The cluster 1RXS J0603.3+4214 is a merging galaxy cluster that hosts three radio relics and a giant radio halo .
The northern relic , the Toothbrush , is 1.9-Mpc long and has an unusual linear morphology .
According to simple diffusive shock acceleration theory , its radio spectral index indicates a Mach number of 3.3 - 4.6 .
Here , we present results from a deep XMM-Newton observation of the cluster .
We observe two distinct cluster cores that have survived the merger .
The presence of three shocks at or near the locations of the radio relics is confirmed by density and temperature discontinuities .
However , the observation poses several puzzles that challenge our understanding of radio relics : ( i ) at the Toothbrush , the shock Mach number is not larger than 2 , in apparent conflict with the shock strength predicted from the radio spectrum ; ( ii ) at the Toothbrush , the shock front is , in part , spatially offset from the radio emission ; ( iii ) at the eastern relic , we detect a temperature jump corresponding to a Mach number of approximately 2.5 , but there is no associated surface brightness discontinuity .
We discuss possible explanations for these findings .