Publications from IIAP are submitted here http://hdl.handle.net/2248/1 2026-11-09T09:15:47Z 2026-11-09T09:15:47Z Bhowmik, Arkadip Chowdhury, Avijit Chakrabarti, Sayan http://hdl.handle.net/2248/9090 2026-11-05T06:31:34Z 2026-10-15T00:00:00Z

Ringdown and tide: fingerprints of dark matter halo profiles Bhowmik, Arkadip; Chowdhury, Avijit; Chakrabarti, Sayan Astrophysical black holes (BHs) are not isolated, but embedded in matter supplied by their host galaxies. We study how the shape of a surrounding dark matter halo modifies the ringdown and tidal response of an asymptotically flat, static, spherically symmetric BH. The halo is modeled as an anisotropic Einstein cluster with vanishing radial pressure and a generalized (α,β,γ) density profile, supplemented by an inner cutoff near the BH and, where required, an outer tidal truncation. We derive the axial gravitational perturbation equation and compute the quasinormal mode (QNM) spectrum using sixth-order Wentzel-Kramers-Brillouin (WKB) methods and time-domain evolutions. The halo redshifts both the oscillation frequency and the damping rate, by an amount set not only by the halo compactness but also by the profile parameters: the inner logarithmic slope γ dominates for centrally concentrated halos, while α and β give subleading but profile-dependent corrections. In the eikonal limit, the shift is governed by a single redshift integral encoding the halo mass distribution outside the light ring, explaining the close correspondence between the QNM frequencies, the light ring frequency, and the Lyapunov exponent. We also show that different combinations of compactness and profile shape can yield nearly degenerate ringdown spectra. Time-domain evolutions confirm the WKB frequencies and display the expected late-time Price-law decay, with an intermediate tail controlled by the outer density falloff for slowly decaying profiles. Finally, we compute the static axial tidal Love number and show that it probes the halo with a radial weighting different from the ringdown sector. The combined ringdown and tidal response therefore provides a possible way to distinguish environmental effects from genuine deviations of the vacuum BH geometry. Open Access

2026-10-15T00:00:00Z Dubey, Nitesh K Kolekar, Sanved http://hdl.handle.net/2248/9089 2026-11-05T06:28:54Z 2026-10-15T00:00:00Z

Hawking-page phase transition for pure lovelock black holes Dubey, Nitesh K; Kolekar, Sanved We investigate the thermodynamic properties of static, spherically symmetric anti--de Sitter (AdS) black holes, focusing on the interplay between characteristic temperatures, as well as on the universality of Ruppeiner scalar curvature at the Hawking-Page (HP) phase transition. In particular, we study the relation between the minimum temperature and the HP phase transition temperature for static, spherically symmetric AdS black holes in pure Lovelock gravity. For the electromagnetically neutral case in Einstein gravity, the minimum temperature in (d+1) dimensions coincides with the HP transition temperature in d dimensions, while in higher pure Lovelock theories this relation is modified by a dimension- and order-dependent factor, reducing to the Einstein result in appropriate limits. For charged AdS black holes, in the grand canonical ensemble, in general relativity, the two temperatures differ by a simple dimension-dependent factor, whereas no universal relation persists in higher curvature pure Lovelock theories. We further analyze the normalized Ruppeiner scalar curvature at the HP transition and show that it is a universal constant depending only on the spacetime dimension for electromagnetically neutral black holes in pure Lovelock theories. The normalized scalar curvature remains a constant, under appropriate conditions, even for the charged static spherically symmetric black holes in the grand canonical ensemble for the Einstein theory case, whereas in general pure Lovelock theories it depends on thermodynamic parameters such as pressure and electrostatic potential, asymptotically approaching a constant in the large-pressure or simultaneous large-potential and large-pressure limits. Open Access

2026-10-15T00:00:00Z Kumar, Hirdesh Rajaguru, S. P Brajesh Kumar http://hdl.handle.net/2248/9088 2026-11-05T06:25:43Z 2026-10-01T00:00:00Z

Nonzero phase shift of evanescent acoustic waves in the lower solar atmosphere Kumar, Hirdesh; Rajaguru, S. P; Brajesh Kumar Context. The phase behavior of acoustic waves in the lower solar atmosphere provides important information about wave propagation. While previous studies have reported nonzero phase shifts in the evanescent frequency range and possible sign reversals near the frequency 3.0 mHz, the observational robustness and physical interpretation of these signatures remain uncertain. Aims. We investigated the phase shifts and travel times of acoustic waves within the photosphere and across the photosphere-chromosphere interface in the quiet-Sun atmosphere and also assessed their height and frequency-dependent behavior. Methods. Multi-height line-of-sight velocities were inferred using the bisector method applied to the photospheric Fe I 6173 Å and chromospheric Hα 6563 Å spectral lines observed with the Swedish Solar Telescope (SST). Fast Fourier transform analysis was employed to determine the phase shifts and travel times between the velocity signals derived at different bisector levels. In addition, k--ω phase-difference diagnostics were used to examine the wave number and frequency-dependent characteristics of wave propagation. Results. Nonzero phase shifts are detected for acoustic waves in the evanescent frequency range within the photosphere, corresponding to phase travel times on the order of 1 s. In contrast to previous studies, no reversal in the sign of the phase shift or travel time is observed near 3 mHz in the Fe I 6173 Å observations. The measured phase shifts maintain the same sign throughout the investigated frequency range, suggesting the influence of complex wave dynamics. Measurements between velocities inferred from the Fe I and Hα lines exhibit a decrease in the 6--8 mHz frequency range. Our k--ω phase-difference analysis shows that this behavior is mainly caused by phase wrapping near 6.5 mHz rather than by an intrinsic change in wave propagation. Conclusions. Our findings support the presence of nonzero phase differences within the evanescent frequency range while revealing discrepancies with earlier reports of phase-shift sign reversals near 3 mHz. We also highlight the importance of proper phase unwrapping for an accurate interpretation of acoustic-wave propagation in the lower solar atmosphere. Open Access; Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

2026-10-01T00:00:00Z Agarwal, Anjali Mishra, Wageesh Ramesh, R Priyal, M Zhukov, Andrei N Singh, J Gopalswamy, N Khuntia, Soumyaranjan Sasikumar Raja, K Bourgoignie, B Dolla, L Shestov, S Fineschi, S Gunar, S Lamy, P Mierla, M Peter, H Rudawy, P Tsinganos, K http://hdl.handle.net/2248/9087 2026-11-05T06:22:58Z 2026-10-01T00:00:00Z

Coordinated coronagraphic observations from proba-3 and Aditya-L1: Investigating coronal mass ejection energetics in the inner corona Agarwal, Anjali; Mishra, Wageesh; Ramesh, R; Priyal, M; Zhukov, Andrei N; Singh, J; Gopalswamy, N; Khuntia, Soumyaranjan; Sasikumar Raja, K; Bourgoignie, B; Dolla, L; Shestov, S; Fineschi, S; Gunar, S; Lamy, P; Mierla, M; Peter, H; Rudawy, P; Tsinganos, K Context. Constraining the plasma properties and energetics of coronal mass ejections (CMEs) in the inner corona is essential for understanding their early evolution, yet it remains challenging because of limited observations. Aims. We investigate the mass and density evolution as well as energy partitioning of two CMEs observed on 14 and 16 September 2025, and assess the potential of coordinated Proba-3/ASPIICS and Aditya-L1/VELC observations to constrain CME energetics in the low corona. Methods. We present the first coordinated observations of CMEs obtained simultaneously by Proba-3/ASPIICS and Aditya-L1/VELC. Using ASPIICS white-light observations, we estimated the CME mass, volume, number density, and the evolution of kinetic, thermal, and magnetic energies. Magnetic energies were estimated from observed CME properties using observationally constrained, physically motivated assumptions. Simultaneous VELC Fe XIV 5303 A observations provide independent estimates of the emission measure, electron number density, thermal energy, and CME lateral extent. Results. The electron number density evolves as ne χ r-33 for the 14 September CME and as ne ∝ r-6 for the 16 September CME. The two events exhibit markedly different energy partitioning in the low corona. For the 14 September CME, the kinetic and magnetic energies are comparable, while the thermal energy remains nearly two orders of magnitude smaller, indicating limited plasma heating. In contrast, the 16 September CME exhibits a substantial thermal-energy enhancement, with thermal energy eventually becoming comparable to kinetic energy. For both CMEs, the estimated magnetic energy remains comparable to or exceeds the kinetic energy over the observed height. Conclusions. Our results demonstrate the scientific potential of synergetic ASPIICS and VELC observations for constraining the CME mass, density, and energetics in the inner corona, providing new observational constraints on the early evolution of CMEs. Open Access; Open Access article, published by EDP Sciences, under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

2026-10-01T00:00:00Z