Speaker
Description
We present timing and spectral analysis of XMM-Newton observations of the Be/X-ray pulsar 4U 0115+63 following its 2023 giant outburst. In the quiescent state, we detect coherent X-ray pulsations with a high pulsed fraction (>50%) but no significant low-frequency red noise, indicating the absence of active accretion. The spectrum is well described by a single blackbody with a small emitting area, which supports this interpretation. These results provide strong evidence that the source has entered the propeller regime, where accretion onto the neutron star surface is inhibited. We discuss possible origins of the pulsations, including anisotropic cooling of a neutron star. This work is a key step towards understanding emission mechanisms in highly magnetized neutron stars in quiescence.