2011/09/12 by Markus M. Hohle, Frank Haberl, Jacco Vink +2 · 1 citation
Physics and Astronomy · #astro-ph.SR #astro-ph.HE
paper · pdf · doi:10.1111/j.1365-2966.2011.19809.x
14 pages, 10 figures and 10 tables. Accepted for publication by MNRAS (Sep 12th, 2011)
arxiv created 2011/09/12 · arxiv updated 2015/05/29
We co-added the available XMM-Newton RGS spectra for each of the isolated X-ray pulsars RX J0720.4-3125, RX J1308.6+2127 (RBS 1223), 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 2σ to 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 ionised oxygen (in particular OVII and/or OVI 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) OVIII.