Mapping the Surface of the Magnetar 1e 1048.1–5937 in Outburst and Quiescence Through Phase-Resolved X-Ray Spectroscopy

Abstract

We model the pulse profiles and the phase-resolved spectra of the anomalous X-ray pulsar 1E 1048.1−5937 obtained with XMM-Newton to map its surface temperature distribution during an active and a quiescent epoch. We develop and apply a model that takes into account the relevant physical and geometrical effects on the neutron star surface, magnetosphere, and spacetime. Using this model, we determine the observables at infinity as a function of pulse phase for different numbers and sizes of hot spots on the surface. We show that the pulse profiles extracted from both observations can be modeled with a single hot spot and an antipodal cool component. The size of the hot spot changes from ≈80• in 2007, three months after the onset of a dramatic flux increase, to ≈30• during the quiescent observation in 2011, when the pulsed fraction returned to the pre-outburst ≈65% level. For the 2007 observation, we also find that a model consisting of a single 0.4 keV hot spot with a magnetic field strength of 1.8 × 10 14 G accounts for the spectra obtained at three different pulse phases but underpredicts the flux at the pulse minimum, where the contribution to the emission from the cooler component is non-negligible. The inferred temperature of the spot stays approximately constant between different pulse phases, in agreement with a uniform temperature, single hot spot model. These results suggest that the emitting area grows significantly during outbursts but returns to its persistent and significantly smaller size within a timescale of a few years.

X-ray spectra and polarization from magnetar candidates

“…Detailed calculations, based on Montecarlo simulations, confirmed this picture (Fernàndez & Thompson 2007;Nobili, Turolla & Zane 2008), and their application to spectral fitting of SGRs/AXPs allowed to estimate the physical parameters of magnetar magnetospheres . Following the same approach, the expected polarization pattern in magnetars has been also investigated in the wake of the growing interest in X-ray polarimetry (Fernández & Davis 2011;Taverna et al 2014;Güver, Gögüs ¸& Özel 2015).…”

“…Magnetar RCS spectral and polarimetric models were investigated in the idealized case of BB seed photons (Fernández & Thompson 2007;Nobili et al 2008;Zane et al 2009;Fernández & Davis 2011;Taverna et al 2014). An exception is the work by Güver, Gögüs ¸& Özel (2015), in which modelling of the spectral properties of the AXP 1E 1048.1-5937 was carried out assuming that thermal surface radiation comes from a magnetized, fully-ionized H atmosphere. In this investigation we consider surface emission from both a magnetized H atmosphere and a condensed surface.…”