element Remotely Linked Interferometer Network, the NOrthern Extended Millimeter Array, and the Atacama Large Millimetre Array at frequencies ranging from 5 GHz up to 345 GHz in several epochs during 2017, 2018, and 2019. Results. We found radio emission at 6 GHz and 33 GHz coincident with the expected position of the central binary of VHS 1256−1257. The Stokes I density fluxes detected were 73 ± 4 μJy and 83 ± 13 μJy, respectively, with no detectable circular polarisation or pulses. No emission is detected at higher frequencies (230 GHz and 345 GHz), nor at 5 GHz with VLBI arrays. The emission appears to be stable over almost three years at 6 GHz. To explain the constraints obtained both from the detections and non-detections, we considered multiple scenarios including thermal and nonthermal emission, and different contributions from each component of the binary. Conclusions. Our results can be well explained by nonthermal gyrosynchrotron emission originating at radiation belts with a low plasma density (ne = 300−700 cm−3), a moderate magnetic field strength (B ≈ 140 G), and an energy distribution of electrons following a power-law (dN/dE ∝ E−δ) with δ fixed at 1.36. These radiation belts would need to be present in both components and also be viewed equatorially. © ESO 2022., We sincerely thank the anonymous referee for his/her very useful and constructive criticisms and suggestions. This paper is based on observations carried out with the IRAM NOEMA interferometer and the IRAM 30-m telescope. IRAM is supported by INSU/CNRS (France), MPG (Germany), and IGN (Spain). JBC and JCG were partially supported by the Spanish MINECO projects AYA2015-63939-C2-2-P, PGC2018-098915-B-C22 and by the Generalitat Valenciana project GVPROMETEO2020−080. MPT acknowledges financial support from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709) and through grants PGC2018-098915-B-C21 and PID2020-117404GB-C21 (MCI/AEI/FEDER, UE). RA was supported by the Generalitat Valenciana postdoctoral grant APOSTD/2018/177. BG acknowledges support from the UK Science and Technology Facilities Council (STFC) via the Consolidated Grant ST/R000905/1. MRZO and VJSB acknowledge the financial support from PID2019-109522GB-C51 and PID2019-109522GB-C53, respectively.

3C84 (NGC1275) is one of the brightest radio sources in the mm radio-bands, which led to a plethora of VLBI observations at numerous frequencies over the years. They reveal a two-sided jet structure, with an expanding but not well-collimated parsec-scale jet, pointing southward. High resolution mm-VLBI observations allow the study and imaging of the jet base on the sub-parsec scale. This could facilitate the investigation of the nature of the jet origin, also in view of the previously detected two-railed jet structure and east-west oriented core region seen with RadioAstron at 22 GHz. We produce VLBI images of this core and inner jet region, observed during the past twenty years at 15, 43, and 86 GHz. We determine the kinematics of the inner jet and ejected features at 43 and 86 GHz and compare their ejection times with radio and $\gamma$-ray variability. For the moving jet features, we find an average velocity of $\beta^\textrm{avg}_\textrm{app} = 0.055-0.22$c ($\mu^\textrm{avg} = 0.04-0.18\,$mas/yr). From the time-averaged VLBI images at the three frequencies, we measure the transverse jet width along the bulk flow. On the $\leq 1.5$ parsec scale, we find a clear trend of the jet width being frequency dependent, with the jet being narrower at higher frequencies. This stratification is discussed in the context of a spine-sheath scenario, and is compared to other possible interpretations. From quasi-simultaneous observations at 43 and 86\,GHz we obtain spectral index maps, revealing a time-variable orientation of the spectral index gradient, due to structural variability of the inner jet., Comment: 23 pages, 12 figures, accepted for publication in A&A

We have re-analysed part of the middle and upper atmosphere (MU) radar meteor head echo data set collected during 2009–2010 and confirmed the existence of a rare high-altitude radar meteor population reaching up to ∼150 km altitude. The number of detections decreases significantly as a function of initial altitude. Out of the total amount of 106 000 events, 74 had an initial altitude >130 km while four of those had an initial altitude >145 km. High-altitude radar meteor observations have been reported before, e.g. using the EISCAT VHF radar and the Jicamarca Radio Observatory. The main novelty of this study is that the observations were performed using methods that render the final data set unambiguous in direction of arrival together with rigorously tested analysis routines that were validated by noisy raw data simulations. Due to our experimental set-up the maximum detectable range was limited to 148 km. Hence, we cannot confirm or deny the existence of radar meteors above that altitude.

Total intensity variability light curves offer a unique insight into the ongoing debate about the launching mechanism of jets. For this work, we utilise the availability of radio and $\gamma$-ray light curves over a few decades of the radio source 3C 84 (NGC 1275). We calculate the multiband time lags between the flares identified in the light curves via discrete cross-correlation and Gaussian process regression. We find that the jet particle and magnetic field energy densities are in equipartition ($k_\textrm{r} = 1.08\pm0.18$). The jet apex is located $z_\textrm{91.5 GHz}= 22 - 645$ $R_\textrm{s}$ ($2 - 20 \times 10^{-3}$ pc) upstream of the 3 mm radio core; at that position, the magnetic field amplitude is $B_\textrm{core}^\textrm{91.5 GHz}= 3 - 10$ G. Our results are in good agreement with earlier studies, which utilised very-long-baseline interferometry. Furthermore, we investigate the temporal relation between the ejection of radio and $\gamma$-ray flares. Our results are in favour of the $\gamma$-ray emission being associated with the radio emission. We are able to tentatively connect the ejection of features identified at 43 and 86 GHz to prominent $\gamma$-ray flares. Finally, we compute the multiplicity parameter $\lambda$ and the Michel magnetisation $\sigma_\textrm{M}$ and find that they are consistent with a jet launched by the Blandford & Znajek 1977 mechanism., Comment: 13 pages, 6 figures, accepted for publication in A&A