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An optical counterpart candidate for the isolated neutron star RBS 1774

Zane, S; Mignani, RP; Turolla, R; Treves, A; Haberl, F; Motch, C; Zampieri, L; (2008) An optical counterpart candidate for the isolated neutron star RBS 1774. ASTROPHYS J , 682 (1) 487 - 491.

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Multiwavelength studies of the seven identified X-ray-dim isolated neutron stars (XDINSs) offer a unique opportunity to investigate their surface thermal and magnetic structure and the matter-radiation interaction in presence of strong gravitational and magnetic fields. As a part of an ongoing campaign aimed at a complete identification and spectral characterization of XDINSs in the optical band, we performed deep imaging with the ESO Very Large Telescope (VLT) of the field of the XDINS RBS 1774 (1RXS J214303.7 + 065419). The recently upgraded FORS1 instrument mounted on the VLT provided the very first detection of a candidate optical counterpart in the B band. The identification is based on a very good positional coincidence with the X-ray source (chance probability similar to 2 x 10(-3)). The source has B = 27.4 +/- 0.2 (1 sigma confidence level), and the optical flux exceeds the extrapolation of the X-ray blackbody at optical wavelengths by a factor similar to 35 (+/- 20 at 3 sigma confidence level). This is barely compatible with thermal emission from the neutron star surface, unless the source distance is d approximate to 200-300 pc, and the star is an almost aligned rotator or its spin axis is nearly aligned with the line of sight. At the same time, such a large optical excess appears difficult to reconcile with rotation-powered magnetospheric emission, unless the source has an extremely large optical emission efficiency. The implications and possible similarities with the optical spectra of other isolated NSs are discussed.

Type: Article
Title: An optical counterpart candidate for the isolated neutron star RBS 1774
Keywords: stars : individual (RBS 1774), stars : neutron, techniques : photometric, X-rays : stars, COHERENT TIMING SOLUTION, X-RAY-EMISSION, RX J1856.5-3754, PROPER MOTION, 1RXS J214303.7+065419/RBS-1774, SPECTRAL FEATURE, MAGNETIC-FIELDS, RADIO, J0720.4-3125, PULSARS
URI: http://discovery.ucl.ac.uk/id/eprint/177369
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