Journal Article

Narrow absorption features in the co-added <i>XMM–Newton</i> RGS spectra of isolated neutron stars

M. M. Hohle, F. Haberl, J. Vink, C. P. de Vries and R. Neuhäuser

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 419, issue 2, pages 1525-1536
Published in print January 2012 | ISSN: 0035-8711
Published online December 2011 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2011.19809.x
Narrow absorption features in the co-added XMM–Newton RGS spectra of isolated neutron stars

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We co-added the available XMM–Newton Reflection Grating Spectrometer (RGS) spectra for each of the isolated X-ray pulsars RX J0720.4−3125, RX J1308.6+2127 (RBS1223), RX J1605.3+3249 and RX J1856.4−3754 (four members of the ‘Magnificent Seven’) and the ‘Three Musketeers’ Geminga, PSR B0656+14 and PSR B1055−52. We confirm the detection of a narrow absorption feature at 0.57 keV in the co-added RGS spectra of RX J0720.4−3125 and RX J1605.3+3249 (including most recent observations). In addition, we found similar absorption features in the spectra of RX J1308.6+2127 (at 0.53 keV) and maybe PSR B1055−52 (at 0.56 keV). The absorption feature in the spectra of RX J1308.6+2127 is broader than the feature e.g. in RX J0720.4−3125. The narrow absorption features are detected with 2–5.6σ significance.

Although very bright and frequently observed, there are no absorption features visible in the spectra of RX J1856.4−3754 and PSR B0656+14, while the co-added XMM–Newton RGS spectrum of Geminga has not enough counts to detect such a feature.

We discuss a possible origin of these absorption features as lines caused by the presence of highly ionized oxygen (in particular O vii and/or O vi at 0.57 keV) in the interstellar medium and absorption in the neutron star atmosphere, namely the absorption features at 0.57 keV as gravitational redshifted (gr= 1.17) O viii.

Keywords: stars: neutron; pulsars: individual: Geminga; pulsars: individual: PSR B0656+14; pulsars: individual: PSR B1055−52; pulsars: individual: RX J0720.4−3125; pulsars: individual: RX J1308.6+2127; pulsars: individual: RX J1605.3+3249; pulsars: individual: RX J1856.4−3754

Journal Article.  7686 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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