arXiv subjects

Tobia D. Carozzi

Publications and source records attributed to Tobia D. Carozzi.

7 recordsLinked to original sources

arXiv2026

Characterising the response of an International LOFAR Station

Phased-array radio interferometers with fixed antennas are a highly scalable design which can achieve a large gain. However they are complex systems and challenging to calibrate. Here we examine the response of an International LOFAR Station, the high-band antennas of the Irish LOFAR station. In modelling our measured responses, we account for projection effects, the frequency-dependence of the aperture efficiency and pulsar spectra, as well as sky and instrumental noise contributions. We perform long-track observations of 11 bright pulsars as they move across the sky, apply RFI mitigation and determine the signal-to-noise ratio response as a function of time, elevation and azimuth. We use the DreamBeam software to model the beam response of the station to compare with what is observed. The sensitivity map so obtained was validated using observations of PSR B0329+54 on the Swedish LOFAR station. As expected, the sensitivity is higher near the zenith. However, an asymmetry with respect to the zenith point is detected. Characterising the instrumental response in azimuth reveals a better performance as the targets rise, as compared to when they set. This trend is seen for all pulsars and is consistent with other International Stations. The magnitude of the effect can exceed 20%. We consider variations in the beam model and noise level, both frequency- and time- dependent, to try to account for this. A possible explanation for the hysteresis-like response in elevation could be an imbalanced signal weighting of the polarisation components. This work addresses the importance of accurate beam modelling and noise evaluation for the LOFAR 2.0 system upgrade as well as being relevant to the under-construction SKA-Low facility.

astro-ph.IM↗

arXiv2026

Evidence of Long-Lived Powerful Gyrosynchrotron Radio Emission in the Close Binary FF UMa

RS Canum Venaticorum (RS CVn) close binaries, characterized by tidal locking, rapid rotations, and strong magnetic fields, are ideal laboratories for high-resolution radio observations to probe emission processes, magnetic field configurations, and interaction activity. Despite their importance, only a few RS CVn sources have been explored by polarimetric observations of very long baseline interferometry (VLBI). To expand the effort, we have analyzed the existing Very Long Baseline Array (VLBA) astrometric data for the RS CVn binary FF Ursae Majoris (FF UMa). In the 5GHz VLBA experiments conducted between 2021 and 2024, both total intensity and circularly polarized emission were clearly detected at six of seven epochs. The consistently high brightness temperatures (10^7 K) and the moderate fractional circular polarization (10%-30%) over about three years indicate that the radio emission is mainly produced by gyrosynchrotron radiation from mildly relativistic electrons in the highly-ordered magnetic field. The radio luminosities are also comparable to those of previously studied powerful RS CVn binaries and show a significant anti-correlation with fractional circular polarization. A mean centroid offset of 13.4 +/- 3.1 solar radii between the Stokes I and V emission was found across multiple epochs, indicating a possible additional contribution from the secondary star via a magnetically active corona, a giant magnetic loop, or significant interaction activity with the primary star in the quiescent state.

astro-ph.SR↗

arXiv2023

A Simultaneous Dual-site Technosignature Search Using International LOFAR Stations

The Search for Extraterrestrial Intelligence aims to find evidence of technosignatures, which can point toward the possible existence of technologically advanced extraterrestrial life. Radio signals similar to those engineered on Earth may be transmitted by other civilizations, motivating technosignature searches across the entire radio spectrum. In this endeavor, the low-frequency radio band has remained largely unexplored; with prior radio searches primarily above 1 GHz. In this survey at 110-190 MHz, observations of 1,631,198 targets from TESS and Gaia are reported. Observations took place simultaneously with two international stations (noninterferometric) of the Low Frequency Array in Ireland and Sweden. We can reject the presence of any Doppler drifting narrowband transmissions in the barycentric frame of reference, with equivalent isotropic radiated power of 10 17 W, for 0.4 million (or 1.3 million) stellar systems at 110 (or 190) MHz. This work demonstrates the effectiveness of using multisite simultaneous observations for rejecting anthropogenic signals in the search for technosignatures.

astro-ph.IM↗

arXiv2019

beamModelTester: software framework for testing radio telescope beams

The flux, polarimetric and spectral response of phased array radio telescopes with no moving parts such as LOFAR is known to vary considerably with orientation of the source to the receivers. Calibration models exist for this dependency such as those that are used in the LOFAR pipeline. Presented here is a system for comparing the predicted outputs from any given model with the results of an observation. In this paper, a sample observation of a bright source, Cassiopeia A, is used to demonstrate the software in operation, by providing an observation and a model of that observation which can be compared with one another. The package presented here is flexible to allow it to be used with other models and sources. The system operates by first calculating the predictions of the model and the results of an observation of linear fluxes and Stokes parameters separately. The model and observed values are then joined using the variables common to both, time and frequency. Normalisation and RFI excision are carried out and the differences between the prediction and the observation are calculated. A wide selection of 2-, 3- and 4-dimensional plots are generated to illustrate the dependence of the model and the observation as well as the difference between them on independent parameters time, frequency, altitude and azimuth. Thus, beamModelTester provides a framework by which it is possible to calibrate and propose refinements to models and to compare models with one another.

astro-ph.IM↗

arXiv2009

Canonical Electromagnetic Observables for Systematic Characterization of Electric and Magnetic Wave Field Data on board Spacecraft

We present a new characterization of partially coherent electric and magnetic wave vector fields.This characterization is based on the 36 auto/cross correlations of the 3+3 complex Cartesian components of the electric and magnetic wave fields and is particularly suited for analyzing electromagnetic wave data on board spacecraft. Data from spacecraft based electromagnetic wave instruments are usually processed as data arrays. These data arrays however do not have a physical interpretation in themselves; they are simply a convenient storage format. In contrast, the characterization proposed here contains exactly the same information but are in the form of manifestly covariant space-time tensors. We call this data format the Canonical Electromagnetic Observables (CEO) since they correspond to unique physical observables. Some of them are already known, such as energy density, Poynting flux, stress tensor, etc, while others should be relevant in future space research. As an example we use this formalism to analyze data from a chorus emission in the mid-latitude magnetosphere, as recorded by the STAFF-SA instrument on board the Cluster-II spacecraft.

physics.geo-ph↗

arXiv2008

Conservation Laws in Generalized Riemann-Silberstein Electrodynamics

Starting from positive and negative helicity Maxwell equations expressed in Riemann-Silberstein vectors, we derive the ten usual and ten additional Poincar{é} invariants, the latter being related to the electromagnetic spin, i.e., the intrinsic rotation, or state of polarization, of the electromagnetic fields. Some of these invariants have apparently not been discussed in the literature before.

physics.optics↗

arXiv2006

Systematic Characterization of Low Frequency Electric and Magnetic Field Data Applicable to Solar Orbiter

We present a systematic and physically motivated characterization of incoherent or coherent electric and magnetic fields, as measured for instance by the low frequency receiver on-board the Solar Orbiter spacecraft. The characterization utilizes the 36 auto/cross correlations of the 3+3 complex Cartesian components of the electric and magnetic fields; hence, they are second order in the field strengths and so have physical dimension energy density. Although such 6x6 correlation matrices have been successfully employed on previous space missions, they are not physical quantities; because they are not manifestly space-time tensors. In this paper we propose a systematic representation of the 36 degrees-of-freedom of partially coherent electromagnetic fields as a set of manifestly covariant space-time tensors, which we call the Canonical Electromagnetic Observables (CEO). As an example, we apply this formalism to analyze real data from a chorus emission in the mid-latitude magnetosphere, as registered by the STAFF-SA instrument on board the Cluster-II spacecraft. We find that the CEO analysis increases the amount of information that can be extracted from the STAFF-SA dataset; for instance, the reactive energy flux density, which is one of the CEO parameters, identifies the source region of electromagnetic emissions more directly than the active energy (Poynting) flux density alone.

physics.space-ph↗