EDP Sciences
Free Access
Volume 424, Number 2, September III 2004
Page(s) 635 - 645
Section Stellar structure and evolution
DOI https://doi.org/10.1051/0004-6361:20040440
Published online 23 August 2004

A&A 424, 635-645 (2004)
DOI: 10.1051/0004-6361:20040440

The isolated neutron star X-ray pulsars RX J0420.0-5022 and RX J0806.4-4123 : New X-ray and optical observations

F. Haberl1, C. Motch2, V. E. Zavlin1, 2, K. Reinsch3, B. T. Gänsicke4, M. Cropper5, A. D. Schwope6, R. Turolla7 and S. Zane5

1  Max-Planck-Institut für extraterrestrische Physik, Giessenbachstraße, 85748 Garching, Germany
    e-mail: fwh@mpe.mpg.de
2  Observatoire Astronomique, CNRS UMR 7550, 11 rue de l'Université, 67000 Strasbourg, France
3  Universitäts-Sternwarte, Geismarlandstr. 11, 37083 Göttingen, Germany
4  Department of Physics, University of Warwick, Coventry CV4 7AL, UK
5  Mullard Space Science Laboratory, University College London, Holmbury St. Mary, Dorking, Surrey RH5 6NT, UK
6  Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
7  Dipartimento di Fisica, Universitá di Padova, via Marzolo 8, 35131 Padova, Italy

(Received 15 March 2004 / Accepted 18 May 2004)

We report on the analysis of new X-ray data obtained with XMM-Newton and Chandra from two ROSAT-discovered X-ray dim isolated neutron stars (XDINs). was observed with XMM-Newton in April 2003, 2.5 years after the first observation. The EPIC-pn data confirm that this object is an X-ray pulsar with 11.371 s neutron star spin period. The X-ray spectrum is consistent with absorbed black-body emission with a temperature kT = 96 eV and $N_{\rm H}$ = 4 $\,\times \,10^{19}$ cm -2 without significant changes between the two observations. Four XMM-Newton observations of between December 2002 and July 2003 did not confirm the 22.7 s pulsations originally indicated in ROSAT data, but clearly reveal a 3.453 s period. A fit to the X-ray spectrum using an absorbed black-body model yields kT = 45 eV, the lowest value found from the small group of XDINs and $N_{\rm H}$ = 1.0 $\,\times \,10^{20}$ cm -2. Including a broad absorption line improves the quality of the spectral fits considerably for both objects and may indicate the presence of absorption features similar to those reported from , and . For both targets we derive accurate X-ray positions from the Chandra data and present an optical counterpart candidate for with $B = 26.6\pm0.3$ mag from VLT imaging.

Key words: X-rays: stars -- stars: neutron -- stars: magnetic fields -- stars: individual: ,

SIMBAD Objects

© ESO 2004

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