Measurements of the diffuse Galactic synchrotron spectral index and curvature from MeerKLASS pilot data

Abstract

21 cm intensity mapping experiments are bringing an influx of high spectral resolution observational data in the similar to 100 MHz1 GHz regime. We use pilot 971-1075 MHz data from MeerKAT in single-dish mode, recently used to test the calibration and data reduction scheme of the upcoming MeerKLASS survey, to probe the spectral index of diffuse synchrotron emission below 1 GHz within 145 degrees < alpha < 180 degrees, -1 degrees < delta < 8 degrees. Through comparisons with data from the OVRO Long Wavelength Array and the Maipu and MU surveys, we find an average spectral index of -2.75 < beta < -2.71 between 45 and 1055 MHz. By fitting for spectral curvature with a spectral index of the form beta + c ln(nu/73 MHz), we measure beta = -2.55 +/- 0.13 and c = -0.12 +/- 0.05 within our target field. Our results are in good agreement (within 1s) with existing measurements from experiments such as ARCADE2 and EDGES. These results show the calibration accuracy of current data and demonstrate that MeerKLASS will also be capable of achieving a secondary science goal of probing the interstellar medium.