| 1. |
- Carozzi, Tobia, 1966, et al.
(författare)
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Differentially Rotated SKALA4.1 Antennas in Vogel Configurations
- 2023
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Ingår i: 2023 35th General Assembly and Scientific Symposium of the International Union of Radio Science, URSI GASS 2023.
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Konferensbidrag (refereegranskat)abstract
- We have studied the effects of non-aligned SKALA4.1 antennas in dense arrays with a Vogel layout. We find that the Vogel array is too dense at 2 m minimum inter-element distance for differential alignments to mitigate mutual-coupling, but polarimetric performance can be improved regardless.
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| 2. |
- Johnson, Owen A., et al.
(författare)
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A Simultaneous Dual-site Technosignature Search Using International LOFAR Stations
- 2023
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Ingår i: Astronomical Journal. - 1538-3881 .- 0004-6256. ; 166:5
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Tidskriftsartikel (refereegranskat)abstract
- 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 1017 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.
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| 3. |
- Ninni, Paola Di, et al.
(författare)
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Intrinsic Polarization in Polarimetrically Beamformed Arrays with Differentially Rotated Elements
- 2023
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Ingår i: 2023 International Conference on Electromagnetics in Advanced Applications, ICEAA 2023. ; , s. 532-537
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Konferensbidrag (refereegranskat)abstract
- Prior characterization of the sub-systems of a radio telescope which also works as a radio polarimeter is essential in view of the polarimetric performance understanding and the implementation of the most appropriate calibration procedure. In this paper the polarimetric characterization of two phased antenna arrays having identical antennas and array factors but different antenna alignment will be discussed. These arrays have been proposed as possible layouts in the SKA-Low framework. The polarimetric beamforming, i.e. the beamforming for dual-polarized antennas, has been applied to calculate the polarization purity of the two arrays across the sky. In particular we investigated the variation of instrumental polarization along azimuthal cuts and found that the variation was less in the array in which elements had different alignments compared to the one where all elements had the same alignment.
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| 4. |
- Pétri, Jérôme A., et al.
(författare)
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Constraining the magnetic field geometry of the millisecond pulsar PSRJ0030+0451 from joint radio, thermal X-ray, and γ-ray emission
- 2023
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Ingår i: Astronomy and Astrophysics. - 0004-6361 .- 1432-0746. ; 680
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Tidskriftsartikel (refereegranskat)abstract
- Context. With the advent of multi-wavelength electromagnetic observations of neutron stars - spanning many decades in photon energies - from radio wavelengths up to X-rays and γ-rays, it has become possible to significantly constrain the geometry and the location of the associated emission regions. Aims. In this work, we use results from the modelling of thermal X-ray observations of PSR J0030+0451 from the Neutron Star Interior Composition Explorer (NICER) mission and phase-aligned radio and γ-ray pulse profiles to constrain the geometry of an off-centred dipole that is able to reproduce the light curves in these respective bands simultaneously. Methods. To this aim, we deduced a configuration with a simple dipole off-centred from the location of the centre of the thermal X-ray hot spots. We show that the geometry is compatible with independent constraints from radio and -ray pulsations only, leading to a fixed magnetic obliquity of α ≈ 75° and a line-of-sight inclination angle of ζ ≈ 54°. Results. We demonstrate that an off-centred dipole cannot be rejected by accounting for the thermal X-ray pulse profiles. Moreover, the crescent shape of one spot is interpreted as the consequence of a small-scale surface dipole on top of the large-scale off-centred dipole.
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| 5. |
- Van Der Wateren, E., et al.
(författare)
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The LOFAR Tied-Array All-Sky Survey: Timing of 35 radio pulsars and an overview of the properties of the LOFAR pulsar discoveries
- 2023
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 669
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Tidskriftsartikel (refereegranskat)abstract
- The LOFAR Tied-Array All-Sky Survey (LOTAAS) is the most sensitive untargeted radio pulsar survey performed at low radio frequencies (119-151 MHz) to date and has discovered 76 new radio pulsars, including the 23.5-s pulsar J0250+5854, which up until recently was the slowest spinning radio pulsar known. In this paper, we report on the timing solutions of 35 pulsars discovered by LOTAAS, which include a nulling pulsar and a mildly recycled pulsar, and thereby complete the full timing analysis of the LOTAAS pulsar discoveries. We give an overview of the findings from the full LOTAAS sample of 76 pulsars, discussing their pulse profiles, radio spectra, and timing parameters. We found that the pulse profiles of some of the pulsars show profile variations in time or frequency, and while some pulsars show signs of scattering, a large majority display no pulse broadening. The LOTAAS discoveries have on average steeper radio spectra and longer spin periods (1.4×), as well as lower spin-down rates (3.1×) compared to the known pulsar population. We discuss the cause of these differences and attribute them to a combination of selection effects of the LOTAAS survey as well as previous pulsar surveys, though we cannot rule out that older pulsars tend to have steeper radio spectra.
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