arXiv subjects

Mauro Roma

Publications and source records attributed to Mauro Roma.

3 recordsLinked to original sources

arXiv2026

A High-frequency Geodetic VLBI Experiment for Optical Clock Comparison

An intercontinental metrological clock comparison between Italy and the Republic of Korea was performed by means of geodetic K-band VLBI observations. The comparison involved the hydrogen masers (H-masers) used at Medicina and Sejong radio telescopes. The same clocks were simultaneously compared by a satellite link and by high-precision optical clocks maintained at the National Metrology Institutes, KRISS in Korea and INRIM in Italy, and delivered to VLBI antennas via optical fiber. The H-masers frequency difference was estimated by extrapolating the clock rate from VLBI data using two geodetic VLBI software. This was subsequently compared with clock differences derived by satellite link and by local optical clocks. Results obtained with different approaches were in agreement at the level of $10^{-15}$ s/s. This pilot study demonstrates that standard high-frequency (K-band) geodetic VLBI campaigns could be a viable approach to conduct intercontinental clock comparisons, now only possible via satellite links. This uncertainty can be reduced thanks to the planned installation of new-generation, broadband, high-frequency receivers on the involved telescopes. K/Q/W-band geodetic observations will allow an improvement of the accuracy of the resulting group delays through broad bandwidth synthesis from 20 to 100 GHz. Furthermore, the Frequency Phase Transfer (FPT) method will also be explored together with the use of PCAL systems installed at the radio telescopes to improve phase stability and thus allow a better estimation of the station clock parameters.

astro-ph.IM↗

arXiv2023

The Northern Cross Fast Radio Burst project -- III. The FRB-magnetar connection in a sample of nearby galaxies

Fast radio bursts (FRBs) are millisecond radio transients observed at cosmological distances. The nature of their progenitors is still a matter of debate, although magnetars are invoked by most models. The proposed FRB-magnetar connection was strengthened by the discovery of an FRB-like event from the Galactic magnetar SGR J1935+2154. In this work, we aim to investigate how prevalent magnetars such as SGR J1935+2154 are within FRB progenitors. We carried out an FRB search in a sample of seven nearby (< 12 Mpc) galaxies with the Northern Cross radio telescope for a total of 692 h. We detected one 1.8 ms burst in the direction of M101 with a fluence of $58 \pm 5$ Jy ms. Its dispersion measure of 303 pc cm$^{-3}$ places it most-likely beyond M101. Considering that no significant detection comes indisputably from the selected galaxies, we place a 38 yr$^{-1}$ upper limit on the total burst rate (i.e. including the whole sample) at the 95\% confidence level. This upper limit constrains the event rate per magnetar $λ_{\rm mag} < 0.42$ magnetar$^{-1}$ yr$^{-1}$ or, if combined with literature observations of a similar sample of nearby galaxies, it yields a joint constraint of $λ_{\rm mag} < 0.25$ magnetar$^{-1}$ yr$^{-1}$. We also provide the first constraints on the expected rate of FRBs hypothetically originating from ultraluminous X-ray (ULX) sources, since some of the galaxies observed during our observational campaign host confirmed ULXs. We obtain $< 13$ yr$^{-1}$ per ULX for the total sample of galaxies observed. Our results indicate that bursts with energies $E>10^{34}$ erg from magnetars like SGR J1935+2154 appear more rarely compared to previous observations and further disfavour them as unique progenitors for the cosmological FRB population, leaving more space open to the contribution from a population of more exotic magnetars, not born via core-collapsed supernovae.

astro-ph.HE↗

arXiv2022

Towards coordinated site monitoring and common strategies for mitigation of Radio Frequency Interference at the Italian radio telescopes

We present a project to implement a national common strategy for the mitigation of the steadily deteriorating Radio Frequency Interference (RFI) situation at the Italian radio telescopes. The project involves the Medicina, Noto, and Sardinia dish antennas and comprised the definition of a coordinated plan for site monitoring as well as the implementation of state-of-the-art hardware and software tools for RFI mitigation. Coordinated monitoring of frequency bands up to 40 GHz has been performed by means of continuous observations and dedicated measurement campaigns with fixed stations and mobile laboratories. Measurements were executed on the frequency bands allocated to the radio astronomy and space research service for shared or exclusive use and on the wider ones employed by the current and under-development receivers at the telescopes. Results of the monitoring campaigns provide a reference scenario useful to evaluate the evolution of the interference situation at the telescopes sites and a case series to test and improve the hardware and software tools we conceived to counteract radio frequency interference. We developed a multi-purpose digital backend for high spectral and time resolution observations over large bandwidths. Observational results demonstrate that the spectrometer robustness and sensitivity enable the efficient detection and analysis of interfering signals in radio astronomical data. A prototype off-line software tool for interference detection and flagging has been also implemented. This package is capable to handle the huge amount of data delivered by the most modern instrumentation on board of the Italian radio telecsopes, like dense focal plane arrays, and its modularity easen the integration of new algorithms and the re-usability in different contexts or telescopes.

astro-ph.IM↗