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http://hdl.handle.net/20.500.12386/24823
Titolo: | The accretion regimes of a highly magnetized NS: the unique case of NuSTAR J095551+6940.8 | Autori: | Dall'Osso, Simone Perna, Rosalba PAPITTO, ALESSANDRO Bozzo, Enrico STELLA, Luigi |
Data pubblicazione: | 2016 | Rivista: | MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY | Numero: | 457 | Fascicolo: | 3 | Da pagina:: | 3076 | Abstract: | 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 × 10<SUP>40</SUP> erg s<SUP>-1</SUP> through intermediate values ∼ a few × 10<SUP>39</SUP> erg s<SUP>-1</SUP>, and down to a minimum below 2 × 10<SUP>38</SUP> erg s<SUP>-1</SUP> 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 r<SUB>m</SUB> ∼ 10<SUP>8</SUP> cm is approximately half the corotation radius r<SUB>co</SUB>, and radiation pressure dominates the disc out to r<SUB>tr</SUB> ≲ 10<SUP>9</SUP> cm. In the radiation-pressure-dominated regime, r<SUB>m</SUB> grows very slowly as the mass inflow rate drops: as a result, r<SUB>m</SUB> < r<SUB>co</SUB> remains valid until dot{M} ≳dot{M}_E, the Eddington accretion rate, allowing a wide range of accretion luminosities to the NS. Once dot{M} < dot{M}_E accretion on to the NS is inhibited because r<SUB>m</SUB> > r<SUB>co</SUB>, 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 ≲ 10<SUP>13</SUP> 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. | URI: | http://hdl.handle.net/20.500.12386/24823 | URL: | https://academic.oup.com/mnras/article/457/3/3076/2588907 https://arxiv.org/abs/1512.01532 |
ISSN: | 0035-8711 | DOI: | 10.1093/mnras/stw110 | Bibcode ADS: | 2016MNRAS.457.3076D | Fulltext: | open |
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