IIA RAMYA, SNew age observing facilities for Indian astronomy: 2020–2035
In this article, we present the current state of observing facilities available for Indian astronomers in various wavelength bands existing in the country. We also mention a few state-of-the-art astronomical facilities across the globe and contrast them with the Indian facilities. We then present a vision for improving our facilities to raise world-class capabilities. This process involves (a) upgrading the current facilities, (b) partnering in mega-science projects across the globe, (c) continued involvement in International projects, and (d) creating our large-scale facilities. These steps are divided into short, medium, and long-term tasks/projects. Recommendations for building large telescopes with versatile back-end instruments on Indian soil for Indian astronomers have been provided for each wavelength band. All these world-class astronomical observing facilities warrant cutting-edge technologies ranging from signal/image processing, high-performance computing, algorithms, and AI/ML. We hope this exercise will start a discussion and eventually lead to the initiation of these projects, which will result in significant scientific breakthroughs in the coming decades.
IIA SRIRAM, SOptical design studies for national large optical-IR telescope
A 10–12 m class national large optical-IR telescope (NLOT) is envisaged to meet the growing scientific requirements in astronomy and astrophysics. Telescopes of such dimensions can only be made by segmenting the primary mirror, as it eases a more prominent primary mirror’s fabrication, transportation, operation, and maintenance process. This paper presents the various optical designs analyzed for NLOT that can be fabricated using the India TMT Optics Fabrication Facility (ITOFF) at the Centre for Research and Education in Science and Technology (CREST) campus. We present the primary mirror segmentation details, its ideal optical performance, and study each design’s advantages and technical complexities. Based on the above analysis, we have narrowed it down to an optimal design, and its performance analysis is also discussed.
IIA RAJAGURU, S. PStructure and dynamics of the sun’s interior revealed by the helioseismic and magnetic Imager
High-resolution helioseismology observations with the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO) provide a unique three-dimensional view of the solar interior structure and dynamics, revealing a tremendous complexity of the physical processes inside the Sun. We present an overview of the results of the HMI helioseismology program and discuss their implications for modern theoretical models and simulations of the solar interior.
IIA ANUPAMA, G. CThe nature of optical afterglows without Gamma-ray bursts: Identification of AT2023lcr and multiwavelength modeling
In the past few years, the improved sensitivity and cadence of wide-field optical surveys have enabled the discovery of several afterglows without associated detected gamma-ray bursts (GRBs). We present the identification, observations, and multiwavelength modeling of a recent such afterglow (AT2023lcr), and model three literature events (AT2020blt, AT2021any, and AT2021lfa) in a consistent fashion. For each event, we consider the following possibilities as to why a GRBwas not observed: (1) the jet was off-axis; (2) the jet had a low initial Lorentz factor; and (3) the afterglow was the result of an on-axis classical GRB (on-axis jet with physical parameters typical of the GRB population), but the emission was undetected by gamma-ray satellites. We estimate all physical parameters using afterglowpy and Markov Chain Monte Carlo methods from emcee. We find that AT2023lcr, AT2020blt, and AT2021any are consistent with on-axis classical GRBs, and AT2021lfa is consistent with both on-axis low Lorentz factor (Γ0 ≈ 5–13) and off-axis (θobs = 2θjet) high Lorentz factor (Γ0 ≈ 100) jets.
IIA JAYANT JOSHIQuiet Sun Ellerman bombs as a possible proxy for reconnection-driven spicules
Context. Spicules are elongated, jet-like structures that populate the solar chromosphere and are rooted in the lower solar atmosphere. In recent years, high-resolution observations and advanced numerical simulations have provided insights into their properties, structures, and dynamics. However, the formation mechanism of spicules, particularly the more dynamic type II spicules, which are primarily found in the quiet Sun and coronal holes, remains elusive. Aims. This study explores whether quiet Sun Ellerman bombs (QSEBs), which are ubiquitous small-scale magnetic reconnection events in the lower atmosphere, are linked to the formation of type II spicules. Methods. We analysed a high-quality 40-minute time sequence acquired with the Swedish 1-m Solar Telescope. Hβ data were used to observe QSEBs and spicules, while spectropolarimetric measurements in the photospheric Fe I 6173 Å line provided line-of-sight magnetic field information. We employed k-means clustering to automatically detect QSEBs and explored their potential association with spicules. Results. We identified 80 clear cases in which spicules occurred soon after the QSEB onset and not later than 30 s after the ending of the QSEBs. In all these instances, the events involved type II spicules, rapidly fading from the images. The footpoints of the spicules seemed to be rooted in QSEBs, where the onset of QSEBs often preceded the formation of the associated spicules. In addition to these clear cases, we found around 500 other events that hinted at a connection but with some ambiguities. The combined clear and ambiguous cases constitute 34% of the total detected QSEBs and a smaller percentage of the spicules in our dataset. Conclusions. Our findings suggest that a fraction of the type II spicules originate from QSEBs, supporting magnetic reconnection as a potential driving mechanism. In this context, QSEBs and spicules represent the conversion of magnetic energy into thermal and kinetic energy, respectively. We suggest that an observational programme including multiple Balmer lines would likely detect more unambiguous connections between QSEBs and spicules.
IIA DEBIKA CHOWDHURYExploring cosmological gravitational wave backgrounds through the synergy of LISA and the Einstein Telescope
The gravitational wave (GW) interferometers Laser Interferometer Space Antenna (LISA) and the Einstein Telescope (ET) are expected to be functional in the next decade(s), possibly around the same time. They will operate over different frequency ranges, with similar integrated sensitivities to the amplitude of a stochastic GW background (SGWB). We investigate the synergies between these two detectors, in terms of a multiband detection of a cosmological SGWB characterized by a large amplitude, and a broad frequency spectrum. We develop the notion of integrated sensitivity and propose a novel signal-to-noise ratio optimal for characterization of the geometrical properties of the interferometer systems of LISA and the ET operating simultaneously. By investigating various examples of SGWBs, such as those arising from cosmological phase transition, cosmic string, and primordial inflation, we show that LISA and the ET operating together will have the opportunity to assess more effectively the characteristics of the GW spectrum produced by the same cosmological source, but at separate frequency scales. Moreover, the two experiments in tandem can be sensitive to features of early Universe cosmic expansion before big bang nucleosynthesis (BBN), which affects the SGWB frequency profile and which would not be possible to detect otherwise, since two different frequency ranges correspond to two different pre-BBN (or postinflationary) epochs. Besides considering the GW spectrum, we additionally undertake a preliminary study of the sensitivity of LISA and the ET to soft limits of higher-order tensor correlation functions. Given that these experiments operate at different frequency bands, their synergy constitutes an ideal direct probe of squeezed limits of higher-order GW correlators, which cannot be measured operating with a single instrument only.
IIA PRAVABATI CHINGANGBAMGlobal 21 cm signal: a promising probe of primordial features
Inflationary models that involve bursts of particle production generate bump-like features in the primordial power spectrum of density perturbations. These features influence the evolution of density fluctuations, leaving their unique signatures in cosmological observations. A detailed investigation of such signatures would help constrain physical processes during inflation. With this motivation, the goal of this paper is two-fold. First, we conduct a detailed analysis of the effects of bump-like primordial features on the sky-averaged 21 cm signal. Using semi-numerical simulations, we demonstrate that the primordial features can significantly alter the ionization history and the global 21 cm profile, making them a promising probe of inflationary models. We found a special scale (namely, the turnover wavenumber, kturn) at which the effect of primordial bump-like features on the global 21 cm profile vanishes. Also, we found that the behaviour of the primordial features on the global profile and ionization history are quite opposite for k > kturn and k < kturn. We trace the root cause of these behaviours to the effects of primordial features on the halo mass function at high redshifts. Furthermore, we discuss the degeneracy between the astrophysical parameters and the primordial features in detail. Secondly, for a fixed set of astrophysical parameters, we derive upper limits on the amplitude of bump-like features in the range 10-1 < k [ Mpc^-1] < 102 using current limits on optical depth to reionization from CMB data by Planck.
IIA TANMOY SAMANTAThe Detectability of coronal mass ejections in the low corona using multislit extreme-ultraviolet spectroscopy
The spectra of coronal mass ejections (CMEs) in the low corona play a crucial role in understanding their origins and physical mechanisms and enhancing space weather forecasting. However, capturing these spectra faces significant challenges. This paper introduces a scheme of a multislit spectrometer design with five slits, acquiring the global spectra of the solar corona simultaneously with a focus on the spectra of CMEs in the low corona. The chosen wavelength range of the spectrometer (170–180 Å) includes four extreme ultraviolet emission lines (Fe x 174.53 Å, Fe ix 171.07 Å, Fe x 175.26 Å, Fe x 177.24 Å), which provides information on the plasma velocity, density, and temperature. Utilizing a numerical simulation of the global corona for both the on-disk and the off-limb scenarios, we focus on resolving the ambiguity associated with various Doppler velocity components of CMEs, particularly for a fast CME in the low corona. A new application of our decomposition technique is adopted, enabling the successful identification of multiple discrete CME velocity components. Our findings demonstrate a strong correlation between the synthetic model spectra and the inverted results, indicating the robustness of our decomposition method and its significant potential for global monitoring of the solar corona, including CMEs.
IIA NAGARAJU, KTest and Calibration of the Solar Ultraviolet Imaging Telescope (SUIT) on Board Aditya-L1
The Solar Ultraviolet Imaging Telescope (SUIT) on board the Aditya-L1 mission observes the Sun in the 200 – 400 nm wavelength range. This paper presents the results of various on ground and on-board tests and their comparison with the specifications. Moreover, we also present the scheme for data calibration. We demonstrate that the test results are compliant with the specified numbers, except the spatial resolution. Such discrepancy will limit the photometric measurements only, at a scale of 2.2 instead of 1.4 as originally envisioned.The results obtained here show that SUIT observations open a new window for solar observations.
IIA JAYANT MURTHYUltraviolet Background Radiation from Not-So-Dark Matter in the Galactic Halo
Murthy et al. (2025) (hereafter Paper I) have recently reported the discovery of unexpectedly bright diffuse extreme-ultraviolet radiation at high latitudes in both the Northern and Southern Galactic Hemispheres. After correction for extinction by the total interstellar dust in the direction of each observation, the spectra are nearly identical, suggesting that the radiation has a unique source and likely originates in the halo of our galaxy. The observed spectrum extends down to 912 Å, the interstellar hydrogen absorption edge. Radiation even slightly short of that edge would, if ubiquitous, be sufficient to explain the high degree of ionization in our galaxy and throughout the universe. We hypothesize that this newly discovered radiation originates in the slow decay of dark matter. The intensity of the radiation implies that the decay cannot be via the weak interaction, suggesting the existence of a new, even weaker fundamental interaction, consistent with the exceedingly long decay lifetime required.