2025/04/15 by Salganik, Alexander, Tsygankov, Sergey S., Chernyakova, Maria +2 · 1 citation
#FOS: Physical sciences #High Energy Astrophysical Phenomena (astro-ph.HE)
paper · doi:10.48550/arxiv.2504.11263
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 revealing possibly a new accretion regime. Using data from NuSTAR, Swift, XMM-Newton, and Chandra observatories, we investigate changes in the pulsar's timing and spectral properties. After more than 20 years of continuous spin-up, the pulsar's spin period stabilized, marking the onset of spin equilibrium. This transition was accompanied by the emergence of a previously unobserved accretion regime at L\rm bol = (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 time from a luminosity of 1035 erg s-1 to 1034 erg s-1 taking less than 2.3 day. The analysis of the spectral data collected during this new low-luminosity state revealed a two-hump shape which 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, demonstrates 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.