ItemArticle

Spectral and type I X-ray burst studies of M15 X-2 using NICER observations

Title
Spectral and type I X-ray burst studies of M15 X-2 using NICER observations
Creator
Varun, M.; Thomas, Neal Titus; Giridharan, L.; Gudennavar, S.B.; Bubbly, S.G.
Description
In this work, we present spectral and burst analyses of three thermonuclear type I X-ray bursts (B1, B2, and B3) detected from the ultracompact neutron star low-mass X-ray binary M15 X-2, using data from the Neutron Star Interior Composition Explorer (NICER). Time-averaged spectral fitting with the model tbabsthcompiskbb) suggests that the source was in a soft or soft-intermediate spectral state, characterized by a photon power law index of ??2 and an average mass accretion rate of ?0.09 m?Edd. The type I X-ray bursts exhibited rapid rise times of 1.25?2.75 s, followed by longer decay phases lasting 14.50?23.25 s, with characteristic burst timescales (?) of ?11 s, which are consistent with pure helium burning. Notably, burst B3 displayed a double-peaked profile indicative of a photospheric radius expansion event, from which we inferred the neutron star radius to be 10.8+2.4?2.2 km. Based on the peak flux of the burst, we estimated the source distance to be 10.54+1.43?1.26 kpc under the assumption of isotropic emission, and 14.06+1.90?1.68 kpc for anisotropic emission geometry. A strong ?420 Hz burst oscillation candidate was detected in the cooling tail of burst B1. 2025 Elsevier B.V.
Source
Journal of High Energy Astrophysics;Volume;49;Issue;;Article No.;100461;
Date
01-01-2026
Publisher
Elsevier B.V.
Subject
Accretion; Accretion discs; Stars: neutron; X-rays: binaries; X-rays: bursts, burst oscillation; X-rays: individual: M15 X-2
Coverage
Varun M., 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; Giridharan L., 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

Citation

Varun, M.; Thomas, Neal Titus; Giridharan, L.; Gudennavar, S.B.; Bubbly, S.G., “Spectral and type I X-ray burst studies of M15 X-2 using NICER observations,” CHRIST (Deemed To Be University) Institutional Repository, accessed June 18, 2026, https://archives.christuniversity.in/items/show/22346.

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