Integrated spectrum of the radio halo. Left panel: plot of H1. The upper limit at 74 MHz is shown as a red triangle. Right panel: plot of H2. Filled blue circles highlight the measurements with good u−v coverage at short spacings; the remaining measurements are shown as filled green dots see Sect. 4.2). In both panels the weighted linear fits are shown with the same colour code and the upper limit at 74 MHz is shown as a red triangle.
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