Combined LOFAR-uGMRT analysis of the diffuse radio emission in the massive clusters Abell 773 and Abell 1351

¹ Istituto Nazionale di Astrofisica (INAF) – Istituto di Radioastronomia (IRA), via Gobetti 101, 40129 Bologna, Italy
² Dipartimento di Fisica e Astronomia (DIFA), Universitá di Bologna, via Gobetti 93/2, 40129 Bologna, Italy
³ Istituto Nazionale di Astrofisica – Istituto di Astrofisica Spaziale e Fisica Cosmica (IASF), Via A. Corti 12, 20133 Milano, Italy
⁴ Hamburger Sternwarte, Universität Hamburg, Gojenbergsweg 112, 21029 Hamburg, Germany
⁵ Center for Radio Astronomy Techniques and Technologies, Rhodes University, Grahamstown 6140, South Africa
⁶ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands
⁷ Max-Planck-Institut für Extraterrestrische Physik (MPE), Gießenbachstraße 1, D-85748 Garching bei München, Germany
⁸ National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, S. P. Pune University Campus, Ganeshkhind, Pune 411007, India
⁹ University of Kashmir, Hazratbal, Srinagar, J&K 190006, India
¹⁰ Manipal Centre for Natural Sciences, Manipal Academy of Higher Education, Karnataka, Manipal 576104, India
¹¹ Indian Institute of Technology Indore, Indore, 453552 M.P., India

^⋆ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 31 October 2025
Accepted: 17 January 2026

Abstract

Context. Radio halos are diffuse megaparsec-scale nonthermal radio sources located at the center of galaxy clusters. They trace relativistic particles and magnetic fields in the intra-cluster medium. The source of energy for their formation is believed to be the merging of galaxy clusters, which generates turbulence and reaccelerates aged electrons.

Aims. We studied the diffuse radio emission, spectral properties, and the connection between thermal and nonthermal emission in the massive (M₅₀₀ ∼ 7 × 10¹⁴ M_⊙), dynamically disturbed galaxy clusters Abell 773 and Abell 1351.

Methods. We combined observations from the LOFAR Two-meter Sky Survey Data Release 2 at 144 MHz and the new upgraded Giant Meterwave Radio Telescope at 650 MHz for both clusters. Archival XMM-Newton X-ray images were utilized to supplement our analysis.

Results. We confirm that both clusters host a radio halo, each of which has a largest linear size of ∼2 Mpc. We measure an integrated spectral index (${\alpha }_{144}^{650}$) of ∼ − 1.0 for both clusters. Via point-to-point analysis, we show that the radio halo in A773 resembles a classical radio halo that follows a sublinear relation between radio and X-ray surface brightness. Conversely, A1351 exhibits a more complex and asymmetric radio halo that is embedded with several radio sources, including the brightest cluster galaxy, a tail galaxy, and the ridge. We find a deviation from the sublinear relation in the point-to-point analysis that is due to the presence of these contaminating radio sources.