A5010292524- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Galaxies: Formation, Evolution, Phenomena
- Radio Wave Propagation Studies
- Antenna Design and Optimization
- Superconducting and THz Device Technology
- Soil Moisture and Remote Sensing
- Solar and Space Plasma Dynamics
- Gyrotron and Vacuum Electronics Research
- Gamma-ray bursts and supernovae
- Scientific Research and Discoveries
- Dark Matter and Cosmic Phenomena
- Atmospheric Ozone and Climate
- Particle Accelerators and Free-Electron Lasers
- Microwave Engineering and Waveguides
- Pulsed Power Technology Applications
- Geophysics and Gravity Measurements
- Pulsars and Gravitational Waves Research
- Astrophysical Phenomena and Observations
- Astronomical Observations and Instrumentation
- Seismic Imaging and Inversion Techniques
- Particle accelerators and beam dynamics
- Ionosphere and magnetosphere dynamics
- Astronomy and Astrophysical Research
- Astrophysics and Star Formation Studies
University of Johannesburg
2024
University of the Western Cape
2017-2024
Indian Institute of Technology Madras
2024
South African Radio Astronomy Observatory
2020
SKA Telescope, South Africa
2017-2019
University of Groningen
2013-2017
Indian Institute of Technology Kharagpur
2010-2014
Astronomy and Space
2014
University of Maryland, College Park
1999
Institute of Terrestrial Magnetism Ionosphere and Radio Wave Propagation
1985
We present the first limits on Epoch of Reionization 21 cm H i power spectra, in redshift range z = 7.9–10.6, using Low-Frequency Array (LOFAR) High-Band Antenna (HBA). In total, 13.0 hr data were used from observations centered North Celestial Pole. After subtraction sky model and noise bias, we detect a non-zero (1-σ) excess variance best 2-σ upper limit at k 0.053 h cMpc−1 9.6–10.6. The decreases when optimizing smoothness direction- frequency-dependent gain calibration, with increasing...
ABSTRACT A new upper limit on the 21 cm signal power spectrum at a redshift of z ≈ 9.1 is presented, based 141 h data obtained with Low-Frequency Array (LOFAR). The analysis includes significant improvements in spectrally smooth gain-calibration, Gaussian Process Regression (GPR) foreground mitigation and optimally weighted inference. Previously seen ‘excess power’ due to spectral structure gain solutions has markedly reduced but some excess still remains correlation distinct from thermal...
Foreground removal is a major challenge for detecting the redshifted 21 cm neutral hydrogen (H i) signal from Epoch of Reionization. We have used 150 MHz Giant Metrewave Radio Telescope observations to characterize statistical properties foregrounds in four different fields view. The measured multifrequency angular power spectrum Cℓ(Δν) found values range 104–2 × 104 mK2 across 700 ≤ ℓ 2 and Δν 2.5 MHz, which consistent with model predictions where point sources are most dominant foreground...
ABSTRACT Observations of the redshifted 21-cm hyperfine line neutral hydrogen from early phases Universe such as Cosmic Dawn and Epoch Reionization promise to open a new window onto formation stars galaxies. We present first upper limits on power spectrum brightness temperature fluctuations in redshift range z = 19.8–25.2 (54–68 MHz frequency range) using 14 h data obtained with LOFAR-Low Band Antenna (LBA) array. also demonstrate application multiple pointing calibration technique calibrate...
Detecting and characterizing the Epoch of Reionization (EoR) Cosmic Dawn via redshifted 21-cm hyperfine line neutral hydrogen will revolutionize study formation first stars, galaxies, black holes, intergalactic gas in infant Universe. The wealth information encoded this signal is, however, buried under foregrounds that are many orders magnitude brighter. These must be removed accurately precisely order to reveal feeble signal. This requires not only modelling Galactic extragalactic emission,...
ABSTRACT We derive constraints on the thermal and ionization states of intergalactic medium (IGM) at redshift ≈ 9.1 using new upper limits 21-cm power spectrum measured by LOFAR radio telescope a prior ionized fraction that estimated from recent cosmic microwave background (CMB) observations. have used results reionization simulation code grizzly Bayesian inference framework to constrain parameters which describe physical state IGM. find that, if gas heating remains negligible, an IGM with...
ABSTRACT The ARCADE2 and LWA1 experiments have claimed an excess over the cosmic microwave background (CMB) at low radio frequencies. If cosmological high-redshift contribution to this is between 0.1 per cent 22 of CMB 1.42 GHz, it could explain tentative EDGES low-band detection anomalously deep absorption in 21-cm signal neutral hydrogen. We use upper limit on from Epoch Reionization (z = 9.1) based 141 h observations with LOFAR evaluate Universe detected background. Marginalizing...
Abstract This paper presents the design and deployment of Hydrogen Epoch Reionization Array (HERA) phase II system. HERA is designed as a staged experiment targeting 21 cm emission measurements Reionization. First results from I array are published early 2022, system nearing completion. We describe discuss progress on commissioning future upgrades. As designated Square Kilometre pathfinder instrument, we also show number “case studies” that investigate systematics seen while system, which...
This study aims to characterize linear polarization structures in LOFAR observations of the interstellar medium (ISM) 3C196 field, one primary fields LOFAR-Epoch Reionization key science project. We have used high band antennas (HBA) image this region and Rotation Measure (RM) synthesis unravel distribution polarized Faraday depth. The brightness temperature detected Galactic emission is $5-15~{\rm K}$ intensity covers range from -3 +8 ${\rm rad~m^{-2}}$ most interesting morphological...
This study aims to characterise the polarized foreground emission in ELAIS-N1 field and address its possible implications for extraction of cosmological 21-cm signal from Low-Frequency Array - Epoch Reionization (LOFAR-EoR) data. We use high band antennas LOFAR image this region RM-synthesis unravel structures at Galactic latitudes. The brightness temperature detected is on average 4 K intensity covers range -10 +13rad m^-2 Faraday depth. total polarization angle show a wide morphological...
Detection of the 21-cm signal coming from epoch reionization (EoR) is challenging especially because, even after removing foregrounds, residual Stokes I maps contain leakage polarized emission that can mimic signal. Here, we discuss instrumental polarization Low Frequency Array (LOFAR) and present realistic simulations leakages between parameters. From LOFAR observations in 3C196 field, have quantified level caused by nominal model beam LOFAR, compared it with EoR using power spectrum...
ABSTRACT Using the latest upper limits on 21-cm power spectrum at z ≈ 9.1 from Low Frequency Array (LOFAR), we explore regions of parameter space which are inconsistent with data. We use 21cmmc, a Monte Carlo Markov chain sampler 21cmfast directly forward models three dimensional (3D) cosmic signal in fully Bayesian framework. astrophysical parametrization 21cmfast, includes mass-dependent star formation rates and ionizing escape fractions as well soft-band X-ray luminosities to place...
LOFAR is the LOw Frequency Radio interferometer ARray located at mid-latitude ($52^{\circ} 53'N$). Here, we present results on ionospheric structures derived from 29 nighttime observations during winters of 2012/2013 and 2013/2014. We show that able to determine differential TEC values with an accuracy better than 1 mTECU over distances ranging between 100 km. For all power law behavior phase structure function confirmed a long range baseline lengths, $1$ $80$ km, slope in general larger...
Several experiments are underway to detect the cosmic redshifted 21-cm signal from neutral hydrogen Epoch of Reionization (EoR). Due their very low signal-to-noise ratio, these observations aim for a statistical detection by measuring its power spectrum. We investigate extraction variance as first step towards detecting and constraining global history EoR. Signal is integral signal's spectrum, it expected be measured with high significance. demonstrate this through results simulation...
We compare various foreground removal techniques that are being utilised to remove bright foregrounds in experiments aiming detect the redshifted 21cm signal of neutral hydrogen from Epoch Reionization. In this work, we test performance (FastICA, GMCA, and GPR) on 10 nights LOFAR data investigate possibility recovering latest upper limit signal. Interestingly, find GMCA FastICA reproduce most recent 2$\sigma$ $\Delta^2_{21} <$ (73)$^2$ mK$^2$ at $k=0.075~ h \mathrm{cMpc}^{-1}$, which...
We present two estimators to quantify the angular power spectrum of sky signal directly from visibilities measured in radio interferometric observations. This is relevant for both foregrounds and cosmological 21-cm buried therein. The discussion here restricted Galactic synchrotron radiation, most dominant foreground component after point source removal. Our theoretical analysis validated using simulations at 150 MHz, mainly GMRT also briefly LOFAR. Bare Estimator uses pairwise correlations...
Foreground removal is a challenge for 21-cm tomography of the high redshift Universe. We use archival GMRT data (obtained completely different astronomical goals) to estimate foregrounds at ~ 1. The statistic we cross power spectrum between two frequencies separated by \Delta{\nu} angular multipole l, or equivalently multi-frequency C_l(\Delta{\nu}). An earlier measurement C_l(\Delta{\nu}) using this had revealed presence oscillatory patterns along \Delta{\nu}, which turned out be severe...
We present the improved visibility based Tapered Gridded Estimator (TGE) for power spectrum of diffuse sky signal. The visibilities are gridded to reduce computation, and tapered through a convolution suppress contribution from outer regions telescope's field view. TGE also internally estimates noise bias, subtracts this out give an unbiased estimate spectrum. An earlier version 2D angular $C_{\ell}$ is then extended obtain 3D $P({\bf k})$ 21-cm brightness temperature fluctuations. Analytic...
The redshifted 21-cm signal from neutral hydrogen (H i) is an important future probe of the high-redshift Universe. We have analysed 610 MHz Giant Metrewave Radio Telescope (GMRT) observations towards detecting this z= 1.32. multi-frequency angular power spectrum Cℓ(Δν) used to characterize statistical properties background radiation across scales ∼20 arcsec 10 arcmin, and a frequency bandwidth 7.5 with resolution 125 kHz. measured which ranges 7 18 mK2 dominated by foregrounds, expected H i...
It is important to correctly subtract point sources from radio-interferometric data in order measure the power spectrum of diffuse radiation like Galactic synchrotron or Epoch Reionization 21-cm signal. computationally very expensive and challenging image a large area accurately all image. The problem particularly severe at sidelobes outer parts main lobe where antenna response highly frequency dependent calibration also differs that phase centre. Here, we show it possible overcome this by...
Leakage of diffuse polarized emission into Stokes I caused by the primary beam instrument might mimic spectral structure 21-cm signal coming from epoch reionization (EoR) making their separation difficult. Therefore, understanding polarimetric performance antenna is crucial for a successful detection EoR signal. Here, we have calculated accuracy nominal model LOFAR in predicting leakage to Q, U comparing them with corresponding compact sources actually observed 3C295 field. We found that has...
The 21 cm-galaxy cross-power spectrum is expected to be one of the promising probes Epoch Reionization (EoR), as it could offer information about progress reionization and typical scale ionized regions at different redshifts. With upcoming observations cm emission from EoR with Low Frequency Array (LOFAR), high-redshift Ly α emitters Subaru's Hyper Suprime-Cam (HSC), we investigate observability such these two instruments, which are both planning observe ELAIS-N1 field z = 6.6. In this...