Phase-resolved NuSTAR and SWIFT-XRT observations of magnetar 4U 0142+61

Shriharsh P. Tendulkar, Romain Hascöet, Chengwei Yang, Victoria M. Kaspi, Andrei M. Beloborodov, Hongjun An, Matteo Bachetti, Steven E. Boggs, Finn Erland Christensen, William W. Craig, Sebastien Guiilot, Charles A. Hailey, Fiona A. Harrison, Daniel Stern, William Zhang

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Abstract

We present temporal and spectral analysis of simultaneous 0.5-79 keV Swift-XRT and Nuclear Spectroscopic Telescope Array observations of the magnetar 4U 0142+61. The pulse profile changes significantly with photon energy between 3 and 35 keV. The pulse fraction increases with energy, reaching a value of ≈20%, similar to that observed in 1E 1841-045 and much lower than the ≈80% pulse fraction observed in 1E 2259+586. We do not detect the 55 ks phase modulation reported in previous Suzaku-HXD observations. The phase-averaged spectrum of 4U 0142+61 above 20 keV is dominated by a hard power law (PL) with a photon index ΓH ~ 0.65, and the spectrum below 20 keV can be described by two blackbodies, a blackbody plus a soft PL, or by a Comptonized blackbody model. We study the full phase-resolved spectra using the e± outflow model of Beloborodov. Our results are consistent with the parameters of the active j-bundle derived from INTEGRAL data by Hascoe¨t et al. We find that a significant degeneracy appears in the inferred parameters if the footprint of the j-bundle is allowed to be a thin ring instead of a polar cap. The degeneracy is reduced when the footprint is required to be the hot spot inferred from the soft X-ray data.
Original languageEnglish
JournalAstrophysical Journal
Volume808
Issue number1
Pages (from-to)1-13
Number of pages13
ISSN0004-637X
DOIs
Publication statusPublished - 2015

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