B. K. Gehlot
A5033184981- Radio Astronomy Observations and Technology
- Astrophysics and Cosmic Phenomena
- Superconducting and THz Device Technology
- Radio Wave Propagation Studies
- Antenna Design and Optimization
- Galaxies: Formation, Evolution, Phenomena
- Astronomy and Astrophysical Research
- Particle Accelerators and Free-Electron Lasers
- Soil Moisture and Remote Sensing
- Gyrotron and Vacuum Electronics Research
- Astronomical Observations and Instrumentation
- Gamma-ray bursts and supernovae
- Millimeter-Wave Propagation and Modeling
- Scientific Research and Discoveries
- Pulsed Power Technology Applications
- Microwave Engineering and Waveguides
- GNSS positioning and interference
- Pulsars and Gravitational Waves Research
- Geophysics and Gravity Measurements
- Hydraulic flow and structures
- Particle accelerators and beam dynamics
- Electromagnetic Compatibility and Measurements
- Geophysics and Sensor Technology
- Dark Matter and Cosmic Phenomena
- Water Systems and Optimization
Arizona State University
2019-2025
University of Groningen
2016-2024
University of Pennsylvania
2024
Astronomical Institute of the Slovak Academy of Sciences
2022
Astronomy and Space
2019
Maulana Azad National Institute of Technology
2014
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...
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...
The redshifted 21 cm line of neutral hydrogen is a promising probe the Epoch Reionization (EoR). However, its detection requires thorough understanding and control systematic errors. We study two biases observed in LOFAR EoR residual data after calibration subtraction bright discrete foreground sources. first effect suppression diffuse foregrounds, which could potentially mean signal. second an excess noise beyond thermal noise. shows fluctuations on small frequency scales, hence it can not...
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...
The redshifted 21 cm signal from neutral hydrogen is a direct probe of the physics early universe and has been an important science driver many present upcoming radio interferometers. In this study we use single night observations with New Extension in Nançay Upgrading LOFAR (NenuFAR) to place upper limits on power spectrum cosmic dawn at redshift z = 20.3. NenuFAR new low-frequency interferometer, operating 10–85 MHz frequency range, currently under construction Radio Observatory France. It...
Studying the redshifted 21-cm signal from neutral hydrogen during Epoch of Reionisation and Cosmic Dawn is fundamental for understanding physics early universe. One challenges that experiments face contamination by bright foreground sources, such as Cygnus,A, which accurate spatial spectral models are needed to minimise residual after their removal. In this work, we develop a new, high-resolution model Cygnus,A using Low Frequency Array (LOFAR) observations in 110--250,MHz range, improving...
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...
Abstract The precise characterization and mitigation of systematic effects is one the biggest roadblocks impeding detection fluctuations cosmological 21 cm signals. Missing data in radio experiments, often due to frequency interference (RFI), pose a particular challenge power spectrum analysis as this could lead ringing bright foreground modes Fourier space, heavily contaminating Here we show that problem missing becomes even more arduous presence effects. Using realistic numerical...
ABSTRACT Detection of the faint 21 cm line emission from Cosmic Dawn and Epoch Reionization will require not only exquisite control over instrumental calibration systematics to achieve necessary dynamic range observations but also validation analysis techniques demonstrate their statistical properties signal loss characteristics. A key ingredient in achieving this is ability perform high-fidelity simulations kinds data that are produced by large, many-element, radio interferometric arrays...
The 21-cm absorption feature reported by the EDGES collaboration is several times stronger than that predicted traditional astrophysical models. If genuine, a deeper may lead to fluctuations on signal degree scales (up 1~Kelvin in rms), allowing these be detectable nearly 50~times shorter integration compared previous predictions. We commenced "AARTFAAC Cosmic Explorer" (ACE) program, employs AARTFAAC wide-field imager, measure or set limits power spectrum of redshift range $z = 17.9-18.6$...
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...
Leakage of polarized Galactic diffuse emission into total intensity can potentially mimic the 21-cm signal coming from epoch reionization (EoR), as both them might have fluctuating spectral structure. Although we are sensitive to EoR only in small fields view, chromatic side-lobes further away contaminate inner region. Here, explore effects leakage 'EoR window' cylindrically averaged power spectra (PS) within wide view using observation and simulation 3C196 North Celestial Pole (NCP) fields,...
The Dark Ages and Cosmic Dawn are largely unexplored windows on the infant Universe (z ~ 200-10). Observations of redshifted 21-cm line neutral hydrogen can provide valuable new insight into fundamental physics astrophysics during these eras that no other probe provide, drives design many future ground-based instruments such as Square Kilometre Array (SKA) Hydrogen Epoch Reionization (HERA). We review progress in field high-redshift Cosmology, particular focussing what questions be addressed...
Contamination due to foregrounds (Galactic and Extra-galactic), calibration errors ionospheric effects pose major challenges in detection of the cosmic 21 cm signal various Epoch Reionization (EoR) experiments. We present results a pilot study field centered on 3C196 using LOFAR Low Band (56-70 MHz) observations, where we quantify wide such as gain errors, polarized foregrounds, effects. observe `pitchfork' structure 2D power spectrum intensity delay-baseline space, which leaks into modes...
The key challenge in the observation of redshifted 21-cm signal from cosmic reionization is its separation much brighter foreground emission. Such relies on different spectral properties two components, although, real life, intrinsic spectrum often corrupted by instrumental response, inducing systematic effects that can further jeopardize measurement signal. In this paper, we use Gaussian Process Regression to model both emission and systematics $\sim 2$ hours data Hydrogen Epoch...
We investigate systematic effects in direction dependent gain calibration the context of Low-Frequency Array (LOFAR) 21-cm Epoch Reionization (EoR) experiment. The LOFAR EoR Key Science Project aims to detect signal neutral hydrogen on interferometric baselines $50-250 \lambda$. show that suppression faint signals can effectively be avoided by calibrating these short using only longer baselines. However, this approach causes an excess variance due small errors induced overfitting during...
We analyse the accuracy of radio interferometric gridding visibilities with aim to quantify Epoch Reionization (EoR) 21-cm power spectrum bias caused by gridding, ultimately determine suitability different imaging algorithms and settings for analysis. simulate realistic LOFAR data, construct spectra convolutional w-stacking, w-projection, image domain without w-correction. These are compared against directly Fourier transformed data. The influence oversampling, kernel size, w-quantization,...
Interferometric experiments designed to detect the highly redshifted 21-cm signal from neutral hydrogen are producing increasingly stringent constraints on power spectrum, but some k-modes remain systematics-dominated. Mutual coupling is a major systematic that must be overcome in order signal, and simulations reproduce effects seen data can guide strategies for mitigating mutual coupling. In this paper, we analyse 12 nights of Hydrogen Epoch Reionization Array compare against include...
The 21 cm transition from neutral Hydrogen promises to be the best observational probe of Epoch Reionisation (EoR). This has led construction low-frequency radio interferometric arrays, such as Reionization Array (HERA), aimed at systematically mapping this emission for first time. Precision calibration, however, is a requirement in observations. Due spatial compactness HERA, array prone effects mutual coupling, which inevitably lead non-smooth calibration errors that contaminate data. When...
The turbulent ionosphere causes phase shifts to incoming radio waves on a broad range of temporal and spatial scales. When an interferometer is not sufficiently calibrated for the direction-dependent ionospheric effects, time-varying can cause signal decorrelate. ionosphere's influence over various spatiotemporal scales introduces baseline-dependent effect interferometric array. We study impact decorrelation high-redshift observations with Low Frequency Array (LOFAR). Datasets corruptions...
Context. Detecting the 21 cm signal from epoch of reionisation (EoR) has been highly challenging due to strong astrophysical foregrounds, ionospheric effects, radio frequency interference (RFI), and instrumental effects. Better characterisation their effects precise calibration are, therefore, crucial for EoR detection. Aims. In this work we introduce a newly developed direction-dependent algorithm called DDECAL , compare its performance with an existing SAGECAL in context LOFAR-EoR power...
Context. The detection of the 21 cm signal neutral hydrogen from Epoch Reionization (EoR) is challenging due to bright foreground sources, radio frequency interference (RFI), and ionosphere as well instrumental effects. Even after correcting for these effects in calibration step applying removal techniques, remaining residuals observed power spectra are still above thermal noise, which referred “excess variance.” Aims. We study a number potential causes this excess variance based on 13...