arXiv subjects

Gokul Singh Mehra

Publications and source records attributed to Gokul Singh Mehra.

3 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.

astro-ph.IM↗

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.

astro-ph.IM↗

arXiv2026

Detection and identification of asteroids with the 4-m ILMT

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.

astro-ph.EP↗