James Webb Space Telescope Feed Post

Probing the spectrum of the magnetar 4U 0142+61 with JWST

The NIRCam F250M (left) and F140M (right) images of the magnetar. North is up, East to the left. The 1/f noise pattern is clearly visible in both images. For F250M (F140M), we use 55 (30) white background apertures with the same size as the source aperture in the “empty aperture” approach, see text. Abstract: JWST observed the magnetar 4U 0142+61 with the MIRI and NIRCam instruments within a 77 min time interval on 2022 September 20-21. The low-resolution MIRI spectrum and NIRCam photometry show that the spectrum in the wavelength range 1.4-11 µm range can be satisfactorily described by an absorbed power-law model, f???-a, with a spectral slope a=0.96±0.02, interstellar extinction AV=3.9±0.2, and normalization f0=59.4±0.5 µJy at ?=8 µm. These observations do not support the passive disk model proposed by Wang et al. (2006), based on the Spitzer photometry, which was interpreted as evidence for a fallback disk from debris formed during the supernova explosion. We suggest a nonthermal origin for this emission and source variability as the most likely cause of discrepancies between the JWST data and other IR-optical observing campaigns. However, we cannot firmly exclude the presence of a large disk with a different dependence of the effective disk temperature on distance from the magnetar. Comparison with the power-law fit to the hard X-ray spectrum above 10 keV, measured by NuSTAR contemporaneously with JWST, shows that the X-ray spectrum is significantly harder. This may imply that the X-ray and IR nonthermal emission come from different sites in the magnetosphere of the magnetar.