A1 Refereed original research article in a scientific journal
Discovery of a bimodal luminosity distribution in the persistent Be/X-ray pulsar 2RXP J130159.6-635806
Authors: Salganik, Alexander; Tsygankov, Sergey S.; Chernyakova, Maria; Malyshev, Denys; Poutanen, Juri
Publisher: EDP SCIENCES S A
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: A71
Volume: 698
Number of pages: 10
ISSN: 0004-6361
eISSN: 1432-0746
DOI: https://doi.org/10.1051/0004-6361/202453378
Web address : https://doi.org/10.1051/0004-6361/202453378
Self-archived copy’s web address: https://research.utu.fi/converis/portal/detail/Publication/498722215
We present a comprehensive analysis of 2RXP J130159.6−635806, a persistent low-luminosity Be/X-ray pulsar, focusing on its transition to a spin equilibrium state and the discovery of a bimodal luminosity distribution that possibly reveals a new accretion regime. Using data from the NuSTAR, Swift, XMM-Newton, and Chandra observatories, we investigated changes in the pulsar’s timing and spectral properties. After more than 20 years of continuous spin-up, the pulsar’s spin period has stabilized, marking the onset of spin equilibrium. This transition was accompanied by the emergence of a previously unobserved accretion regime at Lbol = (2.0−1.0+2.3) × 1034 erg s−1, an order of magnitude lower than its earlier quiescent state. After that, the source occasionally switched between these regimes, remaining in each state for extended periods, with the transition from a luminosity of 1035 erg s−1 to 1034 erg s−1 taking less than 2.3 days. The analysis of the spectral data collected during this new low-luminosity state revealed a two-hump shape that is different from the cutoff power-law spectra observed at higher luminosities. The discovery of pulsations in this state, together with the hard spectral shape, indicates ongoing accretion. We estimate the magnetic field strength to be ∼1013 G based on indirect methods. Additionally, we report a hint of a previously undetected ∼90-day orbital period in the system.
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Funding information in the publication:
AS acknowledges support from the EDUFI Fellowship and Jenny and Antti Wihuri Foundation. DM acknowledge support by the state of Baden-Württemberg through bwHPC.