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We study diffuse radio emission in the galaxy cluster A1550, with the aim ofconstraining particle re-acceleration in the intra-cluster medium. We exploitobservations at four different frequencies: 54, 144, 400 and 1400 MHz. Tocomplement our analysis, we make use of archival Chandra X-ray data. At allfrequencies we detect an ultra-steep spectrum radio halo ($S_\nu \propto\nu^{-1.6}$) with an extent of 1.2 Mpc at 54 MHz. Its morphology follows thedistribution of the thermal intra-cluster medium inferred from the Chandraobservation. West of the centrally located head-tail radio galaxy, we detect aradio relic with projected extent of 500 kpc. From the relic, a 600 kpc longbridge departs and connect it to the halo. Between the relic and the radiogalaxy, we observe what is most likely a radio phoenix, given its curvedspectrum. The phoenix is connected to the tail of the radio galaxy through twoarms, which show a nearly constant spectral index for 300 kpc. The halo couldbe produced by turbulence induced by a major merger, with its axis lying in theNE-SW direction. This is supported by the position of the relic, whose origincould be attributed to a shock propagating along the merger axis. It ispossible that the same shock has also produced the phoenix through adiabaticcompression, while the bridge could be generated by electrons which werepre-accelerated by the shock, and then re-accelerated by turbulence. Finally,we detect hints of gentle re-energisation in the two arms which depart from thetail of the radio galaxy.

Particle re-acceleration and diffuse radio sources in the galaxy cluster Abell 1550