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NASA NTRS · 20140013214

RXJ0440.9+4431: a Persistent Be-x-ray Binary in Outburst

Ferrigno, C.·Farinelli, R.·Bozzo, E.·Pottschmidt, K.·Klochkov, D.·Kretschmar, P.
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Abstract

The persistent Be/X-ray binary RXJ0440.9+4431 flared in 2010 and 2011 and has been followed by various X-ray facilities (Swift, RXTE, XMM-Newton, and INTEGRAL).We studied the source timing and spectral properties as a function of its X-ray luminosity to investigate the transition from normal to flaring activity and the dynamical properties of the system. We have determined the orbital period from the long-term Swift/BAT light curve, but our determinations of the spin-period are not precise enough to constrain any orbital solution. The source spectrum can always be described by a bulk-motion Comptonization model of black body seed photons attenuated by a moderate photoelectric absorption. At the highest luminosity, we measured a curvature of the spectrum, which we attribute to a significant contribution of the radiation pressure in the accretion process. This allows us to estimate that the transition from a bulk-motion-dominated flow to a radiatively dominated one happens at a luminosity of approx 2 × 10(exp 36) erg/ s. The luminosity dependency of the size of the black body emission region is found to be r(sub BB) varies as L(sub x) (exp 0.39 +/- 0.02). This suggests that either matter accreting onto the neutron star hosted in RXJ0440.9+4431 penetrates through closed magnetic field lines at the border of the compact object magnetosphere or that the structure of the Neutron star magnetic field is more complicated than a simple dipole close to the surface.

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Ferrigno, C., Farinelli, R., Bozzo, E., Pottschmidt, K., Klochkov, D., Kretschmar, P.. 2013-05-01. RXJ0440.9+4431: a Persistent Be-x-ray Binary in Outburst. https://ntrs.nasa.gov/citations/20140013214

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