NuSTAR Discovery of an Unusually Steady Long-term Spin-up of the Be Binary 2RXP J130159.6-635806
Abstract
We present spectral and timing analyses of Nuclear Spectroscopic Telescope Array (NuSTAR) observations of the accreting X-ray pulsar 2RXP J130159.6-635806. The source was serendipitously observed during a campaign focused on the gamma-ray binary PSR B1259-63 and was later targeted for a dedicated observation. The spectrum has a typical shape for accreting X-ray pulsars, consisting of a simple power law with an exponential cutoff starting at ∼7 keV with a folding energy of {E}{fold}≃ 18 keV. There is also an indication of the presence of a 6.4 keV iron line in the spectrum at the ∼ 3σ significance level. NuSTAR measurements of the pulsation period reveal that the pulsar has undergone a strong and steady spin-up for the last 20 years. The pulsed fraction is estimated to be ∼ 80%, and is constant with energy up to 40 keV. The power density spectrum shows a break toward higher frequencies relative to the current spin period. This, together with steady persistent luminosity, points to a long-term mass accretion rate high enough to bring the pulsar out of spin equilibrium.
- Publication:
-
The Astrophysical Journal
- Pub Date:
- August 2015
- DOI:
- 10.1088/0004-637X/809/2/140
- arXiv:
- arXiv:1507.04534
- Bibcode:
- 2015ApJ...809..140K
- Keywords:
-
- pulsars: individual: 2RXP J130159.6–635806;
- stars: emission-line;
- Be;
- X-rays: binaries;
- Astrophysics - High Energy Astrophysical Phenomena
- E-Print:
- 13 pages, 7 figures, accepted for publication in The Astrophysical Journal