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Galaxy clusters are the most massive gravitationally bound structures in the Universe.They grow by accreting smaller structures in a merging process that produces shocks and turbulence in the intracluster gas. We observed a ridge of radio emission connecting the merging galaxy clusters Abell 0399 and Abell 0401 with the Low-Frequency Array (LOFAR) telescope network at 140 megahertz. This emission requires a population of relativistic electrons and a magnetic field located in a filament between the two galaxy clusters. We performed simulations to show that a volume-filling distribution of weak shocks may reaccelerate a preexisting population of relativistic particles, producing emission at radio wavelengths that illuminates the magnetic ridge.

Pulsars are magnetized neutron stars which have provided us a great insight into the evolution of the neutron stars themselves. We here present the application of the existing LOFAR technology on Pulsar observation, since LOFAR observes the unexplored frequencies of 10-240 MHz. This paper summarizes the system design of LOFAR and shows how this can be used to observe the Pulsars, since recent studies have presented that pulsars observation is possible in the low frequency range.

Underwater target recognition is an important supporting technology for the development of marine resources, which is mainly limited by the purity of feature extraction and the universality of recognition schemes. The low-frequency analysis and recording (LOFAR) spectrum is one of the key features of the underwater target, which can be used for feature extraction. However, the complex underwater environment noise and the extremely low signal-to-noise ratio of the target signal lead to breakpoints in the LOFAR spectrum, which seriously hinders the underwater target recognition. To overcome this issue and to further improve the recognition performance, we adopted a deep-learning approach for underwater target recognition, and a novel LOFAR spectrum enhancement (LSE)-based underwater target-recognition scheme was proposed, which consists of preprocessing, offline training, and online testing. In preprocessing, we specifically design a LOFAR spectrum enhancement based on multi-step decision algorithm to recover the breakpoints in LOFAR spectrum. In offline training, the enhanced LOFAR spectrum is adopted as the input of convolutional neural network (CNN) and a LOFAR-based CNN (LOFAR-CNN) for online recognition is developed. Taking advantage of the powerful capability of CNN in feature extraction, the recognition accuracy can be further improved by the proposed LOFAR-CNN. Finally, extensive simulation results demonstrate that the LOFAR-CNN network can achieve a recognition accuracy of 95.22%, which outperforms the state-of-the-art methods.

Ultralight dark photons and axions are well-motivated hypothetical dark matter candidates. Both dark photon dark matter and axion dark matter can resonantly convert into electromagnetic waves in the solar corona when their mass is equal to the solar plasma frequency. The resultant electromagnetic waves appear as monochromatic signals within the radio-frequency range with an energy equal to the dark matter mass, which can be detected via radio telescopes for solar observations. Here we show our search for converted monochromatic signals in the observational data collected by the high-sensitivity Low Frequency Array (LOFAR) telescope and establish an upper limit on the kinetic mixing coupling between dark photon dark matter and photon, which can reach values as low as 10 −13 within the frequency range of 30 − 80 MHz. This limit represents an improvement of approximately one order of magnitude better than the existing constraint from the cosmic microwave background observation. Additionally, we derive an upper limit on the axion-photon coupling within the same frequency range, which is better than the constraints from Light-Shining-through-a-Wall experiments while not exceeding the CERN Axion Solar Telescope (CAST) experiment or other astrophysical bounds. Hypothetical dark photon (DP) dark matter (DM) and axion DM might resonantly convert into electromagnetic waves in the solar corona. Here, the authors show upper limits on the axion-photon coupling and on the kinetic mixing coupling of DPDM and photon within 30-80 MHz in the solar corona radio observations.

We have used the LOw‐Frequency ARray (LOFAR) to image a few lightning flashes during a particularly severe thunderstorm. The images show an exceptional amount of VHF activity at altitudes above 10 km. Much of this is in the form of small‐scale discharges, not exceeding a few hundred meter, occurring seemingly randomly around the centers of active storm cells. To emphasize the incidental nature of these small‐scale discharges or sparks we refer to them as “sparkles.” A detailed investigation shows evidence that these sparkles are indicative of positive leader channels and that they are equivalent to the needle activity seen around positive leader tracks at lower altitudes. Plain Language Summary At the height of the tropopause in very active lightning cells many seemingly unrelated small discharges have been observed. Using the LOw‐Frequency ARray radio telescope, mainly intended for astronomical observations, we have imaged these structures in unprecedented detail and found strong evidence that these are negative discharges that form around a network of positive leaders. Key Points In the tops of severe thunderstorms many seemingly isolated sources for VHF radiation are observed The VHF sources in these tops are small negative discharges, conjectured to be related to an extensive positive leader structure The charge‐layer structure in these tops is mixed

This talk describes a proposed transformation of LOFAR, the world’s largest, most sensitive high-resolution radio telescope that operates at low frequencies (<300 MHz), into a multidisciplinary intercontinental facility that will be a unique engine for capacity building and development throughout Europe, North Africa, the Middle East and West Asia. As an astronomical array, GLORAY would be the “Hubble Space Telescope” of low-frequency radio astronomy, having a resolution more than 50 times better than any other presently planned low-frequency facility, including SKA-LOW. The mutually interdependent network of LOFAR antenna stations that presently stretch from Ireland to Latvia would be extended to cover North Africa, the Middle East and West Asia and converted into “innovation hubs”. These would form an intercontinental network for pure research, applied research, capacity building, education and science diplomacy within and between the participating countries.

This study surveys methods for improvements in the processing and visualization of Low Frequency Analysis and Recording (LOFAR) in sonar systems. The surveyed method employs a weighted Fast Fourier Transform (FFT) technique to compute LOFAR (Low Frequency Analysis and Recording) spectrum, with the weighting function inversely proportional to the variance of phase estimates for each frequency bin. The approach leverages the observation that stable line spectra display lower variance in phase estimates when compared to broadband signals and ambient noise. Simulation results substantiate the effectiveness of the proposed technique. The technique is applied to the DeepShip underwater dataset available in the public domain, and the performance of the proposed algorithm is recorded.

Despite their relative sparseness, during the recent years it has become more and more clear that extragalactic radio sources (both AGN and star-forming galaxies) constitute an extremely interesting mix of populations, not only because of their intrinsic value, but also for their fundamental role in shaping our universe the way we see it today. Indeed, radio-active AGN are now thought to be the main players involved in the evolution of massive galaxies and clusters. At the same time, thanks to the possibility of being observed up to very high redshifts, radio galaxies can also provide crucial information on both the star-formation history of our universe and on its large-scale structure properties and their evolution. In the light of present and forthcoming facilities such as LOFAR, MeerKAT and SKA that will probe the radio sky to unprecedented depths and widths, this review aims at providing the current state of the art on our knowledge of extragalactic radio sources in connection with their hosts, large-scale environments and cosmological context.

While broadband short-duration radio pulses from airplanes are commonly detected and used for calibration or as background in astrophysical observations, the precise locations of the emission regions cannot be determined in these studies. We show that it is possible to locate the few places on the body of an airplane, while it is flying through high clouds, from which broad-band, pulsed, radiation is emitted at very high frequency radio frequencies. This serendipitous discovery was made whilst imaging a lightning flash using the Low-Frequency Array (LOFAR). This observation provides insights into the way the airplane sheds the electrical charge it acquires when flying through clouds. Furthermore, this observation allowed us to test and improve the precision and accuracy for our lightning observation techniques. Our results indicate that with the improved procedure the location precision for strong pulses is better than 50 cm, with the orientation of linear polarization being accurate to within 25°. For the present case of a Boeing 777-300ER, very high frequency radio pulses were observed exclusively associated with the two engines, as well as a specific spot on the tail. Despite the aircraft flying through clouds at an altitude of 8 km, we did not detect any emissions from electrostatic wicks. Here, the authors propose a method for determining the three-dimensional locations of sources that emit extremely brief radio pulses. As an illustration, they demonstrate that a plane flying at an altitude of 8 km through clouds emits short radio pulses exclusively from its two engines and a particular point on the tail.

Highlights are presented about the science to be done with SKA. as well as state of the art science already done today with its precursors (MeerKAT, ASKAP) and pathfinders (LOFAR, NenuFAR), with accent on the expected breakthroughs.