arXiv subjects

Sander ter Veen

Publications and source records attributed to Sander ter Veen.

12 recordsLinked to original sources

arXiv2026

Reconstruction of anomalous air showers with SKA-Low

Double-bump showers are a surprising class of extensive air showers (EAS) predicted by Monte Carlo simulations, which, so far, no experiment has been able to directly detect. They occur when a high-energy secondary particle, the leading particle, travels significantly farther than the rest, creating a distinct double-peaked longitudinal profile. The unique radio footprint of double-bump showers, characterized by multiple pulses in the signals and interference patterns in the frequency spectra, enables reconstruction of longitudinal profiles from radio observations. With its dense antenna array and broad frequency range, SKA-Low will be the first observatory capable of detecting these features, offering a new opportunity to probe hadronic interactions and use the distinctive signatures of elements to provide new mass composition measurements. The goal of this analysis is to take the first steps toward using these radio signatures to reconstruct the relevant parameters of the longitudinal profile of a double-bump shower. We will start by explaining the radio signal of double-bump}showers compared to that of average showers. Then we will create a simple 2-point emission model to explain the interference patterns in the frequency spectra, which can be inverted to obtain rudimentary estimates of atmospheric depth of both peaks. Lastly, we implement a brute-force approach to reconstruct multiple parameters of the double bump.

astro-ph.HE↗

arXiv2026

Beyond $X_\mathrm{max}$ : Reconstructing Air Shower Profiles with Information Field Theory with SKA-Low

While radio measurements of extensive air showers have shown to achieve a high precision of $X_\mathrm{max}$ sensitivity, it has been shown that parameters beyond $X_\mathrm{max}$ can also be reconstructed. These shape parameters contain additional sensitivity to the hadronic physics in the shower as well as its mass composition. In this work, we showcase a reconstruction framework to recover the full longitudinal profile from realistic radio measurements. The framework is based on Information Field Theory that infers the full profile with a forward-based model, which uses a Gaisser-Hillas profile with weakly informative shower priors, SMIET with a template library to synthesise pulses at any event geometry, and a realistic antenna response and noise level emulating that of SKA-Low. We verify the self-consistency of our framework with $\sim 900$ events generated with SMIET with antennas placed on the $\vec{v} \times (\vec{v} \times \vec{B})$ axis. The framework recovers the full profile within uncertainty and capture correlations between shower parameters. We yield an $X_\mathrm{max}$ resolution of $< 9$ g cm$^{-2}$ as well as resolutions of the width and asymmetry with minimal bias. The profile is also recovered with a bias of $< 4$% at all atmospheric depths $< 1200$ g cm$^{-2}$. We aim to apply this framework with pulses simulated from CoREAS with measured noise, ultimately extending the framework to realistic antenna layouts such as from LOFAR or SKA-Low.

astro-ph.IM↗

arXiv2025

Measuring the locations and properties of VHF sources emitted from an aircraft flying through high clouds

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 (VHF) 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 new 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$^\circ$. For the present case of a Boeing 777-300ER, VHF emissions 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.

physics.plasm-ph↗

arXiv2023

The Apertif Radio Transient System (ARTS): Design, Commissioning, Data Release, and Detection of the first 5 Fast Radio Bursts

Fast Radio Bursts must be powered by uniquely energetic emission mechanisms. This requirement has eliminated a number of possible source types, but several remain. Identifying the physical nature of Fast Radio Burst (FRB) emitters arguably requires good localisation of more detections, and broadband studies enabled by real-time alerting. We here present the Apertif Radio Transient System (ARTS), a supercomputing radio-telescope instrument that performs real-time FRB detection and localisation on the Westerbork Synthesis Radio Telescope (WSRT) interferometer. It reaches coherent-addition sensitivity over the entire field of the view of the primary dish beam. After commissioning results verified the system performed as planned, we initiated the Apertif FRB survey (ALERT). Over the first 5 weeks we observed at design sensitivity in 2019, we detected 5 new FRBs, and interferometrically localised each of these to 0.4--10 sq. arcmin. All detections are broad band and very narrow, of order 1 ms duration, and unscattered. Dispersion measures are generally high. Only through the very high time and frequency resolution of ARTS are these hard-to-find FRBs detected, producing an unbiased view of the intrinsic population properties. Most localisation regions are small enough to rule out the presence of associated persistent radio sources. Three FRBs cut through the halos of M31 and M33. We demonstrate that Apertif can localise one-off FRBs with an accuracy that maps magneto-ionic material along well-defined lines of sight. The rate of 1 every ~7 days next ensures a considerable number of new sources are detected for such study. The combination of detection rate and localisation accuracy exemplified by the 5 first ARTS FRBs thus marks a new phase in which a growing number of bursts can be used to probe our Universe.

astro-ph.HE↗

arXiv2021

Interferometric imaging of Intensely Radiating Negative Leaders

The common phenomenon of lightning still harbors many secrets and only recently a new propagation mode was observed for negative leaders. While propagating in this `Intensely Radiating Negative Leader' (IRNL) mode a negative leader emits 100 times more very-high frequency (VHF) and broadband radiation than a more normal negative leader. We have reported that this mode occurs soon after initiation of all lightning flashes we have mapped as well as sometimes long thereafter. Because of the profuse emission of VHF the leader structure is very difficult to image. In this work we report on measurements made with the LOFAR radio telescope, an instrument primarily built for radio-astronomy observations. For this reason, as part of the present work, we have refined our time resolved interferometric 3-Dimensional (TRI-D) imaging to take into account the antenna function. The images from the TRI-D imager show that during an IRNL there is an ionization front with a diameter in excess of 500~m where strong corona bursts occur. This is very different from what is seen for a normal negative leader where the corona bursts happen at the tip, an area of typically 10~m in diameter. The observed massive ionization wave supports the idea that this mode is indicative of a dense charge pocket.

physics.ao-ph↗

arXiv2021

Time resolved 3Dinterferometric imaging of a section of a negative leader with LOFAR

We have developed a three dimensional (3D) interferometric beamforming technique for imaging lightning flashes using Very-High Frequency (VHF) radio data recorded from several hundreds antennas with baselines up to 100~km as offered by the Low Frequency Array (LOFAR). The long baselines allow us to distinguish fine structures on the scale of meters while the large number of antennas allow us to observe processes that radiate at the same intensity as the background when using a time resolution that is close to the impulse-response time of the system, 100~ns. The new beamforming imaging technique is complementary to our existing impulsive imaging technique. We apply this new tool to the imaging of a four stepped negative leaders in two flashes. For one flash, we observe the dynamics of coronal flashes that are emitted in the stepping process. Additionally, we show that the intensity emitted in VHF during the stepping process follows a power-law over 4 orders of magnitude in intensity for four leaders in two different lightning storms.

physics.ao-ph↗

arXiv2020

Chromatic periodic activity down to 120 MHz in a Fast Radio Burst

Fast radio bursts (FRBs) are extragalactic astrophysical transients whose brightness requires emitters that are highly energetic, yet compact enough to produce the short, millisecond-duration bursts. FRBs have thus far been detected between 300 MHz and 8 GHz, but lower-frequency emission has remained elusive. A subset of FRBs is known to repeat, and one of those sources, FRB 20180916B, does so with a 16.3 day activity period. Using simultaneous Apertif and LOFAR data, we show that FRB 20180916B emits down to 120 MHz, and that its activity window is both narrower and earlier at higher frequencies. Binary wind interaction models predict a narrower periodic activity window at lower frequencies, which is the opposite of our observations. Our detections establish that low-frequency FRB emission can escape the local medium. For bursts of the same fluence, FRB 20180916B is more active below 200 MHz than at 1.4 GHz. Combining our results with previous upper-limits on the all-sky FRB rate at 150 MHz, we find that there are 3-450 FRBs/sky/day above 50 Jy ms at 90% confidence. We are able to rule out the scenario in which companion winds cause FRB periodicity. We also demonstrate that some FRBs live in clean environments that do not absorb or scatter low-frequency radiation.

astro-ph.HE↗

arXiv2017

Overview of lunar detection of ultra-high energy particles and new plans for the SKA

The lunar technique is a method for maximising the collection area for ultra-high-energy (UHE) cosmic ray and neutrino searches. The method uses either ground-based radio telescopes or lunar orbiters to search for Askaryan emission from particles cascading near the lunar surface. While experiments using the technique have made important advances in the detection of nanosecond-scale pulses, only at the very highest energies has the lunar technique achieved competitive limits. This is expected to change with the advent of the Square Kilometre Array (SKA), the low-frequency component of which (SKA-low) is predicted to be able to detect an unprecedented number of UHE cosmic rays. In this contribution, the status of lunar particle detection is reviewed, with particular attention paid to outstanding theoretical questions, and the technical challenges of using a giant radio array to search for nanosecond pulses. The activities of SKA's High Energy Cosmic Particles Focus Group are described, as is a roadmap by which this group plans to incorporate this detection mode into SKA-low observations. Estimates for the sensitivity of SKA-low phases 1 and 2 to UHE particles are given, along with the achievable science goals with each stage. Prospects for near-future observations with other instruments are also described.

astro-ph.IM↗

arXiv2016

The lunar Askaryan technique with the Square Kilometre Array

The lunar Askaryan technique is a method to study the highest-energy cosmic rays, and their predicted counterparts, the ultra-high-energy neutrinos. By observing the Moon with a radio telescope, and searching for the characteristic nanosecond-scale Askaryan pulses emitted when a high-energy particle interacts in the outer layers of the Moon, the visible lunar surface can be used as a detection area. Several previous experiments, at Parkes, Goldstone, Kalyazin, Westerbork, the ATCA, Lovell, LOFAR, and the VLA, have developed the necessary techniques to search for these pulses, but existing instruments have lacked the necessary sensitivity to detect the known flux of cosmic rays from such a distance. This will change with the advent of the SKA. The Square Kilometre Array (SKA) will be the world's most powerful radio telescope. To be built in southern Africa, Australia and New Zealand during the next decade, it will have an unsurpassed sensitivity over the key 100 MHz to few-GHZ band. We introduce a planned experiment to use the SKA to observe the highest-energy cosmic rays and, potentially, neutrinos. The estimated event rate will be presented, along with the predicted energy and directional resolution. Prospects for directional studies with phase 1 of the SKA will be discussed, as will the major technical challenges to be overcome to make full use of this powerful instrument. Finally, we show how phase 2 of the SKA could provide a vast increase in the number of detected cosmic rays at the highest energies, and thus to provide new insight into their spectrum and origin.

astro-ph.IM↗

arXiv2013

Detecting Radio Emission from Air Showers with LOFAR

LOFAR (the Low Frequency Array) is the largest radio telescope in the world for observing low frequency radio emission from 10 to 240 MHz. In addition to its use as an interferometric array, LOFAR is now routinely used to detect cosmic ray induced air showers by their radio emission. The LOFAR core in the Netherlands has a higher density of antennas than any dedicated cosmic ray experiment in radio. On an area of $12 \mathrm{km}^2$ more than 2300 antennas are installed. They measure the radio emission from air showers with unprecedented precision and, therefore, give the perfect opportunity to disentangle the physical processes which cause the radio emission in air showers. In parallel to ongoing astronomical observations LOFAR is triggered by an array of particle detectors to record time-series containing cosmic-ray pulses. Cosmic rays have been measured with LOFAR since June 2011. We present the results of the first year of data.

astro-ph.HE↗

arXiv2013

Searching for Neutrino Radio Flashes from the Moon with LOFAR

Ultra-high-energy neutrinos and cosmic rays produce short radio flashes through the Askaryan effect when they impact on the Moon. Earthbound radio telescopes can search the Lunar surface for these signals. A new generation of low- frequency, digital radio arrays, spearheaded by LOFAR, will allow for searches with unprecedented sensitivity. In the first stage of the NuMoon project, low-frequency observations were carried out with the Westerbork Synthesis Radio Telescope, leading to the most stringent limit on the cosmic neutrino flux above 10$^{23}$ eV. With LOFAR we will be able to reach a sensitivity of over an order of magnitude better and to decrease the threshold energy.

astro-ph.IM↗

arXiv2012

The Dynamic Spectrum of Interplanetary Scintillation: First Solar Wind Observations on LOFAR

The LOw Frequency ARray (LOFAR) is a next-generation radio telescope which uses thousands of stationary dipoles to observe celestial phenomena. These dipoles are grouped in various 'stations' which are centred on the Netherlands with additional 'stations' across Europe. The telescope is designed to operate at frequencies from 10 to 240\,MHz with very large fractional bandwidths (25-100%). Several 'beam-formed' observing modes are now operational and the system is designed to output data with high time and frequency resolution, which are highly configurable. This makes LOFAR eminently suited for dynamic spectrum measurements with applications in solar and planetary physics. In this paper we describe progress in developing automated data analysis routines to compute dynamic spectra from LOFAR time-frequency data, including correction for the antenna response across the radio frequency pass-band and mitigation of terrestrial radio-frequency interference (RFI). We apply these data routines to observations of interplanetary scintillation (IPS), commonly used to infer solar wind velocity and density information, and present initial science results.

astro-ph.SR↗