arXiv subjects

Mayuri Sathyanarayana Rao

Publications and source records attributed to Mayuri Sathyanarayana Rao.

At least 19 recordsLinked to original sources

arXiv2026

Peering Beyond the Veil of Last Scattering: A View of the Universe with CMB Spectral Distortions

The frequency spectrum of the cosmic microwave background is the most precise blackbody ever measured in nature, with deviations constrained at the level of almost one part per million from the COBE satellite. Nevertheless, departures away from a perfect blackbody are present in standard $Λ$CDM cosmology, lurking just beneath the surface of our current observational bounds. These spectral distortions provide invaluable information on our thermal history in both the post- and pre-recombination epochs, allowing us to peer beyond last scattering and into the primordial Universe. Here, we present an overview of the underlying physics responsible for generating CMB spectral distortions at all epochs. As an illustration of this rich physics, we review a comprehensive set of mechanisms capable of generating distortions both within and beyond the standard $Λ$CDM paradigm. We also discuss the information that can be gleaned by going beyond the monopole (sky-averaged) spectrum and exploiting the spatial information present in anisotropic spectral distortions. To supplement our discussion of the diverse science of spectral distortions, we provide an overview of the upcoming and proposed experimental landscape. We highlight that the combination of the TMS, COSMO, and BISOU experiments will provide the first discovery of a monopole $y$-type distortion within the coming decade. From space, the proposed FOSSIL experiment is forecasted to improve upon the original COBE/FIRAS measurement by roughly three orders of magnitude in sensitivity, bringing with it the detection of the $Λ$CDM $μ$-type distortion sourced by the dissipation of small scale acoustic modes in the pre-recombination plasma. With transformational measurements on the horizon, CMB spectral distortions offer a uniquely sensitive probe of the thermal history of the Universe at redshifts $z \lesssim 2 \times 10^6$.

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arXiv2026

A novel technique for reflection coefficient measurement in precision cosmology

The detection of the global 21-cm signal from the Cosmic Dawn and Epoch of Reionisation remains a challenge to experiments worldwide. Emitted at a rest-frame frequency of 1420.405~MHz, this signal from the early Universe is redshifted to 40-200~MHz with a maximum brightness temperature of a few 100~mK. Efforts to detect this sky-averaged signal include experiments such as the Shaped Antenna measurement of the background RAdio Spectrum (SARAS) and Probing ReionizATion of the Universe using Signal from Hydrogen (PRATUSH). Detecting this faint signal requires precise calibration of the antenna, which includes a high-precision measurement of its reflection coefficient. This measurement must be performed \textit{in situ} at the observation site, as the antenna characteristics vary significantly with the environment. PRATUSH, a space-based radiometer, faces the additional challenge of structural distortions induced by thermal cycling, necessitating multiple measurements of the reflection coefficient. This work highlights the development of an \textit{in situ} Vector Network Analyser, which utilises a novel noise source-based calibration scheme and a cross-correlation spectrometer to perform magnitude and phase measurements of the complex reflection coefficient of the antenna. Further, we demonstrate the performance of the designed network analyser using independent measurements from a precision network analyser and reflection coefficient modelling of the device under test. We find the level of non-smooth calibration systematics, which need critical control for 21-cm signal detection, to be about $10^{-5}$. Finally, we study the impact of reflection coefficient correction on sky measurements, highlighting its usability for precision 21-cm observations.

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arXiv2026

STARFIRE-2: Can we detect the global redshifted 21-cm signal from the cosmic dawn in Earth orbit?

Detecting the redshifted global 21-cm signal from the cosmic dawn (CD) remains a major challenge due to strong terrestrial Radio Frequency Interference (RFI), particularly dominated by Frequency Modulation (FM) transmissions in the 88-110 MHz range. While observations from the radio-quiet lunar farside are ideal, Earth orbit offers an intermediate and simpler alternative that may mitigate several limitations of ground-based experiments. We assess the feasibility of detecting the global 21-cm signal from Earth orbit by quantifying FM-based RFI at different altitudes and orbital configurations. We present STARFIRE-2 (Simulation of TerrestriAl Radio Frequency Interference in oRbits around Earth -- 2), an algorithm that estimates FM transmitter-based RFI intercepted by radiometers in orbit. The model constructs a global FM transmitter database and compensates for incomplete data using statistical methods. Using PRATUSH as the reference experiment, we simulate a range of orbital scenarios to identify configurations that minimize RFI and optimize sensitivity for global 21-cm detection. The algorithm can also be adapted for other experiments. Simulations indicate that conducting such an experiment from Earth orbit is feasible for a thermal noise limited instrument placed in a low-Earth, near-polar orbit. Mock sky observations further demonstrate that most theoretically plausible cosmic dawn 21-cm signals can be recovered with high confidence under these optimized orbital conditions.

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arXiv2026

Site Quality Analysis for an Indian Submillimeter Telescope: A Reanalysis-Based Approach

The Himalayan plateau region of Ladakh, India, is a potential host for a science-class submillimeter observatory, building on existing astronomical infrastructure near Hanle and Merak. Using the fifth-generation European Centre for Medium-Range Weather Forecasts (ECMWF) Reanalysis (ERA5) data, we analyze precipitable water vapor (PWV) at monthly resolution over 184 months from January 2010 to April 2025, map PWV statistics across Ladakh, and identify candidate regions that reach PWV $\leq 1$ mm. For promising locations, we compute atmospheric transmittance and the corresponding atmospheric photon noise using the am (Atmospheric Model) radiative transfer code; we present transmittance and brightness temperature estimates over 10--1000 GHz and compare the inferred performance to sites hosting current or planned submillimeter facilities worldwide. We find Ladakh to be favorable for submillimeter observations, with multiple ERA5 grid cells reaching PWV $\leq 1$ mm. Within ERA5's spatial resolution, two regions emerge as particularly promising: Site A ($\approx 34.25^\circ$N, $78.75^\circ$E) and Site B ($\approx 32.50^\circ$N, $79.00^\circ$E), which satisfy PWV $\leq 1$ mm for about 23% and 19% of the study duration, respectively, compared to about 5% and 8% for the Hanle and Merak grid cells. These results motivate targeted in situ radiometer measurements for final site selection.

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arXiv2025

A Multi-Site Study of Radio Environment for Cosmology Experiments

Radio Frequency Interference (RFI) presents a significant challenge for carrying out precision measurements in radio astronomy. In particular, RFI can be a showstopper when looking for faint cosmological signals such as the red-shifted 21-cm line from cosmic dawn (CD) and epoch of reionization (EoR). As wireless communications, satellite transmissions, and other RF technologies proliferate globally, understanding the RFI landscape has become essential for site selection and data integrity. We present findings from RFI surveys conducted at four distinct locations: three locations in India, the Gauribidanur Radio Observatory in Karnataka, Twin Lakes in Ladakh, Kalpong Dam in the Andaman Islands, and the Gruvebadet Atmosphere Laboratory in Ny-Ålesund, Svalbard, Norway. These sites, selected based on their geographical diversity and varying levels of human activity, were studied to assess RFI presence in 30-300 MHz bands, critical for low-frequency observations and experiments targeting the 21-cm CD/EoR signal. Using an automated RFI detection approach via the Hampel filter and singular value decomposition, the surveys identified both persistent and transient interference, which varies with location and time. The results provide a comprehensive view of the RFI environment at each site, informing the feasibility of long-term cosmological observations and aiding in the mitigation of RFI in radio astronomical data. The methods developed to characterize RFI can be easily generalized to any location and experiment.

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arXiv2025

PRATUSH experiment concept and design overview

PRATUSH -- Probing ReionizATion of the Universe using Signal from Hydrogen -- is a proposed cosmology experiment to detect the global red-shifted 21-cm signal from the Cosmic Dawn and Epoch of Reionization (CD/EoR). PRATUSH orbiting the Moon will seek to precisely measure the low-frequency radio sky-spectrum over 40 to 200 MHz. The scientific observations would be made in the radio-quiet region when in the farside of the Moon, and the data would be transmitted back to Earth when in the near-side. PRATUSH was proposed to the Indian Space Research Organization (ISRO) during a call for proposals in the announcement of opportunity for science payloads in 2018. PRATUSH is in the pre-project studies phase. Here we present a mission concept and baseline design of the proposed payload optimized to operate over the Cosmic Dawn signal band of 55 - 110 MHz. Starting with a description of the fundamental design principles followed, we discuss the PRATUSH baseline design and sensitivity. We further enumerate the challenges that are common to most PRATUSH like experiments, which have been proposed to seek a detection of the CD/EoR signal in orbit in the lunar farside. Due to the highly sensitive nature of the measurement, PRATUSH is designed to operate as a solo experiment with a dedicated spacecraft. Our simulations, assuming a mission lifetime of two years, estimate that PRATUSH would have the sensitivity required to detect the CD signal predicted by the standard models with varying degrees of confidence.A concept model of PRATUSH is under development, which is expected to lead to the engineering model followed by flight model subject to mission approval.

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arXiv2025

An SBC-based controller and processor for the laboratory model of PRATUSH Digital Receiver

Probing ReionizATion of the Universe using Signal from Hydrogen (PRATUSH) is a proposed space-based radiometer that aims to detect the sky-averaged 21-cm signal from Cosmic Dawn - a crucial phase in the cosmic evolution of the Universe. PRATUSH will operate in the frequency range of 55-110 MHz. PRATUSH will conduct observations in low earth orbit in its first phase, followed by lunar orbit in the second phase. Digital correlation spectrometer is an integral subsystem of PRATUSH radiometer, enabling phase switching, digitization and generation of sky spectrum. The digital correlation spectrometer for PRATUSH laboratory model features 10-bit analog-to-digital converters (ADCs) and a Virtex-6 Field Programmable Gate Array (FPGA). A Raspberry Pi 4 Model B-based single-board computer (SBC) serves as the master controller, real-time processor and data recorder, to minimize the power, mass and volume requirement of the laboratory model. This paper presents the implementation of the PRATUSH laboratory model digital receiver, challenges arising from the use of an SBC in place of a conventional computer, and demonstrates the performance of the spectrometer when integrated with the PRATUSH laboratory model analog receiver.

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arXiv2024

Detecting cosmological recombination lines with a non-ideal antenna -- a first step to practical realization

Photons emitted during the formation of primordial hydrogen and helium atoms over the Epoch of Recombination are expected to be preserved as additive distortions to the Cosmic Microwave Background (CMB) spectrum. The 'ripple' like spectral features from Cosmological Recombination Radiation (CRR) have never been detected, and are expected to be 9 orders of magnitude fainter than the CMB. Array of Precision Spectrometers for the Epoch of Recombination - APSERa - is an upcoming ground-based experiment to detect the CRR signal over 2-6 GHz. While astrophysical foregrounds may be theoretically separated from the CRR signal using their inherently different spectral characteristics, instrument generated systematics present a practical problem. We present a first ever study to detect the CRR lines in the presence of a non-ideal antenna adopting a toy model for antenna beam chromaticity. Using Euclidean distance and Pearson correlation coefficient as metrics to distinguish between CRR signal presence and absence in a simulation pipeline, we demonstrate that it is indeed possible to detect the signal using a chromatic antenna. Furthermore, we show that there are different tolerances to the antenna non-ideality based on the type of chromaticity, observing location, and LST. These can inform antenna and experiment design for a practical detection.

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arXiv2024

The Simons Observatory: Design, integration, and testing of the small aperture telescopes

The Simons Observatory (SO) is a cosmic microwave background (CMB) survey experiment that includes small-aperture telescopes (SATs) observing from an altitude of 5,200 m in the Atacama Desert in Chile. The SO SATs will cover six spectral bands between 27 and 280 GHz to search for primordial B-modes to a sensitivity of $σ(r)=0.002$, with quantified systematic errors well below this value. Each SAT is a self-contained cryogenic telescope with a 35$^\circ$ field of view, 42 cm diameter optical aperture, 40 K half-wave plate, 1 K refractive optics, and $<0.1$ K focal plane that holds $>12,000$ TES detectors. We describe the nominal design of the SATs and present details about the integration and testing for one operating at 93 and 145 GHz.

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arXiv2023

STARFIRE: An algorithm for estimating radio frequency interference in orbits around Earth

Ground-based 21-cm experiments targeting the global signal from the periods of Cosmic Dawn (CD) and Epoch of Reionization (EoR) are susceptible to adverse effects presented by i) the ionosphere ii) antenna chromaticity induced by objects in its vicinity iii) terrestrial radio frequency interference (RFI). Terrestrial RFI is particularly challenging as the FM radio band spanning over 88-108 MHz lies entirely within the frequency range of the CD/EoR experiments ($\sim 40-200$ MHz). Multiple space-based experiments have been proposed to operate in the radio-quiet zone on the lunar farside. An intermediate option in cost and complexity is an experiment operating in space in an orbit around Earth, which readily alleviates the first two challenges. However, the effect of RFI in Earth's orbit on the detection of global signal needs to be quantitatively evaluated. We present STARFIRE -- Simulation of TerrestriAl Radio Frequency Interference in oRbits around Earth -- an algorithm that provides an expectation of FM seeded RFI at different altitudes over Earth. Using a limited set of publicly available FM transmitter databases, which can be extended by the user community, we demonstrate the use of the STARFIRE framework to generate a three-dimensional spatio-spectral cube of RFI as would be measured in Earth orbit. Applications of STARFIRE include identifying minimum RFI orbits around Earth, producing RFI spectra over a particular location, and generating RFI heatmaps at specific frequencies for a range of altitudes. STARFIRE can be easily adapted for different frequencies, altitudes, antenna properties, RFI databases, and combined with astrophysical sky-models. This can be used to estimate the effect of RFI on the detection of global 21-cm signal from Earth-orbit, and hence for sensitivity estimates and experiment design of an Earth orbiting CD/EoR detection experiment.

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arXiv2022

Synthetic Observations with the Square Kilometre Array (SKA) -- development towards an end-to-end pipeline

Detection of the redshifted 21-cm signal of neutral hydrogen from the Cosmic Dawn and the Epoch of Reionization is one of the final frontiers of modern observational cosmology. The inherently faint signal makes it susceptible to contamination by several sources like astrophysical foregrounds and instrumental systematics. Nevertheless, developments achieved in the recent times will combine to make signal detection possible with the upcoming Square Kilometer Array (SKA), both statistically and via tomography. This review describes an indigenously developed end-to-end pipeline that simulates sensitive interferometric observations. It mainly focuses on the requirements for \hi detection in interferometers. In its present form, it can mimic the effects of realistic point source foregrounds and systematics- calibration error and position error on 21-cm observations. The performance of the pipeline is demonstrated for test cases with 0.01\% calibration error and position error. Its performance is consistent across telescope, foreground, and signal models. The focus of the simulation pipeline during the initial stages was for EoR science. But since this is a general interferometric simulation pipeline, it will be helpful to the entire SKA user community, irrespective of the science goals.

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arXiv2021

On the detection of a cosmic dawn signal in the radio background

The astrophysics of cosmic dawn, when star formation commenced in the first collapsed objects, is predicted to be revealed as spectral and spatial signatures in the cosmic radio background at long wavelengths. The sky-averaged redshifted 21-cm absorption line of neutral hydrogen is a probe of cosmic dawn. The line profile is determined by the evolving thermal state of the gas, radiation background, Lyman-$α$ radiation from stars scattering off cold primordial gas and the relative populations of the hyperfine spin levels in neutral hydrogen atoms. We report a radiometer measurement of the spectrum of the radio sky in the 55--85~MHz band, which shows that the profile found by Bowman et al. in data taken with the Experiment to Detect the Global Epoch of Reionization Signature (EDGES) low-band instrument is not of astrophysical origin; their best-fitting profile is rejected with 95.3\% confidence. The profile was interpreted to be a signature of cosmic dawn; however, its amplitude was substantially higher than that predicted by standard cosmological models. Explanations for the amplitude of the profile included non-standard cosmology, additional mechanisms for cooling the baryons, perhaps via interactions with millicharged dark matter and an excess radio background at redshifts beyond 17. Our non-detection bears out earlier concerns and suggests that the profile found by Bowman et al. is not evidence for new astrophysics or non-standard cosmology.

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arXiv2021

The Simons Observatory: Galactic Science Goals and Forecasts

Observing in six frequency bands from 27 to 280 GHz over a large sky area, the Simons Observatory (SO) is poised to address many questions in Galactic astrophysics in addition to its principal cosmological goals. In this work, we provide quantitative forecasts on astrophysical parameters of interest for a range of Galactic science cases. We find that SO can: constrain the frequency spectrum of polarized dust emission at a level of $Δβ_d \lesssim 0.01$ and thus test models of dust composition that predict that $β_d$ in polarization differs from that measured in total intensity; measure the correlation coefficient between polarized dust and synchrotron emission with a factor of two greater precision than current constraints; exclude the non-existence of exo-Oort clouds at roughly 2.9$σ$ if the true fraction is similar to the detection rate of giant planets; map more than 850 molecular clouds with at least 50 independent polarization measurements at 1 pc resolution; detect or place upper limits on the polarization fractions of CO(2-1) emission and anomalous microwave emission at the 0.1% level in select regions; and measure the correlation coefficient between optical starlight polarization and microwave polarized dust emission in $1^\circ$ patches for all lines of sight with $N_{\rm H} \gtrsim 2\times10^{20}$ cm$^{-2}$. The goals and forecasts outlined here provide a roadmap for other microwave polarization experiments to expand their scientific scope via Milky Way astrophysics.

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arXiv2021

BoloCalc: a sensitivity calculator for the design of Simons Observatory

The Simons Observatory (SO) is an upcoming experiment that will study temperature and polarization fluctuations in the cosmic microwave background (CMB) from the Atacama Desert in Chile. SO will field both a large aperture telescope (LAT) and an array of small aperture telescopes (SATs) that will observe in six bands with center frequencies spanning from 27 to 270~GHz. Key considerations during the SO design phase are vast, including the number of cameras per telescope, focal plane magnification and pixel density, in-band optical power and camera throughput, detector parameter tolerances, and scan strategy optimization. To inform the SO design in a rapid, organized, and traceable manner, we have created a Python-based sensitivity calculator with several state-of-the-art features, including detector-to-detector optical white-noise correlations, a handling of simulated and measured bandpasses, and propagation of low-level parameter uncertainties to uncertainty in on-sky noise performance. We discuss the mathematics of the sensitivity calculation, the calculator's object-oriented structure and key features, how it has informed the design of SO, and how it can enhance instrument design in the broader CMB community, particularly for CMB-S4.

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arXiv2021

SARAS 3 CD/EoR Radiometer: Design and Performance of the Receiver

SARAS is an ongoing experiment aiming to detect the redshifted global 21-cm signal expected from Cosmic Dawn (CD) and the Epoch of Reionization (EoR). Standard cosmological models predict the signal to be present in the redshift range $z \sim $6--35, corresponding to a frequency range 40--200~MHz, as a spectral distortion of amplitude 20--200~mK in the 3~K cosmic microwave background. Since the signal might span multiple octaves in frequency, and this frequency range is dominated by strong terrestrial Radio Frequency Interference (RFI) and astrophysical foregrounds of Galactic and Extragalactic origin that are several orders of magnitude greater in brightness temperature, design of a radiometer for measurement of this faint signal is a challenging task. It is critical that the instrumental systematics do not result in additive or multiplicative confusing spectral structures in the measured sky spectrum and thus preclude detection of the weak 21-cm signal. Here we present the system design of the SARAS~3 version of the receiver. New features in the evolved design include Dicke switching, double differencing and optical isolation for improved accuracy in calibration and rejection of additive and multiplicative systematics. We derive and present the measurement equations for the SARAS~3 receiver configuration and calibration scheme, and provide results of laboratory tests performed using various precision terminations that qualify the performance of the radiometer receiver for the science goal.

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arXiv2021

SARAS CD/EoR Radiometer: Design and performance of the Digital Correlation Spectrometer

In the currently accepted model for cosmic baryon evolution, Cosmic Dawn and the Epoch of Reionization are significant times when first light from the first luminous objects emerged, transformed and subsequently ionized the primordial gas. The 21 cm hyperfine transition of neutral hydrogen, redshifted from these cosmic times to a frequency range of 40 to 200 MHz, has been recognized as an important probe of the physics of CD/EoR. The global 21-cm signal is predicted to be a spectral distortion of a few 10's to a few 100's of mK, which is expected to be present in the cosmic radio background as a trace additive component. SARAS, Shaped Antenna measurement of the background RAdio Spectrum, is a spectral radiometer purpose designed to detect the weak 21-cm signal from CD/EoR. An important subsystem of the radiometer, the digital correlation spectrometer, is developed around a high speed digital signal processing platform called pSPEC. pSPEC is built around two quad 10 bit analog-to-digital converters and a Virtex 6 field programmable gate array, with provision for multiple Gigabit Ethernet and 4.5 Gbps fibre optic interfaces. Here we describe the system design of the digital spectrometer, the pSPEC board, and the adaptation of pSPEC to implement a high spectral resolution of about 61 kHz, high dynamic range correlation spectrometer covering the entire CD/EoR band. As the SARAS radiometer is required to be deployed in remote locations where terrestrial radio frequency interference is a minimum, the spectrometer is designed to be compact, portable and operating off internal batteries. The paper includes an evaluation of the spectrometer's susceptibility to radio frequency interference and capability to detect signals from CD/EoR.

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arXiv2021

Simons Observatory Small Aperture Telescope overview

The Simons Observatory (SO) is a cosmic microwave background (CMB) experiment from the Atacama Desert in Chile comprising three small-aperture telescopes (SATs) and one large-aperture telescope (LAT). In total, SO will field over 60,000 transition-edge sensor (TES) bolometers in six spectral bands centered between 27 and 280 GHz in order to achieve the sensitivity necessary to measure or constrain numerous cosmological quantities. In this work, we focus on the SATs which are optimized to search for primordial gravitational waves that are detected as parity-odd polarization patterns called a B-modes on degree scales in the CMB. Each SAT employs a single optics tube with TES arrays operating at 100 mK. The high throughput optics system has a 42 cm aperture and a 35-degree field of view coupled to a 36 cm diameter focal plane. The optics consist of three metamaterial anti-re ection coated silicon lenses. Cryogenic ring baffles with engineered blackbody absorbers are installed in the optics tube to minimize the stray light. The entire optics tube is cooled to 1 K. A cryogenic continuously rotating half-wave plate near the sky side of the aperture stop helps to minimize the effect of atmospheric uctuations. The telescope warm baffling consists of a forebaffle, an elevation stage mounted co-moving shield, and a fixed ground shield that together control the far side-lobes and mitigates ground-synchronous systematics. We present the status of the SAT development.

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arXiv2020

Simons Observatory Microwave SQUID Multiplexing Readout -- Cryogenic RF Amplifier and Coaxial Chain Design

The Simons Observatory (SO) is an upcoming polarization-sensitive Cosmic Microwave Background (CMB) experiment on the Cerro Toco Plateau (Chile) with large overlap with other optical and infrared surveys (e.g., DESI, LSST, HSC). To enable the readout of \bigO(10,000) detectors in each of the four telescopes of SO, we will employ the microwave SQUID multiplexing technology. With a targeted multiplexing factor of \bigO{(1,000)}, microwave SQUID multiplexing has never been deployed on the scale needed for SO. Here we present the design of the cryogenic coaxial cable and RF component chain that connects room temperature readout electronics to superconducting resonators that are coupled to Transition Edge Sensor bolometers operating at sub-Kelvin temperatures. We describe design considerations including cryogenic RF component selection, system linearity, noise, and thermal power dissipation.

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