M. Pérez-Torres’s research while affiliated with University of Zaragoza and other places

Context. V1298 Tau is a very young and magnetically active K1V star that hosts a benchmark multi-planetary system to study planet formation and evolutionary history at the earliest stages. Thanks to the high interest, it has been the target of a multi-wavelength follow-up. Aims. We selected V1298 Tau for a first targeted follow-up at radio frequencies with the Karl G. Jansky Very Large Telescope (JVLA), the upgraded Giant Metrewave Radio Telescope (uGMRT), and the Sardinia Radio Telescope (SRT) to search for emission in the overall frequency range 0.55–7.2 GHz. Detecting radio emission from such a very active star is key to characterising its magnetosphere, allowing us in principle to probe the strength of the coronal magnetic field and plasma density. Methods. Observations were carried out between October 2023 and September 2024: three epochs (total of ∼180 min on-source) with uGMRT band-4 (0.55–0.75 GHz), 12 epochs (total of ∼427 min on-source) with the JVLA using L (1–2 GHz) and C (4.5–6.5 GHz) bands, and three epochs (total of ∼56 min on-source) with SRT using C -high band (6–7.2 GHz). Results. We report the first detection of radio emission from V1298 Tau at different epochs using the JVLA. The emission has maximum peak flux densities of 91±10 and 177±6 µJy/beam in the L - and C -band, respectively. From a comparison with contemporary optical photometry, we found that the detected emission with the highest fluxes are located around a phase of minimum of the photospheric light curve. Although the uGMRT and SRT observations could not detect the source, we measured 3σ flux density upper limits in the range ∼41–56 µJy/beam using uGMRT, while with SRT we reached upper limits down to 13 mJy. The lack of a significant fraction of circular polarisation indicates that the observed flux is not due to electron cyclotron maser emission from star-planet interaction, and it is likely produced by gyrosynchroton and/or cyclotron emission from the corona triggered by stellar magnetic activity, although we cannot exclude thermal emission, due to a lack of constraints on the brightness temperature.

V1298 Tau is a very young and magnetically active star which hosts a benchmark multi-planetary system to study planet formation and evolutionary history at the earliest stages. We selected V1298 Tau for a first targeted follow-up at radio frequencies with the Karl G. Jansky Very Large Telescope (JVLA), the upgraded Giant Metrewave Radio Telescope (uGMRT), and the Sardinia Radio Telescope (SRT), to search for emission in the overall frequency range 0.55-7.2 GHz. Detecting radio emission from such a very active star is key to characterise its magnetosphere, allowing in principle to probe the strength of the coronal magnetic field and plasma density. Observations were carried out between Oct 2023 and Sept 2024: three epochs with uGMRT band-4 (0.55-0.75 GHz), 12 epochs with the JVLA using L (1-2 GHz) and C (4.5-6.5 GHz) bands, and three epochs with SRT using C-high band (6-7.2 GHz). We report the first detection of radio emission from V1298 Tau at different epochs using the JVLA. The emission has maximum peak flux densities of 91$\pm$10 and 177$\pm$6 $\mu$Jy/beam in the L- and C-band, respectively. From a comparison with contemporary optical photometry, we found that the detected emission with the highest fluxes are located around a phase of minimum of the photospheric light curve. Although the uGMRT and SRT observations could not detect the source, we measured 3$\sigma$ flux density upper limits in the range ~41-56 $\mu$Jy/beam using uGMRT, while with SRT we reached upper limits down to 13 mJy. The lack of a significant fraction of circular polarisation indicates that the observed flux is not due to electron cyclotron maser emission from star-planet interaction, and it is likely produced by gyrosynchroton/cyclotron emission from the corona triggered by stellar magnetic activity, although we cannot exclude thermal emission due to a lack of constraints on the brightness temperature.

Context: The long-standing question concerning jetted subgalactic-size (JSS) radio sources is whether they will evolve into large radio galaxies, die before escaping the host galaxy, or remain indefinitely confined to their compact size. Aims: Our main goal is to propose a scenario that explains the relative number of JSS radio sources and their general properties. Methods: We studied the parsec-scale radio morphology of a complete sample of 21 objects using Very Long Baseline Array (VLBA) observations at various frequencies and analyzed the morphological characteristics of their optical hosts. Results: Many of these radio sources exhibit radio morphologies consistent with transverse motions of their bright edges and are found in dynamically disturbed galaxies. VLBA images suggest the possible presence of large-angle, short-period precessing jets, and an orbital motion of the radio-loud active galactic nucleus (AGN) in a dual or binary system. The majority of JSS radio sources appear to be in systems in different stages of their merging evolution. Conclusions: We propose a scenario where rapid jet redirection, through precession or orbital motion, prevents the jet from penetrating the interstellar medium (ISM) sufficiently to escape the host galaxy. Most JSS radio sources remain compact due to their occurrence in merging galaxies.

Aims. We search for radio emission from star–planet interactions in the M dwarf system GJ 486, which hosts an Earth-like planet. Methods. We observed the GJ 486 system with the upgraded Giant Metrewave Radio Telescope (uGMRT) from 550 to 750 MHz in nine different epochs between October 2021 and February 2022, covering almost all orbital phases of GJ 486b from different orbital cycles. We obtained radio images and dynamic spectra of the total and circularly polarized intensity for each individual epoch. Results. We did not detect any quiescent radio emission in any epoch above 3 σ . Similarly, we did not detect any bursty emission in our dynamic spectra. Conclusions. While we cannot completely rule out that the absence of a radio detection is due to time variability of the radio emission or to the maximum electron-cyclotron maser emission being below our observing range, these cases seem unlikely. We discuss two possible scenarios: an intrinsic dim radio signal and, alternatively, a situation where the anisotropic beamed emission is pointed away from the observer. If the non-detection of radio emission from the star-planet interaction in GJ 486 is due to an intrinsically dim signal, this implies that independent of whether the planet is magnetized or not, the mass-loss rate is small ( Ṁ ⋆ ≲ 0.3 Ṁ ⊙ ) and that, concomitantly, the efficiency of the conversion of the Poynting flux into radio emission must be low ( β ≲ 10 ⁻³ ). Free-free absorption effects are negligible, given the high value of the coronal temperature. Finally, if the anisotropic beaming pointed away from the observer, this would imply that GJ 486 has very low values of magnetic obliquity and inclination.

We search for radio emission from star-planet interactions in the M-dwarf system GJ~486, which hosts an Earth-like planet. We observed the GJ~486 system with the upgraded Giant Metrewave Radio Telescope (uGMRT) from 550 to 750 MHz in nine different epochs, between October 2021 and February 2022, covering almost all orbital phases of GJ~486 b from different orbital cycles. We obtained radio images and dynamic spectra of the total and circularly polarized intensity for each individual epoch We do not detect any quiescent radio emission in any epoch above 3$\sigma$. Similarly, we do not detect any bursty emission in our dynamic spectra. While we cannot completely rule out that the absence of a radio detection is due to time variability of the radio emission, or to the maximum electron-cyclotron maser emission being below our observing range, this seems unlikely. We discuss two possible scenarios: an intrinsic dim radio signal, or alternatively, that the anisotropic beamed emission pointed away from the observer. If the non-detection of radio emission from star-planet interaction in GJ~486 is due to an intrinsically dim signal, this implies that, independently of whether the planet is magnetized or not, the mass-loss rate is small (\dot{M}_\star $\lesssim$ 0.3 \dot{M}_\sun) and that, concomitantly, the efficiency of the conversion of Poynting flux into radio emission must be low ($\beta \lesssim 10^{-3}$). Free-free absorption effects are negligible, given the high value of the coronal temperature. Finally, if the anisotropic beaming pointed away from us, this would imply that GJ~486 has very low values of its magnetic obliquity and inclination.

Context. The Arches cluster, one of the most massive clusters in the Milky Way, is located about 30 pc in projection from the central massive black hole Sagittarius A* at a distance of ≈8 kpc from Earth. With its high mass, young age, and location in the Galaxy’s most extreme star forming environment, the Arches is an extraordinary laboratory for studying massive stars and clusters. Aims. Our objective is to improve our knowledge of the properties of massive stars and the Arches cluster through high-angular-resolution radio continuum studies. Methods. We observed the Arches cluster with the Karl G. Jansky Very Large Array in the C - and X -bands (central frequencies of 6 and 10 GHz respectively) in two epochs at C -band and five epochs at X -band throughout 2016, 2018, and 2022, covering time spans ranging from 22 days to 6 years. We used the A-configuration to achieve the highest possible angular resolution and cross-matched the detected point-sources with stars detected in the infrared, using proper motion catalogues to ensure cluster membership. Results. We report the most extensive radio point-source catalogue of the cluster to date, with a total of 25 radio detections (7 more than the most recent study). We also created the deepest (2.5 μ Jy in X -band) images of the cluster so far in the 4 to 12 GHz frequency range. Most of our stellar radio sources (12 out of 18) show a positive spectral index, indicating that the dominant emission process is free-free thermal radiation, which probably originates from stellar winds. We find that radio variability is more frequent than what was inferred from previous observations, and affects up to 60% of the sources associated with bright stellar counterparts, with two of them, F18 and F26, showing extreme flux variability. We propose four of our detections (F6, F18, F19, and F26) as primary candidates for colliding-wind binaries (CWBs) based on their consistent flat-to-negative spectral index. We classify F7, F9, F12, F14, and F55 as CWB binary candidates based on their high flux and/or spectral index variability, and X-ray counterparts. Thus, we infer a 14/23 ≈ 61% multiplicity fraction for the radio stars of the Arches cluster when combining our findings with recent infrared radial velocity studies.

Approximately one hundred sources of very-high-energy (VHE) gamma rays are known in the Milky Way, detected with a combination of targeted observations and surveys. A survey of the entire Galactic Plane in the energy range from a few tens of GeV to a few hundred TeV has been proposed as a Key Science Project for the upcoming Cherenkov Telescope Array Observatory (CTAO). This article presents the status of the studies towards the Galactic Plane Survey (GPS). We build and make publicly available a sky model that combines data from recent observations of known gamma-ray emitters with state-of-the-art physically-driven models of synthetic populations of the three main classes of established Galactic VHE sources (pulsar wind nebulae, young and interacting supernova remnants, and compact binary systems), as well as of interstellar emission from cosmic-ray interactions in the Milky Way. We also perform an optimisation of the observation strategy (pointing pattern and scheduling) based on recent estimations of the instrument performance. We use the improved sky model and observation strategy to simulate GPS data corresponding to a total observation time of 1620 hours spread over ten years. Data are then analysed using the methods and software tools under development for real data. Under our model assumptions and for the realisation considered, we show that the GPS has the potential to increase the number of known Galactic VHE emitters by almost a factor of five. This corresponds to the detection of more than two hundred pulsar wind nebulae and a few tens of supernova remnants at average integral fluxes one order of magnitude lower than in the existing sample above 1 TeV, therefore opening the possibility to perform unprecedented population studies. The GPS also has the potential to provide new VHE detections of binary systems and pulsars, to confirm the existence of a hypothetical population of gamma-ray pulsars with an additional TeV emission component, and to detect bright sources capable of accelerating particles to PeV energies (PeVatrons). Furthermore, the GPS will constitute a pathfinder for deeper follow-up observations of these source classes. Finally, we show that we can extract from GPS data an estimate of the contribution to diffuse emission from unresolved sources, and that there are good prospects of detecting interstellar emission and statistically distinguishing different scenarios. Thus, a survey of the entire Galactic plane carried out from both hemispheres with CTAO will ensure a transformational advance in our knowledge of Galactic VHE source populations and interstellar emission.

Radio detections of stellar systems provide a window onto stellar magnetic activity and the space weather conditions of extrasolar planets, information that is difficult to attain at other wavelengths. There have been recent advances observing auroral emissions from radio-bright low-mass stars and exoplanets largely due to the maturation of low-frequency radio instruments and the plethora of wide-field radio surveys. To guide us in placing these recent results in context, we introduce the foremost local analogues for the field: Solar bursts and the aurorae found on Jupiter. We detail how radio bursts associated with stellar flares are foundational to the study of stellar coronae, and time-resolved radio dynamic spectra offers one of the best prospects of detecting and characterising coronal mass ejections from other stars. We highlight the prospects of directly detecting coherent radio emission from exoplanetary magnetospheres, and early tentative results. We bridge this discussion to the field of brown dwarf radio emission, in which their larger and stronger magnetospheres are amenable to detailed study with current instruments. Bright, coherent radio emission is also predicted from magnetic interactions between stars and close-in planets. We discuss the underlying physics of these interactions and implications of recent provisional detections for exoplanet characterisation. We conclude with an overview of outstanding questions in theory of stellar, star-planet interaction, and exoplanet radio emission, and the prospects of future facilities in answering them.

We observed upgamma -ray burst (GRB) 221009A using very long baseline interferomety (VLBI) with the European VLBI Network (EVN) and the Very Long Baseline Array (VLBA), over a period spanning from 40 to 262 days after the initial GRB. The high angular resolution (mas) of our observations allowed us, for the second time ever, after GRB\,030329, to measure the projected size, s, of the relativistic shock caused by the expansion of the GRB ejecta into the surrounding medium. Our observations support the expansion of the shock with a $>4 significance, and confirm its relativistic nature by revealing an apparently superluminal expansion rate. Fitting a power law expansion model,$s t^a$, to the observed size evolution, we find a slope$. Fitting the data at each frequency separately, we find different expansion rates, pointing to a frequency-dependent behaviour. We show that the observed size evolution can be reconciled with a reverse shock plus forward shock, provided that the two shocks dominate the emission at different frequencies and, possibly, at different times.