Abstract Details

Name: Akash Kumar Patwa
Affiliation: RRI
Conference ID: ASI2020_216
Title : The 21-cm Signal Power Spectrum using Drift Scan: Correlation of Time-ordered Visibilities
Authors and Co-Authors : Akash Kumar Patwa and Shiv Sethi
Abstract Type : Oral
Abstract Category : General Relativity and Cosmology
Abstract : In the early universe the first luminous sources formed with the end of Dark ages (z~30). The UV photons from these sources ionized the IGM in their neighbourhood (30 > z > 6). The science of the formation of these sources and the ionization process are poorly understood. The redshifted 21-cm signal of the neutral hydrogen (HI) is one of the most promising probes to understand the time period of cosmic dawn (z~30) and epoch of reionization (EoR; 30 > z > 6). However, current theoretical models predict the strength of this signal (at z~8-10) about 10 mK. This is at least four orders of magnitude weaker than the foreground contamination (~300 K), e.g. point-like extragalactic radio sources, diffuse galactic synchrotron, and system noise. Detecting such a weak signal requires the stability of the system as well as novel approaches. In this work we develop an analytical formalism for drift scan observations using radio interferometers. We discern the various factors responsible for the correlation of time-ordered visibilities. Based on this formalism we analytically estimate the coherence (or decorrelation) time of the visibility correlation function. It is found to be 2-30min depending upon baseline and beam-size. We also identify how the decorrelation time varies with baseline, primary beam, and latitude of the radio interferometer. We also extend our formalism to foregrounds. While the decorrelation time of diffuse galactic synchrotron is of the same order as that of HI-signal, it is < 1 min for the point-like radio sources. These results allow us to extract the HI-signal power spectrum from EoR optimally from drift scan data without the signal loss.