Detection of the magnetar XTE J1810-197 at 150 and 260 GHz with the NIKA2 kinetic inductance detector camera

Context. The investigation of pulsars between millimetre and optical wavelengths is challenging due to the faintness of the pulsar signals and the relative low sensitivity of the available facilities compared to 100 m class telescopes operating in the centimetre band. The kinetic inductance detector (KID) technology offers large instantaneous bandwidths and a high sensitivity that can help to increase the ability of existing observatories at short wavelengths substantially to detect pulsars and transient emission.
Aims: To investigate whether pulsars can be detected with KIDs, we observed the anomalous X-ray pulsar XTE J1810-197 with the New IRAM KIDs Array-2 (NIKA2) camera installed at the IRAM 30 m telescope in Spain.
Methods: Several short observations of XTE J1810-197 were made on 2019 March 25 under good weather conditions to verify the stability of the KIDs and to try to detect the expected broadband pulsations from the neutron star.
Results: We detected the pulsations from the pulsar with NIKA2 at its two operating frequency bands, 150 and 260 GHz (λ = 2.0 and 1.15 mm, respectively). This is the first time that a pulsar is detected with a receiver based on KID technology in the millimetre band. In addition, this is the first report of short millimetre emission from XTE J1810-197 after its reactivation in December 2018, and it is the first time that the source is detected at 260 GHz, which gives us new insights into the radio emission process of the star.
Conclusions: We demonstrate that KIDs can fulfil the technical requirements for detecting pulsed emission from neutron stars in the millimetre band. We show that the magnetar XTE J1810-197 is again emitting strong pulsations in the short millimetre band.