Breakthrough Listen

Abstract:

The Earth’s ionosphere can be driven by the Sun, the solar wind, the magnetosphere, as well as the neutral atmosphere. These drivers influence the ionosphere on a variety of spatial and temporal scales. The ionosphere is highly dependent on the driving processes and is highly dynamic. Modelling this plasma and capturing its full dynamic range is challenging.Swarm is the European Space Agency’s (ESA) first constellation mission for Earth Observation (EO), comprising multiple satellites in Low Earth Orbit (LEO). Numerous data products are available, including measures of the ionosphere at a range of spatial scales. During the Swarm-VIP-Dynamic project, which ended in February 2026, the technique of Generalised Linear Modelling was used to create a suite of statistical models. These models predict the electron density and the variability in the ionospheric plasma at spatial scales between 100 km and 7.5 km. The models were based upon proxies for the heliogeophysical processes, as well as measurements of the thermosphere and ionospheric current systems. In addition to the Swarm data, datasets from other satellites and ground-based instruments were used for model evaluation and validation activities.The performance of the models of the electron density approached the theoretical best values for some of the goodness-of-fit statistics that were to evaluate these models. This suggests that the modelling method is appropriate for the task undertaken. The models of ionospheric variability at larger spatial scales (~100 km) also performed well, however the model performance decreased at smaller spatial scales. This suggested that there is a physical process missing from the models. Possible candidates are instability processes or driving of the ionosphere by wave activity from below, neither of which are captured by the models at present. It is possible to test whether atmospheric waves originating in the lower atmosphere are driving the variability at European midlatitudes using different proxies for wave activity, and the ways in which this could be tested are discussed.

Abstract:

We revisit cooling bounds on light Kaluza-Klein (KK) gravitons, as arise in the dark dimension scenario, considering globular clusters, neutron stars, and supernovae. In addition to bremsstrahlung, we account for two novel production channels: resonant mixing with the in-medium photon and a pion-induced process in supernovae. The strongest limits arise from SN 1987A, with the emissivity from the pion process exceeding that from bremsstrahlung by a factor of a few albeit with substantial uncertainties, while resonant production is heavily suppressed. We obtain a bound on the KK mass scale of mKK ≳ 0.6 eV (≳ 500 eV) for 2 (3) extra dimensions, which, having accounted for these previously neglected processes, is broadly compatible with existing analyses. Improved understanding of the properties of pions in supernovae could strengthen these limits to roughly eV (keV). For 1 extra dimension, the bounds are weaker than those from laboratory searches. We also show that constraints from KK graviton decays to Standard Model particles are less stringent than the cooling bounds if there is KK number violation at the level typically assumed in the dark dimension scenario, although these bounds could be strengthened by future observations.

Abstract:

<jats:p>The May 2024 Mother’s Day superstorm, the strongest since November 2003, triggered significant ionospheric disturbances. Indeed, during the superstorm, the ionosphere above Europe was transformed into a severely depleted, super-high-altitude plasma structure extending beyond 1500 km above Earth’s surface. We highlight the unique contributions of the LOw Frequency ARray (LOFAR) to ionospheric weather research on this extreme event. Originally designed for radio astronomy, LOFAR’s extensive European network of 52 stations and wide-band capabilities enable high-resolution ionospheric monitoring at both local and regional scales. Leveraging LOFAR measurements, we characterise a plethora of ionospheric effects that occurred during the main and early recovery phases of the storm. We did this by observing significant signal fading associated with the equatorward expansion of the auroral oval during the main phase and by capturing high-speed moving ionospheric irregularities (up to ~800 m/s), and quantifying extreme ionospheric uplift (up to 1500 km) under conditions where conventional HF instruments were not usable due to the occurrence of D-layer absorption, ionospheric G-conditions and uplift above ionosonde altitude range. In this investigation, we harness the unique capabilities of LOFAR to direct view into the structure and dynamics of the ionosphere under the most extreme space weather conditions. Our results confirm LOFAR as an insightful instrument for ionospheric research, offering critical capabilities for advancing storm impact assessment, forecasting, and mitigation strategies.</jats:p>

Abstract:

We present the discovery of radio emission from the Be/X-ray binary A0538−66 with the Australian Square Kilometre Array Pathfinder, and results from a subsequent weekly monitoring campaign with the MeerKAT radio telescope. A0538−66, located in the Large Magellanic Cloud, hosts a neutron star with a short spin period ( ms) in a highly eccentric -d orbit . Its rare episodes of super-Eddington accretion, rapid optical and X-ray flares, and other peculiar properties make it an interesting system among high-mass X-ray binaries. Our MeerKAT data reveal that it is also one of the most radio-luminous neutron star X-ray binaries observed to date, reaching (at 1.28 GHz), with radio emission that appears to be orbitally modulated. We consider several possible mechanisms for the radio emission, and place A0538−66 in context by comparing it to similar systems.

Abstract: