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$\begin{figure} \par\includegraphics[width=13cm,clip]{9459fig1.eps}\end{figure}$ Figure 1: GMRT 327 MHz contours of the $30^{\prime } \times 30^{\prime }$ region containing A 521. Contour levels are spaced by a factor 2 starting from $5\sigma =\pm 0.5$ mJy b^-1. The resolution is $10.6^{\prime \prime } \times 9.6^{\prime \prime }$ , in PA $-19^{\circ }$ . The cross marks the X-ray centre of the cluster (Arnaud et al. 2000). The radius of the solid circle corresponds to the cluster virial radius $R_{\rm v}=2.8$ Mpc (GVB06). The dashed circle has a radius of $\sim$ 1 Mpc, and indicates the region covered by the optical analysis in Ferrari et al. (2003).
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In the text

$\begin{figure} \par\includegraphics[width=7.8cm,clip]{9459fig2a.eps}\hspace*{4mm} \includegraphics[width=7.8cm,clip]{9459fig2b.eps}\end{figure}$ Figure 2: Left panel: full resolution GMRT contours at 327 MHz of the relic, overlaid on the red POSS-2 optical image. The resolution is $10.6^{\prime \prime } \times 9.6^{\prime \prime }$ , in PA $-19^{\circ }$ . Contours are spaced by a factor 2 starting from $\pm$ $3\sigma =0.27$ mJy b^-1. A, B and C indicate the position of the radio galaxies embedded in the relic emission. Right panel: low resolution GMRT image at 327 MHz of the relic (contours and grey scale). The resolution is $15.0^{\prime \prime } \times 12.0^{\prime \prime }$ , in PA 0 $^{\circ }$ . Contours are spaced by a factor 2 starting from $\pm$ $3\sigma =0.27$ mJy b^-1.
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In the text

$\begin{figure} \par\includegraphics[width=13cm,clip]{9459fig3.eps}\end{figure}$ Figure 3: Panel a) GMRT 610 MHz full resolution contours of the relic on the POSS-2 image. The HPBW is $5.0^{\prime \prime } \times 4.0^{\prime \prime }$ . The 1 $\sigma$ noise level is 40 $\mu$ Jy b^-1. A, B and C indicate the position of radio galaxies embedded in the relic emission. Panel b) VLA-CnB 4.9 GHz contours of J0454-1016a on the POSS-2; ${\it HPBW}=4.0^{\prime \prime } \times 2.0^{\prime \prime }$ ; 1 $\sigma=15~\mu$ Jy b^-1. Panel c) VLA-BnA 4.9 GHz image (contours and grey scale) of J0454-1016a; ${\it HPBW}=1.0^{\prime \prime } \times 0.8^{\prime \prime }$ ; 1 $\sigma =10$ $\mu$ Jy b^-1. Panel d) VLA-BnA 8.4 GHz image (contours and grey scale) of J0454-1016a. ${\it HPBW}=0.6^{\prime \prime } \times 0.5^{\prime \prime }$ ; 1 $\sigma=8~\mu$ Jy b^-1. In all the panels, the contour levels are spaced by a factor 2 starting from a significance level $\pm$ 3 $\sigma$ .
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{9459fig4.eps}\end{figure}$ Figure 4: Integrated radio spectrum of J0454-1016a between 327 MHz and 8.5 GHz. The solid line is the best fit of the CI model to the data. The value of $\alpha _{\rm inj}$ provided by the fit, along with the reduced $\chi ^2$ , is also reported.
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In the text

$\begin{figure} \par\includegraphics[width=14cm,clip]{9459fig5.eps}\end{figure}$ Figure 5: VLA 4.9 GHz image of the radio relic as contours ( left panel), and grey scale on the GMRT 610 MHz image ( right panel). The resolution of the 4.9 GHz image is $22.0^{\prime \prime } \times 15.0^{\prime \prime }$ , and the 1 $\sigma$ noise level is 15 $\mu$ Jy b^-1. The resolution of the 610 MHz image is $13.1^{\prime \prime } \times 8.1^{\prime \prime }$ , and the 1 $\sigma$ noise level is 40 $\mu$ Jy b^-1. The radio contours are spaced by a factor 2, starting from $\pm$ 0.045 mJy b^-1 and $\pm$ 0.012 mJy b^-1 at 4.9 GHz ( left panel) and 610 MHz ( right panel), respectively.
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In the text

$\begin{figure} \par\includegraphics[angle=0,width=6.5cm,clip]{9459fig6.eps}\end{figure}$ Figure 6: Spectral image of the relic in A 521 in the 327-610 MHz range, with the GMRT 610 MHz contours at levels 0.12, 0.24, 0.48, 0.96, 2, 4 mJy b^-1 overlaid. In both images (spectral index and total intensity) the resolution is $15^{\prime \prime } \times 12^{\prime \prime }$ , PA 0 $^{\circ }$ , as shown by the ellipse in the upper-left corner of the image. A, B and C indicate the position of radio galaxies embedded in the relic emission (see Figs. 2 and 3).
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In the text

$\begin{figure} \par\mbox{\includegraphics[angle=0,width=6.6cm,clip]{9459fig7a.ep... ...ce{4mm} \includegraphics[angle=0,width=6.6cm,clip]{9459fig7b.eps} } \end{figure}$ Figure 7: Left - Grids used to derive the spectral index trend overlaid on the 327-610 MHz spectral index image (grey scale; same as Fig. 6). Right - Trend of the spectral index $\alpha ^{610}_{327}$ in the northern (filled triangles) and southern (empty triangles) parts of the relic.
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In the text

$\begin{figure} \par\includegraphics[angle=0,width=7.5cm,clip]{9459fig8.eps}\end{figure}$ Figure 8: Radio spectrum of the radio relic between 74 MHz and 4.9 GHz. The solid circle is the relic flux density measured on the new GMRT image at 327 MHz. The empty triangles represent the 610 MHz data point from GVB06, and the 1.4 GHz value from VLA archival data. The solid triangle is the source flux density measured on the new VLA image at 4.9 GHz. The empty circle is the flux density from a preliminary GMRT image at 235 MHz (see Appendix). The empty square is the 74 MHz flux density from the VLSS image. The solid line represents the linear fit to the data by using the points between 235 MHz and 4.9 GHz.
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In the text

$\begin{figure} \par\mbox{\includegraphics[angle=0,width=7.4cm,clip]{9459fig9a.ep... ...{0.5cm} \includegraphics[angle=0,width=7.4cm,clip]{9459fig9b.eps} } \end{figure}$ Figure 9: Left panel - Smoothed Chandra image of A 521 in the 0.5-4 keV energy band. Right panel - Same image as left panel with the GMRT 610 MHz contours of the A 521 field overlaid. The resolution of the radio image is 13.1 $^{\prime \prime } \times 8.1^{\prime \prime }$ , PA 56 $^{\circ }$ . Contour levels are spaced by a factor 2 starting from 0.2 mJy b^-1.
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In the text

$\begin{figure} \par\mbox{\includegraphics[angle=0,width=7.3cm,clip]{9459fig10a.e... ...0.5cm} \includegraphics[angle=0,width=6.9cm,clip]{9459fig10b.eps} } \end{figure}$ Figure 10: Left panel: X-ray 0.5-4.0 keV brighntess profile across the edge in the relic region, extracted in the sector indicated in the left panel of Fig. 9. Error bars are $1\sigma$ . Right panel: X-ray 0.5-4.0 keV brightness profiles extracted in sectors covering the South-West (blue), North-East (red) and North-West (green) portions of the cluster. Error bars are $1\sigma$ .
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In the text

$\begin{figure} \par\includegraphics[angle=0,width=7.4cm,clip]{9459fig11.eps}\end{figure}$ Figure 11: X-ray brighntess profile (same as left panel of Fig. 10) compared to different models. The green and red lines are the fit with and without a shock discontinuity, respectively. The blue line is the profile expected for a shock with M=2.3.
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In the text

$\begin{figure} \par\includegraphics[angle=0,width=6.5cm,clip]{9459figA1.eps}\end{figure}$ Figure A.1: Preliminary GMRT image (contours and grey scale) of radio relic at 235 MHz. The resolution is 15.6 $^{\prime \prime } \times 12.4^{\prime \prime }$ , in PA 56. The noise level is 1 $\sigma =270~\mu$ J b^-1. Contours are spaced by a factor 2 starting from $\pm$ $3 \sigma$ .
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In the text

$\begin{figure} \par\includegraphics[width=7.5cm,clip]{9459fig4.eps}\end{figure}$	Figure 4: Integrated radio spectrum of J0454-1016a between 327 MHz and 8.5 GHz. The solid line is the best fit of the CI model to the data. The value of $\alpha _{\rm inj}$ provided by the fit, along with the reduced $\chi ^2$ , is also reported.
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$\begin{figure} \par\mbox{\includegraphics[angle=0,width=6.6cm,clip]{9459fig7a.ep... ...ce{4mm} \includegraphics[angle=0,width=6.6cm,clip]{9459fig7b.eps} } \end{figure}$	Figure 7: Left - Grids used to derive the spectral index trend overlaid on the 327-610 MHz spectral index image (grey scale; same as Fig. 6). Right - Trend of the spectral index $\alpha ^{610}_{327}$ in the northern (filled triangles) and southern (empty triangles) parts of the relic.
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$\begin{figure} \par\mbox{\includegraphics[angle=0,width=7.4cm,clip]{9459fig9a.ep... ...{0.5cm} \includegraphics[angle=0,width=7.4cm,clip]{9459fig9b.eps} } \end{figure}$	Figure 9: Left panel - Smoothed Chandra image of A 521 in the 0.5-4 keV energy band. Right panel - Same image as left panel with the GMRT 610 MHz contours of the A 521 field overlaid. The resolution of the radio image is 13.1 $^{\prime \prime } \times 8.1^{\prime \prime }$ , PA 56 $^{\circ }$ . Contour levels are spaced by a factor 2 starting from 0.2 mJy b^-1.
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$\begin{figure} \par\mbox{\includegraphics[angle=0,width=7.3cm,clip]{9459fig10a.e... ...0.5cm} \includegraphics[angle=0,width=6.9cm,clip]{9459fig10b.eps} } \end{figure}$	Figure 10: Left panel: X-ray 0.5-4.0 keV brighntess profile across the edge in the relic region, extracted in the sector indicated in the left panel of Fig. 9. Error bars are $1\sigma$ . Right panel: X-ray 0.5-4.0 keV brightness profiles extracted in sectors covering the South-West (blue), North-East (red) and North-West (green) portions of the cluster. Error bars are $1\sigma$ .
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$\begin{figure} \par\includegraphics[angle=0,width=7.4cm,clip]{9459fig11.eps}\end{figure}$	Figure 11: X-ray brighntess profile (same as left panel of Fig. 10) compared to different models. The green and red lines are the fit with and without a shock discontinuity, respectively. The blue line is the profile expected for a shock with M=2.3.
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$\begin{figure} \par\includegraphics[angle=0,width=6.5cm,clip]{9459figA1.eps}\end{figure}$	Figure A.1: Preliminary GMRT image (contours and grey scale) of radio relic at 235 MHz. The resolution is 15.6 $^{\prime \prime } \times 12.4^{\prime \prime }$ , in PA 56. The noise level is 1 $\sigma =270~\mu$ J b^-1. Contours are spaced by a factor 2 starting from $\pm$ $3 \sigma$ .
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