uGMRT sub-GHz view of the Sausage cluster diffuse emission: a textbook example of a double radio relic system

Majidul Rahaman^1*, Ramij Raja⁴, Hsiang-Yi Karen Yang^1,2,3

¹Institute of Astronomy, National Tsing Hua University, Hsinchu City, Taiwan
²Physics Division, National Center for Theoretical Sciences, Taipei, Taiwan
³Department of Physics, National Tsing Hua University, Hsinchu City, Taiwan
⁴Department of Physics and Electronics, Rhodes University, Makhanda, South Africa

* Presenter:Majidul Rahaman, email:rmajidul@gmail.com

CIZA J2242.8+5301, popularly known as the Sausage cluster, is a textbook example of double radio relics formed in a massive cluster merger. Using the upgraded Giant Metrewave Radio Telescope (uGMRT) at Band 3 (400–850 MHz) and Band 4 (550–950 MHz), we present new sub-GHz observations that reveal several previously unresolved morphological features in its diffuse radio emission. In the northern relic, we observe a clear variation in the spectral index across the relic width, possibly reflecting a decrease in downstream cooling rate from east to west. We re-confirm the presence of an additional ∼930 kpc relic and classify a filamentary downstream source as a narrow-angle-tail (NAT) radio galaxy. The eastern relic exhibits fine substructures in its spectral index profile, suggesting the presence of multiple filaments or shock fronts. In the southern region, we identify an ‘L’-shaped NAT galaxy embedded within a ∼1.1 Mpc relic and confirm a faint southern extension, extending the total relic length to ∼1.8 Mpc. Based on the morphological symmetry between the northern and southern relics, we propose a schematic merger-shock scenario to explain their origin. These results demonstrate the power of uGMRT to probe complex radio morphology and shock structures in merging clusters.

Keywords: Galaxy Cluster, cluster of galaxies, Sausage cluster, Multi-wavelength Astronomy