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Narrow phase-dependent features in X-ray Dim Isolated Neutron Stars: a new detection and upper limits

Borghese, A; Rea, N; Zelati, FC; Tiengo, A; Turolla, R; Zane, S; (2017) Narrow phase-dependent features in X-ray Dim Isolated Neutron Stars: a new detection and upper limits. Monthly Notices of the Royal Astronomical Society , 468 (3) 10.1093/mnras/stx632. Green open access

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Abstract

We report on the results of a detailed phase-resolved spectroscopy of archival XMM–Newton observations of X-ray dim isolated neutron stars (XDINSs). Our analysis revealed a narrow and phase-variable absorption feature in the X-ray spectrum of RX J1308.6+2127. The feature has an energy of ∼740 eV and an equivalent width of ∼15 eV. It is detected only in ∼1/5 of the phase cycle, and appears to be present for the entire timespan covered by the observations (2001 December to 2007 June). The strong dependence on the pulsar rotation and the narrow width suggest that the feature is likely due to resonant cyclotron absorption/scattering in a confined high-B structure close to the stellar surface. Assuming a proton cyclotron line, the magnetic field strength in the loop is Bloop ∼ 1.7 × 1014 G, about a factor of ∼5 higher than the surface dipolar magnetic field (Bsurf ∼ 3.4 × 1013 G). This feature is similar to that recently detected in another XDINS, RX J0720.4-3125, showing (as expected by theoretical simulations) that small-scale magnetic loops close to the surface might be common to many highly magnetic neutron stars (although difficult to detect with current X-ray instruments). Furthermore, we investigated the available XMM–Newton data of all XDINSs in search for similar narrow phase-dependent features, but could derive only upper limits for all the other sources.

Type: Article
Title: Narrow phase-dependent features in X-ray Dim Isolated Neutron Stars: a new detection and upper limits
Open access status: An open access version is available from UCL Discovery
DOI: 10.1093/mnras/stx632
Publisher version: http://doi.org/10.1093/mnras/stx632
Language: English
Additional information: This version is the version of record. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords: stars, individual, RX J1308.6+2127– stars, neutron, X-rays stars
UCL classification: UCL > School of BEAMS
UCL > School of BEAMS > Faculty of Maths and Physical Sciences
URI: http://discovery.ucl.ac.uk/id/eprint/1549815
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