Context : Some merging galaxy clusters host diffuse elongated radio sources , also called radio relics .
It is proposed that these radio relics trace shock waves in the intracluster medium ( ICM ) created during a cluster merger event .
Within the shock waves particles are accelerated to relativistic energies , and in the presence of a magnetic field synchrotron radiation will be emitted .
Here we present Giant Metrewave Radio Telescope ( GMRT ) and Westerbork Synthesis Radio Telescope ( WSRT ) observations of a new double relic in the galaxy cluster ZwCl 0008.8+5215 .

Aims : The aim of the observation is to understand the phenomenon of radio relics .

Methods : We carried out radio continuum observations at 241 and 610 MHz with the GMRT , and 1.3 - 1.8 GHz observations with the WSRT in full polarization mode .
Optical V , R , and I band images of the cluster were taken with the 2.5m Isaac Newton Telescope ( INT ) .
An optical spectrum , to determine the redshift of the cluster , was taken with the William Herschel Telescope ( WHT ) .

Results : Our observations show the presence of a double radio relic in the galaxy cluster ZwCl 0008.8+5215 , for which we find a spectroscopic redshift of z = 0.1032 \pm 0.0018 from an optical spectrum of one of the cD galaxies .
The spectral index of the two relics steepens inwards to the cluster center .
For part of the relics , we measure a polarization fraction in the range { \sim 5 - 25 \% } .
A ROSAT X-ray image displays an elongated ICM and the large-scale distribution of galaxies reveals two cluster cores , all pointing towards a binary cluster merger event .
The radio relics are located symmetrically with respect to the X-ray center of the cluster , along the proposed merger axis .
The relics have a linear extent of 1.4 Mpc and 290 kpc .
This factor of five difference in linear size is unlike that of previously known double relic systems , for which the sizes do not differ by more than a factor of two .

Conclusions : We conclude that the double relics in ZwCl 0008.8+5215 are best explained by two outward moving shock waves in which particles are ( re ) accelerated trough the diffusive shock acceleration ( DSA ) mechanism .