arXiv subjects

E. L. Escott

Publications and source records attributed to E. L. Escott.

4 recordsLinked to original sources

arXiv2026

Low-frequency VLBI with the SKA-Low

The Square Kilometre Array Observatory (SKAO) will provide unprecedented observational capabilities, revolutionizing radio astronomy in the next decade. Of particular interest for many science areas is the low-frequency component: the SKA-Low. This array, operating at frequencies between 50 and 350 MHz, will be able to observe the Southern hemisphere with an angular resolution of several arcseconds. However, many science cases demand finer angular resolutions than the current design baseline for the SKA-Low. In this chapter, we present the Low-frequency Australian Megametre-Baseline Demonstrator Array (LAMBDA) project: the construction of a several SKA-Low-like stations throughout Australia which can be employed to extend the SKA-Low's baselines to the scale of megameters. This allows LAMBDA to not only probe the scientific opportunities accessible at higher angular resolutions, but also prove the feasibility of a potential extension of the SKA-Low to such baselines. Finally, LAMBDA also serves to characterize the performance of the SKA-Low as part of a Very Long Baseline Interferometry (VLBI) network and by providing an early testbed for the calibration strategies which would be required. With LAMBDA, the SKA-Low will be able to make a major impact in many science areas, including but not limited to exoplanets, resolved active galactic nuclei (AGN), young stellar objects and supernova remnants, pulsar astrometry and scintillometry, gravitational lensing and fast radio bursts (FRBs).

astro-ph.IM↗

arXiv2025

Revealing the intricacies of radio galaxies and filaments in the merging galaxy cluster Abell 2255. II. Properties of filaments using multi-frequency radio data

In this paper, we aim to further analyze the filaments in Abell 2255 combining LOFAR data with uGMRT (1260 MHz) and VLA (1520 MHz) data to constrain the spectral shape of the filaments. This allows studying their morphological properties, required to understand their origin, at unprecedentedly high resolution (~2.3 kpc), crucial to disentangle the different cosmic ray components that populate the Original TRG. We produced a LOFAR-VLBI map at 1.5" resolution using the wide-field technique with 56 hours of observations. This was the first time this technique was used for a galaxy cluster, especially for such deep observations. uGMRT and VLA data have been calibrated and imaged to produce spectral index maps and to apply further techniques to extract additional information, such as the radiative ages of the filaments or their equipartition magnetic field. Polarization information was also obtained using VLA through the rotation measure synthesis technique. Thanks to the LOFAR-VLBI wide-field image at 144 MHz, we revealed additional, very steep ($α> 2$) filaments beyond those attached to the radio galaxy, extending for around 250 kpc and previously known as the Trail. Combining LOFAR-VLBI with uGMRT and VLA, we found integrated spectral values between 1.1-1.7 for the filaments. Spectral analysis revealed also that the Original TRG has a complex structure, showing overlapping features with distinct spectral indices that extend throughout its tail. Polarized emission emerges only from the tail and the brightest part of the filaments, with values up to $22\%$. Although there is no clear scenario regarding the formation of filaments, we highlight the importance of the Original TRG as the main driver of such structures, even at larger distances from the core.

astro-ph.CO↗

arXiv2024

WEAVE First Light Observations: Origin and Dynamics of the Shock Front in Stephan's Quintet

We present a detailed study of the large-scale shock front in Stephan's Quintet, a byproduct of past and ongoing interactions. Using integral-field spectroscopy from the new William Herschel Telescope Enhanced Area Velocity Explorer (WEAVE), recent 144 MHz observations from the LOFAR Two-metre Sky Survey (LoTSS), and archival data from the Very Large Array and James Webb Space Telescope (JWST), we obtain new measurements of key shock properties and determine its impact on the system. Harnessing the WEAVE large integral field unit's (LIFU) field of view (90 $\times$ 78 arcsec$^{2}$), spectral resolution ($R\sim2500$) and continuous wavelength coverage across the optical band, we perform robust emission line modeling and dynamically locate the shock within the multi-phase intergalactic medium (IGM) with higher precision than previously possible. The shocking of the cold gas phase is hypersonic, and comparisons with shock models show that it can readily account for the observed emission line ratios. In contrast, we demonstrate that the shock is relatively weak in the hot plasma visible in X-rays (with Mach number of $\mathcal{M} \sim 2 - 4$), making it inefficient at producing the relativistic particles needed to explain the observed synchrotron emission. Instead, we propose that it has led to an adiabatic compression of the medium, which has increased the radio luminosity ten-fold. Comparison of the Balmer line-derived extinction map with the molecular gas and hot dust observed with JWST suggests that pre-existing dust may have survived the collision, allowing the condensation of H$_{2}$ - a key channel for dissipating the shock energy.

astro-ph.GA↗

arXiv2024

Into the depths: Unveiling ELAIS-N1 with LOFAR's deepest sub-arcsecond wide-field images

We present the deepest wide-field 115-166 MHz image at sub-arcsecond resolution spanning an area of 2.5 by 2.5 degrees centred at the ELAIS-N1 deep field. To achieve this, we improved the calibration for the International LOFAR Telescope. This enhancement enabled us to efficiently process 32 hrs of data from four different 8-hr observations using the high-band antennas (HBAs) of all 52 stations, covering baselines up to approximately 2,000 km across Europe. The DI calibration was improved by using an accurate sky model and refining the series of calibration steps on the in-field calibrator, while the DD calibration was improved by adopting a more automated approach for selecting the DD calibrators and inspecting the self-calibration on these sources. We also added an additional round of self-calibration for the Dutch core and remote stations in order to refine the solutions for shorter baselines. To complement our highest resolution at 0.3", we also made intermediate resolution wide-field images at 0.6" and 1.2". Our resulting wide-field images achieve a central noise level of 14 muJy/beam at 0.3", doubling the depth and uncovering four times more objects than the Lockman Hole deep field image at comparable resolution but with only 8 hrs of data. Compared to LOFAR imaging without the international stations, we note that due to the increased collecting area and the absence of confusion noise, we reached a point-source sensitivity comparable to a 500-hr ELAIS-N1 6" image with 16 times less observing time. Importantly, we have found that the computing costs for the same amount of data are almost halved (to about 139,000 CPU hrs per 8 hrs of data) compared to previous efforts, though they remain high. Our work underscores the value and feasibility of exploiting all Dutch and international LOFAR stations to make deep wide-field images at sub-arcsecond resolution.

astro-ph.IM↗