arXiv subjects

T. S. Kumar

Publications and source records attributed to T. S. Kumar.

10 recordsLinked to original sources

arXiv2026

Exploring the multi-wavelength properties of the high energetic event ZTF20abbiixp/GRB 200524A: from prompt emission to afterglow

We conducted a comprehensive multi-wavelength analysis of a high energetic long-duration ZTF20abbiixp / GRB~200524A detected by \textit{Fermi} Gamma Ray Burst Monitor (GBM). Our study combines extended high-energy observations from multiple space-based observatories including \textit{Fermi} with broadband afterglow data spanning X-ray to radio wavelengths, complemented by extensive photometric and spectroscopic follow-up from several ground-based optical facilities worldwide like 3.6-m Devasthal Optical Telescope (DOT). ZTF20abbiixp / GRB~200524A exhibits almost negligible spectral lag, likely arising from the presence of multiple overlapping emission episodes, a property uncommon among long-duration bursts. The burst additionally shows a clear intensity-tracking evolution of the prompt-emission spectral parameters. The broadband afterglow light curve best fits with a broken powerlaw with a break at $10^{5}$ s since the GBM trigger. The electron powerlaw index (p) calculated from the temporal and spectral slopes fail to distinguish between a interstellar medium and a wind environment. Our custom-developed afterglow model fits the panchromatic data well, combining forward shock (FS) and reverse shock (RS) emission. The RS contribution required to fit the early time optical data. The inferred afterglow model parameters suggest that ZTF20abbiixp / GRB~200524A is a high energetic burst expanding into a dense ISM environment, with a relatively large value of the fraction of energy going to accelerating electron and magnetic field ($\epsilon_B$).

astro-ph.HE↗

arXiv2025

Neuromorphic Cameras in Astronomy: Unveiling the Future of Celestial Imaging Beyond Conventional Limits

To deepen our understanding of optical astronomy, we must advance imaging technology to overcome conventional frame-based cameras' limited dynamic range and temporal resolution. Our Perspective paper examines how neuromorphic cameras can effectively address these challenges. Drawing inspiration from the human retina, neuromorphic cameras excel in speed and high dynamic range by utilizing asynchronous pixel operation and logarithmic photocurrent conversion, making them highly effective for celestial imaging. We use 1300 mm terrestrial telescope to demonstrate the neuromorphic camera's ability to simultaneously capture faint and bright celestial sources while preventing saturation effects. We illustrate its photometric capabilities through aperture photometry of a star field with faint stars. Detection of the faint gas cloud structure of the Trapezium cluster during a full moon night highlights the camera's high dynamic range, effectively mitigating static glare from lunar illumination. Our investigations also include detecting meteorite passing near the Moon and Earth, as well as imaging satellites and anthropogenic debris with exceptionally high temporal resolution using a 200mm telescope. Our observations show the immense potential of neuromorphic cameras in advancing astronomical optical imaging and pushing the boundaries of observational astronomy.

astro-ph.IM↗

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.

astro-ph.IM↗

arXiv2023

Characterization of a deep-depletion 4K x 4K CCD Detector System designed for ADFOSC

We present the characterization of the CCD system developed for the ADFOSC instrument on the 3.6m Devasthal Optical Telescope (DOT). We describe various experiments performed to tune the CCD controller parameters to obtain optimum performance in single and four-port readout modes. Different methodologies employed for characterizing the performance parameters of the CCD, including bias stability, noise, defects, linearity, and gain, are described here. The CCD has grade-0 characteristics at temperatures close to its nominal operating temperature of $-120^\circ$C. The overall system is linear with a regression coefficient of 0.9999, readout noise of 6 electrons, and a gain value close to unity. We demonstrate a method to calculate the dark signal using the gradient in the bias frames at lower temperatures. Using the optimized setting, we verify the performance of the CCD detector system on-sky using the ADFOSC instrument mounted on the 3.6m DOT. Some science targets were observed to evaluate the detector's performance in both imaging and spectroscopic modes.

astro-ph.IM↗

arXiv2019

VR CCD photometry of variable stars in globular cluster NGC 4147

We present results of a search for variable stars in a region of the globular cluster NGC 4147 based on photometric observations with 4k x 4k CCD imager mounted at the axial port of the recently installed 3.6 m Devasthal optical telescope at Aryabhatta Research Institute of Observational Sciences, Nainital, India. We performed time series photometry of NGC 4147 in V and R bands, and identified 42 periodic variables in the region of NGC 4147, 28 of which have been detected for the first time. Seventeen variable stars are located within the half light radius $\lesssim$ 0.48 arcmin, of which 10 stars are newly identified variables. Two of 10 variables are located within the core radius $\lesssim$ 0.09 arcmin. Based on the location in the $V/(V-R)$ colour magnitude diagram and variability characteristics, 7, 8, 5 and 1 newly identified probable member variables are classified as RRc, EA/E, EW and SX Phe, respectively. The metallicity of NGC 4147 estimated from light curves of RRab and RRc stars with the help of Fourier decomposition is found to be characteristics of Oosterhoff II. The distance derived using light curves of RRab stars is consistent with that obtained from the observed $V/(V-R)$ colour-magnitude diagram.

astro-ph.SR↗

arXiv2019

Optical detection of a GMRT-detected candidate high-redshift radio galaxy with 3.6-m Devasthal optical telescope

We report optical observations of TGSS J1054+5832, a candidate high-redshift ($z=4.8\pm2$) steep-spectrum radio galaxy, in $r$ and $i$ bands using the faint object spectrograph and camera mounted on 3.6-m Devasthal Optical Telescope (DOT). The source previously detected at 150 MHz from Giant Meterwave Radio Telescope and at 1420 MHz from Very Large Array has a known counterpart in near-infrared bands with $K$-band magnitude of AB 22. The source is detected in $i$-band with AB$24.3\pm0.2$ magnitude in the DOT images presented here. The source remains undetected in the $r$-band image at a 2.5$σ$ depth of AB 24.4 mag over an $1.2''\times1.2''$ aperture. An upper limit to $i-K$ color is estimated to be $\sim$2.3, suggesting youthfulness of the galaxy with active star formation. These observations highlight the importance and potential of the 3.6-m DOT for detections of faint galaxies.

astro-ph.GA↗

arXiv2019

First-light images from low dispersion spectrograph-cum-imager on 3.6-meter Devasthal Optical Telescope

A low dispersion spectrograph-cum-imager has been developed and assembled in ARIES, Nainital. The optical design of the spectrograph consists of a collimator and a focal reducer converting the f/9 beam from the 3.6-m Devasthal optical telescope to a nearly f/4.3 beam. The instrument is capable of carrying out broad-band imaging, narrow-band imaging and low-resolution (λ/Δλ<2000) slit spectroscopy in the wavelength range 350-1050 nm. A closed-cycle cryogenically cooled charge-coupled device camera, also assembled in ARIES, is used as the main imaging device for the spectrograph. The first images from the spectrograph on the telescope assert seeing-limited performance free from any significant optical aberration. An i-band image of the galaxy cluster Abell 370 made using the spectrograph shows faint sources down to ~25 mag. The quality and sensitivity of the optical spectrums of the celestial sources obtained from the spectrograph are as per the expectations from a 3.6-m telescope. Several new modes of observations such as polarimetry, fast-imaging, and monitoring of the atmospheric parameters are being included in the spectrograph. Using a test setup, single optical pulses from the Crab pulsar were detected from the telescope. The spectrograph is one of the main back-end instruments on the 3.6-m telescope for high sensitivity observations of celestial objects.

astro-ph.IM↗

arXiv2009

Development of ARIES Baker-Nunn camera to a wide-field Imaging Telescope with CCD

ARIES Baker-Nunn Schmidt telescope project is converting a Baker-Nunn satellite tracking camera for Astronomical research. Original Baker-Nunn camera produces an extremely large (5X30 degree) curved focal plane at the prime focus for photographic imaging. We present here the re-designing of the camera produces a wide (4 X 4 degree) flat field of view for CCD imaging observations, which have many scientific potentials in Astronomy. Imaging performance of the CCD camera is also estimated.

astro-ph.IM↗

arXiv2008

Optical polarimetric study of open clusters: Distribution of Interstellar matter towards NGC 654

We present new B, V and R linear polarimetric observations for 61 stars towards the region of the young open cluster NGC 654. In this study we found evidence for the presence of at least two layers of dust along the line of sight to the cluster. The distances to the two dust layers are estimated to be ~ 200 pc and ~ 1 kpc which are located much closer to the Sun than the cluster (~ 2.4 kpc). Both the dust layers have their local magnetic field orientation nearly parallel to the direction of the Galactic plane. The foreground dust layer is found to have a ring morphology with the central hole coinciding with the center of the cluster. The foreground dust grains are suggested to be mainly responsible for both the observed differential reddening and the polarization towards the cluster.

astro-ph↗

arXiv2007

Broad Band Optical Polarimetric Study of IC 1805

We present the BVR broad band polarimetric observations of 51 stars belonging to the young open cluster IC 1805. Along with the photometric data from the literature we have modeled and subtracted the foreground dust contribution from the maximum polarization (P_{max}) and colour excess (E_{B-V}). The mean value of the P_max for intracluster medium and the foreground are found to be 5.008 +/-0.005 % and 4.865 +/-0.022 % respectively. Moreover, the mean value of the wavelength of maximum polarization (lambda_{max}) for intracluster medium is 0.541 +/- 0.003 micro m, which is quite similar as the general interstellar medium (ISM). The resulting intracluster dust component is found to have negligible polarization efficiency as compared to interstellar dust. Some of the observed stars in IC 1805 have shown the indication of intrinsic polarization in their measurements.

astro-ph↗