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Arxiv: Probing the spectrum of the magnetar 4U 0142+61 with JWST Published: 5/7/2024 5:11:18 AM Updated: 5/7/2024 5:11:18 AM

Paper abstract: JWST observed the magnetar 4U 0142+61 with the MIRI and NIRCam instrumentswithin a 77 min time interval on 2022 September 20-21. The low-resolution MIRIspectrum and NIRCam photometry show that the spectrum in the wavelength range1.4-11 \mum range can be satisfactorily described by an absorbed power-lawmodel, f_{\nu}\propto \nu^{-\alpha}, with a spectral slope \alpha=0.96\pm0.02, interstellar extinction A_V= 3.9\pm0.2, and normalization f_0= 59.4\pm 0.5 \muJy at \lambda = 8 \mum. These observations do notsupport the passive disk model proposed by Wang et al. (2006), based on theSpitzer photometry, which was interpreted as evidence for a fallback disk fromdebris formed during the supernova explosion. We suggest a nonthermal originfor this emission and source variability as the most likely cause ofdiscrepancies between the JWST data and other IR-optical observing campaigns.However, we cannot firmly exclude the presence of a large disk with a differentdependence 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 spectrumis significantly harder. This may imply that the X-ray and IR nonthermalemission come from different sites in the magnetosphere of the magnetar.