| Authors : | RAMANANDA SANTRA1, RUTA KALE1, SIMONA GIACINTUCCI2, MAXIM MARKEVITCH3, FEDERICO DE. LUCA4,5, HERVE BOURDIN4,5, TIZIANA VENTURI6, DANIELE DALLACASA7, ROSELLA CASSANO6, GIANFRANCO BRUNETTI6, KAUSHAL BUCH8 |
| Authors Affiliation: | 1 RAMANANDA SANTRA, RUTA KALE Affiliation (National Centre for Radio Astrophysics, Tata Institute of Fundamental Research, Pune-411007, India)
2 SIMONA GIACINTUCCI Affiliation (Naval Research Laboratory, 4555 Overlook Avenue SW, Code 7213, Washington, DC 20375, USA)
3 MAXIM MARKEVITCH Affiliation (NASA/Goddard Space Flight Center, Greenbelt, MD 20771, USA)
4 FEDERICO DE.LUCA, HERVE BOURDIN Affiliation (Dipartimento di Fisica, Università di Roma Tor Vergata, Via della Ricerca Scientifica 1, I-00133 Roma, Italy)
5 FEDERICO DE.LUCA, HERVE BOURDIN Affiliation (INFN, Sezione di Roma 2, Università di Roma Tor Vergata, Via della Ricerca Scientifica, 1, Roma, Italy)
6 TIZIANA VENTURI, ROSELLA CASSANO, GIANFRANCO BRUNETTI Affiliation (INAF - IRA, Via Gobetti 101, I-40129 Bologna, Italy; IRA - INAF, via P. Gobetti 101, I-40129 Bologna, Italy)
7 DANIELE DALLACASA Affiliation (Dipartimento di Fisica e Astronomia, Università di Bologna, via P. Gobetti 93/2, 40129, Bologna, Italy)
8 KUSHAL BUCH Affiliation (Digital Backend Group, Giant Metrewave Radio Telescope, NCRA-TIFR, Pune, 410504, India) |
| Abstract : | Radio relics and halos are diffuse radio emissions originating from galaxy clusters, providing crucial insights into the energetic processes due to dynamical activities occurring over billions of years within the intracluster medium (ICM). This study illustrates the first comprehensive analysis of the ultra-steep spectrum radio halo in the Abell 521, leveraging data from the Upgraded Giant Metrewave Radio Telescope (uGMRT) in conjunction with archival Chandra and XMM Newton data (Santra et al. under review, APJ). This unique dataset allows us to investigate complex physical mechanisms in unprecedented detail for the first time. Our in-depth analysis unveils a second relic (~ 650 kpc) opposite the previous one and a faint extension of the previous relic of approximately ~ 1 Mpc, as evident in both frequency images. The radio emission from the halo conforms well to a single power-law spectrum with a spectral index of -1.86 ± 0.12, while the new relic exhibits an spectral index of -1.34 ± 0.03. The resolved spectral map of the halo highlights radial steepening in the outer regions and spatial fluctuations at 100 kpc scale, indicative of an in-homogenous turbulent re-acceleration process. Despite the complex, elongated structure of the halo, its morphology closely mirrors the X-ray surface brightness, highlighting the intricate interplay between thermal gas and non-thermal plasma. Our analysis also establishes a sublinear correlation between radio surface brightness and X-ray emission for all parts of the radio halo. Utilizing available multi-wavelength data, we propose a binary merger scenario between the Northern and Southern subclusters along the SE-NW axis, leading to the propagation of two shock waves and the induction of turbulence in the radio halo regions. |
