A1 Refereed original research article in a scientific journal
Continuous evolution of the polarization properties in the transient X-ray pulsar RX J0440.9+4431/LS V +44 17
Authors: Zhao, Q. C.; Tao, L.; Tsygankov, S. S.; Mushtukov, A. A.; Feng, H.; Ge, M. Y.; Li, H. C.; Zhang, S. N.; Zhang, L.
Publisher: EDP Sciences
Publishing place: LES ULIS CEDEX A
Publication year: 2025
Journal: Astronomy and Astrophysics
Journal name in source: Astronomy & Astrophysics
Journal acronym: ASTRON ASTROPHYS
Article number: A241
Volume: 693
Number of pages: 11
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202452872
Web address : https://doi.org/10.1051/0004-6361/202452872
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/485102688
We present a detailed time-resolved and phase-resolved polarimetric analysis of the transient X-ray pulsar RX J0440.9+4431/LS V +44 17, using data from the Imaging X-ray Polarimetry Explorer (IXPE) during the 2023 giant outburst. We conducted a time-resolved analysis by dividing the data into several intervals for each observation. This analysis reveals a continuous rotation of the phase-averaged polarization angle (PA) across the observations performed during the supercritical and subcritical regimes. To investigate the origin of the PA rotation, we performed a pulse phase-resolved polarimetric analysis over four time intervals, each spanning approximately three days. Applying the rotating vector model (RVM), the geometric parameters of the system were determined for each interval. Despite the short time gap of just similar to 20 days, we observed significant variation in the RVM parameters between the first interval and the subsequent three, indicating the presence of an additional polarized component alongside the RVM component. Using a two-polarized component model with the assumption that this additional component remains constant across pulse phases, we calculated the phase-averaged PA and polarized flux of both the variable and constant components. The phase-averaged PA of each component remained relatively stable over time, but the polarized flux of the constant component decreased, while that of the variable component increased. The observed rotation of the PA is attributed to the gradual shift in the polarized flux ratio between the two components and is not directly related to the different accretion regimes.
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Funding information in the publication:
We acknowledge funding support from the National Natural Science Foundation of China under grants Nos. 12122306, 12025301, & 12103027, and the Strategic Priority Research Program of the Chinese Academy of Sciences. AAM thanks UKRI Stephen Hawking fellowship.
