http://localhost:8080/xmlui/handle/123456789/17 Mon, 20 Apr 2026 15:21:28 GMT 2026-04-20T15:21:28Z http://dspace.aries.res.in:80/xmlui/bitstream/id/249/rese.jpg http://localhost:8080/xmlui/handle/123456789/17 http://localhost:8080/xmlui/handle/123456789/1660 Very-high-frequency oscillations in the main peak of a magnetar giant flare Castro-Tirado, A. J. et.al.; Pandey, S. B. Magnetars are strongly magnetized, isolated neutron stars1–3 with magnetic felds up to around 1015 gauss, luminosities of approximately 1031–1036 ergs per second and rotation periods of about 0.3–12.0 s. Very energetic giant fares from galactic magnetars (peak luminosities of 1044–1047 ergs per second, lasting approximately 0.1 s) have been detected in hard X-rays and soft γ-rays4 , and only one has been detected from outside our galaxy5 . During such giant fares, quasi-periodic oscillations (QPOs) with low (less than 150 hertz) and high (greater than 500 hertz) frequencies have been observed6–9 , but their statistical signifcance has been questioned10. High-frequency QPOs have been seen only during the tail phase of the fare9 . Here we report the observation of two broad QPOs at approximately 2,132 hertz and 4,250 hertz in the main peak of a giant γ-ray fare11 in the direction of the NGC 253 galaxy12–17, disappearing after 3.5 milliseconds. The fare was detected on 15 April 2020 by the Atmosphere–Space Interactions Monitor instrument18,19 aboard the International Space Station, which was the only instrument that recorded the main burst phase (0.8–3.2 milliseconds) in the full energy range (50 × 103 to 40 × 106  electronvolts) without sufering from saturation efects such as deadtime and pile-up. Along with sudden spectral variations, these extremely high-frequency oscillations in the burst peak are a crucial component that will aid our understanding of magnetar giant fares Wed, 01 Dec 2021 00:00:00 GMT http://localhost:8080/xmlui/handle/123456789/1660 2021-12-01T00:00:00Z http://localhost:8080/xmlui/handle/123456789/1659 Investigation of two coronal mass ejections from circular ribbon source region: Origin, Sun-Earth propagation and Geoeffectiveness Ibrahim, Syed ,et.al.; Uddin, Wahab In this article, we compare the properties of two coronal mass ejections (CMEs) that show similar source region characteristics but different evolutionary behaviors in the later phases. We discuss the two events in terms of their near-Sun characteristics, interplanetary evolution and geoeffectiveness. We carefully analyzed the initiation and propagation parameters of these events to establish the precise CME interplanetary CME (ICME) connection and their near-Earth consequences. The first event is associated with poor geomagnetic storm disturbance index (Dst ≈-20 nT) while the second event is associated with an intense geomagnetic storm of DST ≈-119 nT. The configuration of the sunspots in the active regions and their evolution are observed by Helioseismic and Magnetic Imager (HMI). For source region imaging, we rely on data obtained from Atmospheric Imaging Assembly (AIA) on board Solar Dynamics Observatory (SDO) and Hα filtergrams from the Solar Tower Telescope at Aryabhatta Research Institute of Observational Sciences (ARIES). For both the CMEs, flux rope eruptions from the source region triggered flares of similar intensities (≈M1). At the solar source region of the eruptions, we observed a circular ribbon flare (CRF) for both cases, suggesting fan-spine magnetic configuration in the active region corona. The multi-channel SDO observations confirm that the eruptive flares and subsequent CMEs were intimately related to the filament eruption. Within the Large Angle and Spectrometric Coronograph (LASCO) field of view (FOV) the two CMEs propagated with linear speeds of 671 and 631 km s−1 , respectively. These CMEs were tracked up to the Earth by Solar Terrestrial Relations Observatory (STEREO) instruments. We find that the source region evolution of CMEs, guided by the large-scale coronal magnetic field configuration, along with near-Sun propagation characteristics, such as CME-CME interactions, played important roles in deciding the evolution of CMEs in the interplanetary medium and subsequently their geoeffectiveness. Tue, 01 Feb 2022 00:00:00 GMT http://localhost:8080/xmlui/handle/123456789/1659 2022-02-01T00:00:00Z http://localhost:8080/xmlui/handle/123456789/1658 Deciphering Solar Magnetic Activity: 140 Years of the ‘Extended Solar Cycle’ – Mapping the Hale Cycle McIntosh, Scott W. ,et.al.; Banerjee, Dipankar We investigate the occurrence of the “extended solar cycle” (ESC) as it occurs in a host of observational data spanning 140 years. Investigating coronal, chromospheric, photospheric, and interior diagnostics, we develop a consistent picture of solar activity migration linked to the 22-year Hale (magnetic) cycle using superposed epoch analysis (SEA) and previously identified Hale cycle termination events as the key time for the SEA. Our analysis shows that the ESC and Hale cycle, as highlighted by the terminator-keyed SEA, is strongly recur rent throughout the entire observational record studied, some 140 years. Applying the same SEA method to the sunspot record confirms that Maunder’s butterfly pattern is a subset of the underlying Hale cycle, strongly suggesting that the production of sunspots is not the fundamental feature of the Hale cycle, but the ESC is. The ESC (and Hale cycle) pattern highlights the importance of 55◦ latitude in the evolution, and possible production, of solar magnetism. Wed, 01 Dec 2021 00:00:00 GMT http://localhost:8080/xmlui/handle/123456789/1658 2021-12-01T00:00:00Z http://localhost:8080/xmlui/handle/123456789/1657 X-ray confirmation of the intermediate polar IGR J16547-1916 Joshi, A.,et.al.; Pandey, J. C.; Rawat, N. Using X-ray observations from the NuSTAR and Swift satellites, we present temporal and spectral properties of an intermediate polar (IP) IGR J16547-1916. A persistent X-ray period at ∼546 s confirming the optical spin period obtained from previous observations is detected. The detection of a strong X-ray spin pulse reinforces the classification of this system as an intermediate polar. The lack of orbital or side-band periodicities in the X-rays implies that the system is accreting predominantly via a disk. A variable covering absorber appears to be responsible for the spin pulsations in the low energy range. In the high energy band, the pulsations are likely due to the self occultation of tall shocks above the white dwarf surface. The observed double-humped X-ray spin pulse profile indicates two-pole accretion geometry with tall accretion regions in short rotating IP IGR J16547-1916. We present the variation of the spin pulse profile over an orbital phase to account for the effects of orbital motion on the spin pulsation. X-ray spectra obtained from the contemporaneous observations of Swift and NuSTAR in the 0.5–78.0 keV energy band are modeled with a maximum temperature of 31 keV and a blackbody temperature of 64 eV, along with a common column density of 1.8 × 1023 cm−2 and a power-law index of −0.22 for the covering fraction. An additional Gaussian component and a reflection component are needed to account for a fluorescent emission line at 6.4 keV and the occurrence of X-ray reflection in the system. We also present the spin phase-resolved spectral variations of IGR J16547-1916 in the 0.5–78.0 keV energy band and find dependencies in the X-ray spectral parameters during the rotation of the white dwarf. Sat, 01 Jan 2022 00:00:00 GMT http://localhost:8080/xmlui/handle/123456789/1657 2022-01-01T00:00:00Z