Hotspot Emission from a Freely Precessing Neutron Star

Abstract

Recent observations of 1E~161348-5055, the neutron-star candidate at the center of the supernova remnant RCW 103, show that a component of its emission varies sinusoidally with a period of approximately six hours. We argue that this period is what one would expect for a freely precessing neutron star with a spin period of about one second. We produce light curves for a freely precessing neutron star with a hotspot. By a suitable choice of parameters, we obtain light curves which are constant with rotational phase when the flux from the star reaches a maximum. At other phases of the precession, the flux varies as the star rotates but the total flux decreases by a factor of several. These models can explain the behavior observed from 1E~161348-5055 and predict that the spin period should be detectable at minimum flux from sufficiently sensitive measurements.