EDP Sciences
Free access
Volume 499, Number 1, May III 2009
Page(s) 267 - 272
Section Stellar structure and evolution
DOI http://dx.doi.org/10.1051/0004-6361/200811041
Published online 27 March 2009
A&A 499, 267-272 (2009)
DOI: 10.1051/0004-6361/200811041

The isolated neutron star RBS1774 revisited

Revised XMM-Newton X-ray parameters and an optical counterpart from deep LBT-observations
A. D. Schwope1, T. Erben2, J. Kohnert1, G. Lamer1, M. Steinmetz1, K. Strassmeier1, H. Zinnecker1, J. Bechtold3, E. Diolaiti4, A. Fontana5, S. Gallozzi5, E. Giallongo5, R. Ragazzoni6, C. De Santis5, and V. Testa5

1  Astrophysikalisches Institut Potsdam, An der Sternwarte 16, 14482 Potsdam, Germany
    e-mail: aschwope@aip.de
2  Argelander-Institut für Astronomie (AIfA), University of Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
3  Steward Observatory, University of Arizona, Tucson, AZ 85721, USA
4  INAF – Osservatorio Astronomico di Bologna, via Ranzani 1, 40127 Bologna, Italy
5  INAF – Osservatorio Astronomico di Roma, via di Frascati 33, 00040 Monteporzio, Italy
6  INAF – Osservatorio di Padova, vicolo dell'Osservatorio 5, 35122 Padova, Italy

Received 26 September 2008 / Accepted 18 February 2009

We report optical B-band observations with the Large Binocular Telescope (LBT) of the isolated neutron star RBS1774. The stacked image with a total exposure of $2\fh5$ reveals a candidate optical counterpart at mB = 26.96 $\pm$ 0.20 at position $\alpha {\rm (2000)} = {\rm 21^h43^m03\fs40}$, $\delta{\rm (2000)} = +06\degr54^\prime17\farcs5$, within the joint Chandra and XMM-Newton error circles. We analyse archival XMM-Newton observations and derive revised spectral and positional parameters. The predicted optical flux from the extrapolated X-ray spectrum is likely twice as high as reported before. The measured optical flux exceeds the extrapolated X-ray spectral flux by a factor ${\sim}40$ (15-60 at 1$\sigma$ confidence). We interpret our detection and the spectral energy distribution as further evidence of a temperature structure over the neutron star's surface and present a pure thermal model reflecting both the SED and the pulsed fraction of the light curve.

Key words: X-rays: stars -- stars: neutron -- stars: individual: RBS1774

© ESO 2009