Detecting 21 cm EoR Signal using Drift Scans: Correlation of
Time-ordered Visibilities
A. Patwa, and S. Sethi. (2019)cite arxiv:1905.05772Comment: 22 pages and 6 figures. Submitted for publication. Comments and suggestions are welcome.
Abstract
We present a formalism to extract the EoR HI power spectrum for drift scans
using radio interferometers. Our main aim is to determine the coherence time
scale of time-ordered visibilities. We compute the two-point correlation
function of the HI visibilities measured at different times to address this
question. We determine, for a given baseline, the decorrelation of the
amplitude and the phase of this complex function. Our analysis uses primary
beams of four ongoing and future interferometers---PAPER, MWA, HERA, and
SKA1-LOW. We identify physical processes responsible for the decorrelation of
the HI signal and isolate their impact by making suitable analytic
approximations. For large beams (PAPER, MWA) and large baselines the
decorrelation is dominated by the rotation of the sky intensity pattern and is
proportional to the inverse of the primary beam. For smaller beams (HERA,
SKA1-LOW), the translation of the intensity pattern also plays an important
role. The decorrelation time of the amplitude of the correlation function lies
in the range of 2--20~minutes for baselines of interest for the extraction of
the HI signal. The phase angle of the correlation function can be made small
after scaling out an appropriate phase term, which also causes the coherence
time scale of the phase to be longer than the amplitude of the correlation
function. We find that our results are insensitive to the input HI power
spectrum and therefore they are directly applicable to the analysis of the
drift scan data. We also apply our formalism to a set of point sources and
statistically homogeneous diffuse correlated foregrounds. We find that point
sources decorrelate on a time scale much shorter than the HI signal. This
provides a novel mechanism to partially mitigate foregrounds on the plane of
the sky in a drift scan.
Description
Detecting 21 cm EoR Signal using Drift Scans: Correlation of Time-ordered Visibilities
%0 Generic
%1 patwa2019detecting
%A Patwa, Akash Kumar
%A Sethi, Shiv
%D 2019
%K library
%T Detecting 21 cm EoR Signal using Drift Scans: Correlation of
Time-ordered Visibilities
%U http://arxiv.org/abs/1905.05772
%X We present a formalism to extract the EoR HI power spectrum for drift scans
using radio interferometers. Our main aim is to determine the coherence time
scale of time-ordered visibilities. We compute the two-point correlation
function of the HI visibilities measured at different times to address this
question. We determine, for a given baseline, the decorrelation of the
amplitude and the phase of this complex function. Our analysis uses primary
beams of four ongoing and future interferometers---PAPER, MWA, HERA, and
SKA1-LOW. We identify physical processes responsible for the decorrelation of
the HI signal and isolate their impact by making suitable analytic
approximations. For large beams (PAPER, MWA) and large baselines the
decorrelation is dominated by the rotation of the sky intensity pattern and is
proportional to the inverse of the primary beam. For smaller beams (HERA,
SKA1-LOW), the translation of the intensity pattern also plays an important
role. The decorrelation time of the amplitude of the correlation function lies
in the range of 2--20~minutes for baselines of interest for the extraction of
the HI signal. The phase angle of the correlation function can be made small
after scaling out an appropriate phase term, which also causes the coherence
time scale of the phase to be longer than the amplitude of the correlation
function. We find that our results are insensitive to the input HI power
spectrum and therefore they are directly applicable to the analysis of the
drift scan data. We also apply our formalism to a set of point sources and
statistically homogeneous diffuse correlated foregrounds. We find that point
sources decorrelate on a time scale much shorter than the HI signal. This
provides a novel mechanism to partially mitigate foregrounds on the plane of
the sky in a drift scan.
@misc{patwa2019detecting,
abstract = {We present a formalism to extract the EoR HI power spectrum for drift scans
using radio interferometers. Our main aim is to determine the coherence time
scale of time-ordered visibilities. We compute the two-point correlation
function of the HI visibilities measured at different times to address this
question. We determine, for a given baseline, the decorrelation of the
amplitude and the phase of this complex function. Our analysis uses primary
beams of four ongoing and future interferometers---PAPER, MWA, HERA, and
SKA1-LOW. We identify physical processes responsible for the decorrelation of
the HI signal and isolate their impact by making suitable analytic
approximations. For large beams (PAPER, MWA) and large baselines the
decorrelation is dominated by the rotation of the sky intensity pattern and is
proportional to the inverse of the primary beam. For smaller beams (HERA,
SKA1-LOW), the translation of the intensity pattern also plays an important
role. The decorrelation time of the amplitude of the correlation function lies
in the range of 2--20~minutes for baselines of interest for the extraction of
the HI signal. The phase angle of the correlation function can be made small
after scaling out an appropriate phase term, which also causes the coherence
time scale of the phase to be longer than the amplitude of the correlation
function. We find that our results are insensitive to the input HI power
spectrum and therefore they are directly applicable to the analysis of the
drift scan data. We also apply our formalism to a set of point sources and
statistically homogeneous diffuse correlated foregrounds. We find that point
sources decorrelate on a time scale much shorter than the HI signal. This
provides a novel mechanism to partially mitigate foregrounds on the plane of
the sky in a drift scan.},
added-at = {2019-05-16T04:09:14.000+0200},
author = {Patwa, Akash Kumar and Sethi, Shiv},
biburl = {https://www.bibsonomy.org/bibtex/239f9468c9dd7b5631e85dcec4409adaa/gpkulkarni},
description = {Detecting 21 cm EoR Signal using Drift Scans: Correlation of Time-ordered Visibilities},
interhash = {d720b447fa43d2fdae2df3414f7ad086},
intrahash = {39f9468c9dd7b5631e85dcec4409adaa},
keywords = {library},
note = {cite arxiv:1905.05772Comment: 22 pages and 6 figures. Submitted for publication. Comments and suggestions are welcome},
timestamp = {2019-05-16T04:09:14.000+0200},
title = {Detecting 21 cm EoR Signal using Drift Scans: Correlation of
Time-ordered Visibilities},
url = {http://arxiv.org/abs/1905.05772},
year = 2019
}