The International Liquid Mirror Telescope (ILMT) covers a 22.3' wide strip of sky in declination (δ), centred at δ = +29° 21' 41.4” and right ascension (α) in the range 0 h <= α < 24 h. Having a short focal length (f /D 2.4) and a large diameter (4 m), makes the ILMT an excellent asteroid hunter. The ILMT began its 4th cycle in October 2024, running through May 2025. The astrometric accuracy has been improved to 0.1” , and the PyLMT - a detection and classification pipeline -, has been fine-tuned using data from previous cycles. The current detection rate is tens of transients detected each night with high accuracy in classification and identification. We present statistical results for the asteroids detected during ILMT's Cycles 1-4. We first evaluate the astrometric performance of the detections across different ecliptic latitude ranges. We then describe the positions, apparent motions, and V magnitudes predicted by the Minor Planet Center (MPC) for the asteroids observed in the SDSS g', r', and i' bands. Finally, we assess the ILMT's potential for detecting near-Earth objects (NEOs), potentially hazardous asteroids (PHAs), and comets.

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.

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 (Liège 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.

Recent research suggests a correlation between the variability and intrinsic brightness of quasars. If calibrated, this could lead to the use of quasars on the cosmic distance ladder, but this work is currently limited by lack of quasar light curve data with high cadence and precision. The Python photometric data pipeline SunPhot is being developed as part of preparations for an upcoming quasar variability survey with the International Liquid Mirror Telescope (ILMT). SunPhot uses aperture photometry to directly extract light curves for a catalogue of sources from calibrated ILMT images. SunPhot v.2.1 is operational, but the project is awaiting completion of ILMT commissioning.

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.

Gravitationally lensed quasars (GLQs) are known to potentially provide an independent way of determining the value of the Hubble-Lemaître parameter H0, 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 i’ and r’ spectral bands.

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 nine consecutive nights in October-November 2022 during the first commissioning phase of the ILMT. Each of these fields has an angular extent of 22′ in declination by 9×22′ in right ascension. Combining both a visual search for optical transients and an automatic search for these using an image subtraction technique (see Pranshu et al., 2024), 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 nine 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 ≃ 2.4), the ILMT turns out to be an excellent asteroid hunter.

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.

The 4m International Liquid Mirror Telescope (ILMT) facility continuously scans the same sky strip (∼22′ 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.

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°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.

В статье приведены результаты фотометрического исследования наблюдательных данныхчетырехкомпонентного гравитационно-линзированного квазара GRAL J024848.7+191331в Майданакской обсерватории. Показаны кривые блеска системы в целом и ее отдельныхкомпонентов. Система в целом показала умеренную амплитуду переменности, однакоблеск компонентов меняется более активно, до 0.25m звездных величин. Явных признаковмикролинзирования не обнаружено. Вычислены наиболее вероятные значения временныхзадержек: ΔtAB=−1.7±1.6 дней, ΔtAC=−2.2±1.8 дней, ΔtAD=–4.8±2.8 дней. Эти величины согласуются с найденными ранее модельными расчетами.

Low surface brightness (LSB) galaxies make up a significant fraction of the luminosity density of the local universe. Their low surface brightness suggests a different formation and evolution process compared to more-typical high-surface-brightness galaxies. This study presents an analysis of LSB galaxies found in images obtained by the International Liquid Mirror Telescope during the observation period from October 24 to November 1, 2022. 3,092 LSB galaxies were measured and separated into blue and red LSB categories based on their $g'-i'$ colours. In these samples, the median effective radius is 4.7 arcsec, and the median value of the mean surface brightness within the effective radius is 26.1 mag arcsec$^{-2}$. The blue LSB galaxies are slightly brighter than the red LSB galaxies. No significant difference of ellipticity was found between the blue and the red LSB galaxies.

The article presents the results of long-term photometric monitoring of two binary gravitationally lensed quasars, SDSS J2124 + 1632 and SDSS J0806 + 2006, carried out at the Maidanak Observatory in 2017–2022. The obtained light curves of the lensed components of both systems are analyzed. The variability of SDSS J2124 + 1632 turned out to be quite large: up to 0m.50 for the system as a whole and up to 0m.75 for component A. Long-term microlensing was found against the background of a general increase in the apparent brightness of the quasar source. The brightness variations in SDSS J0806 + 2006 are less intense: the range is about 0m.20 for the system as a whole, and up to 0m.25 for both components. Analysis of the light curves did not show the presence of microlensing here. We also calculated the probable values of the time delay: Δ t_AB=102± 20 days (component B is in the lead) and Δ t_AB=-53.0± 6.0 days (component A is in the lead) in SDSS J2124 + 1632 and SDSS J0806 + 2006, respectively. The value of Δ t_AB for SDSS J2124 + 1632 is consistent with previously found time delays for binary gravitationally lensed systems. In the case of the second system, the time delay is consistent with earlier theoretical calculations, which suggested that the time delay should be about 50 days.

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.

The International Liquid Mirror Telescope (ILMT) is a 4-meter class survey telescope. It achieved its first light on 29th April 2022 and is now undergoing the commissioning phase. It scans the sky in a fixed wide strip centred at the declination of and works in Time Delay Integration (TDI) mode. We present a full catalog of sources in the ILMT strip derived by crossmatching 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 ∼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.

The International Liquid Mirror Telescope (ILMT) project is a scientific collaboration in observational astrophysics between the Liège Institute of Astrophysics and Geophysics (Liège University, Belgium), the Aryabatta Research Institute of observational sciencES (ARIES, Nainital, India) and several Canadian universities (British Columbia, Laval, Montréal, 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 Poznan Observatory (Poland). The Liège company AMOS (Advanced Mechanical and Optical Systems) has built 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 29th 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.

The present article is based upon an invited talk delivered at the occasion of the inauguration of the 4m International Liquid Mirror Telescope (ILMT) which took place in Devasthal (ARIES, Uttarakhand, India) on 21st of March 2023. We present hereafter a short history of the liquid mirror telescopes and in particular of the 4m ILMT which is the first liquid mirror telescope entirely dedicated to astrophysical observations. We discuss a few preliminary scientific results and illustrate some direct CCD images taken during the first commissioning phase of the telescope. We invite the reader to refer to the series of ILMT poster papers published in these same proceedings of the BINA3 workshop for more details about the instrument, operation, first observations, performance and scientific results.

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.

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×4K CCD camera. In about 10–12 hours of observations during a single night, ∼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.

В работе представлены результаты фотометрической обработки цифровых изображенийнового двойного гравитационно-линзированного квазара SDSS J2124+1632, наблюдавшаяся в Майданакской обсерватории. Кривые блеска показали, что яркость компонентов в течение 2018-2021 г.г. имеет активную переменность, вызванную, в том числе, микролинзированием. Вычислено вероятное значение времени задержки ∆tAB = 105.3±18.8 дней, причем лидирующим оказался компонент В. Эта величина согласуется с ранее найденнымивременными задержками для двойных гравитационно-линзированных квазаров с подобнойконфигурацией.