Alex van Kooten | Searcharxiv

arXiv2026

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

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~min 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 $f_ν= 22.9\pm0.6$ $μ$Jy and detected pulsations at a frequency of $115.059\pm0.035$ 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.

astro-ph.HE↗

arXiv2025

X-ray polarization of the magnetar 1E 1841-045

We report on IXPE and NuSTAR observations beginning forty days after the 2024 outburst onset of magnetar 1E 1841-045, marking the first IXPE observation of a magnetar in an enhanced state. Our spectropolarimetric analysis indicates that both a blackbody (BB) plus double power-law (PL) and a double blackbody plus power-law spectral model fit the phase-averaged intensity data well, with a hard PL tail ($Γ$=1.19 and 1.35, respectively) dominating above $\approx 5$ keV. For the former model, we find the soft PL (the dominant component at soft energies) exhibits a polarization degree (PD) of $\approx 30\%$ while the hard PL displays a PD of $\approx 40\%$. Similarly, the cool BB of the 2BB+PL model possesses a PD of $\approx 15\%$ and a hard PL PD of $\approx 57\%$. For both models, each component has a polarization angle (PA) compatible with celestial north. Model-independent polarization analysis supports these results, wherein the PD increases from$ \approx 15\%$ to $\approx 70\%$ in the 2-3 keV and 6-8 keV ranges, respectively, while the PA remains nearly constant. We find marginal evidence for phase-dependent variability of the polarization properties, namely a higher PD at phases coinciding with the hard X-ray pulse peak. We compare the hard X-ray PL to the expectation from resonant inverse Compton scattering (RICS) and secondary pair cascade synchrotron radiation from primary high-energy RICS photons; both present reasonable spectropolarimetric agreement with the data, albeit, the latter more naturally. We suggest that the soft PL X-ray component may originate from a Comptonized corona in the inner magnetosphere.

astro-ph.HE↗