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Issue A&A
Volume 437, Number 3, July III 2005
Page(s) 997 - 1005
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361:20052633



A&A 437, 997-1005 (2005)
DOI: 10.1051/0004-6361:20052633

Three XMM-Newton observations of the anomalous X-ray pulsar 1E 1048.1-5937: Long term variations in spectrum and pulsed fraction

A. Tiengo1, 2, S. Mereghetti1, R. Turolla3, S. Zane4, N. Rea5, 6, L. Stella5 and G. L. Israel5

1  Istituto di Astrofisica Spaziale e Fisica Cosmica, Sezione di Milano "G.Occhialini", via Bassini 15, 20133 Milano, Italy
    e-mail: tiengo@mi.iasf.cnr.it
2  Università degli Studi di Milano, Dipartimento di Fisica, via Celoria 16, 20133 Milano, Italy
3  Università di Padova, Dipartimento di Fisica, via Marzolo 8, 35131 Padova, Italy
4  Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking Surrey, RH5 6NT, UK
5  INAF - Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Roma, Italy
6  SRON - National Institute for Space Research, Sorbonnelaan, 2, 3584 CA, Utrecht, The Netherlands

(Received 3 January 2005 / Accepted 12 March 2005 )

Abstract
We report the results of a recent (July 2004) XMM-Newton Target of Opportunity observation of the Anomalous X-ray Pulsar 1E 1048.1-5937 together with a detailed re-analysis of previous observations carried out in 2000 and 2003. In July 2004 the source had a 2-10 keV flux of 6.2 $\times$ 10-12 erg cm-2 s-1 and a pulsed fraction $P_{\rm F}$ = 0.68. Comparison of the three data sets shows the presence of 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. In this case the temperatures are kT1 ~ 0.2-0.3 keV and kT2 ~ 0.4-0.5 keV and the emitting area of the cooler component is consistent with the whole neutron star surface. The long-term luminosity variation of a factor $\ga$2 is accompanied by relatively small variations in the spectral shape. Phase-resolved spectroscopy indicates a harder spectrum together with the pulse maximum. No spectral features have been detected with 4$\sigma$ limits on the equivalent width in the range ~10-220 eV, depending on line energy and width.


Key words: stars: individual: 1E 1048.1-5937 -- X-rays: stars

SIMBAD Objects



© ESO 2005


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