Kavli Affiliate: Jacqueline N. Hewitt
| First 5 Authors: Pascal M. Keller, Bojan Nikolic, Nithyanandan Thyagarajan, Chris L. Carilli, Gianni Bernardi
| Summary:
Radio interferometers aiming to measure the power spectrum of the redshifted
21 cm line during the Epoch of Reionisation (EoR) need to achieve an
unprecedented dynamic range to separate the weak signal from overwhelming
foreground emissions. Calibration inaccuracies can compromise the sensitivity
of these measurements to the effect that a detection of the EoR is precluded.
An alternative to standard analysis techniques makes use of the closure phase,
which allows one to bypass antenna-based direction-independent calibration.
Similarly to standard approaches, we use a delay spectrum technique to search
for the EoR signal. Using 94 nights of data observed with Phase I of the
Hydrogen Epoch of Reionization Array (HERA), we place approximate constraints
on the 21 cm power spectrum at $z=7.7$. We find at 95% confidence that the 21
cm EoR brightness temperature is $le$(372)$^2$ "pseudo" mK$^2$ at 1.14
"pseudo" $h$ Mpc$^{-1}$, where the "pseudo" emphasises that these limits are to
be interpreted as approximations to the actual distance scales and brightness
temperatures. Using a fiducial EoR model, we demonstrate the feasibility of
detecting the EoR with the full array. Compared to standard methods, the
closure phase processing is relatively simple, thereby providing an important
independent check on results derived using visibility intensities, or related.
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