BIGHORNS - Broadband Instrument for Global HydrOgen ReioNisation Signal

Abstract

The redshifted 21cm line of neutral hydrogen (Hi), potentially observable at low radio frequencies (∼50-200 MHz), should be a powerful probe of the physical conditions of the inter-galactic medium during Cosmic Dawn and the Epoch of Reionisation (EoR). The sky-averaged Hi signal is expected to be extremely weak (∼100 mK) in comparison to the foreground of up to 10 4 K at the lowest frequencies of interest. The detection of such a weak signal requires an extremely stable, well characterised system and a good understanding of the foregrounds. Development of a nearly perfectly (∼mK accuracy) calibrated total power radiometer system is essential for this type of experiment. We present the BIGHORNS (Broadband Instrument for Global HydrOgen ReioNisation Signal) experiment which was designed and built to detect the sky-averaged Hi signal from the EoR at low radio frequencies. The BIGHORNS system is a mobile total power radiometer, which can be deployed in any remote location in order to collect radio frequency interference (RFI) free data. The system was deployed in remote, radio quiet locations in Western Australia and low RFI sky data have been collected. We present a description of the system, its characteristics, details of data analysis, and calibration. We have identified multiple challenges to achieving the required measurement precision, which triggered two major improvements for the future system.

PAPER-64 CONSTRAINTS ON REIONIZATION: THE 21 cm POWER SPECTRUM ATz= 8.4

“…So-called "global" experiments such as EDGES (Bowman & Rogers 2010), the LWA (Ellingson et al 2013), LEDA (Greenhill & Bernardi 2012;Bernardi et al 2015), DARE (Burns et al 2012), SciHi (Voytek et al 2014), BigHorns (Sokolowski et al 2015), and SARAS (Patra et al 2015) seek to measure the mean brightness temperature of 21 cm relative to the CMB background. These experiments typically rely on auto-correlations from a small number of dipole elements to access the sky-averaged 21 cm signal, although recent work is showing that interferometric cross-correlations may also be used to access the signal (Vedantham et al 2015;Presley et al 2015).…”

Modeling the Radio Foreground for Detection of CMB Spectral Distortions from the Cosmic Dawn and the Epoch of Reionization

“…Polynomials of different orders in different frequency windows were used to jointly fit and model the foreground and instrumental systematics. The BIGHORNS experiment (Sokolowski et al 2015) used a ninth-order polynomial to model the receiver noise and the Global Sky Model (GSM) of de Oliveira-Costa et al (2008), together with the simulated radiation pattern of their antenna, to estimate the foreground contribution in their data. The SCI-HI 21-cm all-sky experiment (Voytek et al 2014) also used the interpolated GSM to calibrate the foreground in their data.…”

ON THE DETECTION OF GLOBAL 21-cm SIGNAL FROM REIONIZATION USING INTERFEROMETERS

“…There are many ongoing experiments that attempt to detect the global 21-cm signal using single antenna elements: EDGES (Bowman et al 2008;Bowman & Rogers 2010), SARAS (Patra et al 2013), LEDA (Bernardi et al 2015), SCI-HI (Voytek et al 2014), and BIGHORNS (Sokolowski et al 2015). However, the detection of this signal remains unsuccessful to date because the design of a spectral radiometer with the required accuracy in calibration of systematics is a formidable challenge.…”