IIAP Publications

Exploring an X1.8 flare and associated quasi-periodic pulsations using SDO and Aditya-L1 observations, alongside NFFF extrapolation

Thu, 01 Oct 2026 00:00:00 GMT

Exploring an X1.8 flare and associated quasi-periodic pulsations using SDO and Aditya-L1 observations, alongside NFFF extrapolation Kumar, Pawan; Kumar, Sanjay; Sadashiv; Kanaujiya, Sachin Rajkapoor; Maurya, Yogesh Kumar The paper seeks to explore the initiation of an X1.8 class solar flare (SOL2024-10-09T0125) and the related quasi-periodic pulsations (QPPs), which are situated within NOAA active region 13848. To achieve this, we perform a multi-wavelength analysis of the event utilizing data from the Solar Dynamic Observatory (SDO) and Aditya-L1. Importantly, the observations indicate the emergence of a sigmoidal brightening at the onset of the flare, alongside the evolution of a complex morphology of flare brightenings and ribbons around the peak time of the flare. Furthermore, QPPs are detected during the impulsive phase of the flare, exhibiting a dominant period of approximately 4 minutes in the hard X-ray light curve. In order to comprehend the initiation of the flare, we construct the coronal magnetic field at a pre-flare stage by employing the non-force-free-field (NFFF) extrapolation model. The extrapolated magnetic field illustrates the existence of various significant magnetic features, including a magnetic flux rope, a three-dimensional (3D) null, sheared arcade, and quasiseparatrix layers (QSLs) within the flaring region. The recurrent reconnection occurring at these features is proposed to play a role in the initiation of the flare as well as the associated QPPs. Restricted Access; The original publication is available at springerlink.com.

Transients and stellar activity as revealed by ultraviolet diagnostic tracers

Tue, 01 Dec 2026 00:00:00 GMT

Transients and stellar activity as revealed by ultraviolet diagnostic tracers de Grijs, R; Barstow, Martin A; Chahal, Deepak; Favata, Fabio; Fu, Xiaoting; Gomez De Castro, Ana; Hota, Sipra; Sutaria, F. K Ultraviolet (UV) observations offer unique insights into transient and variable astrophysical phenomena, from the Sun and nearby stars to supernovae and star-forming galaxies. Here, we summarise and review the diagnostic power of the UV spectrum for probing the physical conditions, dynamics and energetics of these events. We trace the historical development of UV astronomy from early satellite missions to the current landscape shaped by the Hubble Space Telescope, the GALaxy Evolution eXplorer, the Neil Gehrels Swift Observatory and AstroSat/UVIT. Particular emphasis is placed on resonance lines such as Mg II h and k, C II, Si IV, C IV and N V, which probe the (solar and) stellar chromosphere and transition region, revealing magnetic heating, shocks and mass loss across stellar types.We examine UV diagnostics of stellar flares, pre-main-sequence activity and rotation–activity correlations, linking them to exoplanetary irradiation and habitability. We then explore the UV view of supernova shock breakout and early-time emission, as well as the far-UV mapping of young stellar populations and hierarchical star formation in the Magellanic Clouds. Together, these aspects illustrate how the UV connects small-scale plasma processes to galactic-scale star formation. Despite remarkable progress, UV transient astronomy remains limited by instrument availability and cadence. Forthcoming missions promise to transform this field by capturing the rapid, luminous phenomena that define the dynamic Universe. Open Access; This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder.

ROCKETS I: Investigating the impact of the rocket effect on two nearby young open clusters encased in infrared bubbles

Thu, 01 Oct 2026 00:00:00 GMT

ROCKETS I: Investigating the impact of the rocket effect on two nearby young open clusters encased in infrared bubbles Arun, R; Maheswar, G; Subramaniam, A; Saha, Piyali; Sudheesh, T. P; Shridharan, B; Mathew, B; Akhil, Krishna R We introduce ROCKETS (Rocket-driven Cluster Kinematics & Triggered Star-formation), a Gaia-based programme investigating kinematic fingerprints of stellar feedback or rocket effect in young star-forming regions. We analyse two young clusters with O-type stars enclosed by mid-infrared bubbles, Collinder 69 and IC 1396 as a methodological demonstration on two nearby benchmark regions. Co-moving candidates are selected within an astrometric ellipse defined by the median and median absolute deviation of Class I/II YSOs with Gaia data. For each star, we compute a relative proper-motion angle (RPMA) relative to the ionising source. In both regions the RPMA distribution shows a strong excess at RPMA <15°, corresponding to sources moving away from the respective ionising sources. We quantify this using the rocket effect index (REI), finding REI≃ 1.1 for Collinder 69 and REI≃ 1.7 for IC 1396. When considering only Class I/II YSOs, the REI of both regions increases to REI ≳ 10. Velocity-structure analysis of the sample shows that the RPMA <15° subset has stronger positive pairwise expansion than the full co-moving population, providing additional support for the rocket effect. The outward-moving stars are not uniformly distributed; instead, their position angles are strongly anisotropic and preferentially aligned towards the bright-rimmed clouds. Gaia colour--magnitude diagrams show no strong age offset between sources moving outward and literature cluster members. The observed kinematic signatures support feedback-driven acceleration of gas and triggered star formation preferentially towards higher density regions of expanding bubbles due to the rocket effect. Open Access; This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence, which permits unrestricted re-use, distribution and reproduction, provided the original article is properly cited.

SDSS-V BHM: Evidence for a link between X-ray weakness and galaxy-scale ionised gas outflows in quasars

Thu, 01 Oct 2026 00:00:00 GMT

SDSS-V BHM: Evidence for a link between X-ray weakness and galaxy-scale ionised gas outflows in quasars Demke, Delvin; Wylezalek, D; Wik, Daniel R; Vivek, M; Rankine, Amy L; Brandt, W. N; Schneider, D. P; Assef, Roberto J; Aydar, Catarina; Anderson, S. F Active galactic nuclei (AGNs) are among the most powerful engines in the Universe. A central open question is how accretion physics, obscuration, and feedback are intertwined in shaping these systems. This paper presents an analysis of SDSS-V–eROSITA Data Level 1 (DL1) data from the 19th data release (DR19). The work is based on SDSS spectra for 2119 soft X-ray selected quasars (0 < z < 0.95), drawn from the eROSITA all-sky catalogue (eRASS1), and complemented by mid-infrared (MIR) data from the Wide-field Infrared Survey Explorer (WISE). We assessed the outflow strength using the W80 measurement of the [O III] λ5007 emission line and derived the virial black hole mass from the broad Hβ emission line. The rest-frame 2–10 keV X-ray luminosity and the 6 µm MIR luminosity were used to determine the X-ray weakness, relative to established luminosity scaling relations. We compared the W80line width, X-ray luminosity, and black hole mass and report a weak negative trend between X-ray weakness and outflow strength for quasarswith W80 ≥ 800 km s−1. These results support the interpretation that the observed X-ray weakness in AGNs may be linked to dense, nuclear-scale outflows. 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.