Title:	Changes in the distribution of circum-binary material around the HMXB GX 301-2 during a rapid spin-up episode of the neutron star
Authors:	Manikantan, Hemanth Paul, Biswajit Roy, Kinjal Rana, Vikram
Keywords:	accretion accretion discs stars: neutron pulsars: general X-rays: binaries X-rays: individual GX 301-2
Issue Date:	9-Jan-2023
Publisher:	Oxford University Press
Citation:	Monthly Notices of the Royal Astronomical Society, 2023, Vol.520, p1411
Abstract:	Some accretion-powered X-ray pulsars with supergiant companion stars undergo occasional rapid spin-up episodes that last for weeks to a few months. We explore the changes in the accretion environment of the pulsar GX 301-2 during its latest 80 days long spin-up episode in 2019 when the spin frequency of the pulsar increased by ∼2 per cent over two orbits of the binary. By performing time-resolved spectroscopy with the MAXI/GSC spectra of the source, we estimated the equivalent hydrogen column density and equivalent width of the iron fluorescence line during the spin-up episode, and compared them with the long-term average values estimated by orbital-phase-resolved spectroscopy. The measured absorption column density during the spin-up episode is about twice that of an average orbit, while the equivalent width of the iron line is less than half of an average orbit. Though the spin-up episode started immediately after a pre-periastron flare and lasted for the two consecutive orbits of the binary, the associated enhancement in luminosity started a few days after the pre-periastron flare and lasted only during the first orbit, and some enhancement was seen again during the pre-periastron passage of the second orbit. The absorption column density and iron line equivalent width vary throughout the spin-up episode and are distinct from an average orbit. These observations indicate a significant change in the accretion and reprocessing environment in GX 301-2 during the spin-up episode and may hold important clues for the phenomenon in this source and several other sources with supergiant companions.
Description:	Restricted Access. An open-access version is available at arXiv.org (one of the alternative locations)
URI:	http://hdl.handle.net/2289/8070
ISSN:	0035-8711 1365-2966 (Online)
Alternative Location:	https://ui.adsabs.harvard.edu/abs/2023MNRAS.520.1411M/abstract https://arxiv.org/abs/2301.02815 https://inspirehep.net/literature/2621589 https://doi.org/10.1093/mnras/stad037
Copyright:	2023 The Author(s)
Appears in Collections:	Research Papers (A&A)

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