Spectral index of the Galactic foreground emission in the 50-87 MHz range

Total-power radiometry with individual meter-wave antennas is a potentially effective way to study the Cosmic Dawn (z similar to 20) through measurement of the sky brightness arising from the 21 cm transition of neutral hydrogen, provided this can be disentangled from much stronger Galactic and extra-galactic foregrounds. In the process, measured spectra of integrated sky brightness temperature can be used to quantify the foreground emission properties. In this work, we analyse a subset of data from the Large-aperture Experiment to Detect the Dark Age (LEDA) in the 50-87 MHz range and constrain the foreground spectral index beta in the northern sky visible from mid-latitudes. We focus on two zenith-directed LEDA radiometers and study how estimates of beta vary with local sidereal time (LST). We correct for the effect of gain pattern chromaticity and compare estimated absolute temperatures with simulations. We select a reference data set consisting of 14 d of observations in optimal conditions. Using this data set, we find, for one radiometer, that beta varies from -2.55 at LST