On the optical excess of dim isolated neutron stars
Abstract
The large optical excess in the spectrum is one of the defining characteristics of dim isolated neutron stars (XDINs). We have studied the optical excess of XDINs in the context of the fallback disk model. In this model, XDINs are neutron stars that evolve in the propeller phase, slowing down by the magnetic torques resulting from the disk-field interaction. In this work, we have shown through spectral fits that the optical excess of XDINs can be produced from the inner disk being heated by magnetic stresses. The blackbody temperature of the heated inner rim of the disk is higher than the temperatures sustained by X-ray irradiation and viscous dissipation alone. Since XDINs are in similar evolutionary phases, it is expected that they have similar torque mechanisms and ratios of the magnetic work that heats up the inner disk. Consistently with this idea, we have found that a similar and significant fraction of the work done by the magnetic torques can explain the optical excess of all XDINs. We have also found that heating by X-ray irradiation is negligible compared to the effects of magnetic heating. We propose that this is a common property of the systems with rotational power to L_X ratios greater than about 10^{-2}.
- Publication:
-
42nd COSPAR Scientific Assembly
- Pub Date:
- July 2018
- Bibcode:
- 2018cosp...42E.495C