AstroSat's view of kHz quasi-periodic oscillations from 4U 1820?30

Title

AstroSat's view of kHz quasi-periodic oscillations from 4U 1820?30

Creator

Giridharan, L.; Thomas, Neal Titus; Gudennavar, S.B.; Bubbly, S.G.

Description

This study presents the spectro-temporal analysis of the neutron star low mass X-ray binary 4U 1820?30, using data from three observations conducted by AstroSat 's Soft X-ray Telescope and Large Array X-ray Proportional Counter. Spectral analysis revealed that the source spectra could be modelled using an absorbed blackbody and a multi-temperature disk model along with a Comptonization model with ?=1.24 ? 1.89 and the inner accretion disk located at an distance of ?17 km from the neutron star. This showed the source to be in the hard spectral state. Temporal analysis revealed the presence of kHz quasi-periodic oscillations (QPOs) with frequencies in the 640 ? 1090 Hz range with root mean squared (RMS) amplitudes between 6 ? 10 per cent and quality factors between 8 ? 42. The RMS amplitude?energy and time lag?energy spectra of the upper and lower kHz QPOs hint them to be caused by modulations of photons having a common radiative mechanism. Moreover, the maximum RMS amplitude and time lag exhibited an anti-correlation with mass accretion rate. Using an analytical relation based on the relativistic precession model, the mass of the neutron star in the system was estimated to be 1.8 M?. The emission radius of one of the detected kHz QPOs was estimated to be ? 17 km. 2025 Elsevier B.V.

Source

Journal of High Energy Astrophysics;Volume;50;Issue;;Article No.;100494;

Date

01-01-2026

Publisher

Elsevier B.V.

Subject

Accretion, accretion discs; Stars: neutron; X-rays: binaries; X-rays: individual: 4U 1820?30

Coverage

Giridharan L., Department of Physics and Electronics, CHRIST University, Karnataka, Bangalore, 560029, India; Thomas N.T., Department of Physics and Electronics, CHRIST University, Karnataka, Bangalore, 560029, India; Gudennavar S.B., Department of Physics and Electronics, CHRIST University, Karnataka, Bangalore, 560029, India; Bubbly S.G., Department of Physics and Electronics, CHRIST University, Karnataka, Bangalore, 560029, India

Rights

Restricted Access; Hardcopy may be available in the library

Relation

ISSN: 22144048;

Format

online

Language

English

Type

Article

Identifier

https://doi.org/10.1016/j.jheap.2025.100494

https://www.scopus.com/pages/publications/105022186237?origin=resultslist