Paper

NuSTAR Observations of Magnetar 1E 1048.1-5937

Yang, C, Vogel, J K, Guillot, S, Kaspi, V M, Archibald, R F, H An, Pivovaroff, M, Beloborodov, A M

2016

Overview

We report on simultaneous NuSTAR and XMM-Newton observations of the magnetar 1E 1048.1\\(-\\)5937 obtained in July 2013, along with Rossi X-ray Timing Explorer (RXTE) data for the same source obtained from December 2002 through March 2012. The NuSTAR data provide a clear detection of this magnetar's persistent emission up to 20 keV. We detect a previously unreported small secondary peak in the average pulse profile in the 7-10 keV band, which grows to an amplitude comparable to that of the main peak in the 10--20 keV band. We show using RXTE data that this secondary peak is likely transient. We find that the pulsed fraction increases with energy from a value of \\(\\sim\\)0.55 at \\(\\sim\\)2 keV to a value of \\(\\sim\\)0.75 near 8 keV but shows evidence for decreasing at higher energies. After filtering out multiple bright X-ray bursts during the observation, we find that the phase-averaged spectrum from combined NuSTAR and XMM data is well described by an absorbed double blackbody plus power-law model, with no evidence for the spectral turn-up near \\(\\sim\\)10 keV as has been seen in some other magnetars. Our data allow us to rule out a spectral turn-up similar to those seen in magnetars 4U 0142+61 and 1E 2259+586 of \\(\\Delta\\Gamma >= 2\\), where \\(\\Delta\\Gamma\\) is the difference between the soft-band and hard-band photon indexes. The absence of a significant spectral turn-up is consistent with what has been observed from a particularly active subset of magnetars having high spin-inferred magnetic fields, and with previously reported trends suggesting the degree of spectral turn-up is correlated with spin-down rate and/or spin-inferred magnetic field strength.

• Publisher: Cornell University Library, arXiv.org
• Subject: Blackbody / Field strength / Magnetars / Magnetic fields / Spectra / XMM (spacecraft)