XMM-Newton observations of the two Anomalous X-ray pulsars 1E 1048.1-5937 and 1RXS J170849.0-400910
Mullard Space Science Laboratory, University College of London
We report the results of XMM-Newton observations of two Anomalous X-ray
pulsars: 1E 1048.1-5937 and 1RXS J170849.0-400910. 1E 1048.1-5937 was
observed in 2000, 2003, and 2004. The comparison of the three data sets shows an anti-correlation between flux and pulsed fraction, implying that previous estimates of the source energetics based on the assumption of a large and constant pulsed fraction might be significantly underestimated. The source spectrum is well described by a power law plus blackbody model (kT~0.63 keV, photon index \Gamma~ 2.7-3.5) or,
alternatively, by the sum of two blackbodies of which the hotter is
Comptonized by relativistic electrons. The long term luminosity
variation of a factor >2 is accompanied by relatively small variations in
the spectral shape. Phase resolved spectroscopy indicates a harder
spectrum in correspondence of the pulse maximum.
1RXS J170849.0-400910 was observed in 2003 August and was found at a flux
level a factor of about two lower than previous observations.A significant
spectral evolution appears to be
present, the source exhibiting a much softer spectrum than in the past.
Comparison of the present properties with those from archival data shows a
clear correlation between the X-ray flux and the spectral hardness. We
discuss a possible explanation for the glitches and for the softening of
the source emission which followed the flux decrease, in the framework of
the magnetar model.
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