Deep NuSTAR and Swift Monitoring Observations of the Magnetar 1E 1841-045
An, Hongjun; Hailey, Charles J.; Kaspi, Victoria M.; Kouveliotou, Chryssa; Younes, George; Stern, Daniel; Boggs, Steven E.; Harrison, Fiona A.; Christensen, Finn E.; Craig, William W.; Zhang, William W.; Beloborodov, Andrei M.; Archibald, Anne M.; Hascoët, Romain; Kennea, Jamie; Archibald, Robert F.; Beardmore, Andy; Gehrels, Niel
Canada, United States, Netherlands, United Kingdom, Denmark
Abstract
We report on a 350 ks NuSTAR observation of the magnetar 1E 1841-045 taken in 2013 September. During the observation, NuSTAR detected six bursts of short duration, with T90 ≲ 1 s. An elevated level of emission tail is detected after the brightest burst, persisting for ∼1 ks. The emission showed a power-law decay with a temporal index of 0.5 before returning to the persistent emission level. The long observation also provided detailed phase-resolved spectra of the persistent X-ray emission of the source. By comparing the persistent spectrum with that previously reported, we find that the source hard-band emission has been stable for over approximately 10 yr. The persistent hard-X-ray emission is well fitted by a coronal outflow model, where e± pairs in the magnetosphere upscatter thermal X-rays. Our fit of phase-resolved spectra allowed us to estimate the angle between the rotational and magnetic dipole axes of the magnetar, {α }{mag}=0.25, the twisted magnetic flux, 2.5 × 1026 G cm2, and the power released in the twisted magnetosphere, {L}j = 6 × 1036 erg s-1. Assuming this model for the hard-X-ray spectrum, the soft-X-ray component is well fit by a two-blackbody model, with the hotter blackbody consistent with the footprint of the twisted magnetic field lines on the star. We also report on the 3 yr Swift monitoring observations obtained since 2011 July. The soft-X-ray spectrum remained stable during this period, and the timing behavior was noisy, with large timing residuals.