Pulsed Infrared Emission from Magnetar 4U 0142+61 Detected by JWST

Abstract We report on a JWST observation of the magnetar 4U 0142+61 on 2024 August 18 with the Near-Infrared Camera (NIRCam). NIRCam observed the magnetar for 33 minutes in timing mode, providing a time resolution of 2.5 s. In the F410M filter (pivot wavelength 4.08 μ m), we measured the flux density f ν = 22.9 ± 0.6 μ Jy and detected pulsations at a frequency of 115.059 ± 0.035 mHz, in agreement with the magnetar’s spin period at the epoch of the JWST observation. The observed pulse profile has one peak per period (although this may be due to the poor time resolution), with a lower limit on the pulsed fraction of about 10%. We compare the IR pulse profile to the NICER and NuSTAR X-ray pulse profiles and find that the IR peak overlaps with the hard X-ray peak, suggesting a magnetospheric origin for the pulsed IR emission.