A deep XMM-Newton look on the thermally emitting isolated neutron star RX J1605.3+3249

Understand

Previous XMM-Newton observations of the thermally emitting isolated neutron star RX J1605.3+3249 provided a candidate for a shallow periodic signal and evidence of a fast spin down, which suggested a high dipolar magnetic field and an evolution from a magnetar.

• We obtained a large programme with XMM-Newton to confirm its candidate timing solution, understand the energy-dependent amplitude of the modulation, and investigate the spectral features of the source.
• We performed extensive high-resolution and broadband periodicity searches in the new observations, using the combined photons of the three EPIC cameras and allowing for moderate changes of pulsed fraction and the optimal energy range for detection.
• A deep $4\sigma$ upper limit of $1.33(6)\%$ for modulations in the relevant frequency range conservatively rules out the candidate period previously reported.