Free access article

A&A 440, L63-L66 (2005)
DOI: 10.1051/0004-6361:200500170

Letter

The calm after the storm: XMM-Newton observation of SGR 1806-20 two months after the Giant Flare of 2004 December 27

A. Tiengo^{1, 2}, P. Esposito¹, S. Mereghetti¹, N. Rea^{3, 4}, L. Stella³, G. L. Israel³, R. Turolla⁵ and S. Zane<sup>6

1</sup>  NAF, 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  INAF, Osservatorio Astronomico di Roma, via Frascati 33, 00040 Monteporzio Catone, Roma, Italy
⁴  SRON - National Institute for Space Research, Sorbonnelaan 2, 3584 CA, Utrecht, The Netherlands
⁵  Università di Padova, Dipartimento di Fisica, via Marzolo 8, 35131 Padova, Italy
⁶  Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking Surrey, RH5 6NT, UK

(Received 1 July 2005 / Accepted 4 August 2005 )

Abstract
XMM-Newton observed the soft gamma repeater SGR 1806-20 about two months after its 2004 December 27 giant flare. A comparison with the previous observations taken with the same instrument in 2003-2004 shows that the pulsed fraction and the spin-down rate have significantly decreased and that the spectrum slightly softened. These changes may indicate a global reconfiguration of the neutron star magnetosphere. The spectral analysis confirms that the presence of a blackbody component in addition to the power-law is required. Since this additional component is consistent with being constant with respect to the earlier observations, we explore the possibility of describing the long-term spectral evolution as only due to the power-law variations. In this case, the slope of the power-law does not significantly change and the spectral softening following the giant flare is caused by the increase of the relative contribution of the blackbody over the power-law component.

Key words: stars: individual: SGR 1806-20 -- X-rays: stars

SIMBAD Objects

© ESO 2005

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