Poster presentations

Presenter: Sindhu Gaddam

Title: Electromagnetic Simulations of the HIRAX Antenna

The presentation is centered on the EM simulations of the HIRAX antenna to enhance the antenna return loss and radiation characteristics. HIRAX antenna is a 6m parabolic dish with a clover leaf dipole feed placed at a f/D of 0.21. The antenna’s design is one of the crucial design factors that must be considered in order to detect the signal with good precision. Hence  careful design of the antenna is essential to achieve the desired antenna characteristics like return loss, radiation efficiency, and the radiation pattern properties. The discussion focuses on how different structural and design aspects of the HIRAX antenna result in improved return loss and radiation characteristics

Presenter: Ajith Sampath

Title: An analytic approach to understand beam systematics in HIRAX.

Any 21cm experiment, especially intensity mapping experiments like HIRAX (the Hydrogen Intensity and Real-time Analysis eXperiment – an intensity mapping experiment under construction at Karoo desert in South Africa), aiming to detect BAO signatures to constrain the Dark Energy equation of state parameters, suffer from systematics inherent to the instrument. The primary factor causing this effect is the chromaticity of the antenna, i.e., the frequency-dependent structure of the primary beam. In this study, we use the analytical Fourier counterparts of Zernike polynomials to model the CST simulated HIRAX primary beams, which will be applied to Drone mapping data. This beam modeling technique is based on physical considerations in aperture space, which involves a linear combination of analytical basis functions. Furthermore, we investigate the impact of sidelobe chromaticity in delay space and look at their effects in the calibration stage by investigating the  calibration solutions using different beam models. Our study demonstrates the effectiveness of our beam modeling approach in general and provides insights into the implications of sidelobe chromaticity for accurate estimation of the 21 cm power spectrum.

Presenter: Elizabeth Kamau

Title: Flux Variability Study on Calibrators Observed by MeerKAT

Calibration is a crucial process undertaken to ensure that radio interferometers such as MeerKAT or the upcoming SKAO are well tuned and characterised to provide accurate science products. Calibrating data from such arrays is a challenge due to its sheer volume and various phenomena contributing errors. This can be tackled by the use of sources whose properties are known to calibrate the instruments and data.  An important characteristic of a suitable calibrator for radio interferometers is to be a strong, non-variable radio source over a short time scale in the order of days to months. Strong radio sources are most often Active Galactic Nuclei whose flux varies over time. Previous studies have investigated the flux variability of a sub-sample of southern calibrators observed by the MeerKAT precusor KAT7. We have undertaken a similar analysis because MeerKAT provides a higher resolution and sensitivity than KAT7. We focus on the data reduction of uncalibrated radio data to produce images and light curves that are analysed for possible intrinsic variability. We also conduct a statistical analysis of the flux variability of a sub-sample of southern calibrators observed by MeerKAT. This analysis is important because it contributes to the understanding of the behaviour over time of calibrator sources and the phenomena that causes variability. This can then inform the calibration process for radio arrays such as MeerKAT to ensure their proper performance and veracity of science products produced.

Presenter: Thuto Ndlovu

Title: A Multiwavelength Study of Be/X-ray Binary Stars

Be/X-ray binary stars are the largest subclass of high-mass X-ray binaries which comprise a neutron star in an eccentric orbit around a massive B spectral type star. They undergo X-ray outbursts which come in two flavours: Type I and Type II. We perform a systematic study of circumstellar discs of Be/X-ray binary 4U 0115+63 to demonstrate observational signatures of the Kozai- Lidov mechanism. The X-ray outbursts of the Be/X-ray binaries might be connected with the mass ejections from the Be star. 

Presenter: Keshav Bechoo

Title:On-sky characterization and analysis of HIRAX prototype and dish verification arrays

It is essential to make an exhaustive study of possible causes of systematics through extensive simulations and observations. At this stage, HIRAX has a prototype 6m dish at HartRAO, and construction of the 2-element dish verification array is underway at Klerefontein. Data from these arrays are analysed to develop insight into the receiver temperature, gain, and its variation with time. The beam shape of the MMS dish at HartRAO from source transits is also analysed, using data that is already in hand. Analysis of the long term gain and noise-temperature stability of the receiver system at HartRAO, and its variation with ambient temperature on site, is also being done using data that is already in hand. The effect of strong and weak RFI on the estimates of the system gain, and how these signals couple between the dishes is also studied.

Presenter: Tasmiya Papiah 

Title: Drone beam mapping of HIRAX

Beam calibration for radio telescopes is traditionally done using astronomical point sources. However, HIRAX’s dishes are not mounted motorised assemblies, making it insufficient for accurate beam response measurements. To address this issue, we are exploring the possibility of using an artificial calibration source. In this project we focus on the technique of characterizing the beam pattern using a drone equipped with a noise source. This approach allows for high signal-to-noise measurements of the telescope response at several positions in its beam, in a short amount of time. This will be done by optimizing the drone flight path, combining the intensity measured at the telescope and the recorded drone position to reconstruct the beam, and fitting a model to the measurements. Here, I will present details of the pipeline and some early analysis results.

Presenter: Isibabale Qhoboshiyane

Title: Development and prototyping of a HIRAX temperature monitoring system

The talk  focuses on developing and prototyping a temperature monitoring system for HIRAX to study its effects on HIRAX measurements and its impact on calibration. The temperature of the analogue electronics, RF power, optical power at the fibre transmitter,etc. are parameters to be investigated. Some can be obtained from observational data, but physical quantities like temperature on site, etc. have to be monitored in parallel. The 

study further aims to develop the hardware components and computational techniques that enable the temperature monitoring of the array to provide users with meta-data that will assist in the data analysis, notably, the amplification of temperature-induced gain drift within the Low-Noise Amplifier (LNA) constitutes a critical concern that demands meticulous calibration during data analysis. These techniques will be demonstrated at the existing HIRAX prototype dish at HartRAO and the upcoming 2-element interferometer at Klerefontein, with inferences to be fed into design refinements and optimization for the 256 array at Karoo.

Presenter: Edwin Retana-Montenegro

Title: Radio-frequency interference mitigation for the HIRAX radio-telescope

Cosmological signals are many orders of magnitude weaker than the radio-telescopes system noise level. The HIRAX radio-telescope operating from the Karoo desert between 400 and 800 MHz will achieve the necessary sensitivity to make cosmological measurements using a combination of a large collecting area, long integration times, and large bandwidth. Because of this relatively large bandwidth and the variable radio spectrum at Karoo, finding a robust approach to identify radio-frequency interference (RFI) in HIRAX is important. In this talk, I will present some of the different RFI detection approaches that could be used with HIRAX, and potential RFI contaminants in the HIRAX radio spectrum. 

Presenter: Nokulunga Dlamini

Title: Immersive virtual reality as a pedagogical tool for training in Astronomy.

The rapid increase and usage of digitalization have quickly become part of our daily lives. At the same time, the Fourth Industrial Revolution (4IR) has paved a new way of life, thus causing a tremendous shift from the traditional way of training in institutions of learning to immersive virtual reality training for students. Immersive virtual reality has made a significant impact in this era and is increasingly being used as a training tool. The inequality gap and limited exposure of black African women in the astronomy discipline can be alleviated through the development of immersive virtual environments and immersive virtual reality training that can expose and enhance black women to the career field of astronomy and space technology. Immersive virtual reality using a head-mounted display can be used to visually stimulate space technology education, lectures, and laboratory classes to provide authentic, student-centred experiences to teach different astronomy fundamental principles and act as a career guidance tool.  Keywords; Immersive virtual reality, pedagogical, astronomy, immersive virtual reality

Presenter: Warren Naidoo

Title: Cosmological constraints from future synergistic large-scale structure surveys

Current observations of the universe suggest that the cosmic energy budget is dominated by dark energy (DE) which accounts for approximately 70% of the energy budget and a further 25% of this energy distribution is from the dark matter (DM) distribution. Cosmic microwave background (CMB) radiation experiments have already provided a wealth of information constraining the current cosmological model. Galaxy surveys have also provided valuable information on the evolution of the universe at later times. Future surveys will probe the larger volumes of the large-scale structure to much higher precision. Here we discuss how we can use future surveys such as HI intensity mapping using HIRAX, CMB lensing from AdvACT, and galaxy surveys with LSST in cross-correlation to provide unprecedented constraints on the Cosmological model and test extensions to the standard model. In particular, we show constraints on the ΛCDM model, then we extend the model to include constraints on the DE equation of state parameters, as well as inflation through the non-Gaussianity parameter and neutrino mass constraints.

Presenter: Marina Mello

Title: Polarimetric Catalog

The demand for observational data has always been an important issue in astronomy. In the last decades, the amount of astronomical data became huge and the development of tools to analyze this plethora of data became essential. Hence, the advent of data science along with machine learning to explore big data comes in handy. Making use of this new approach to explore astronomical data, we aim to produce a catalog of optical polarization based on the publicly available database of the observations obtained at Observatório do Pico dos Dias (OPD) in Brazil. The project focuses on linear polarimetric data obtained using the IAG-POL polarimeter. The data were obtained over more than 20 years in different telescopes, by different observers, with different scientific objectives. The project is to collect all available data with the mentioned characteristics, reduce it, and release it in a Virtual Observatory (VO) format.

Presenter: Marcus André Morais Valiati 

Title: Data analysis and modeling of the Gamma-ray radiation from supermassive black hole jets

An active galactic nucleus (AGN) refers to a supermassive black hole that is actively consuming large amounts of matter from its accretion disk. Such system is typically surrounded by a torus filled with dust which obscures its direct view. The AGN produces a collimated jet of relativistic particles as a result of the accretion process. These jets can extend over vast distances, reaching hundreds of thousands of parsecs. If the jet is nearly aligned with the observer’s line of sight (< 15º-20º), the AGN is classified as a ”blazar”. Blazars are considered to be potential multi-messenger counterparts to cosmic-ray and astrophysical neutrinos. In the case of binary black holes they could also be sources of gravitational waves. The objective of this project is to analyze blazar gamma-ray data using the fermipy tool, and develop Python programs to model the energy flux emission by the relativistic jets across the electromagnetic spectrum, focusing on the high-energy x- to gamma-ray spectrum spectral energy distribution (SED). Through the analysis of the blazar Markarian 501 in the year of 2014, in which the object showed extremely high fluxes, as seen by the NASA’s Fermi-LAT and Swift-XRT satellite instruments, we obtained the spectral energy distribution (SED) and light curves of the source. Additionally, we developed Python codes to model the SED, considering both leptonic models, in the case of electrons being the parent particle population responsible for the emission, and hadronic models, when the radiation had origin in proton interactions. These programs were used to fit the model parameters, enabling a description of the multiwavelength data from Markarian 421. Data from ground-based instruments such as the MAGIC telescopes were also added to the SED modeling.

Present: Xiaoxiong Zuo

Title: Machine Learning Approaches for Target Classification in X-ray Time-Domain Astronomy

The X-ray wavelength range is crucial for exploring time-domain astrophysics. The Einstein Probe (EP), a Chinese astronomical satellite dedicated to time-domain astrophysics and high-energy astrophysical phenomena, conducts systematic surveys in the soft X-ray band. One of its primary objectives is the discovery of high-energy transient and variable sources in the X-ray domain. In this work, utilizing light curves, spectral data obtained from the Lobster Eye Imager for Astronomy (LEIA), and EP simulated data, we design and implement machine learning models for source classification based on statistical features extracted from light curves and the energy distribution in the spectra. We compare the performance of algorithms including Random Forest and Gradient Boosting Decision Trees. The resulting model achieves a classification accuracy of 98% on simulated data and 97% on LEIA observational data. Given the limited number of photons in EP data, this work also investigates machine learning methods for classification using raw event data. The classification model is deployed as a pipeline on the LEIA server to provide rapid, real-time source classification for observations. This work enables fast classification of sources in EP data, facilitating the detection of unknown celestial objects and eruptive sources, while also serving as a reference for other X-ray observation missions. Future work will focus on further algorithm optimization and exploration of additional time-domain target classification methods.

Presenter: Zipei Zhu

Title: Time-domain projects at NAO/CAS: EP, SVOM, and JinShan

Einstein Probe (EP) and Space-based multi-band astronomical Variable Objects Monitor (SVOM) are missions at National Astronomical Observatories (NAO), Chinese Academy of Sciences (CAS) dedicated to time-domain high-energy astrophysics. The primary goal of EP is to discover high-energy transients and monitor variable objects. The SVOM mission is a French-Chinese mission dedicated to the study of the most distant explosions of stars, i.e., gamma-ray bursts. EP will be launched at the end of 2023 and SVOM in March of next year. Meanwhile, our team at NAO has been building a ground-based telescope array at Altay, Xinjiang, China. The array consists of two large FOV 1m telescopes, one small FOV 1m telescope, and four large FOV 0.5m telescopes, aiming to search for gravitational wave optical counterparts and follow-up transients detected by other projects.

Presenter: Maria Pruzhinskaya

Title: Unveiling Unusual Astrophysical Events using Machine Learning in the Fink Alert Broker

The detection of new astronomical sources is one of the most anticipated outcomes of the next generation of large-scale sky surveys. Experiments such as the Vera Rubin Observatory Legacy Survey of Space and Time are expected to continuously monitor large areas of the sky with remarkable deliberation, which will undoubtedly lead to the detection of unforeseen astrophysical phenomena. At the same time, the volume of data gathered every night will also increase to unprecedented levels, rendering serendipitous discoveries unlikely. In the era of big data, most detected sources will never be visually inspected, and the use of automated algorithms is unavoidable. I would like to present the anomaly detection module developed for the Fink community broker – one of the official LSST brokers — to search for unusual astrophysical events in the Zwicky Transient Facility alert stream and LSST in future. I will present the first discoveries made with the module including AT2023awt – rare subtype of AM CVn variables. The spectral and photometric follow-up observations of AT2023awt will be discussed. Other discoveries like fast transients, supernova candidates will be discussed. I will also talk about the Fink anomaly Slack- and Telegram-bot, which makes the process of anomalies analysis to be more efficient and convenient for the user.

Presenter: Naveen Dukiya

Title: Astrometric and photometric calibrators for the 4-m International Liquid Mirror Telescope

The International Liquid Mirror Telescope (ILMT) is a 4-meter class survey telescope. It scans the sky in a fixed 22’ wide strip centred at the declination of 29o21’41’’ and works in Time Delay Integration (TDI) mode.  We present a full catalog of sources lying in the ILMT strip with very precise measurements of astrometric properties provided by Gaia. The catalog is derived by crossmatching Gaia DR3 with SDSS DR17 and PanSTARRS-1 (PS1) to remove spurious objects and to supplement the catalog with apparent magnitudes of these sources in g, r, and i filters. We find counterparts of ~3.93 million (from ~5.46 million) Gaia sources either in SDSS or PS1. These sources are suitable as astrometric calibrators for the ILMT images. We have achieved astrometric accuracy of ~0.1 arcsec in the astrometrically calibrated commissioning phase images. We also developed strategies and codes to generate FITS WCS compatible headers when performing astrometry on the ILMT images. Gaia DR3 also bring synthetic photometry in popular broadband photometric systems, including the SDSS g, r, and i bands for ~20 million sources across the whole sky. We have used this synthetic photometry to verify our crossmatching performance and, in turn, create a subset of the catalog with accurate photometric measurements from two reliable sources.

Presenter: Kumar Pranshu

Title: Automated transient detection in the context of the 4m International Liquid Mirror Telescope (ILMT)

The 4m International Liquid Mirror Telescope (ILMT) is the first telescope dedicated to optical survey in India. It uses a continuously spinning bowl of mercury as the primary reflector. This makes it the only operational liquid mercury telescope in the world. The FoV of the telescope is 22’  with a limiting magnitude of ~22 in the g’ band. The ILMT acquires up to 15 GB of data on any given night of observation resulting in close to 30 science frames. One of the primary science goals with the ILMT is to discover new optical transients and variables. An automated transient detection pipeline has been developed to discover and perform broad classification of transients and variable sources lying in the ILMT field. 

The pipeline hosts an image subtraction algorithm that performs image subtraction of acquired science frames to give difference frames. A convolutional neural network (CNN) based classifier detects real sources in the difference image by classifying all the sources in the difference image as real and artefact. Another CNN classifier classifies these real sources into three broad categories. The pipeline was tested on acquired ILMT data which led to the detection of several asteroids and variable stars.  

Given the high limiting magnitude of the telescope, the pipeline is expected to discover several transient and variable objects and phenomenon including supernovae, AGNs, blazars, events like episodic outbursts in pre-main sequence T Tauri stars and Herbig Ae/Be stars,  post-main sequence variable stars like RR Lyrae, Cepheid Variables, Luminous Blue Variables (LBVs) and other known and unknown sources of variability. The discovered transients and variable objects will be shared with the larger scientific community through a dedicated alert stream. 

Presenter: Bhavya Ailawadhi

Title: An automated photometric pipeline for the intensive ILMT data

The International Liquid Mirror Telescope (ILMT) is a cutting-edge 4-meter survey telescope continuously engaged in zenith-focused observations across the SDSS g’, r’, and i’ bands. Its primary objective is the detection of a wide array of astrophysical transients like supernovae, and extremely faint celestial objects like multiple-imaged quasars and low surface brightness galaxies. With each scan covering a 22′ portion of the sky, a substantial amount of photometric data is collected, resulting in an approximate daily data volume of 15 GB. Efficiently managing this considerable data flow demands the development of robust tools or pipelines capable of accurately and expeditiously processing the incoming data while minimizing human-induced biases. To address this challenge, we introduce a fully automated pipeline, developed in Python, that performs aperture photometry analysis on the ILMT data captured in Time Delayed Integration (TDI) mode via CCD. This pipeline ensures meticulous calibration of instrumental magnitudes through reference to well-established standards like the Pan-STARRS-1 and SDSS catalogues. The ensuing light curves, derived from these calibrated magnitudes, enable us to effectively categorize the objects as either variable stars or rapidly decaying transients. This pipeline serves as a practical illustration of our strategy for managing data-intensive research within the time-domain astronomy.