arXiv subjects

Paul Hickson

Publications and source records attributed to Paul Hickson.

At least 19 recordsLinked to original sources

arXiv2026

Demonstrating the Time-Domain Capabilities of the 4-m International Liquid Mirror Telescope: An Early Census of Transient and Variable Detections

The PyLMT transient detection pipeline has been operational since November 2023, detecting transient and variable objects in the ILMT images in almost real time. Using the image subtraction technique, nearly 3700 CCD frames have been analyzed by the automated pipeline, generating nearly 23,000 alerts for the detection of verified transient candidates and cataloged variable sources. Around 21,000 of the alerts correspond to known MPC asteroids, nearly 2000 correspond to variable stars (including eclipsing binaries, RR Lyrae, Delta Scuti, T-Tauri, etc.), 509 correspond to variable AGNs (including QSOs, Seyfert galaxies, and blazars), 21 supernova candidates, and several other interesting candidates. We provide a concise overview of the detections and their significance, emphasizing the surveys potential contributions to a broad class of astrophysical and scientific cases. A transient detection dashboard called DART was developed using Streamlit to visualize and categorize candidates based on PyLMT and SIMBAD classifications. It includes cone-search functionality and displays key metadata, offering an intuitive interface that is publicly accessible. Our results demonstrate the viability of liquid mirror telescopes such as the ILMT for time-domain astronomy, emphasizing the important role that small-field survey facilities can play in systematic transient science programs.

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arXiv2026

Astrometric Calibration of the 4-m International Liquid Mirror Telescope Observations

The 4-m International Liquid Mirror Telescope (ILMT) is a dedicated time domain survey telescope that continuously scans the zenithal sky over the Indian Himalayas in the g', r' and i' optical bands. Its unique capability to repeatedly image the same strip of sky every night makes it a highly useful instrument for the photometric and astrometric studies of Solar System, Galactic and extragalactic objects. We present a robust astrometric calibration pipeline developed for the ILMT data obtained in the time delay integration (TDI) mode. The pipeline uses a linear transformation model from pixel to world coordinates, with a second order correction for the asymmetric optical distortions introduced by the telescope's optical corrector, and ties the astrometric solution to the Gaia DR3 reference frame. The pipeline is integrated to the routine ILMT data processing workflow. Using data from the first four observing cycles (2022-2025), we present the first assessment of the astrometric performance of the pipeline based on positional residuals of sources cross-matched with Gaia DR3. The pipeline achieves a typical astrometric precision of ~100 milliarcseconds (mas), reaching ~70-80 mas for moderately bright sources (G~16.5-18.5). These results, based on 347 nights of data, demonstrate the stability and reliability of ILMT astrometry over multi-year timescales. The astrometrically calibrated data from these four observing cycles have been made publicly available to the astronomical community. This work establishes a validated framework for precision astrometry with zenith-pointing TDI surveys and provides a foundation for future time-domain studies with ILMT, including variability characterization, transient localization, and long-term positional monitoring.

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arXiv2026

Performance of the 4-m International Liquid Mirror Telescope tested in two fields at high and low ecliptic and galactic latitudes

The 4-m International Liquid Mirror Telescope (ILMT) offers a unique opportunity to detect transients in a narrow strip of sky. We explore ILMT's potential to detect astrometric and photometric transients at various ecliptic and galactic latitudes. We inspected CCD frames observed at both low and high ecliptic and galactic latitudes during the commissioning phase and the November 2023 - May 2024 observation cycle, respectively. We analysed these images using both visual inspection and the ILMT's transient detection and candidate classification pipeline. In the low ecliptic and galactic latitude field, we detected more than 500 transient candidates. We cross-matched these with the Minor Planet Checker (MPC) database, identifying 504 catalogued asteroids, all with predicted V-magnitudes brighter than 24 mag, representing a total of 152 distinct asteroids. We performed the same steps on the high ecliptic and galactic latitude field, detecting 30 MPC-catalogued asteroids, and one newly discovered photometric transient, named AT 2024fxn. We present the positions, trajectories, and magnitudes of the detected asteroids observed in the SDSS g', r', and i' spectral bands and compare results from both fields. We explore the lightcurve of AT 2024fxn, which shows partial compatibility with a supernova (SN) hypothesis, while the data invites further insights.

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arXiv2026

Atmospheric turbulence profiling with the Multistar Turbulence Monitor

Accurate characterization of atmospheric optical turbulence is essential for evaluating astronomical sites and optimizing adaptive optics systems. The Multistar Turbulence Monitor (MTM) infers the vertical distribution of the refractive-index structure constant Cn2(z) from differential image motion measured between multiple stellar pairs in short-exposure frames. We present a comprehensive investigation of the MTM method, combining theoretical analysis, instrument-performance assessment, numerical simulations, and on-sky observations obtained at the Daocheng Astronomical Site. Simulations based on a standard HV turbulence model demonstrate that the inversion pipeline robustly recovers both the integrated seeing and the vertical turbulence profile under realistic centroiding noise and varying pixel scales. The Markov Chain Monte Carlo (MCMC) inversion achieves stable results with thirteen discrete height nodes and provides reliable uncertainties. Three nights of MTM measurements at the Daocheng Astronomical Site show that MTM-derived seeing closely tracks simultaneous Differential Image Motion Monitor (DIMM) results, accurately reproducing both short-term fluctuations and nightly averages. These results confirm that MTM provides a simple, portable, and versatile solution for atmospheric turbulence profiling and routine seeing monitoring.

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arXiv2025

PyLMT: A transient detection pipeline for the 4-m International Liquid Mirror Telescope

The International Liquid Mirror Telescope (ILMT) is a 4-m aperture, zenith-pointing telescope with a field-of-view of 22', situated in the foothills of the Himalayas. The telescope operates in continuous survey mode, making it a useful instrument for time-domain astronomy, particularly for detecting transients, variable stars, active galactic nuclei variability, and asteroids. This paper presents the PyLMT transient detection pipeline to detect such transient/varying sources in the ILMT images. The pipeline utilises the image subtraction technique to compare a pair of images from the same field, identifying such sources in subtracted images with the help of convolutional neural networks (CNN) based real/bogus classifiers. The test accuracies determined for the real/bogus classifiers ranged from 94% to 98%. The resulting precision of the pipeline calculated over candidate alerts in the ILMT frames is 0.91. It also houses a CNN-aided transient candidate classifier that classifies the transient/variable candidates based on host morphology. The test accuracy of the candidate classifier is 98.6%. It has the provision to identify catalogued asteroids and other solar system objects using public databases. The median execution time of the pipeline is approximately 29 minutes per image of 17 minutes exposure. Relevant CNNs have been trained on data acquired with the ILMT during the cycle of October-November 2022. Subsequent tests on those images have confirmed the detection of numerous catalogued asteroids, variable stars, and other uncatalogued sources. The pipeline has been operational and has detected 12 extragalactic transients, including 2 new discoveries in the November 2023-May 2024 observation cycle.

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arXiv2025

The 4m International Liquid Mirror Telescope: Construction, operation, and science

The International Liquid Mirror Telescope (ILMT) project was motivated by the need for an inexpensive 4 metre diameter optical telescope that could be devoted entirely to astronomical surveys. Its scientific programmes include the detection and study of transients, variable objects, asteroids, comets, space debris and low surface brightness galaxies. To this end, a collaboration was formed between the Institute of Astrophysics and Geophysics (Li\`ege University, Belgium), several Canadian universities (University of British Columbia, Laval University, University of Montreal, University of Toronto, York University, University of Victoria) and the Aryabhatta Research Institute of Observational Sciences (ARIES, India). After several years of design work in Belgium and construction in India on the ARIES Devasthal site, the telescope saw its first light on 29 April 2022. Its commissioning phase lasted from May 2022 until June 2023 (beginning of the monsoon). The ILMT was inaugurated on 21 March 2023 and has been in regular operation since October 2023. The telescope continuously observes the sky passing at the zenith using the SDSS g', r', and i' filters. This paper describes the ILMT, its operation, performance and shows some initial results.

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arXiv2023

Necessity of a TDI optical corrector for ILMT observations

The International Liquid Mirror Telescope (ILMT) has recently become operational at the Devasthal Observatory of ARIES, Nainital, India. The ILMT observes in the Time delay integration (TDI) mode where the images are formed by electronically stepping the charges over the pixels of the CCD, along a column. Observations near the zenith impose certain constraints dependent on the latitude such as image deformation due to the star-trail curvature and differential speed. These effects make the stellar trajectories in the focal plane of the ILMT to be hyperbolic, which are corrected for by the introduction of a TDI optical corrector, designed specifically for the ILMT. Here, we report the first results on the effect of this corrector on the trajectories followed by the stars in the ILMT focal plane. Astrometrically calibrating nine nights of data recorded with the ILMT during its first commissioning phase, we find simple (nearly linear) relations between the CCD-y coordinate and the right ascension (RA) of stars and between the CCD-x coordinate and their declination (DEC), respectively, which confirms that the TDI corrector works very fine in converting the stellar trajectories into straight lines.

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arXiv2023

An automated photometric pipeline for the ILMT data

The International Liquid Mirror Telescope (ILMT) is a 4-meter survey telescope continuously observing towards the zenith in the SDSS g', r', and i' bands. This survey telescope is designed to detect various astrophysical transients (for example, supernovae) and very faint objects like multiply-imaged quasars and low surface brightness galaxies. A single scan of a 22$'$ strip of sky contains a large amount of photometric information. To process this type of data, it becomes critical to have tools or pipelines that can handle it efficiently and accurately with minimal human biases. We offer a fully automated pipeline generated in Python to perform aperture photometry over the ILMT data acquired with the CCD in Time Delayed Integration (TDI) mode. The instrumental magnitudes are calibrated with respect to the Pan-STARRS-1 catalogue. The light curves generated from the calibrated magnitudes will allows us to characterize the objects as variable stars or rapidly decaying transients.

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arXiv2023

Automated transient detection in the context of the 4m ILMT

In the era of sky surveys like Palomar Transient Factory (PTF), Zwicky Transient Facility (ZTF) and the upcoming Vera Rubin Observatory (VRO) and ILMT, a plethora of image data will be available. ZTF scans the sky with a field of view of 48 deg$^{2}$ and VRO will have a FoV of 9.6 deg$^{2}$ but with a much larger aperture. The 4m ILMT covers a 22$'$ wide strip of the sky. Being a zenith telescope, ILMT has several advantages like low observation air mass, best image quality, minimum light pollution and no pointing time loss. Transient detection requires all these imaging data to be processed through a Difference Imaging Algorithm (DIA) followed by subsequent identification and classification of transients. The ILMT is also expected to discover several known and unknown astrophysical objects including transients. Here, we propose a pipeline with an image subtraction algorithm and a convolutional neural network (CNN) based automated transient discovery and classification system. The pipeline was tested on ILMT data and the transients as well as variable candidates were recovered and classified.

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arXiv2023

Accessibility of the ILMT survey data

The 4m International Liquid Mirror Telescope (ILMT) continuously scans a 22$'$ wide strip of the zenithal sky and records the images in three broadband filters (g', r' and i') using a 4K$\times$4K CCD camera. In about 10--12 hours of observations during a single night, $\sim$15 GB of data volume is generated. The raw images resulting from the observations in October--November 2022 have been pre-processed and astrometrically calibrated. In order to exploit the scientific capabilities of the ILMT survey data by the larger scientific community, we are disseminating the raw data (along with dark and flat fields) and the astrometrically calibrated data. These data sets can be downloaded by the users to conduct the scientific projects of their interest. In future, the data will be processed in near real-time and will be available via the ARIES data archive portal.

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arXiv2023

Detection and Identification of Asteroids with the 4-m ILMT

A very unique strength of the Devasthal Observatory is its capability of detecting optical transients with the 4-m International Liquid Mirror Telescope (ILMT) and to rapidly follow them up using the 1.3-m Devasthal Fast Optical Telescope (DFOT) and/or the 3.6-m Devasthal Optical Telescope (DOT), installed right next to it. In this context, we have inspected 20 fields observed during 9 consecutive nights in October-November 2022 during the first commissioning phase of the ILMT. Each of these fields has an angular extent of $22^\prime$ in declination by $9 \times 22^\prime$ in right ascension. Combining both a visual search for optical transients and an automatic search for these using an image subtraction technique (see the ILMT poster paper by Pranshu et al.), we report a total of 232 significant transient candidates. After consulting the Minor Planet Center database of asteroids, we could identify among these 219 positions of known asteroids brighter than $V=22$. These correspond to the confirmed positions of 78 distinct known asteroids. Analysis of the remaining CCD frames covering 19 more fields (out of 20) should lead to an impressive number of asteroids observed in only 9 nights. The conclusion is that in order to detect and characterize new supernovae, micro-lensing events, highly variable stars, multiply imaged quasars, etc. among the ILMT optical transients, we shall first have to identify all known and new asteroids. Thanks to its large diameter and short focal length (f/D $\sim$ 2.4), the ILMT turns out to be an excellent asteroid hunter.

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arXiv2023

Serendipitous Detection of Orbital Debris by the International Liquid Mirror Telescope: First Results

Orbital debris presents a growing risk to space operations, and is becoming a significant source of contamination of astronomical images. Much of the debris population is uncatalogued, making the impact more difficult to assess. We present initial results from the first ten nights of commissioning observations with the International Liquid Mirror Telescope, in which images were examined for streaks produced by orbiting objects including satellites, rocket bodies and other forms of debris. We detected 83 streaks and performed a correlation analysis to attempt to match these with objects in the public database. 48\% of these objects were uncorrelated, indicating substantial incompleteness in the database, even for some relatively-bright objects. We were able to detect correlated objects to an estimated magnitude of 14.5 and possibly about two magnitudes greater for the faintest uncorrelated object.

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arXiv2023

The 4m International Liquid Mirror Telescope project

The International Liquid Mirror Telescope (ILMT) project is a scientific collaboration in observational astrophysics between the Li{\`e}ge Institute of Astrophysics and Geophysics (Li{\`e}ge University, Belgium), the Aryabatta Research Institute of observational sciencES (ARIES, Nainital, India) and several Canadian universities (British Columbia, Laval, Montr{\'e}al, Toronto, Victoria and York). Meanwhile, several other institutes have joined the project: the Royal Observatory of Belgium, the National University of Uzbekistan and the Ulugh Beg Astronomical Institute (Uzbekistan) as well as the Pozna{\'n} Observatory (Poland). The Li{\`e}ge company AMOS (Advanced Mechanical and Optical Systems) has fabricated the telescope structure that has been erected on the ARIES site in Devasthal (Uttarakhand, India). It is the first liquid mirror telescope being dedicated to astronomical observations. First light was obtained on 29 April 2022 and commissioning is being conducted at the present time. In this short article, we describe and illustrate the main components of the ILMT. We also highlight the ILMT papers presented during the third BINA workshop, which discuss various aspects of the ILMT science programs.

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arXiv2023

A year-long representation of the ILMT observations in different coordinate systems

The 4m International Liquid Mirror Telescope (ILMT) is the first optical survey telescope in India that performs zenithal observations of a 22$'$ wide strip of the sky. To determine the portion of the sky covered by the ILMT during the entire year, we represent the ILMT Field of View (FoV) in three different coordinate systems - galactic, ecliptic, and equatorial. We adopt a constant declination of $+29^{\circ}21'41.4"$ and varying right ascension (RA) ranges corresponding to the Local Sidereal Time (LST). The observations from June to September are hampered due to the monsoon season. The handiness of such representations will allow us to locate a transient event in the ILMT FoV. This will enable prompt follow-up observations with other facilities.

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arXiv2023

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 achieved its first light on 29$^{\rm th}$ April 2022 and is now undergoing the commissioning phase. It scans the sky in a fixed \ang{;22;} wide strip centred at the declination of $+$\ang{29;21;41.4} and works in \emph{Time Delay Integration (TDI)} mode. We present a full catalog of sources in the ILMT strip derived by crossmatching \textit{Gaia} DR3 with SDSS DR17 and PanSTARRS-1 (PS1) to supplement the catalog with apparent magnitudes of these sources in $g, r$, and $i$ filters. These sources can serve as astrometric calibrators. The release of Gaia DR3 provides synthetic photometry in popular broadband photometric systems, including the SDSS $g, r$, and $i$ bands for $\sim$220 million sources across the 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.

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arXiv2023

Follow-up strategy of ILMT discovered supernovae

The 4m International Liquid Mirror Telescope (ILMT) facility continuously scans the same sky strip ($\sim$22$^\prime$ wide) on each night with a fixed pointing towards the zenith direction. It is possible to detect hundreds of supernovae (SNe) each year by implementing an optimal image subtraction technique on consecutive night images. Prompt monitoring of ILMT-detected SNe is planned under the secured target of opportunity mode using ARIES telescopes (1.3m DFOT and 3.6m DOT). Spectroscopy with the DOT facility will be useful for the classification and detailed investigation of SNe. During the commissioning phase of the ILMT, supernova (SN) 2023af was identified in the ILMT field of view. The SN was further monitored with the ILMT and DOT facilities. Preliminary results based on the light curve and spectral features of SN 2023af are presented.

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arXiv2023

Observation of mulitply imaged quasars with the 4-m ILMT

Gravitationally lensed quasars (GLQs) are known to potentially provide an independent way of determining the value of the Hubble-Lema\^{i}tre parameter $H_{0}$, to probe the dark matter content of lensing galaxies and to resolve tiny structures in distant active galactic nuclei. That is why multiply imaged quasars are one of the main drivers for a photometric monitoring with the 4-m International Liquid Mirror Telescope (ILMT). We would like to answer the following questions -- how many multiply imaged quasars should we be able to detect with the ILMT? And how to derive accurate magnitudes of the GLQ images? Our estimation of the possible number of multiply imaged quasars is $15$, although optimistic forecasts predict up to $50$ of them. We propose to use the adaptive PSF fitting method for accurate flux measurements of the lensed images. During preliminary observations in spring 2022 we were able to detect the quadruply imaged quasar - SDSS J1251+2935 in the $\it{i}$ and $\it{r}$ spectral bands.

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arXiv2023

Survey of Variables with the ILMT

Nestled in the mountains of Northern India, is a 4-metre rotating dish of liquid mercury. Over a 10-year period, the International Liquid Mirror Telescope (ILMT) will survey 117 square degrees of sky, to study the astrometric and photometric variability of all detected objects. One of the scientific programs will be a survey of variable stars. The data gathered will be used to construct a comprehensive catalog of light curves. This will be an essential resource for astronomers studying the formation and evolution of stars, the structure and dynamics of our Milky Way galaxy, and the properties of the Universe as a whole. This catalog will be an aid in our advance to understanding the cosmos and provide deeper insights into the fundamental processes that shape our Universe. In this work, we describe the survey and give some examples of variable stars found in the early commissioning data from the ILMT.

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