2015/12/04 by Simone Dall'Osso, S. Dall’Osso, Rosalba Perna +5
Earth and Planetary Sciences · Physics and Astronomy · #Accretion (finance) #Astronomy #Astrophysical Phenomena and Observations #Astrophysics #Eddington luminosity #Galaxy #High-pressure geophysics and materials #Luminosity #Neutron star #Physics #Pulsar #Pulsars and Gravitational Waves Research #RADIUS #Radiation pressure #astro-ph.HE
paper · pdf · doi:10.1093/mnras/stw110
8 pages, 3 figures, submitted to MNRAS
arxiv created 2015/12/04 · openalex publication_date 2016/02/18 · arxiv updated 2016/03/09 · openalex created_date 2016/06/24 · openalex updated_date 2026/08/05
The ultraluminous accreting pulsar M82-X2 (NuSTAR J095551+6940.8) offers an unprecedented opportunity to study the disc-magnetosphere interaction in a new regime of supercritical accretion. The source X-ray emission has been highly variable during the last 15 yrs. It ranged from a maximum of ∼2 × 1040 erg s−1 through intermediate values ∼ a few × 1039 erg s−1, and down to a minimum below 2 × 1038 erg s−1 that we have determined here, by analysing archival Chandra HRC observations of the source at an epoch at which it was undetected. We interpret the source variability via a magnetically threaded disc model: when at peak luminosity, the neutron star (NS) is close to spin equilibrium, its inner disc edge rm ∼ 108 cm is approximately half the corotation radius rco, and radiation pressure dominates the disc out to rtr ≲ 109 cm. In the radiation-pressure-dominated regime, rm grows very slowly as the mass inflow rate drops: as a result, rm < rco remains valid until |M \gtrsim||ME|, the Eddington accretion rate, allowing a wide range of accretion luminosities to the NS. Once |M < ME| accretion on to the NS is inhibited because rm > rco, and the source luminosity is expected to drop by a large factor. We conclude that a magnetically threaded accretion disc surrounding a highly magnetized NS (B ≲ 1013 G), and transitioning between the radiation-pressure and gas-pressure dominated regimes, offers the best interpretation for all the currently observed properties of NuSTAR J095551+6940.8.